QB78 Cap O ringsJune 21 2002 at 7:39 AM Ppadgett Ppadgett (Login Ppadgett)from IP address 209.86.176.153
Response to What size if order from allOrings.com?NT
They are #113 Burna N. They are about $7 plus $7 to ship for about 200 of them. Maybe I should go into the business, it took me about 3 weeks to find the right size and place to get them in bulk.
JimC(Login JimCC)198.152.13.70 Breech removal June 17 2002, 4:18 PM
Bill,Remove the safety by turning it to the "S" positionand punching it out with a dowel, etc. Remove the knurled thumb knob and remove the action.Next remove the rearmost screw that holds the trigger assembly on.Loosen the barrel band. Remove the set screw in the top of the breech that anchors the barrel.Pull the barrel. This will expose the front screw that holds the breech on. HTH
Do you need to take out barrel and separate breech from tube to get to the hammer bolt? NT
I would say yes,May 7 2002 at 2:45 AM Anders (Login agu)from IP address 193.14.203.179
but I did not get that far, just took the barrel out to get the breech off so I could slide the breech bolt out to change the o-ring. So far I havent taken the rest of the gun apart. Taking the barrel out will propably make some minor damage to 2 of the 3 o-rings that holds it in place. I replaced them, but doubt that it was neccessary.It really came apart easily./Anders
I got o-rings at Ace Hdwe . . .May 4 2002 at 9:41 AM crider crider (Login crider)from IP address 66.190.170.3
The measurements I have in my Sony Clie are:Barrel Rings: #ORM-204-008; ID 8mm OD 12mm W 2mmBolt ring: #ORM-204-003: ID 3mm OD 7mm W 2mm These are not the best and wont hold up as well as others but will do in a pinch.Geron
QB-78 Barrel TweaksMay 2 2002 at 9:22 AM TWeakster TWeakster (Login Tweakster)from IP address 65.71.8.12
This is not my idea, but I don't remember where I got it so I can't give the credit to whom it belongs, sorry. Remove the barrel , drill a second set screw hole in the receiver about (warning: I'm going from memory here)1/2 an inch back of the existing one and tap it for the set screw. Be careful of the location of the second set screw as you need to make sure it will not be in the location of one of the o-ring seals on the barrel. I ground a flat spot on the barrel that will match the spot of the second set screw to give the set screw a flat spot to grab on. If you look at the existing set screw engagement on the barrel, you will see the factory has ground a flat recess for the existing set screw to grab onto. Check the inside of the receiver to make sure there is not bur left from drilling and tapping the second set screw hole, and check the first set screw hole while you're looking. Try to line the second set screw up with the first one for aesthetic reasons. Most hardware stores will have small set screws to use for this, along with the tap and matching drill bit. The second set screw does a lot to lock the barrel down so it doesn't wiggle back and forth. CJ Pitts' (Co2une) barrel band will also help a lot. It is milled from aluminum and has set screws on both the CO2 tube and the barrel, which locks things down tight. I use CJ's barrel band and highly recommend it to everyone. I also reccomend his barrel break for the QB-78. Neither one of these are cheap, but they are, in my opinion, the best you will find.WARNING: at least one of the three o-rings on the barrel will usually get damaged when the barrel is removed. I'm not sure whether they get damaged when the barrel is pushed back into the receiver, when it is removed, or both. But you will usually find one of these damaged when you remove the barrel. It is a good idea to have a few spare on hand. Since these o-rings are never under constant CO2 pressure, they do not need to be the expensive ones specially designed for CO2. I coat them with a little white lithium grease before re-installing to help them slide back in and to help keep them from getting sliced up during the installation. I'm really not sure what slices these o-rings up, but it sure happens.AFTER THOUGHT! Amazingly enough, these rifles are remarkably accurate without the second set screw, as they come from the factory. Sometimes I must wonder just how much peace of mind really costs. When I pick up a rifle I want assurance it is hitting where I'm aiming. The extras give me the peace of mind, but I'm not sure the rifle really needs it, more like I do.Hope this helps!The TWeakster!
2nd set screw not neededMay 2 2002 at 2:44 PM James Kitching Fun Supply (Premier Login jayhawk10)Forum Ownerfrom IP address 216.220.157.89
In my opinion it does nothing, a waste of time, and another place to cut orings wihen installing the barrel.CJ thinks it works, I don't.The one stock screw loctes the rear just fine as fa as I can tell. I could tell no change in performance with two or one screw at the back. The scews are just too close togeter to matter.What really matters is the front band. That is the weakest point in the design.James
I didMay 2 2002 at 10:14 AM Bubba Bubba (Login DanHankins)from IP address 152.163.197.61
I did mention epoxy in a post about securing the barrel on a QB-78.What happened was that the ham fisted Bubba tried to tighten the screw that goes through the barrel band, and broke the little thing.Not having a replacement available, and wanting to shoot the rifle after some mods, I put the rifle back togather. I was concerned with barrel movement until I could get a replacement for the odd shaped little bolt that goes in the barrel clamp. So, I sprayed the afflicted area with Pledge, Epoxy wont stick to waxed surfaces very well. Then using a small diameter Jute twine, I made a lashing under the barrel, in the area of the barrel band. I used jute, not for it's strength, as it has little, but for it's ability to absorb epoxy. So lashing tightly, and adding epoxy, I began to tighten up the barrel clamp. After the epoxy went off, I painted the lashing black. What suprised me was how well this worked. This lashed up booger held the barrel a lot better than the standard clamp. Folks who saw this lash up were inclined toward unkind remarks. Till they shot it. Or I shot it, after I finally pried it away from the shooter, who was quietly amazed at the results. This method of repair is not for the faint of heart, or someone who has fallen off of the cclean living and pure thoughts train bound for glory. The inhalation of the epoxy fumes, could have some effect. Didn't bother me, Ddidn't bother me, didnbom.......Respectfully,BubbaThe above is true. Your results may differ from those of the writer, or be unsatisfactory, and nasty to clean up. Mine was not.
QB breech probe
The extended probes are only required when doing the barrel work that we do on the Custom QB's. Those guns have longer barrels, extended probes, custom breech seals, machine work to fit the breech seal to valve and breech, steel barrel supports as well as oval valve & exhaust ports.
With the oval exhaust port you need to seat the pellet further in to engage the rifling. The factory QB78 gun has a very restrictive hollow probe but the QB22 probes are thinned out and work great with the factory barrel length and exhaust port.
Custom QB22's hit 20 fpe on a warm day and still get 80 shots from an extended bulk set-up.
http://forums.delphiforums.com/gunguru/messages
Tim
Mac1 Airgun
(Barrel Movement) If You Would Install...May 1 2002 at 9:51 PM MR Bulk™ (Login BULK)from IP address 204.210.114.208
...THREE new o-rings around the breech end of the barrel (you'll see the machined grooves for this) and then tighten down the barrel setscrew real well, the thing becomes almost a free floating barrel (lube well with silicone grease or whatever you decide to use when reinserting the barrel into the breech).The o-rings will usually need replacement each time, or at least every other time, you take the barrel out anyway, as they make for a super tight fit and you really have to drag it out of the breech, pretty much ruining the o-rings. The back two create the tranfer port seal, but the front one seems to be there just to stabilize the barrel.Regards and Aloha,
Barrel movementApril 24 2002 at 9:32 AM Bubba Bubba (Login DanHankins)from IP address 205.188.199.174
Zeke,Do not try to stop the movement of the barrel, side to side, by tightening the clamp. The bolt that goes through is very small at one end and will surely break. Been there done that.The best cure for this movement is CJ's idea of using another set screw on the barrel where it goes into the breech assembly. He also has an aluminum barrel band that might solve the problem.Being an ole country boy, and having some jute twine around, when I twisted off the cross bolt in the barrel band, I made a lashing, around the barrel band at the point where the screw was. I lashed it securely, and added some epoxy as I lashed. This stopped the barrel movement. Bought the correct screw from Tim, and when I removed the lashing, and installed the correct screw, I found that the lashing had actually done a better job of holding the barrel than the OEM barrel band and screw.Hope this helps.Respectfully,Bubba
Zathras the answer to the 78/79 .177 "O" ringApril 15 2002 at 11:49 PM jj (Login jay30350)from IP address 12.77.146.50
Zath, it was on my mind and I had some time so I pulled the bolt on one of the setup 78. The proper "O" ring is the (Parker Buna) 002, put the bolt in a vise and put the "O" ring on. The seal is excellent I still can't get the barrel, breech, bolt and bolt handle of my tongue. THERE IS NO NEED TO REMACHINE THE BOLT!!!
Ok here's what to do (to disassemble valve).April 21 2002 at 9:03 AM Co2une Co2une (Login Co2une)from IP address 205.198.245.28
First your going to need new seals, Regular Orings won't get it and if you pulled the cap off charged then the seal on it's gone. Pull the trigger, Pullthe barrel, Remove the breech, remove the hammer, Remove the hammer stop(the part that the stock stud geos into) Take out the small screw that holds the small screw that holds the valve. Useing a 5\8 rod drive the valve out from the cap end. When you take the valve apart press the vale stem out of the valve then useinf removeable locktite press it back together. This will fix you problem. It's a factory flaw that a batch had. If you'ld like I can Fix and tune it for the same price.QB78 .22 cal 14.3gr CP's 92degs612FPS 11.89FPE stock 709FPS 15.96FPE Co2UNEDQB78 .177 cal 7.9gr CPL 85degsF620FPS 6.74FPE stock 770FPS 10.40FPE Co2UNED Springers may be hot But Co2 is COOL!!!CJCo2unehttp://www.rapfire.net/~cjpitts/
QB78 US o ring size txt
by James Kitching Fun Supply
QB78 barrel o ring US size could be called
R05 012 3/8 1/2 1/16
Buna will do, since they are not constantly exposed to co2
Posted on Mar 29, 2001, 9:10 AM
o-rings for the barrel
by Mike in Indy
Hold your hand over the breech area when you fire it. If there is a leak you will feel a blast of gas.
I use rings purchased at ACE Hardware. They aren't metric but fit fine. Made by the Danco Company, a #7 o-ring, 1/2"x3/8"x1/16".
Put some silicon grease on them before reassembly, and when pushing the barrel in try to use a small screwdriver or something to hold the ring down as it slides past the setscrew hole.
Indy
Posted on Mar 29, 2001, 6:28 AM
QB-78 Mods-O-Rama
by John Eckenrode John Eckenrode
I scanned all 75 pages of this forum and gleaned a lot of info on the QB-78 mods, even some of CJ's great mods! I'd like to mention a few mods and ask a few questions, and I hope you more experienced folk will make some suggestions.
1. It seems that the gun should be disassembled and the paint taken off some of the internal trigger parts, to be followed by a smoothing of some rough surfaces. As long as I figure out how to get it apart, and back together again, this one looks easy enough. I've got my Dremel handy, I'll just run it at a slow speed with fine stones or sanding wheels and try not to overdo it, switching to light #600 sandpaper at the end.
2. O-rings. What's the scoop here? I read a msg that suggested replacing the o-rings, preferably with some stiffer material. Urethene or neoprene was suggested. Are the o-rings at Ace hardware superior to the included o-rings? Does anyone have a definite model # for the various o-rings, and if so, for what caliber, .177 or .22?
Here are some Ace hardware numbers I've collected, but not sure what gun each goes to:
orm-204-003 - Bolt o-ring (what caliber?)
3mm id 7mm od 2mm body
orm-204-008 - Barrel o-ring (what caliber?)
12mm od 2mm body
Also read references tp o-rings "#003" and "#7".
3. Micheal Zboray added a .25" thick plumbing washer to increase the force of the hammer spring. Why is this a good thing?
4. CJ cut off the port just in front of the seal and added a probe, made of a .073 number 49 drill blank. What the heck is that? Sears has drill bits that are numbered (instead of labeled by diameter) that they keep by the tap & dies - is that what it is?
Tom @ Buzzard Bluff suggested .062 music wire (used for landing gear in model airplanes) he got at hobby shops for the probe. CJ said he made his probe 1/8" longer to make up for it going into the pellet, and to seat it deeper. Why/how does this help, and how are these probes attached? This mod might get scary. . .I'll look at it, but might pass, depending on what I find when I open it up, and if you guys give me helpful advice on doing it.
5. CJ said he "lapped the lead-in to the breech with some 600 grit sandpaper", stating that the o-rings get tore up at this point, which makes sense given the rough surfaces that are on other internal parts and how the rubber could easily get sliced.
6. Where do I use the molly, what is it's real name, and where can I find a small quantity of it? As I understand it, the silicone grease is good on the O-rings and around the bolt area.
7. Somewhere else, when discussing using paint-gun air tanks, it was suggested that something be put in the co2 loading chamber. . .forget exactly, but it was something like pennies with a 1/4" hole drilled in them. Does that make any sense at all, and would that help with powerlets as well? Would that serve to take up space that would otherwise need pressuring? Maybe this gives you one or two extra shots? Wish I could find this link again. . .
Some of these mods are pretty involved, but as
long as I'm going to be taking it down to clean up the trigger mechanism, I might as well take a look at the rest of the gun.
Hints, tips, suggestions, comments? I had to go back 75 pages to get some of this stuff, so I thought I'd bring it to the front and get some conversation started.
-John
Posted on Mar 24, 2001, 5:47 AM
from IP address 216.0.204.48
Some answers
by TCooper
I am not a pro but I can answer some of your questions. I do not own a QB but I do have CO2 guns and some info is universal. I'm sure others will answer too.
1/ I would use fine emery paper and stones when working on the trigger parts. The dremel might take too much material off quickly.
2/ O-rings- The urethane o-rings last longer than cheap rubber ones. Rubber o-rings will usually become damaged if they are used on piecer caps. Rubber absorbs CO2 and swells up.
O-ring sizes - I dunno.
3/ The washer will preload the hammer spring and give more striking force. This will result in higher velocities.
The quest seems to be increasing the velocity on these guns. If you are not interested in higher speeds the washer is not needed.
4/ The probe allows better flow of the CO2 than the factory port on the QB. The probe is thin and allows more CO2 to flow around it. An ideal situation would be to have nothing interfering with flow but a small probe is needed to push the pellet into the bore.
I have heard of guys using cut nails, piano wire and drill bits for probes.
The probe is inserted into a hole that is drilled into the bolt face. The thickness of the probe is mentioned in your post. Exact is not necessary. Length is important as the pellet usually shoots best when it is seated into the rifling and past the transfer port.
5/ obvious
6/ Moly is used on friction parts. It is called something like molidenum disulphate (sp?). Beeman has 1/2oz jars of moly called BEEMAN M2M($2.95 from Golden Toller). It is a grey paste. Very ittle is needed on the metal. The moly actually adheres to the metal. Apparently moly looks like microscopic ball bearings suspended in a lube. I have never looked at it under a microscope but this is what is said.
Silicon grease is compatable with rubber. You can buy silicon grease at a dive shop. They use it for rubber seals too. An industrial supply shop should also have silicon grease.
BEEMAN sells silicon grease called "spring gel" but it is expensive for the amount you get.
The grease will reduce fiction on the 0-rings and increase their life.
7/ I duuno.
Opinions: The bolt probe is a good idea.
If you want more velocity shim the hammer spring with a washer but expect less shots per CO2 bulb.
Trigger clean-up will make the gun feel more pleasant to shoot and increase the "shootability" of the gun.
Removing roughness from the chamber is good. Also remove roughness from the slot the bolt travels in.
The QB-78 will shoot without any of these mods but performance and dependabiltiy will improve with them. Look at the QB-78 like "a diamond in the rough".
HTH,
Todd
Posted on Mar 24, 2001, 9:33 AM
from IP address 142.106.180.136
Probe
by John Eckenrode John Eckenrode
QUOTE:
The probe allows better flow of the CO2 than the factory port on the QB. The probe is thin and allows more CO2 to flow around it. An ideal situation would be to have nothing interfering with flow but a small probe is needed to push the pellet into the bore.
I have heard of guys using cut nails, piano wire and drill bits for probes.
The probe is inserted into a hole that is drilled into the bolt face. The thickness of the probe is mentioned in your post. Exact is not necessary. Length is important as the pellet usually shoots best when it is seated into the rifling and past the transfer port.
END QUOTE:
This mod, and the washer on the hammer spring looks to be VERY interesting mods. I'll look at them when I get around to breaking down the gun.
IMPORTANT QUESTION:
How it the probe secured in the bolt face? A good epoxy? I figure there's gonna be a lot of pressure there, and I want to do it right the first time.
A lot of great info in this thread. Thanks to everyone for the responses. It's been months since anyone's re-hashed some of these mods, and we newbies appreciate it! Any hints, tips, or opinions are welcome.
-John
Posted on Mar 24, 2001, 1:38 PM
from IP address 208.24.76.99
Respond to this message
Return to Index
Advertisement: Rent DVDs online -- Free Trial for 2 weeks!
Probe reply
by TCooper
First, the thick factory probe is cut off. Then a small hole is drilled into the bolt face . Then the new probe is inserted into the hole. Expoxy should not be necessary because this probe just pushes the pellet into the bore and there should not be any force to pull it out. If the probe is loose fitting and seems to move then a drop of locktite can be used. The hole should provide a close tolerance fit for he probe.
The correct protrusion of the probe from the bolt face can be determined from the other posts from those who have experimented with different lengths. This measurement is pretty important for top performance.
HTH,
Todd
Posted on Mar 24, 2001, 2:34 PM
from IP address 142.106.180.134
More probe stuff
by John Eckenrode John Eckenrode
Actually, I only caught ONE reference to probe length in the time I was looking back over the pages. Back around page 75, CJ mentioned the probe should be .125" (1/8th") longer than the original bolt.
I was thinking of using a 1/16" drill bit for the probe. I'll drill the hole with my 1/16" cobalt drill bit, then use the un-grooved section of a cheap oxide 1/16" bit, cut to size with my Dremel. Just hope I get the hole at a right angle (no bubble-level on my drill). Wonder if I can take it to a shop and get it done with a drill press?
-John
Posted on Mar 24, 2001, 10:16 PM
from IP address 216.0.205.200
How about just drilling one veticle hole half through from the bottom near the tip of the bolt , and
by H.Ma
on the face of the bolt, the two holes will provide an extra path for the CO2 gas. If we do so, would that achieve the same effect as the probe does, without having to cutt off the head of the bolt ? Thanks !
Posted on Mar 25, 2001, 6:40 PM
from IP address 131.225.122.103
I do mine on a Lathe
by CJ((Co2UNE)) CJ((Co2UNE))
And make it press fit . It should be in the center of the bolt due to flipping or cocking the pellet as it goes in. The probe is there to give more room for the Co2 to to expand in the chamber ,It's a 1/8 longer to make up for the cavity in the back and proper seating in the grooves. Later
Posted on Mar 25, 2001, 10:07 PM
from IP address 205.198.245.77
thanks!
by John Eckenrode John Eckenrode
Appreciate the info. It's nice to see you are free with the information. A lot of ppl in your place would keep it to themselves as a trade secret, to bring in more customers.
I was wondering if you might have changed the length of the probe after months of experimentation, but I notice you still believe 1/8" longer than the original is the best length. Thanks for the info, and the instructions.
-John
Posted on Mar 26, 2001, 12:38 AM
from IP address 216.0.204.41
John, you got your email working yet?
by Mike in Indy
Mgoode@in-motion.net
TC has most of the answers. I agree with him don't touch anything with a dremmel tool. I used #600 sandpaper followed by a polish with #1500 on the trigger sear surfaces.
Mike in Indy
Posted on Mar 24, 2001, 11:11 AM
from IP address 206.31.43.156
My rationale
by Michael R. Zboray Michael R. Zboray
John,
I claim no special expertise, but here is my shot at some of your questions.
1. I would not remove the barrel to change O-rings unless there was some evidence of CO2 blow-by.
If you remove the barrel for any reason, I'd be prepared to replace the 3 O-rings. Removing the barrel seems to be pretty hard on the O-rings.
2. Why did I add a .25" washer to the hammer spring?
Well, the gun wasn't fireing any more. The hammer was not hitting the valve with enough force to actuate the valve reliably. I think I may have left the gun cocked when I put it away. After adding the washer, the gun fired like a champ again. In theory, a more forceful hammer strike could hold the valve open longer allowing a more complete discharge of the CO2 from the gas chamber. However there would be a limit to this benefit. CO2 will quickly turn from a gas to a solid once the pressure is removed and the vapor pressure will not be terribly high until the resevior is sealed again and the temputure rises. The solid will convert back to gas over a bit of time.
3. Molly (MOLYBDENUM DiSulfide: MoS(2)) Is wonderful stuff. I lubed up all the metal to metal sliding parts and it smoothed out the operation of the gun noticably. If I bought a new gun, this is the only thing I would absolutly do. But I would not do it immediately. IMHO I would shoot about 2000 pellets first. Molly is tough stuff. It clings to metal but not to itself. I believe if you let the parts rub for a while you will see places where, just though use, the gun smooths out. If you molly first, then eventually you will grind the molly away until it is nolonger there. So grind away first and then add molly. I bought my molly from golden toller but if you search on the internet, you will find it at other airgun stores and from industrial supply houses.
Best of luck and let us know how your clean up turns out.
Mike Zboray
Posted on Mar 24, 2001, 11:31 AM
from IP address 24.189.215.88
hammer springs
by TCooper
I am no pro on CO2 guns but I have done a lot of experimenting with many Crosman Mark 1 guns and a BRNO TAU-7.
The TAU-7 has a variable velocity screw which simply puts MORE tension on the hammer spring. The velocity is adjustable from 350-600fps with the turning of this screw(7.3gr pellets).
The Crosman Mark 1 in factory form shoots 400fps with 14.3 grain pellets. With a heavier hammer spring it will do 440fps. With a 12" barrel and a heavier spring it will do 485fps with 14.3 grain pellets.
In all these cases there was NO mods done to the valve, valve stem or ports.
My guess is that simply increasing the hammer spring tension on the QB will increase velocity every time. I may be wrong, but I would think that with the longer barrel in a rifle there will be large velocity increases noticed.The use of porting and stem contouring will give more velocity.
As I mentioned previously, I do NOT own a QB-78 and have never had the opportunity to tinker with one, yet. I do not intend to cause an arguement with this posting, just point out my personal experiences with the limited CO2 guns I have owned.
Later,
Todd
Posted on Mar 24, 2001, 12:01 PM
from IP address 142.106.180.134
Now you've done it!
by Michael R. Zboray Michael R. Zboray
Todd,
Now I'm really perplexed!
How would your posting cause an argument?
Mike
Posted on Mar 24, 2001, 12:08 PM
from IP address 24.189.215.88
Mike
by TCooper
Some airgun shooters seem to become arguementive if their ideas are challenged. I do not like to start or participate in these disputes. I only seek sound knowledge from those more knowledgable than I.
I was not sure how you would take a different perspective on hammer spring tension. Your posting seemed to indicate that a velcoity gain COULD be obtained with increased tension and I indicated that one WILL be obtained.
Thanks,
Todd
Posted on Mar 24, 2001, 12:23 PM
from IP address 142.106.180.136
Questions for Mike Z.
by TCooper
I have a couple of questions regarding CO2 properties. From my understanding CO2 will try and maintain approximately 800-850psi at room temparature when it is contained. The contained CO2 will be part liquid and part gas(70% liquid when full). When a shot is taken with a CO2 gun some gas will be released and pressure will drop in the contained area (CO2 reservoir). Then when the valve is shut some liquid inside the pressurized tank will evaporate to a gas and restore the internal pressure to 850psi. When all the liquid is evaporated (many shots) the pressure will continually drop with each shot until the gas is gone. Then there will be no pressure.
When air temperature is stable at 60-80 degrees, CO2 is a great, self regulating propellant.
Am I correct in this understanding?
When CO2 is under no pressure (not contained) what state is it in?
When suddenly released in a very large quantity (fire extinguisher) does it become a solid and then slowly turn to gas? I actually have never used a CO2 extinguisher.
Thanks in advance for your reply,
Todd Cooper
Posted on Mar 24, 2001, 12:18 PM
from IP address 142.106.180.136
Long Reply: I think your on the money
by Michael R. Zboray Michael R. Zboray
Todd,
I think your on the money.
I don't know the exact ratio between liquid, solid and gas at 850 psi, but at 1 atm pressure co2 is either solid or gas, no liquid.
So here is the thought experiment that I think explains the data.
Open the valve for a very long time.
The pressure and temp drops as the pellet moves down the barrel the liquid in the resevoir starts to convert to gas and solid trying to maintain pressure.
Eventually, all of the liquid converts either to gas or solid.
Then, the only contribution to the speed of the pellet is the expansion of the remaining pressurized gas.
If the valve is shutting before all of the liquid converts to solid and gas, then the maximum velocity of the system will not be achieved. But the exit velocity will be very consistant because the liquid it conveting to gas and solid very quickly maintaining a very consistant internal pressure. As long as there is some liquid in the resevoir, holding the valve open longer will have an effect on the speed of the pellet. That is, until the pellet leaves the barrel. Keep on holding the valve open after the pellet leaves the barrel, and you have a waste of CO2.
The best consistancy will be achieved if there is some CO2 liquid in the reservoir when the valve closes.
(I'm assuming that the pressure contribution due to sublimation is mimimal. The majority of pressure pushing the pellet down the barrel is comming from first, the conversion of a quantity of liquid into gas amd then the volume of expanding pressurized gas in the resevior.)
This explains why you can get some higher velocities with longer barrels. CO2 liquid is still being converted to gas mainbtaining a high pressure while the pellet is traveling down the barrel. The pellet can continue to accellerate.
Eventually a longer barrel works against you.
The liquid completely converts to solid and gas, then as the pellet moves down the barrel the pressure drops until barrel friction is greater than the pressure applied. The pellet then starts to slow down.
All this being said, I think is is safe to assume that a stronger hammer spring will increase velocity most of the time. The place this might not be true is when the barrel is very short (say a 4" pistol barrel). Then the pellet may have already exited the muzzle.
Posted on Mar 24, 2001, 2:02 PM
from IP address 24.189.215.88
My thoughts exactly
by TCooper
We seem to have the same understanding on CO2 properties.
Often CO2 pistols will have a valve duration that produces more velocity with only the switching of a barrel. A few guys have experimented with the Crosman 2240 and found a velocity jump from 416fps to 472fps by switching from the factory 7.25" barrel to a 10.25" barrel from a 1322. Switching to the 14" barrel from a 2250 increases velocity to approx 535fps. This increase is realized without hammer spring changes or porting.
I found the same thing when tinkering with a few Crosman Mark 1 guns. I could not get past 440fps with a 14.3 grain pellet (at 68 degrees)when I only changed hammer springs. Excess CO2 was blasting out the muzzle and no increase in velocity was had. By adding a 12" barrel the velocity jumped to 484fps with the same hammer spring that gave 435-440fps with the factory barrel length.
I hope our chat enlightens others about the wonderful properties of CO2, as a propellant.
Thanks,
Todd
Posted on Mar 24, 2001, 2:24 PM
from IP address 142.106.180.134
Dittos
by Michael R. Zboray Michael R. Zboray
Tod,
I knew that we would end up at the same point.
One more item, and then I'll shut up.
If what we conjectured is correct, then you can predict what the additional velocity will be when you lengthen or shorten the barrel length.
Should be
Vnew=Voriginal x sqrt(LENGTHnew/LENGHTold)
I tried the formula on your data and it is close, not perfect. It does not account for the additional force of sliding friction so the actual numbers should always be lower than what the formula predicts.
I suspect a little variation in pellet diameter and weight cause some of the variation as well.
Mike
ps. I'll confess, I really like figureing this out, but I'll shut up now. Before I'm baned from the board.
Posted on Mar 24, 2001, 4:37 PM
from IP address 24.189.215.88
Molly link:
http://www.beslub.com/moly.htm
by Michael R. Zboray Michael R. Zboray
Really good explaination of how molly works
http://www.beslub.com/moly.htm
Posted on Mar 24, 2001, 11:41 AM
from IP address 24.189.215.88
Shopping spree
by John Eckenrode John Eckenrode
Ok, I went out and picked up some supplies.
The sandpaper/emory paper/cloth was tougher than I thought. I tried an Ace Hardware, a hobby store, Home Depot, and Lowes, and I can't find anything anything finer than 600 grit sandpaper, and the emory cloth I found was labeled in course, medium, and fine, not in grit.
At Ace Hardware, I got 1/4-in. S (or #00) faucet washers, flat, for increasing the force of the hammer spring(Model# 46101, $.89 for six). They're rubber. I hadn't expected that, but I guess I should have. Ace had a lot of rubber o-rings, but they were in little drawers, and most of them were not labeled. Better to bring your bad o-ring to them. They had a variety pack that I might go back for. . .
At Home Depot, I picked up three 1/2" x 3/8" x 1/16" #7 O-rings. This is the correct dimension given for the barrel O-rings, but who knows what caliber this is for - maybe either. This may also be availalable at Lowes, but I didn't look for it there.
At Lowes, I got a 9/32" x 5/32" x 1/16" (7mm x 4mm x 2mm) #61 O-ring, and a 1/4" x 1/8" x 1/16" (6mm x 5mm x 2mm) #60 O-ring. Neither seem to exactly match the dimensions given for the bolt O-ring, so I got both. Hopefully one will do the job if necessary.
I picked up a 3/8" wooden dowel for sanding the breach tube, and popping the safety, as per "Mike in Indy". That's available everywhere.
I looked locally for a moly lube, but the closest thing I found was at Auto Zone, "Coastal Industrial Moly EP grease"($1.99) and "Exxon Lidok CG Moly Chassis Grease" ($2.99). Both contain petroleum products, which I understand I should avoid.
I hate to go mail-order JUST for the moly, since the price will probably be double by the time they throw in shipping. Fun Supply didn't have any, and neither does the place I want to order my scope from. Oh well.
I DID pick up something pretty cool, though. At a local army surplus store (I live a couple miles from Ft. Campbell, Ky), I bought a couple 4.5" x 5" olive-drab, heavy-duty, nylon pouches with a fold-over snap fastener at the top, and an "alice clip" belt fastener. Was used to hold a compass. Looks like it will hold 3 or four powerlets, or a couple tins of pellets.
Posted on Mar 24, 2001, 9:49 PM
from IP address 216.0.205.200
New QB-78 - what needs done out of box?
by John Eckenrode John Eckenrode
Ok, it's my first Chinese airgun, first airgun in 20 years, and my first co2 EVER. It should be here in the next couple mail-delivery days.
What to do?
It should be all greasy, so, what do I clean it with? Clean rag? Clean rag with a little 3-in-1 on it?
How do I clean the barrel? I've heard of felt cleaning pellets, but can't find any. . .Do I get one of those cleaning kits with a flexible plastic wire? What do I put on the patches to clean the barrel?
I have a silicone gun & reel cloth I got to wipe the gun down after handling, and I bought some 90% pure silicone grease from Ace hardware, though this stuff is so thick I don't see how it can make anything move more smoothly.
I've read ALL 75 pages of this forum, and I didn't find answers to these questions, or at least clear ones.
Thanks in advance.
-John
Posted on Mar 24, 2001, 4:32 AM
from IP address 216.0.205.30
cleaning
by TCooper
If your gun comes gooped up with petroleum grease you will have to clean the gunk off. I have used WD40 on a rag to do this on guns. Make sure the WD40 does NOT get on any seals. It will eat them after a while if allowed to soak.
To clean the bore on airguns I use a pull-through I made. I made it from a 3ft piece of .080 weed wacker cord. Cut a point on one end and melt a blob on the other end. File the blob until it fits into the bore with a patch on it. To clean, poke a patch on the point and slide it down the cord until it sits on the button you just made.
A alternative is to buy a patchworm unit from www.silverstreaksports.com. Price is $5.00 including shipping.
To clean bores I use Slick 50 Lube-1 because it is safe on seals.
HTH,
Todd
Posted on Mar 24, 2001, 9:41 AM
from IP address 142.106.180.136
Felt cleaning pellets are a waste of money, IMHO
by TCooper
They do not work that great for cleaning. Sometimes I use the felts to quickly oil a bore. I lube them up with LUBE-1 and shoot them though.
HTH,
Todd
Posted on Mar 24, 2001, 9:44 AM
from IP address 142.106.180.136
QB-78 O-rings
by Tom @ Buzzard Bluff
Ting, the machine work on the breech and barrel leave a bit to be desired. With a Dremel tool and a small, fine grit stone you need to clean-up the sharp edges on the breech where you insert the barrel and the set-screw hole that extends through the breech. Some sandpaper wrapped around a rod and chucked into a drill may be used to polish the sharp edges inside the breech. The O-ring grooves on the barrel itself should also have the sharp edges relieved a little. Before inserting the barrel lube it and the o-rings as well as the inside of the breech with some heavy 100% silicone grease. (get it at a skin diving shop) Be sure that you disassemble the breech from the gun for the clean-up procedure so as not to get any grit into the 'innards'. The bolt also will benefit from some polishing while you have it apart as well as lubing it with some of the silicone grease before reassembly. HTH, Tom @ Buzzard Bluff
Posted on Mar 16, 2001, 6:04 PM
QB 78 o-rings
by Mike in Indy
Definately try to do what Tom says before replacing the rings.
The rings are metric size, supposedly 8mm ID X 12mm OD x 2mm dia.
I couldn't find that metric size locally and a recent phone call to Compassico (the importer) found they don't have any in stock.
I used rings purchased at the local Ace Hardware that are 1/2"X3/8"X1/16". These were made by the Danco Company and are are called a #7 o-ring. I have seen the same rings at Sears Hardware and Lowes. Find them in plumbing supoplies, I think they are intended for faucetts. They are slightly thinner but work just fine. Do grease them with silicon grease, makes the barrel slip in easily.
Mike in Indy
Posted on Mar 17, 2001, 12:58 AM
This might help
by Ting Pan
ACE Hardware part numbers for some QB78 o rings
By Ed Highet
Bolt oring #ORM-204-003 3mm ID 7mm OD 2mm body DIA
Barrel orings #ORM-204-008 8mm ID 12mm OD 2mm body DIA.
found it on Funsupply's site
Posted on Jan 12, 2001, 10:39 PM
by CJ CJ
85degs and pretty consistant,These are the first 8 shots then it went to about 680-690fps with CP Lites.Geco's were pushing 735fps. The tune was pretty much the same as it's described at the Funsupply sight except for a few thing I did. First the bolt , I cut off the port just in front of the seal and added a probe. It's .073 number49 drill blank. The probe is .125 longer than the original bolt to seat it in the barrel more and to make up for the probe going in to the back of the pellet. then I turned the groove a little deeper and opened it up to .050 Can't remember how deep but I just touch the bottom to square it off. Then I lapped the lead in of the breach with some 600 grit paper. Seems that was what was tearing up the o-rings. BTW the O-ring is a standered 003 you can get them at just about any seal supply look in the yellow pages if there not close try Mcmaster-Carr. I use the Neoperene I have a sorce for some urethane but have to order 10 at a time at .89cents plus S/H. Next I crowned the barrel with a brass screw and lapping compound. Last was to make a barrel brake with a chamber to take the the edge off the report. Epoxyed on
Shoots very nice.
CJ
Posted on Jun 1, 2000, 5:59 PM
