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B22 barrel chop question

April 1 2002 at 1:59 PM
Ed S  (Login cthulu)
YC

Well i am thinking I would like to cut the barrel length of my B22 to the optimum lenght needed. I am wondering who out there has cut the barrel on the B21/B22 and what length worked out best. I assume if a gun like a TX200 can get away with an 8" barrel the B22 can go substantially shorter than the stock lenght, I am thinking of cutting it to 15" from the stock 20". Any tips or experience appreciated!

 
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James Kitching Fun Supply
(Premier Login doratis)
Forum Owner

I lost about 60 fps at 16 inches txt

April 1 2002, 3:27 PM 

but gained a little accuracy.
The TX was designed from the ground up for a short barrel.


    
This message has been edited by doratis on Apr 1, 2002 6:07 PM


 
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Ed S
(Login cthulu)
YC

chop

April 1 2002, 8:24 PM 

James, so in your exerience shortening barrels on these was there any advantage at any length? Was this a B21 or B22 you shortened? I would imagine due to the volume of air and the bore size you could cut the .22 verson a little shorter than the .177 before effecting velocity. There must be some formula for stroke length of the compression tube, diameter of the tube and the bore/barrel to figure out at what point downt the barrel the pellet is no longer under infulential pressure. I suppose I could try to calculate it, anyone know what the bore specifics for a b22 are, or this formula?

 
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Steve in NC
(Login pneuguy)
Chn

Good luck, Ed, if you try to tackle it. At least I hope you have...

April 1 2002, 9:32 PM 

...better luck than I did.

I worked up a numerical simulation of springer internal ballistics that seemed to look pretty realistic. It predicted that the optimum barrel length for max MV with a 7.9gr pellet (primarily determined by the duration of the piston pressure pulse) for a .177 B18 is 10".

So you can imagine my chagrin when I chopped a B18 to 10" and LOST 40 or 50fps with CPLs over the stock 18" barrel length!

Now the best I can get from my B18 carbine shooting CPLs is 812fps -- 11.6fpe. I, like James with his B22, think I see improved accuracy (maybe due to the shorter lock time), but it did cost about 10% in ME.

Let us know how you get on.

Cheers,
Steve

 
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Ed S
(Login cthulu)
YC

weird

April 1 2002, 9:43 PM 

Steve, well it looks like you already tried my thoughts out. there must be some portion of the equation that takes into effect the compression of the air and what that does to the volume of the chamber. But who knows, it probably doesnt take much to be off alot, like if you are off on the stroke volume just a bit that would really screw up figuring out barrel length as a little air in the chamber is alot more in barrel length. if this was a .177 gun (B21) i would not worry about 40-60fps, but thats alot out of a B22 velocity. Maybe I oughjt to get used to the length!

 
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Jim in Fl.
(Login airforcewon)

keep your ideas going

April 1 2002, 10:07 PM 

It sounds interesting to me cause I have a B22 too. I think there is more to figure in than bore and stroke and how much that displacement will fill the barrel. A big thing would be the microseconds of extreme heat from the air being compressed so high. In another instant the air is cooled back down by the ambiant temperature of steel around it. Any ways air expands when it is heated and that is part of the equation for optimum barrel length. Also I talked to James about his barrel shortening experiments. I may be wrong but I think he was only doing it on .177 B21 rifles, not the B22, I apologise in advance if I am wrong on that. Bottom line is, I want to encourage you to try a barrel chop on a B22. I'd like to know your results. I already put a muzzle brake on my stock barrel so I'm not in a hurry to cut it off...yet.

 
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Ed S
(Login cthulu)
YC

cut

April 2 2002, 10:03 AM 

Well I want to do this but I want to fully investigate it before I make the commitment because the gun really is nice as is, I just think it would be better with a shorter barrel. But I dont want to do it without feeling sure it will be better. Once I get alot of feedback and make a decent decision on length, I will go ahead and post results.

 
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(Login RBest)
YFOT

one thing that helps- the choke

April 2 2002, 12:47 AM 

even though a choke is a restriction in the barrel, it also helps short barelled guns achieve higher velocities. When you cut the choke off a choked barrel, things are bound to happen. RB

Russell Best
BesTunes
BSA Owners Club
C.O.P.S.

 
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(Login cthulu)
YC

choke

April 2 2002, 9:59 AM 

Do you know whether the B21/22 come with choked barrels? That makes sense what you say, good point.

 
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(Login RBest)
YFOT

don't know for sure really

April 2 2002, 10:50 PM 

the only way to tell is slowly poke a pellet down the bore and feel for some resistance right near the end. RB

Russell Best
BesTunes
BSA Owners Club
C.O.P.S.

 
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TF79shooter aka airheaded
(Login TF79shooter)

Check out these pics....

April 1 2002, 11:25 PM 

of my B21, it shows the piece of barrel I removed along with the other "Extensive" work I did to "Sporterize" my B21. BOTTOM LINE: Shoots better than before for accuracy, I haven't chrono'd it so can't say if lost speed but it sure doesn't seem like it. Overal length is now 37 1/2" and it weighs in at about 7 1/2 #'s.
see sight below for pics posted back in January:

Modified B-21, by Airheaded.
January 8 2002 at 8:53 AM Eddie (Login Adiberts)
from IP address 66.50.82.179

--------------------------------------------------------------------------------

Go and see the great job Airheaded did on a B-21 modifying it.
http://home.talkcity.com/PhatAirRd/masterpellet/b21_modified.htm


Regards,
TF79shooter aka airheaded

TF79shooter

Keep em in the black!

 
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(Login jpsaxnc)
YFOT

If you shorten the barrel, you might want to try and

April 2 2002, 7:35 AM 

reduce the transfer port diameter a little, I would try about .003 smaller. This will boost the velocity of the air passing through the port, The volume of air reaching the pellet will be reduced, but then the barrel is now shorter, and should not requier as much air volume. Good Luck James P.


    
This message has been edited by jpsaxnc on Apr 2, 2002 7:52 AM


 
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Steve in NC
(Login pneuguy)
Chn

Interesting logic, James. And quite possibly correct. On the other hand...

April 2 2002, 10:00 AM 

...I was guessing that reducing the transfer port area would tend to lengthen the duration of the piston pressure pulse. Which would seem to be the opposite of what's wanted to deliver max energy over the shorter time the pellet will spend in a shorter barrel.

So I wonder if, all other things being equal, a carbine might want a larger transfer port -- not smaller.

Of course, given my record of "success" in predicting springer behavior, anybody might be wise to seek my sage advice -- and then go bet on the OTHER horse!

Cheers,
Steve

 
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Ed S
(Login cthulu)
YC

transfer port

April 2 2002, 10:05 AM 

Once I put some thought into it I would agree with you Steve, seems like a bigger port with a quicker transfer of the air would go hand in hand with a shorter barrel.

 
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Steve in NC
(Login pneuguy)
Chn

Okay. That's two votes for bigger and one for smaller. Question is...

April 2 2002, 10:12 AM 

...how would the damned GUN vote?

 
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(Login jpsaxnc)
YFOT

LMAO, Hi, Steve, I'm planning on doing unmentionable, and

April 2 2002, 10:51 AM 

blsaphemous, things to one of my superstars, bought soley for this purpose, I want to turn it into a carbine. So as time permits I will try various experiments on it. James P.

 
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Steve in NC
(Login pneuguy)
Chn

Sounds fascinating, James. Not to mention brave...

April 2 2002, 11:14 AM 

...a whole lot more ambitious anyway, than cowards like me who confine our whittling to El-Cheapo Chinese products. And on and under-lever besides. So that's an extra thing to cut!

We'll all be watching -- from ringside.

Steve

 
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(Login RBest)
YFOT

at least with the Superstar

April 2 2002, 10:55 PM 

you can remove the rotary breech to work on it. Being aluminum, you could drill and tap it oversized, then buy some full length set screws and drill them out with various sized ports and screw them into the block, leaving the optimal size in the gun for permanent use. RB

Russell Best
BesTunes
BSA Owners Club
C.O.P.S.

 
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Ed S
(Login cthulu)
YC

reducer?

April 2 2002, 10:02 AM 

How could you do this, put a reducer of some sort at the breech seal?

 
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(Login jpsaxnc)
YFOT

Super glue a piece of telescoping brass tubing

April 2 2002, 10:56 AM 

the kind you can get from a hobby supply place, inside the transfer port. Then slowly and carefuly ream it out to the desired size.Or depending on your ability, and resorces, solder, a piece in the port and ream to size. Good Luck James P.

 
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Jim in Fl.
(Login airforcewon)

rejetting your transfer port

April 2 2002, 12:03 PM 

Super glue wouldn't last one shot. The transfer port is one hellacios place to be in a springer. Especially if you have a little too much oil in the gun. You could remove the compression cylinder, remove the breech seal, and braze the transfer port closed with brass. Just don,t fill in the recess for the breech seal. Then redrill the transfer port smaller to the size of choice. Seems like this would smooth out the second recoil, but increase lock time at the same time- not good.

 
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(Login jpsaxnc)
YFOT

Hi, Jim, I have Made interchangeable transfer ports

April 2 2002, 12:49 PM 

for a chiness springer that I have, going smaller did smooth out the recoil, as far as locktime, it was still faster than anything I was doing while holding and shooting the gun, I was also able to increase lock time to a very noticable degree in this gun by skeletinizing and shorting the piston. Still no noticable change in accuracy. James P.


    
This message has been edited by jpsaxnc on Apr 2, 2002 12:51 PM


 
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Steve in NC
(Login pneuguy)
Chn

James, didn't you mean to say that lightening the piston...

April 2 2002, 3:15 PM 

DEcreased the locktime, rather than INcreased it? I'd sure expect that a lighter piston would accelerate faster and so make for a faster-rising pressure pulse and earlier pellet movement.

In the simulations I did, a lighter piston also made for a higher peak pressure -- although the duration of the pulse was made so much shorter that MV actually decreases.

As for the effect of reducing the transfer port size, I'd guess that the minimum locktime would correspond to whatever port size gave the greatest MV.

I know for a fact that increasing the diam of the port on my Tomahawk was one of the mod's Russ made that netted an increase in ME from 13 to nearly 17fpe.

Cheers,
Steve

 
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(Login jpsaxnc)
YFOT

Yes, I did mean to say decease, lock time, sorry about that.

April 2 2002, 3:39 PM 

This mod. also had the effect of causeing premature combustion. A very noticable drop in velocity. James P.

 
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(Login RBest)
YFOT

the dangers of reducing piston weight

April 2 2002, 11:03 PM 

or the total weight of the moving mass ...more likely to experience spring bounce... increased pellet sensitivity... increased liklihood of dieseling...and a sharper (faster) recoil which MAY be rougher on scopes. Maybe a couple other things too. Regards, RB

Russell Best
BesTunes
BSA Owners Club
C.O.P.S.

 
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(Login jpsaxnc)
YFOT

Hi, Russ, Yea lightining the piston in another springer I have

April 3 2002, 9:27 AM 

did increase detinnation, I like the idea of Making threaded TP. inserts for the rotory breech, I was thinking of shorting the barrel, 2-3", I'm sure there will be a velocity loss, it will be interesting to see if it can be regained. James P.

 
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(Login RBest)
YFOT

BSA uses an aluminum rotary breech that is removable. nt

April 2 2002, 10:57 PM 

nt

Russell Best
BesTunes
BSA Owners Club
C.O.P.S.

 
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