Not going to be the popular choice because it gives up really high power.
#1. Lighten the striker "top hat" (it is really the guide, but it's big and heavy and runs back and forth with he striker and works like a springer's "top hat").
#2. Tune it to run at lower pressure. This reduces the stress to the valve stem and allows you to cock the gun with one finger.
LONG post to follow:
Got to trying low pressure fills in this .22 BAM 51 (bought from the classifides). Recent posts made me wonder how well it would do at lower pressure. Did do some changes along the way to get it running as well as I could at a 1500 900 psi fill.
Bam 51 experiments: Lighter striker
Already found how to use the factory setting/parts to get up to 30foot pounds or down to 25. Shot count at any of the various settings hovered around 20-25 shots within a reasonable (30fps) vel. variation. Could get it to run that way with a starting pressure at 170BAR for the higher energy strings or down to 140BAR for the lower energy strings.
Part of the design of this gun is a heavy top hat/spring guide that inserts into the striker and adds to its weight. That top hat/spring guide runs about 38.8 grams. (plus the weight of the striker).
Problem is this. Aluminum makes a crappy spring guide as it tends to gall and increase friction. Brass is great, but its heavy. Delrin can work, but I was out of Delrin rod.
So I made a replacement from mother-of-screwdriver-handle. At least it was an old beat up Stanly screwdriver, and the handle certainly did machine like black Delrin. Know it will break, but at least will get some test numbers (months later and it hasnt broken and I havent changed it.)
The replacement comes in at 7.2grams, so the weight hitting the striker was reduced by 31.6grams (or about 1 and 1/8 ounces).
First up were 14.3gr. CPs.
Not really impressive.
8111-841-811FPS = 28 shots @ 21.7 foot pounds
Tried some 18.1gr. JSBs but they were terrible. Bad enough that I had to resist the urge to take the rifle apart and see what the hell went wrong with it. Vel would vary as much as 35fps between individual shots, making the shot graph look all saw-toothed. Am going to wrote that off as just a bad pellet-barrel combination; really have to logical reason for that pellet to do so badly.
Tired a 3rd time with 15.8gr. JSBs: this pellet the gun likes.
772-802-772 (30fps) = 31 shots
782-802-782 (20fps) = 26 shots @ 22 foot pounds
792-802-882 (10fps) = 18shots.
So with the mother-of-screwdriver-handle top hat/spring guide and the striker set for longer travel, the rifle is a 22 foot pound/ 31shot/ 30FPS hunter (or a 22 foot pounds/26 shot/20fps gun) which is good enough for any hunting I intend to do with her.
Before you suspect the crown, look at the breech end.
This gun bothered me, so I gave it a good cleaning. Seemed fine, but felt a little roughness at the breech end. Didnt let it bother me at first, the difficulty on chambering might have been my replacement bolt probe o-ring.
Got this at 20yards, but with only one pellet.
Was pretty pleased, only 20yards, but still averaging less than .2 at that range.
But the difficulty chambering continued. On a test, took off the o-ring and chambered a few pellets, feeling the same tough spot. Knocking the pellets back out with a rod, found this:
Check out the middle pellet:
Now that I know what to look for , could easily detect the burr with a probe.
How 30 of those burr-sliced JSBs managed to stay under 2/10th at 20yards now seems the mystery. Think the dead soft lead and thin skirts managed to reseal from pressure when smacked in the rear by a burst of air, but there is no cureing a sliced pellet head.
Now that I found a problem, what to do about it? Best would have been to take the barrel off completely and work on that. Perhaps making a nice reamer just to clean up that burr.
Rather than do that, decided to just stone it down.
Can get the idea from those pictures. Rebated rod, glue, and emory paper glued onto the rod. Going careful, keeping no deeper than you have to to remove the burr, and working at the 6 o-clock of the barrel, it wont enlarge the chamber if you have a light touch. Rotate the rod to use a fresh face. Can heat up the rod to remove, then glue a new piece on if needed.
With the burr gone, had time to shoot a couple of test groups at the same 20yards:
Chambering is easy now, and while early indications are that accuracy has gotten better, will have to test a bit more to see if it is as large an improvement it seems and if the pellets rejected lat test are improved.
Picked it back up today. Raining, so not much else to do but fiddle in the workshop, change a few things, get some shot counts, and blast a few 20yard targets.
Still on targetwhich is a nice bonus as Ive left it along and neglected in the safe for a few weeks.
Still getting 22-29 good shots with low fill pressure from 125BAR to 85 BAR (or about 1800 to about 1200Psi)
825 845 825 (20fps) = 22 shots
815 845 815 (30fps) = 29 shots
Got a bit better shot count with heavier pellets, which isnt unexpected with PCPs.
To get it to run well at higher pressure and strangling off the transfer port might earn a longer shot count at this (22 foot pound) level. But the weak part of the BAM design seems to be that skinny bolt with the big tapped hole though the middle of it. Increasing striker spring tension would stress that bolt (at the tapped hole) even more than it does now, and Im not really too keen on finding (or making ) a new bolt.
Looks like Im going to keep it at this power level / pressure/ cocking effort.
120BAR to 85 BAR
779-799-779 = (20fps) = 23 shots = 20 foot pounds
769-799 -769fps = (30fps) = 29 shots
General observations of low pressure fills seem confirmed:
1. Can fiddle with the settings and get the gun to run well.
2. Energy will be less than with high pressure.
3. Shot count will be a bit shorter than could be had with higher pressure.
4. Pump filling to 1500-1600 psi is a whole lot easier than filling to 2,500psi.
5. The valve stem has the reputation for sometimes breaking. Running it at high pressure and smacking the crap out of it with the striker in order to get higher power is probably the cause. Run it a bit slower and at a whole lot lower pressure and that stress is greatly reduced.
6. It KICKS ASS with tank filling!!!
80cf 3000psi scuba tank will fill 200cc to 2500psi/1500refill about 27.8 times. I get 35 sweet spot shots per fill with that setting, so a tank of air could fully fill for 973 shots.
Same tank and 3K fill used to fill to 1600 and refill at 1000psi could fill 129.5 times. I get 22 sweet spot shots per fill, so that same tank could fully fill this rifle for 2,849 shots.