BAM 50 tuning: this wasn't what I expected

[Ribbonstone]

DAY 16:

Not really what I expected, but that’s often the case with tuning the little stiff of PCPs.

I LIKE what happened, it's just not what I EXPECTED to happen.

1. No valve work.
2. Stock transfer port.
3. Striker spring shortened by 1-½ coils (and the ends polished, so call it 1 5/8ths coils)
4. Spring guide/top hat lightened to 24grams.

Where I was:




THOUGHT I might bring it down that little bit to something closer to an even 20 foot pounds even by:

1. INCREASING the striker spring tension by spacing it up ¼”.
2. DECREASING dwell by 1/8” (moving the little screw on the striker nose forward that amount).


Tested today:



#1. Energy stayed just about the same, so this did not bring it down to 20 foot pounds (yet).

#2. Upper AND lower sweet spot fill pressure INCREASED.

#3. The total shot count isn’t much different, but the 2% and 3% shot count got noticeably better.  The changes made the shot-count -plateau flatter but didn’t make the plateau larger.


Do think I’m on the right track.  Also think I’m going to have to very slightly reduce the transfer port to get BOTH 20 foot pounds AND an even longer 2% and 3% shot count.


(Yeah…could put in a regulator.  It may happen, but not until I get the most it can offer without one.  Al-in-all, am pleased with how well this rifle has responded to simple tuning, will get into more complicated tuning after I’ve taken the simple as far as I can.)

Have a chance to get more distance soon (last tests were at 40 yards), and I’ll find out then if this speed is too fast for those 10.5’s.  So far, at 40 yards, they’ve been the best shooting pellets, but that might chance with increased distance.

[Motorhead]

Looking real good !

Going Regulated with a few other parts FWIW can get you @ 70 shots with 10.5's @ 900 fps inside 2% SD 

Never say never 

[Ribbonstone]

Will have to balance the pump-up effort with the shot count.

 Once I get the non regulated rifle tuned to to 20 foot pounds, might be able to move the 35 shots at 3% to 35 shots at 2%.  If I can manage that, then will have to look at the pump-effort.

If the regulated rifle takes 1500psi to shoot that 70 shots at 2% varition (lets say from 3000 to 1500) vs. the unregulated rifle taking 750psi to shoot 35 shots (if I can get it tuned to 900fps and 2%) then I figure it is about "even" in pump effort (although only pumping to 2500 is easier than pumping to 3000psi, I'll give you the extra effort).

[SpiralGroove]

Hey Ribbonstone,
In that last 500 psi, going up to 3000 psi, just put your total mass behind it .  Nothing like a little gravity to help .

[Ribbonstone]

Would have to see a gain in "shots per pump stroke" for it to be worth regulating, but I'll have to seriously consider three things.

1. Do I really get more shots for the pump-effort.
2. How much real world difference isn there between a variation of 3% and 2% (which i can find out as the rifle is now by limiting the fill/refill pressure).
3. Do I want to complicate a very simple rifle?


Pump-fillers might have a different view of regulated rifles.  It's all my personal effort going into the gun and coming out as shots, so for regulation to make sense, would have to offer more shots for the pump effort. "Even" would be getting 17-18 shots for 30 pump strokes, 35 shots for 60 pump strokes, or 70 shots for 120 pump strokes, 140 shots for 240 strokes, etc.

[Booger]

Would have to see a gain in "shots per pump stroke" for it to be worth regulating, but I'll have to seriously consider three things.

1. Do I really get more shots for the pump-effort.
2. How much real world difference isn there between a variation of 3% and 2% (which i can find out as the rifle is now by limiting the fill/refill pressure).
3. Do I want to complicate a very simple rifle?


Pump-fillers might have a different view of regulated rifles.  It's all my personal effort going into the gun and coming out as shots, so for regulation to make sense, would have to offer more shots for the pump effort. "Even" would be getting 17-18 shots for 30 pump strokes, 35 shots for 60 pump strokes, or 70 shots for 120 pump strokes, 140 shots for 240 strokes, etc.

I seriously like your numbers. These things might be better than the MRODs.

[SpiralGroove]

I usually put about 80/90 pumps in my BAM B50 to re-inflate her from 100 bar to 200+ bar.  Three separate strings of (25/30) pumps lasting about 8 minutes combined.  Good for 70+ string at 900+ fps .  2 shots of espresso* are usually consumed preceding or during the session

*another one of my nasty habits...........Kirk