Really can't eyeball efficiency

[Ribbonstone]

Problem with eyeballing shot counts and thinking they are efficient.  I’m as guilty as the next guy, thinking any rifle that gives 132 shots per fill can’t be doing badly.

This is from an OUT THE BOX (no screws turned, no adjustment) Challenger PCP.  Ran from 2000psi to 1000psi for 132 shots (each column is 22 shots). If all you are doing is busting paintballs or bottle caps, all 132 shots would work just fine.

 

Now I could have just figured out the fill pressure for the “best of the best” (about 80 shots) and just lived within that pressure range. Let’s call it 1800-1200psi.  That’s enough for any single day’s use within a solid 2-2.5% variation.

But I figure a PCP with match-gun pretentions should be held to a stricter standard of air use
Inside the 132 shots there are 111 shots inside of 4% (the ones boxed in)
Are 84 shots inside of 3%
Are 71 shots inside of 2%.

Taking all 132 shots into consideration, the efficiency is only 1.1 FPE/cuin.  That’s not terrible efficency for a 50 foot pound non-regulated rifle, but it is pretty horrible efficiency for a sub 5 foot pound rifle.

So evidently, the discussed transfer rod assembly doesn’t do much of anything good for efficiency.

[Motorhead]

More you guys talk about low power guns and getting / finding some GREAT efficiency numbers more I get nudged in powering down the .177 M-rod to run a string at sub 12 ft lbs.

As currently set ( regulated, light hammer & SSG )
Into Lloyds efficiency calculator to crunch the numbers ....    avg FPE/cuin per shot 1.73
( 3k fill, 1.7 set point, 190cc tank, 10.3 g, 95 shots, 910 fps )

IMO taking the power down to sub 12# quite likely able to break 2.0 or better.
With FT season starting in @ a month not sure I'm willing to start changing stuff for the sake of experimentation

[Ribbonstone]

 Efficiency wise, things got a whole lot better when the rifle was set up for about 12 foot pounds.  Not that 40 shots is all that great, but the air use was pretty stingy.

All I did was open the tiny issue transfer port and increase the spring tension slightly (using the issue adjuster).


Why the better efficiency?  Even though it was only 40 shots @ 12 foot pounds, it’s a very low variation 40 shots.

Think the cue is that at 5 foot pounds there is a tendency for the valve retention screws to “sneeze” a little air at each shot.
As the gun didn’t leak air from the air tube and only “sneezed” a little air at the valve retention screws during the shot, the air sneezed hard to come from the exhaust side of the valve cycle. Evidently the tiny transfer port created enough back pressure to blow a little air out of the valve retention screws (and down along the shaft of the valve stem, but that’s pretty contained and not easily detectable in a Challenger).

Not a lot of air at all…I’d not have noticed it, but had slathered some rust preventive oil on the tube and some of the liquid oil gave a little spray at the shot.

So my guess is that the more open transfer port created less back pressure.

I’ve not given up yet.  Will (sooner or later) get it to shoot to about 5 foot pounds AND to about 1.3-1.4FPE/cuin. That would extend the first shot count by about  15-20%, so I could see 90-100 shots inside of 3%.

[Motorhead]

Lol ... the tell tail oil spray when lubing poppet stem.  If stem to body fits loose the lube simple gets blasted away.
In M-rods it easier to detect on the larger hammer face and close proximity to stem.

Good luck ... your getting it sorted !!

[Ribbonstone]

Show you one, from a different rifle, that fooled me, at least until I ran the numbers:



Only 12 shots, so my first thought was “ineffieicent”.  Why, because I’ve associated long shot counts with higher efficiency, not getting the “gut feeling” that air volume and energy are just as important to efficiency.


So that one worked out to:

112CC’s of air
2950-2050PSI
12 shots
30.6gr. pellets
Average vel. 891.7fps / 54 foot pounds per shot

So running the numbers, that little shot-count of 12 came out to be  about 1.5 FPE/cuin, which is pretty efficient.

POINT BEING: don’t rely on just the shot count when working on efficiency