Think I've got the JSAR .177 slugger sorted out

[mackeral5]

Interesting findings on the balanced valve vs. Cobra.  I believe there are so many variables with balanced valves it is very difficult to optimize for a given application. 

I have been a big fan of the Cobra valve ever since your "demystifying" thread.  I have Cobra valves running in guns that produce from 25fpe to over 300fpe. 

So far, I like balanced valves when:  1)  wanting a higher ratio of FPE to required hammer strike 2)  wanting to manage ES across a broad unregulated pressure range, at energy levels that require large for caliber porting, thus taking away the tuning tool of choking the transfer.  Note neither of these are max-energy applications. 

Another item I will add around balanced valves---at least in my testing, significantly oversized throats hurt tuneability. 

I like versions of the Cothran for many applications.  But for max energy in calibers above .300, the Cothran just cannot flow enough. 

[rsterne]

Balanced valves can be a bit tricky to find the right balance characteristics.... The smaller the balance chamber and the larger the vent, the more the valve acts like a conventional valve, except that it is easier to crack open initially.... I made a balanced valve for my .357 cal Hayabusa (throat = 0.375"), and then went progressively down all the way to .224 cal just by installing a tapered transfer port and adjusting the hammer strike.... For the .224 cal (107 FPE) and .257 cal (136 FPE) I used a 77 gr. hammer with 1.09" of travel.... For the .284 cal (177 FPE), the .308 cal (200 FPE) and the .357 cal (248 FPE) I used a 113 gr. hammer with 1.18" of travel.... All used the same hammer spring, with various SSG gaps, and all these tunes were tethered at 3000 psi.... They all ended up with similar efficiency of about 1.15 FPE/CI.... This valve still required a fairly heavy hammer, because I used a small chamber and larger vent, to make the valve easier to tune by varying the hammer strike....

If I had used a larger balance chamber and/or smaller vent, the valve would have had more tendency to "blow open", and required less hammer strike.... However, it would have been much harder to tune, with more of a "plateau and cliff" reaction to SSG gap, like a Cothran valve (I had a valve like that initially).... That wasn't what I wanted, and after the changes what I got was a valve that would work over a huge range of calibers and power settings.... I never found that I needed increased pressure on any of the calibers, compared to the conventional valves I originally installed.... They all retained, or exceeded, their original performance at the same pressure.... I sacrificed a heavier hammer strike for increased tunabilty.... but still a much lighter strike than with a conventional valve....

Scott, regarding your findings, perhaps a heavier hammer would resist the blowing open of your valve, and increase dwell and tunability?....

Bob

[Motorhead]

Indeed a heavier hammer would exhibit a tad more hang time at full travel of poppet open stroke buying a tad bit of dwell time.
and at the same time likely allow a tad less hammer spring tension or lessor spring rate affording even easier cocking ....

Yea a WHOLE LOT of small tweaks to find little gains ....

As to the tuning aspect, it tunes wonderfully over a very broad range ... issue I'm having is .177 cal specific when really leaned on for power.
* With the balanced valve and hammer it had, set with a consistent HST within the SSG device, Dialing in more pressure on the external regulator the power ramps up as pressure increases very linear 
Issue tho being to get the power I'm shooting at and the base line for the valve change is it took 2350 PSI in balanced form and only 1800 psi unbalanced.

This chase is WHY I'm not able to get equal power running balanced at 1800 psi ? ...... I'll try more hammer weight and see if that helps with all else where it was 

My having fun with this is kinda getting old.

[rsterne]

Do I understand correctly that you are running about 38 FPE with this gun?.... on a 22" barrel?....

Bob

[Motorhead]

Do I understand correctly that you are running about 38 FPE with this gun?.... on a 22" barrel?....

Bob

Of late with the above fiddling YES tho on a 23 3/4" LW standard non choke 17.7-1 twist.

[Motorhead]

Ok ... I'm so done fiddling I'm going to stop and run it as is ... THAT BEING, back at balanced with a hammer @ 12 grams heavier !!!
Sure as heck Bob was correct that more hammer weight was all that was required 
Back at 1800 psi with the heavier hammer, choked transfer port as previous ... THO slightly backed off on SSG spring preload it is now making the same power as the conventional valve ( Same hammer actually ) tho much lighter SSG spring fitted.

I need a new gun project !!! taken this poor JSAR apart sooo many times !!

[rsterne]

There is no reason that a balanced valve should need more pressure for the same performance.... Vice versa, there is no reason it should perform better, unless the gun is limited by hammer strike with a conventional valve.... Glad you got it sorted, Scott.... 

You know what the old saying is.... If you can't fix it, get a bigger hammer....   

Bob