JSAR Raptor Tuning guide and thoughts.

[Jacob_M]

I will try and reduce hammer spring a little bit. A 1/4 turn will make a difference. Then I would need to run a shot string to see what’s going on.


The barrel is a 1:22 Twist TJ barrel.

Update on slug shooting:

Tried some 38gr AVS slugs, they were only going 850fps, but the first 3 shots went into the same hole at 30 yards!
Next 2 shots were about a half inch higher.

That is a first for this gun!

[Papy_Yosh]

isn't the length 3/4 of an inch?

[UnderPressure]

The barrel is a 1:22 Twist TJ barrel.

Update on slug shooting:

Tried some 38gr AVS slugs, they were only going 850fps

Do you know the groove diameter on the TJ's barrel?

The reason I am asking is because the AVS .25 slugs are sized .254" rather than .250" like the Neilsen slugs.

P.S. 850 FPS is a good velocity for a 38 grain slug (60 FPE).

[Jacob_M]

Messing with my tune again, just for the *(&^ of it.


Filled to 3500 psi.

Reg pressure at this fill is about 2250-2200. Max FPS with 34gr jsb is 934fps.

 turned my buffer 1/8 turn and now my max FPS is 896.

Very consistent velocities from 3500-2700.  Lots of 885-895 fps.

After 2700psi it was mostly 880-888 and gradually decreased till I got 874-880.


So, from this data, I believe that I CAN fill higher, maybe to 4000? or 4350 and see if my velocities start in the 880's and work its way up to the 890's.

Kind of feels weird that I have to follow the bell curve of my regulators set point.

Learning to get along with creep!

Filling higher I can probably get 70-80 shots at 57-60 fpe. If all shots stay within 875-895 fps I guess that is only a 20 Extreme spread.


Has anyone else had to do this with ANY other guns?

[UnderPressure]

Filled to 3500 psi.

Reg pressure at this fill is about 2250-2200. Max FPS with 34gr jsb is 934fps.

 turned my buffer 1/8 turn and now my max FPS is 896.

Very consistent velocities from 3500-2700.  Lots of 885-895 fps.

After 2700psi it was mostly 880-888 and gradually decreased till I got 874-880.

Sounds like you are still on the back side of the hammer spring bell curve. (reason: velocity is still dropping as bottle pressure decreases).

I suppose you have two choices at this point (from a purely reg pressure and existing hammer spring standpoint).

1. Decrease hammer spring once again. (with some risk of increasing shot to shot variance)

2. Keep hammer spring the same and increase reg pressure. (Could also risk increasing shot to shot variance if reg pressure is increased too much...this first starts occurring when bottle is at high pressure.)

[Jacob_M]

I’m going to increase my reg. Just a little bit and see what happens.

[UnderPressure]

The barrel is a 1:22 Twist TJ barrel.

According to the Kolbe twist calculator you could use any of the AVS .25 slugs (which as previously discussed are sized .254".)



Up to 48 grain also works well with the plenum size of 90cc.

(Not sure how the stock transfer port factors in.... but at least those other two specs (rifling twist rate and plenum size) dovetail nicely)

P.S. For the 48 grain I calculate a sectional density of .106......so slightly below 2000 PSI would be the minimum pressure needed under ideal conditions for 950 FPS in a 24" barrel.

[KnifeMaker]

The barrel is a 1:22 Twist TJ barrel.

According to the Kolbe twist calculator you could use any of the AVS .25 slugs (which as previously discussed are sized .254".)



Up to 48 grain also works well with the plenum size of 90cc.

(Not sure how the stock transfer port factors in.... but at least those other two specs (rifling twist rate and plenum size) dovetail nicely)

P.S. For the 48 grain I calculate a sectional density of .106......so slightly below 2000 PSI would be the minimum pressure needed under ideal conditions for 950 FPS in a 24" barrel.




I am sizing the AV slugs to .250 as per the actual slugged Raptor bbl. Which is 22 not 24 inch. Twist has nothing to do with weight. Strictly length.


.254 is far too large in Dia. with huge friction which will kill fps.

[KnifeMaker]

The barrel port must be enlarged. Factory is .167 unless recently changed. 

[UnderPressure]

.254 is far too large in Dia. with huge friction which will kill fps.

Oh so it does have a .250 groove diameter.

Here is what I posted earlier--> https://www.gatewaytoairguns.org/GTA/index.php?topic=171682.msg155932888#msg155932888

[KnifeMaker]

.254 is far too large in Dia. with huge friction which will kill fps.

Oh so it does have a .250 groove diameter.

Here is what I posted earlier--> https://www.gatewaytoairguns.org/GTA/index.php?topic=171682.msg155932888#msg155932888

Yes Sir, and sing down to .250 (mine are .2497) will give a huge boost in velocity. 

[Jacob_M]

So there is more to the Raptor tune!

My guide earlier in the topic is still good to go. It can be used to find your MAX fps for given regulator pressure, with the MINIMUM amount amount of poppet lift, and JUST RIGHT amount of hammer spring.

Now its time to walk the tight rope!

Turn your hammer buffer in CW maybe 1/4 to 1/2 turn. Your FPS should drop. (Mine dropped about 30fps)

Now Turn your hammer spring adjuster CCW a little bit at a time until you find your MAX fps again.

Now that you have found your Max FPS setting again, its up to you to determine how far you want to be down the plateau, by turning your hammer spring adjuster CCW until desired FPS and Consistency is reached.

Notes:

I would not use the hammer buffer to tune on the knee of the bell curve. When I tried to do this My raptor didn't respond well, just increased my ES.
           
When turning up regulator, my shots started to drop in velocity once I was 400-500psi above the regulator setting I adjusted my hammer spring for.
           
           

After I did this to my Raptor, my shot report got a little more quiet. Even at 950 fps with 34gr jsb.

AND

I filled to 4350 and shot down to 2400. My FPS stayed within 955-935. MUCH better. I would get a lot of inconsistency when filling above 3500psi. This was probably due to very little poppet lift and regulator creep. 

I am by no means an expert. This is just what worked for me.

Good luck guys!

[Papy_Yosh]

Thanks Jacob,

I will try that on mine tomorrow.

[Motorhead]

Excellent results ....  balanced valves are another Animal for sure !

[UnderPressure]

I would not use the hammer buffer to tune on the knee of the bell curve. When I tried to do this My raptor didn't respond well, just increased my ES.

I believe you are, in fact, tuned on the knee of the curve for the higher reg set-point. This because if you increased hammer spring your velocity would increase right?

EDIT: You are saying the best way to tune on the knee is keep hammer spring at some minimum acceptable level and then make adjustments by increasing reg pressure in steps. Yep, that can work.

[Motorhead]

I would not use the hammer buffer to tune on the knee of the bell curve. When I tried to do this My raptor didn't respond well, just increased my ES.

I believe you are, in fact, tuned on the knee of the curve for the higher reg set-point. This because if you increased hammer spring your velocity would increase right?

EDIT: You are saying the best way to tune on the knee is keep hammer spring at some minimum acceptable level and then increase reg pressure in steps. Yep, that can work.

Thats what you do .... smallish steps in speed / velocity changes best done via Pressure changes at the regulator.

[UnderPressure]

I would not use the hammer buffer to tune on the knee of the bell curve. When I tried to do this My raptor didn't respond well, just increased my ES.

I believe you are, in fact, tuned on the knee of the curve for the higher reg set-point. This because if you increased hammer spring your velocity would increase right?

EDIT: You are saying the best way to tune on the knee is keep hammer spring at some minimum acceptable level and then increase reg pressure in steps. Yep, that can work.

Thats what you do .... smallish steps in speed / velocity changes best done via Pressure changes at the regulator.

Yes, small reg pressure changes followed by hammer spring changes as appropriate.

Actually I got to thinking perhaps reg pressure could be increased more than normal before making hammer spring changes in the case of switching to a high velocity (1050 FPS) aerodynamic projectile from a heavier and slower moving one. (re: even if valve dwell time decreased at the higher reg pressure it may not matter because the faster moving aerodynamic projectile is farther down the barrel than the slower moving and heavier one would have been.)

[Jacob_M]

My current Max FPS is 950fps and there is more then 1 way to get there.


Minimal Poppet lift : High hammer spring


Moderate Poppet lift : Medium hammer spring


Lots of poppet lift! : Low hammer spring.


When following the instructions you should end up on the “minimal” poppet lift setting.

And then make your way to the “moderate” setting. Which is where I believe the gun is most happy.

[Motorhead]

I know it is NOT the way JSAR is doing it ... but having been around the balanced valves now nearly as long as anyone, likely manufactured more versions ( R&D ) than anyone have found that there are better ways and more stable miens to operate the firing system.     
JSAR has approached a One Hammer does all with a One Valve does all with one Transfer Port does all .... While this certainly eases the manufacturing process and creates a uniform tuning procedure across ALL CALIBERS. it falls short of being ideal 

Using a BUFFER hammer system where you have direct control over poppet lift is not without its shortcomings however.
Namely being UNDESIRABLE rebound if & when the hammer spring energy is too high and the hammer is violently slamming into the buffer ring.   * It is of my opinion and that of many I've spoken with that it's use is a Crutch to allow having some control of the valves HEAVY BREATHING attributes.

My work around and how my personal guns using these valves ( versions of etc ... ) has been to use MUCH lighter hammers and control them via SSG spring devices.
* This also has a downside ... We loose the WIDE tuning range afforded by the factory configuration, but GAIN a lot more control being one can change hammer weight and spring force to a specific caliber and power setting.  This eliminates the need for a buffer with a result the guns are far more stable being also a whole lot easier to get a solid tune.
** Also in this alternative set up I use TAPERED throat Transfer tubes to create sonic choking which also further help stabilize the output swings these easy opening valves experience.

Scott S

[Jacob_M]

Would lighter weight Marauder MDS hammers work?