Tuning JP SCS system for least dot bounce?

[egd5]

5 hours ago, MemphisMechanic said:

 

Why?

 

IMO there’s a reason a 115 to 124 running around 140pf is really really common among verteran AR9 guys in USPSA.

 

It’s flat, accurate, and it runs the gun quickly with heavy & shortstroked actions.

Because that's what I've been running in my current pcc. That's the PLAN, but plans change. I will do some experimenting. That's why I started the thread.

[Cowboy1629]

16 hours ago, MemphisMechanic said:

 

Why?

 

IMO there’s a reason a 115 to 124 running around 140pf is really really common among verteran AR9 guys in USPSA.

 

It’s flat, accurate, and it runs the gun quickly with heavy & shortstroked actions.

 

I just figured people didn’t want a different load for their PCC from their production gun.

 

What limited testing I did, I didn’t see an advantage to shooting higher power factor ammo from the GMR, but I’m new to this so maybe I’m missing something. 

[RAVAGE88]

There's a wide variation of what you'll experience based on numerous factors.  When I ordered my GMR-15, JP had not introduced the short stroke kit.  As it shipped, the kit was introduced so I ordered one.  I initially shot with the standard stroke and then switched it out; it was definitely a different "feel," but I was new enough to PCC that I decided it was best to develop a good baseline by shooting a season with the standard stroke.  With a bit of experience under my belt, I started testing with the short stroke, varying the weight as I tested. With my load, five tungstens get me where I want to be.  The only way to really know is to progressively test your gun with your load.

 

MB 

[egd5]

Another thing to remember is that whatever nuances in feel that the top shooters can tell will probably be lost on average shmoes like me. But I won't know until I play with it.

[MemphisMechanic]

26 minutes ago, Cowboy1629 said:

 

I just figured people didn’t want a different load for their PCC from their production gun.

 

What limited testing I did, I didn’t see an advantage to shooting higher power factor ammo from the GMR, but I’m new to this so maybe I’m missing something. 

 

130-133 pf ammo through your production handgun WILL BE 140-145 powerfactor through the rifle’s 14-16” barrel.

 

So yes. Exactly that. One load, which runs the PCC a little bit harder and keeps the gun cycling briskly with a heavyweight buffer system & buffer spring. It’s a slight bit more recoil, but it’s just as flat.

 

It’s nice knowing you’re throwing an extra 50fps at poppers, too. I never wait to confirm a heavy or forward-falling one will go down when shooting PCC, like I will sometimes  with a minor handgun if I’ve seen someone else have trouble with it.  

 

Edited April 17, 2019 by MemphisMechanic

[LowSpeedHighDrag]

On 4/14/2019 at 7:34 PM, LowSpeedHighDrag said:

 

I've just decided to leave the short stroke SCS buffer alone, with the stock 5 tungsten weights.  Whatever the effect on dot bounce, I think it will reduce the wear and tear on the lower over the long run.

 

Yeah, well, then again, maybe not...

Just came back from the range where I did some testing with my JP GMR-13.  I used HAP 115 gr bullets with different amounts of VV N320 and N350.  Discovered that since going to the short stroke buffer (5 tungsten weights) that the lightest N350 loads would sometime fail to properly reset my Hyperfire hammer, resulting in light primer strikes.  Didn't happen last year before using the SS buffer, or with either more N350 powder or with N320.  I'm guessing that the slower powder spreads the recoil out over a longer period of time, and that the 5 tungsten results in the rifle being over-buffered.  Does that make sense?

Anyway, I'll need to go back and do some more testing by switching out 1 or more of the tungsten weights for steel and see what I come up with.  No point in using a heavier charge just to move a buffer that's too heavy in the first place.

Edited April 19, 2019 by LowSpeedHighDrag

[egd5]

48 minutes ago, LowSpeedHighDrag said:

 

 No point in using a heavier charge just to move a buffer that's too heavy in the first place. 

My thinking too. That's why I ordered the 5 steel weights since I wanted to start with the lighter loads I already have. I figure I can always either add weights or add powder to increase the PF.  In the end I really wonder how much real difference it will make, but it should be fun playing with.

[LtdShooter]

I'm currently running 3 tungsten and 2 steel in my SS SCS at a 140 PF (124 gr with N320) and it feels nice.  Sharp but dead flat.  

[rowdyb]

But no one is messing with the 3 different spring weights?

[Shadow]

Actually 8 spring weights (5 pack AR15 + 3 pack AR10).

 

I like the green or black spring from the AR15 5 pack.

[egd5]

OK, here's one for all you math geeks out there. How many possibilities are there considering 5 steel weights, coupled with up to 5 tungsten weights, coupled with 8 different springs, and then with (let's say 12 just to put a finite number on it) powder combinations? And that's with only one bullet weight. We won't even go with all 3 popular bullet weights.

[Steve RA]

More than you ever want to try!   

[Wvaughn7]

2 hours ago, egd5 said:

OK, here's one for all you math geeks out there. How many possibilities are there considering 5 steel weights, coupled with up to 5 tungsten weights, coupled with 8 different springs, and then with (let's say 12 just to put a finite number on it) powder combinations? And that's with only one bullet weight. We won't even go with all 3 popular bullet weights.

Ignoring all of the bullet powder combos, there are 48 variations of JP buffer weight/spring combos. If you say there are 3 popular bullet weights and 12 different kids with each of those bullet weights it puts you around 1728 different combos. At least enough combinations to keep us talking about them all on here for another few years until another combination comes out

[Aircooled6racer]

Hello: Unless you make an aluminum weight and then there are more possibilities. I still like the original 4 weight buffer setup with my special weight and spring setup for 131-134Pf loads using 124's. Thanks, Eric

[Sidewinder6]

Searching around for ideas on the possible cause of early lock open with my SCS 3/2 combo on a short stroke GMR 15.  

This thread seems like a good place to ask why a bolt might lock open after only firing a few rounds at speed. When examining the stoppage, the chamber is free and clear of the last round spent and the top round in the magazine is sitting like its the first round in a fresh magazine. No visible reason for the lock back. All that is necessary to bring the gun back into action is to close the bolt again and chamber that round. This has occurred 5 or 6 times but can not be recreated by doing anything in particular when troubleshooting. 

 

Thoughts? Anyone seen this on their JP? 

 

 

[egd5]

What power factor ammo are you using? This is really a guess on my part, and I'm no expert either, but if your ammo is hot could it be slamming the bolt back too hard and catching the bolt hold open? With hot ammo maybe going to 5 tungsten would help.

My 2 cents.

 

eta-or maybe a stronger spring?

Edited October 2, 2019 by egd5

[Sidewinder6]

Good points. I havent chrono'ed this couple batches but it was Atlanta Arms and Syntech 115 range ammo. 

[Aircooled6racer]

Hello: So what is a good starting point for the short stroke 5 weight setup? What weights and spring setup are you using for 131PF 124 grain loads? Thanks, Eric

[LowSpeedHighDrag]

35 minutes ago, Aircooled6racer said:

Hello: So what is a good starting point for the short stroke 5 weight setup? What weights and spring setup are you using for 131PF 124 grain loads? Thanks, Eric

 

It might also matter whether you're using a fast or slow burning powder.

[Aircooled6racer]

Hello: Since I listed the power factor, fast or slow powder will not effect it enough to matter. I guess I will have to do the testing and guess on the starting point. Thanks, Eric

[Silverscooby27]

I was advised 2 tungsten 3 steel, stock spring for PF 135 with 115 gr. Bullets in a GMR-15. Stock spring is the heavy spring (10-110). That's the same spring as the heavy 308 spring.

[egd5]

I'm using a 124 bullet at about 135 pf. I have the 5 steel ss scs in my gmr-15 and it works great.

[LowSpeedHighDrag]

5 hours ago, egd5 said:

I'm using a 124 bullet at about 135 pf. I have the 5 steel ss scs in my gmr-15 and it works great.

 

That's about where I am with my GMR-13.

 

[Sidewinder6]

No love for 147's and 5 steel? 

[LowSpeedHighDrag]

1 hour ago, Sidewinder6 said:

No love for 147's and 5 steel? 

 

I suspect it's just personal preference.  For me the 147's make the action feel slower.