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Tuning JP SCS system for least dot bounce?

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When I started shooting about 4 years ago with a pistol I tried 115,124, and 147. I was so new I couldn't tell any difference so I just went with middle of the road 124. Plus, I read that 124 was the original 9mm round.  Since then I'm just too lazy to reset my reloader to try anything different.

But also, for most all of us, I believe the bullet weight is the least of our handicaps. There's a lot of other low hanging fruit to improve our shooting to worry about first.

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5 hours ago, egd5 said:

There's a lot of other low hanging fruit to improve our shooting to worry about first.

Very true ernie

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I just came back from the range and have done a ton of testing on this subject the past week.  Here is my info and sort of final results:

Gun:  Home built PCC with all JP guts, including short stroke kit, bolt and trigger.  Colt mags with the higher power springs

Load:  145 grain Bayou RN, 3.1 grains of Titegroup, tried with assorted primers, mixed brass.  Don't ask me power factor as I only compete in local club events.

The short stroke kit came with 3 tungsten and 2 steel weights and the red/yellow spring.  I continually got a failure to feed at the end of a magazine (tried 5 magazines- same result).  It did not matter how many bullets I loaded.  I tried all three of the optional short stroke springs and it didn't make a change, still FTF at the end of the magazine.

I went back to the "stock" red/yellow spring and started playing with the weights, one by one.  Adding steel and subtracting tungsten one by one until I got to all steel weights.  That made my FTF problem worse.  So I started subtracting steel and adding tungsten weights, one by one.  Once I got to ALL tungsten (5), my problem went away.  I shot magazine after magazine, about 300 rounds in the all 5 tungsten configuration without issue.  Dot bounce and recoil were minimal. 

This week I'll test all three springs to see if there is any change.

I hope this info helps.

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Running a JP GMR-13 with a short stroke SCS, using 125 gr. heads with VV N350 powder.

 

Played around with spring weights and tungsten vs steel buffer weights, and wound up with the standard spring and 5 steel weights.  Seemed to have the best feel and least dot bounce.

 

As always, YMMV.

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12 hours ago, LowSpeedHighDrag said:

Running a JP GMR-13 with a short stroke SCS, using 125 gr. heads with VV N350 powder.

 

Played around with spring weights and tungsten vs steel buffer weights, and wound up with the standard spring and 5 steel weights.  Seemed to have the best feel and least dot bounce.

 

As always, YMMV.


Same here with my GMR-15 124gr MG JHP and VV N320. 

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1 hour ago, Cowboy1629 said:


Same here with my GMR-15 124gr MG JHP and VV N320. 

 

My rifle seems to like n350 rather than n320.  The extreme spread for velocities shrinks substantially with the slower powder with my 14.5" barrel + comp.

I'm assuming this is specific to my rifle rather than some kind of universal truth, but probably worth checking with your rifle.

 

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Might be worth a try but I have a boat load of N320 and just picked up 8 pounds of Sport Pistol to give it a try.
 

Very low ES and SD with Sport Pistol in my X5 Legion, haven’t tried it in my JP yet. 

 

I will keep N350 in mind. 

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18 minutes ago, Cowboy1629 said:

Might be worth a try but I have a boat load of N320 and just picked up 8 pounds of Sport Pistol to give it a try.
 

Very low ES and SD with Sport Pistol in my X5 Legion, haven’t tried it in my JP yet. 

 

I will keep N350 in mind. 

 

I find N320 excellent in pistols with 5" barrels.  In a rifle with a 14.5" barrel I get different results.

 

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17 hours ago, LowSpeedHighDrag said:

 

My rifle seems to like n350 rather than n320.  The extreme spread for velocities shrinks substantially with the slower powder with my 14.5" barrel + comp.

I'm assuming this is specific to my rifle rather than some kind of universal truth, but probably worth checking with your rifle.

 

Actually, this is an universal truth, at least as far as slower powders reduce extreme spread. However, such a slow powder as N350 is not entirely combusted even in a 16 inch barrel. N340 is almost entirely combusted in a 16 inch barrel, around 99% combustion. Slower powders also give more gas for the comp. For accuracy slower powders have a slight advantage, but In my experience, even quite high extreme spread does not affect accuracy at distances less than 100 meters/yards. Also a shorter recoil impulse with the faster powder can be beneficial for less dot bounce, but recoil impuse seems softer with slower powder. In the end it is mostly about preference, I guess. 

 

 

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2 hours ago, mrd said:

Actually, this is an universal truth, at least as far as slower powders reduce extreme spread. However, such a slow powder as N350 is not entirely combusted even in a 16 inch barrel. N340 is almost entirely combusted in a 16 inch barrel, around 99% combustion. Slower powders also give more gas for the comp. For accuracy slower powders have a slight advantage, but In my experience, even quite high extreme spread does not affect accuracy at distances less than 100 meters/yards. Also a shorter recoil impulse with the faster powder can be beneficial for less dot bounce, but recoil impuse seems softer with slower powder. In the end it is mostly about preference, I guess. 

 

 

 

Thanks, I'll retry will different powders.

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Up to date, I teste 145 and 123gn bullet loads with n340 n320 and n310 and even tho I settled with 123 and n320 I got the smallest SD numbers with N310. N310 however meters really well, so probably thats the cause of low SDs rather than it's burning characteristics.

Edited by impact
small addition

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On 10/29/2019 at 1:05 PM, LowSpeedHighDrag said:

 

Thanks, I'll retry will different powders.

 

I'm going with N320.  I'll use the same load for both PCC and pistol.

 

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I'm going with N320.  I'll use the same load for both PCC and pistol.

 

 

 

I’ll probably be doing the same.

 

I haven’t chrono’d the rifle yet, but if I’m doing 130-ish pf with 124gr bullets out of a 5” pistol, how much of a jump in PF would I expect from a 14.5” barrel?

 

I don’t see myself loading PCC specific loads to shoot through my GMR. Would like the same loads for both pistol and rifle.

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I saw a jump from 131 to 149 going from 4” pistol to 14.5 JP.

 

I run different loads between the two. 

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11 hours ago, Cowboy1629 said:

I saw a jump from 131 to 149 going from 4” pistol to 14.5 JP.

 

I run different loads between the two. 

 

 

I guess that jump is worth a twist on the powder drop.  Thanks!

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I have the short stroke buffer and set on 3 steel 2 tungsten. Today tried recipe of experienced JP shooter 115 gn roundness (also pro) FMJ's with 4,6 gn VV N340.

 

Not sure about PF but (felt same like factory GECO) but man was it flat. 2 alfa's on 15 pared whilst shooting as fast as I can. spot on at 50 yards. Think I found my load. Love my JP!!!!!

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So you like the JP over the MPX?

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I have shot a number of PCC's and setups. My current setup has the least dot bounce I have come across yet. 5 Tungsten JPSCSSv2. The heavy buffer likes loads around 140-145pf the most. I can't tell a huge difference in using 115s or 124s. I think the 115s settle the dot a little faster. 

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56 minutes ago, egd5 said:

So you like the JP over the MPX?

Yes. Matter of personal preference. Sig felt softer, JP had faster sight recovery and (for me) an overall better feel. JP works. Sig sensitive for cleaning and ammo..

Just like the Jp a bit more. Sig found a new owner who loves it.

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I too was concerned about the cleaning of the Sig. Since I hate cleaning a gun that was a big part of why I want with JP.

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On 11/2/2019 at 4:01 AM, RexKramer said:

 

 

I guess that jump is worth a twist on the powder drop.  Thanks!

 

Maybe. I would compare accuracy between the powder loads and take that into consideration too. I think a smidge less softness is something that training can compensate for, but you can never shoot better than the inherent accuracy of the load in your gun. 

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Maybe. I would compare accuracy between the powder loads and take that into consideration too. I think a smidge less softness is something that training can compensate for, but you can never shoot better than the inherent accuracy of the load in your gun. 



Very good point!

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On 11/3/2019 at 7:37 PM, Fasthenk65 said:

I have the short stroke buffer and set on 3 steel 2 tungsten. Today tried recipe of experienced JP shooter 115 gn roundness (also pro) FMJ's with 4,6 gn VV N340.

 

Not sure about PF but (felt same like factory GECO) but man was it flat. 2 alfa's on 15 pared whilst shooting as fast as I can. spot on at 50 yards. Think I found my load. Love my JP!!!!!

No wonder it was flat... measured PF and came only to 120... will increase load to 4,8 and make a batch with 5,0 and try again tomorrow.... time consuming our hobby...

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Also tested 147's with N320, strange thing is that I achieve 128 in pistol and only 125 in my JP, can someone explain this?

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9 minutes ago, Fasthenk65 said:

Also tested 147's with N320, strange thing is that I achieve 128 in pistol and only 125 in my JP, can someone explain this?

 

My very un-expert opinion is that the VV N320 powder was completely burned up well short of the end of the barrel, so the rest of the barrel just provided drag on the bullet.

 

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