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Who has tuned their JP buffer


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Hello: Yes I have and yes it works a lot better with 134-137PF loads. Lighter springs and lighter weights works for me. Buy the 223 spring kit and 2 steel weights. Try the different springs with 2 steel weights and 2 tungsten weights. Then try 3 steel weights and 1 tungsten weight. I am using the green spring right now on one setup. The other setup I have 3 tungsten weights and 1 aluminum weight I made with the black spring. Note I have not tried this on a actual JP rifle yet but have on my JP bolt setup rifle. Anyone know where to get just the JP single springs from? Thanks, Eric

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I have done something very similar to Eric. I replaced a couple of the heavy Tungsten weights with the lighter steel versions. I also got one of the "tuner" spring packs and went to a slightly lighter spring. I definitely like how it has turned out. I am running 135gr bullets at around 132-135PF.

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On 3/29/2017 at 11:04 PM, latenightlegend said:

How does running lighter steel weights affect the recoil or dot movement?


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I would say the reduction in moving mass would lower the felt recoil and dot movement.

 

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On 3/29/2017 at 10:04 PM, latenightlegend said:

How does running lighter steel weights affect the recoil or dot movement?


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Lower total reciprocating mass... same reason we cut up slides on pistols and take weight(s) out of buffer in DI AR's, etc.

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On 3/29/2017 at 4:13 PM, Aircooled6racer said:

 Anyone know where to get just the JP single springs from? Thanks, Eric

 

I dimly remember reading somewhere that these use 1911 recoil springs. Haven't checked validity, but you could compare. 

 

You might look look at something like this and compare color codes. 

http://nictaylor00.blogspot.com/2014/08/1911-recoil-springs.html?m=1

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I looked at the buffer in my GMR-13 today.  Looking at the pictures on the JP website, the matt finished (3) are tungsten and the shiney one is steel.  I checked with a magnet and the steel seemed less magnetic, perhaps stainless.  The spring was marked with red paint which doesn't match up with any in the assorted spring kit.  I have only shot about 500 rounds but many double taps, dot movement does seem related to the buffer.  

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  • 5 months later...

Resurrecting an old(er) thread, but I was wondering if anyone has tuned their JP buffer for lighter loads. I'm running a .380 bullet in a 9mm case for Steel Challenge and it shoots pretty softly (a bit disconcerting at first), but was thinking perhaps going to a lighter spring and maybe another steel vs tungsten weight might make it even faster. I was surprised at the broad range of loads that the GMR-13 buffer will cycle, but, in this case, I'm trying to cycle things around 85-90 PF. Thoughts?

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Hello: Yes, I have played around with a lot of setups on the JP buffer. I would use 3 steel weights and one tungsten weight. Use the white or black spring but the green may work just fine. These are the 223 springs in the JP 223 kit. You will have to check if it feeds from the magazines ok and ejects the brass. You may want to up the power factor a little also. They get to the target faster that way. Thanks, Eric

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When I first received my GMR-13, I looked specifically for a thread like this one but could not find one.   I called JP and ordered the (3) spring pack,

along with one steel weight and one tungsten weight.  The guy seem puzzled why I would want another tungsten weight, but I ordered it anyway.

After receiving the package from JP, I found the thread where Maximundo was commenting on his preferred set-up, but I did not have the springs that

he recommended so I went with what I had.  

 

I felt the stock set-up was over-sprung so I went with the lightest of the 3 springs and replaced a tungsten weight with a steel weight (for 2T + 2S) for the

lightest combination of weight and pressure that I could produce with what I had.   That was a significant improvement over stock.  There was far less

dot movement and I did not feel any impact of the buffer bottoming out. After that success, I ordered the 5 spring pack so that I could go even lighter on

the springs.   I plan to go lighter until I feel the "hit" and then move back up to the sweet spot.   

 

I also hope to test out Maximundo's recommendations where he goes with a full tungsten buffer and the lightest springs of the 5 pack.   While I would assume

that having the lightest reciprocating mass would lead to the least dot movement, we have to remember that these are strictly blow-back actions and we need

to keep the bolt closed until the bullet clears the barrel.  I have been told that my gun released pressure from the ejection port in stock configuration, and reducing

the buffer and spring weight too far would only make that worse.  

 

I will post my observations once I can get to the range.

 

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Another observation, the heaviest of the 5 spring (223) pack is roughly equivalent to the lightest of the 3 spring (308) pack at ~13lbs, as JP claims.  

The 5 spring pack measured out at ~9-10-11-12-13 lbs at full compression with stock stroke.  The 3 spring (308) pack is roughly 13-14-15 lbs  and

the gun is shipped with a ~15lb spring equipped. 

 

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How are you guys going about judging which spring functions best?  Ejection pattern?  Timer?  Felt recoil?  Dot movement?

 

I've got the stock SCS setup, and the dot barely budges with ~132pf ammo.  But I also have the 223 spring pack and a desire to never leave well enough alone.

 

I feel like with a lighter spring, something needs to be in place to slow down the bolt movement at the end of the stroke, like the wavespring setups.

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Hello: I use a timer and hits on target as fast as I can shoot at 7 yards. I shot a friends stock JP today and then tried my buffer setup in his JP. Same ammo for both and shots at 15 yards or so. His stock buffer gave me two shots about 8" apart and my JP buffer setup gave me 2" apart. recoil felt about the same with his 147 grain loads. I think with a stock JP PCC with the heavy hand guard a 124 grain bullet maybe better. My PCC shoots softer with my loads and buffer setup and also flatter. I will try his JP again tomorrow with some of my 145 grain loads and see. All this testing really depends on what works best for you. The timer doesn't lie and the hits on paper confirm if it works for you. Thanks, Eric

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On 9/15/2017 at 3:23 PM, L9X25 said:

When I first received my GMR-13, I looked specifically for a thread like this one but could not find one.   I called JP and ordered the (3) spring pack,

along with one steel weight and one tungsten weight.  The guy seem puzzled why I would want another tungsten weight, but I ordered it anyway.

After receiving the package from JP, I found the thread where Maximundo was commenting on his preferred set-up, but I did not have the springs that

he recommended so I went with what I had.  

 

I felt the stock set-up was over-sprung so I went with the lightest of the 3 springs and replaced a tungsten weight with a steel weight (for 2T + 2S) for the

lightest combination of weight and pressure that I could produce with what I had.   That was a significant improvement over stock.  There was far less

dot movement and I did not feel any impact of the buffer bottoming out. After that success, I ordered the 5 spring pack so that I could go even lighter on

the springs.   I plan to go lighter until I feel the "hit" and then move back up to the sweet spot.   

 

I also hope to test out Maximundo's recommendations where he goes with a full tungsten buffer and the lightest springs of the 5 pack.   While I would assume

that having the lightest reciprocating mass would lead to the least dot movement, we have to remember that these are strictly blow-back actions and we need

to keep the bolt closed until the bullet clears the barrel.  I have been told that my gun released pressure from the ejection port in stock configuration, and reducing

the buffer and spring weight too far would only make that worse.  

 

I will post my observations once I can get to the range.

 

Where is Maximundo's thread located. 

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I followed Max's recommendation and went with 4 tungsten weights, the lightest 223 spring (white), and then inserted CS100-M11 wave spring in between the white buffer and the back of the SCS.  That had the best recoil impulse IMO and runs everything including 115gr subsonic steel challenge ammo.

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45 minutes ago, gnhowell1 said:

I followed Max's recommendation and went with 4 tungsten weights, the lightest 223 spring (white), and then inserted CS100-M11 wave spring in between the white buffer and the back of the SCS.  That had the best recoil impulse IMO and runs everything including 115gr subsonic steel challenge ammo.

 

How does that feel?  

 

Did that significantly reduce your dot movement?

 

 

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9 hours ago, L9X25 said:

 

How does that feel?  

 

Did that significantly reduce your dot movement?

 

 

Best recoil impulse, most trackable reduced dot movement from all the combinations we tried.  

 

The blitzkrieg hydraulic buffer with a 308 carbine spring, a spacer and a wave spring was the only other combination we felt was as good or better.  

 

No doubt Max did his homework.

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18 hours ago, gnhowell1 said:

I followed Max's recommendation and went with 4 tungsten weights, the lightest 223 spring (white), and then inserted CS100-M11 wave spring in between the white buffer and the back of the SCS.  That had the best recoil impulse IMO and runs everything including 115gr subsonic steel challenge ammo.

 I will have to try that! I have wave spring coming and have some jp springs laying around....

 

but need one Tungsten weight. Anyone have a spare you can sell me? =)

Edited by SeattleDude
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Where did you buy the CS100 spring ? Do you have a photo of the setup ?

cheers

20 hours ago, gnhowell1 said:

I followed Max's recommendation and went with 4 tungsten weights, the lightest 223 spring (white), and then inserted CS100-M11 wave spring in between the white buffer and the back of the SCS.  That had the best recoil impulse IMO and runs everything including 115gr subsonic steel challenge ammo.

 

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