PCC Reoil / Bounce

[Kmarsh1966]

Good afternoon fellow PCC lovers, because it only takes one time of playing with a 9mm AR to know you want to do it more.

 

A friend warned me that the 9 has a lot of recoil/muzzle bounce due to the blowback design.   I have had one recommendation to upgrade to a 308 Buffer Spring.  Did that and got some reduction.  I got another recommendation and was suggested to add a 9 oz buffer plus a wolf XS spring.   I went to heavybuffers.com and tried to purchase that, But the Merchant website has been disabled.   Got on Enos and saw several other suggestions of varying opinions.  

I see info about the JP Silent Spring for 9mm, with some positive and negative comments.

 

What is the best (in your opinion) configuration for a 9mm PCC

 

Currently I am running a CMMG MK9 with the factory 9mm buffer that weights 5.4oz.   Carbine length setup

[Sarge]

I got a lot of dot bounce out of mine by turning up the loads. With minor PF ammo mine is very sluggish so I loaded some to about 145 PF with lighter bullets and it tamed it quite a bit.

[CZ85Combat]

You want a lighter buffer, a light spring and a light load. What I am using, JP 9mm Silent Captured Spring with one tungsten weight removed replaced with steel weight, 80% spring, 147 Blue Bullet  2.5gn N310 @ 1.130 132pf out of a 14.5 Barrel.

[Patrick Scott]

I have done the heavy(7oz) buffer and heavy(308) buffer spring while shooting 130-196pf(yes 196pf, I went there) ammo. Gun felt sluggish up until about 145pf and had tons of dot "pull off" when the system bottomed out in the tube.

Now I run 130pf ammo, 4.6oz buffer(H2) and a .223 spring. Less dot "pull off" and the gun cycles fairly fast(Id like to try a reduced power .223 spring). More gooder   First time shooting this lighter stuff in a match was today. I'm definitely a fan of going lighter for the operating system as long as you are loading for the gun. If you are going to shoot factory or hotter stuff, I think you will beat the piss out of the gun with a light system and dot bounce will be worse.

  

[Les Snyder]

I'll second what Patrick said... with the heavy 7.5oz buffer and 17oz bolt with a .308 spring I got some bolt marring of the barrel breech... went to a 5.2 rifle buffer and 5.56 rifle spring in my A1 stock... my power factor is still around 150, so will live with the scope shake and less gun damage

[2MoreChains]

Do you guys think heavier spring would cause muzzle dip, just like a heavy recoil spring in a pistol can cause the muzzle to dip from the extra force of the slide slamming forward (or in the case of PCC the heavy bolt slamming forward due to the heavier buffer spring)? 

My combo is a Spikes buffer (weight 8.4 oz), standard .223 buffer spring, and a CMMG BCG (not sure on weight). After calibrating and realizing I my pistol minor ammo was chrono-ing 148 PF out of the PCC's 16" bbl, I powder-puffed it down to a mere 130 PF out of the PCC.  That alone seemed to minimize dot bounce the most.  

[Patrick Scott]

In my testing heavy buffers and heavy springs did contribute to muzzle dip. 

[Novock]

I run my JP GMR13 just the way it came from JP. I run light bullets with Hodgdon Longshot at 130pf and the dot tracks well. I dialed my load in for the gun vs changing the gun for my load.

[Corey]

I have a ,308 spring and heavy 7.5 oz buffer in mine currently. Shot some WWB and some freedom munition 115gr. recoil seemed a bit less than a friends PCC I had shot previously. dot was staying in the window for the most part. but would like a little less if I can. When I start actually loading 9mm ammo for this thing I will try the lighter combo. In my .223 the less reciprocating mass you had, the lighter the recoil felt and the less scope/sight movement I had. I can't see where this would be different.

If i go that route, ill keep the "heavy" setup in the bag for factory ammo, etc if needed. 

 

[Cavy]

On 10/23/2016 at 5:22 PM, Patrick Scott said:

I have done the heavy(7oz) buffer and heavy(308) buffer spring while shooting 130-196pf(yes 196pf, I went there) ammo. Gun felt sluggish up until about 145pf and had tons of dot "pull off" when the system bottomed out in the tube.

Now I run 130pf ammo, 4.6oz buffer(H2) and a .223 spring. Less dot "pull off" and the gun cycles fairly fast(Id like to try a reduced power .223 spring). More gooder   First time shooting this lighter stuff in a match was today. I'm definitely a fan of going lighter for the operating system as long as you are loading for the gun. If you are going to shoot factory or hotter stuff, I think you will beat the piss out of the gun with a light system and dot bounce will be worse.

  

What load are you using? I assume this a rifle length buffer tube?

[Cavy]

On 10/25/2016 at 8:57 AM, Novock said:

I run my JP GMR13 just the way it came from JP. I run light bullets with Hodgdon Longshot at 130pf and the dot tracks well. I dialed my load in for the gun vs changing the gun for my load.

What do you consider " light" bullets?

[StealthyBlagga]

Great discussion, and definitely an area for innovation in this new division. HOWEVER, if folks are new to blowback designs, I suggest they do some research on bolt/buffer/spring combinations and stay within the realm of the "known safe". Unlike locked breach rifles, blowback designs rely entirely on the inertia of the bolt assembly to prevent case head separation/breach explosions - this webpage is an interesting primer. Lighter reciprocating mass may feel flatter, but you could be on the ragged edge of safety and reliability. Be careful guys.

[Patrick Scott]

7 hours ago, Cavy said:

What load are you using? I assume this a rifle length buffer tube?

147gr Black Bullets International, 2.8gr VV N320, 1.110"oal 

130pf out of my 16" barrel

Milspec carbine buffer tube

[Kmarsh1966]

UPDATE

I took the counsel of several shooters above and went back to the original factory spring, factory 5.4 oz 9mm buffer, I also removed the pinned weight inside the BCG.  It shoots much better.  

 

TO CLARIFY.  I AM A COMPETITIVE SHOOTER, I only shoot low power factor loads, 147 fmj under 900 fps.

 

I did try a buddies 124's loaded to 135+ power factor.  The lighter bullet seemed to slam the BCG back harder than the 147 slower load. 

[Novock]

On 11/1/2016 at 11:58 PM, Cavy said:

What do you consider " light" bullets?

This is my USPSA PCC gun so I run 115's

[Posvar]

I'm struggling a bit with my GMR-13. My pistol load with Extreme 147g and 3.1g TG has too much bounce and dot movement. Last night I tried 3.4 and 3.5 and it got worse. For some reason the Stand One Chubby reduced power factor 147g ammo I have has ZERO movement other than a slight push back into the shoulder. It gets the comp going very well too. I am thinking TG is too fast burning of a powder? I'm not looking to change the gun at all or go to a different bullet but may need to go to a different powder. I really want it to get it close to the Stand One feel and still load my own bullets. Any thoughts???? 

[Les Snyder]

Posvar... I've always had good luck with Win Super Field in my 9mm... like you, am searching for a light 135pf load for the PCC.... just switched to 135 Bayou coated, so starting over from the 147 Precision Delta... so far, 3.9 of WSF is still 1100fps out of the 16" carbine... just added a 3/32" roll pin to use as a pointer to the charge bar adjusting bolt on the Dillon, so I'll have a better reference if I go with a different PCC load than the pistol... the 3.9 load out of the pistol is a 130pf load....thought I would use different color coat to distinguish between loads.... should have chrono results of a couple of lighter loads tomorrow

[bmiller]

After reading a few threads about this, I decided to try this for myself.  I had some time this morning so I whipped up an 8 ounce buffer.  Went off of the specs on a website.  Actually came out at 7.95 ounces with the urethane buffer installed in the end.  Shot the same loads, 115 grain blue bullets at 145 pf, comparing it to the stock buffer at 5.3 ounces and my urethane spacer.  Used the same stock spring with both buffers.  I preferred the lighter buffer.  The heavier buffer had more preceived recoil, as well as more for bounce for me.  I have been battling gremlins in this rifle.  First the gas key sheared off (only had one bolt holding it on), then I had issues with it not ejecting empties and irratic ejection.  I am relatively certain it was a head space issue.  Actually, I was so frustrated I pulled the extractor out of the gun and the damn thing basically had the same failure rate.  Pulled the barrel last night and faced the barrel so there is a small crack of daylight when a round is chambered.  Seemed to fix my light strike and ejection issues.  Will know for sure after the night zombie match Saturday. 

[Les Snyder]

rats... was running late and loaded only one charge 3.7 WSF and 135 Bayou... still 1100fps.. after 35 years of USPSA this is the smallest powder charge I've ever dropped

[Cavy]

On 10/23/2016 at 5:21 PM, CZ85Combat said:

You want a lighter buffer, a light spring and a light load. What I am using, JP 9mm Silent Captured Spring with one tungsten weight removed replaced with steel weight, 80% spring, 147 Blue Bullet  2.5gn N310 @ 1.130 132pf out of a 14.5 Barrel.

Just curious. I have the JP bolt and JPSCS 2nd gen 9mm setup. 3 tungsten and 1 steel weight. It came with the yellow/red spring. From what I read this is the heaviest .308 spring. What color code is the spring you ended up liking? Did you stay with the .308 springs or drop down to AR15 springs. Thanks, Randy

[CZ85Combat]

The AR 15 white spring is the 80%  spring.....

• JPSCS-SPRING15-80: 1 side white
• JPSCS-SPRING15-85: 1 side black
• JPSCS-SPRING15-90: 1 side green
• JPSCS-SPRING15-95: 1 side yellow
• JPSCS-SPRING15-100: no color

[MikeRush]

On 11/8/2016 at 7:24 AM, Posvar said:

I'm struggling a bit with my GMR-13. My pistol load with Extreme 147g and 3.1g TG has too much bounce and dot movement. Last night I tried 3.4 and 3.5 and it got worse. For some reason the Stand One Chubby reduced power factor 147g ammo I have has ZERO movement other than a slight push back into the shoulder. It gets the comp going very well too. I am thinking TG is too fast burning of a powder? I'm not looking to change the gun at all or go to a different bullet but may need to go to a different powder. I really want it to get it close to the Stand One feel and still load my own bullets. Any thoughts???? 

I would reduce the charge. 3.5 grs of TG with a 147 is probably way over the minor PF floor. One of my friends is using a JP barrel and making 130 something with 2.6 grains of TG and 147s. You probably aren't going to be able to feed the comp enough gas to offset the increased recoil from a heavier charge. As far as it being too fast my favorite PCC load is with Promo, which is faster than TG.

On 11/2/2016 at 5:38 AM, StealthyBlagga said:

Great discussion, and definitely an area for innovation in this new division. HOWEVER, if folks are new to blowback designs, I suggest they do some research on bolt/buffer/spring combinations and stay within the realm of the "known safe". Unlike locked breach rifles, blowback designs rely entirely on the inertia of the bolt assembly to prevent case head separation/breach explosions - this webpage is an interesting primer. Lighter reciprocating mass may feel flatter, but you could be on the ragged edge of safety and reliability. Be careful guys.

I totally appreciate the concern for safety and I am on board with you in this respect. I have had several friends kaboom cases in the last few weeks (including one where the case head was an independent disk from any of the cartridge walls at the end). I think people aren't using a chrono, and are using heavy charges, long barrels, and light triggers which all work against a safe, reliable blowback gun. We are all trying to have fun and I hate to see anyone get hurt.

That being said, I looked at the Orion site before and the math doesn't seem to add up to me. For a "safe" bolt weight in 9mm he suggests a 27 oz bolt. This is heavier than a standard 9mm AR from CMMG or Rock River, a JP, a Suomi, an Uzi, or ANY 9mm blowback gun I am familiar with.

There is a book, the "Submachine Gun Designer's Handbook" by George Dmitrieff that goes into great detail on designing a safe blowback gun. It includes formulas for barrel time, extraction rate, bolt speed, etc and also lists barrel lengths, bolt weights, and other characteristics of common subguns. His perspective (not mine) is that a 500 gram (just under 18 oz) bolt is sufficient for a 9x19 from a safety point of view. That is about where I am at with my CMMG now, at 17.x oz combined bolt/buffer weight. I stress that this is what I am comfortable with, and I am not making a recommendation that anyone follows suit. I am putting together a second upper with an 11" barrel and permanently attached 5.5" flash suppressor which will mean pressure is dropping sooner than with a 16" barrel. Using some of the math in this book, I am planning experimenting down to around 15 oz with MY reduced handloads only. This is with an extra power recoil spring, a fast powder, light bullet, minimal charge and relatively heavy hammer spring. I probably will settle around 17-18 oz total weight just to have a "safety factor" built in should someone use factory ammo in it.

I think anyone who wants to experiment blowback guns should get the load set first, and then work on tuning via bolt mass if they feel compelled to do so AND understand the safety implications. Honestly I wouldn't shoot WWB out of my gun as it sits, and the gun shot reduced loads pretty well at 21.x combined bolt/buffer weight.

[Aircooled6racer]

Hello: I am going to try a 15.5oz bolt carrier group, 308 spring and a 5.4oz buffer with 130-135PF reloads using 115,121,124, 147 grain bullets. I am still waiting on some parts so it maybe a week or two before the testing starts. This is turning out to be a fun project! Thanks, Eric

[ChuckS]

1 hour ago, Aircooled6racer said:

Hello: I am going to try a 15.5oz bolt carrier group, 308 spring and a 5.4oz buffer with 130-135PF reloads using 115,121,124, 147 grain bullets. I am still waiting on some parts so it maybe a week or two before the testing starts. This is turning out to be a fun project! Thanks, Eric

I picked up a complete rifle from a local guy. I am not exactly sure what spring I have but I am guessing it is a carbine. I have the 5.4 oz buffer and 15.5 BCG and so far, if feels real manageable. I just took my 124 gr production load and dropped a couple tents to 4.0 N320. I hope to chrono tomorrow. In terms of recoil and dot movement, it is pretty minimal from first impressions. After I chrono, I will decide if I am going to screw around with the hardware or just play with loads for now. I will report back,,

[StealthyBlagga]

20 hours ago, MikeRush said:

... I looked at the Orion site before and the math doesn't seem to add up to me. For a "safe" bolt weight in 9mm he suggests a 27 oz bolt. This is heavier than a standard 9mm AR from CMMG or Rock River, a JP, a Suomi, an Uzi, or ANY 9mm blowback gun I am familiar with...

Yeah, I think his numbers are very theoretical and conservative, and don't take into account other effects. In the case of a blowback semi-auto, the hammer also contributes to bolt retardation - hammer weight, hammer geometry, hammer-bolt relationship and hammer spring strength are all going to play a role (which is why I run a JP trigger with GI hammer and hammer spring). In the case of open-bolt submachine guns, their bolts can be substantially lighter because they work by advance primer ignition (i.e. the bolt is still moving forwards when the propellant ignites).

Edited November 29, 2016 by StealthyBlagga