How to get a heavy buffer in a PCC to work?

[Cy Soto]

I recently finished putting together a 2nd PCC and, this time, I used the heaviest bolt & buffer combination I could find. My idea was that, by using heavier parts, the recoil would be significantly reduced.  I used a 10.5oz 9mm New Frontier Modular Bolt and a 10oz NF buffer combination behind a 16" barrel.  I took it to the range for the first time yesterday and, with the exception of Blazer Brass 115gr factory ammunition, I was unable to get any other factory 115gr load to work.  I understand that the quick answer to my question is "if Blazer Brass ammo worked, then continue using it."  I would, however, prefer to load my own ammo for this heavy bolt/buffer.

 

With this in mind:

1) Will I have better luck using fast powders (Titegroup, Bullseye, N320) or a slower-burning powder (like Autocomp)?

2) Should I try using 124gr bullets instead of 115gr?

3) Would using a lighter buffer spring help?

[Aircooled6racer]

Hello: Try a 223 buffer spring. I think your New Frontier weight is wrong. It should be about 15ozs or more. Use Tite Group powder but your recoil solution is the wrong way. You have to go lighter in buffer.recoil and bolt setup with a light spring setup. That big heavy weight coming back will give you more muzzle flip and dip for a longer duration than a light setup. Use a timer and see how your hits are at 7 yards doing double taps. I have settled on a 147 grain bullet for USPSA pistol matches. 124 grain bullet for a PCC carbine match at distances out to 100 yards or so. Thanks, Eric

[Les Snyder]

to add to what Eric commented...if you have head space and sufficient leade area that does not slow down the bolt while chambering the cartridge, be on the lookout for the bolt battering the rear of the barrel...

 

the NFA modular bolt should be around 17 1/2 oz... I tried a 9oz buffer and .308 spring with mine, but got serious battering of the rear of the barrel... YMMV

[Cy Soto]

You are both correct about the weight of the bolt; it was a typo on my part.  This bolt is roughly 16.5oz.  

 

Eric: In addition to reducing the spring weight, do you believe that a faster powder is what is needed to push the bolt & buffer to the rear more effectively? 

 

Les: The barrel battering is an issue that had not even crossed my mind.  I will keep an eye out for that too.

[Aircooled6racer]

Hello: I think if you use a slower powder at minor loads you may see a lot of unburned powder and it will be dirty. The only powder I have tried at really low power factor is HS-6 and it is very dirty at 130PF loads. I have seen some Auto Comp loads at 130PF and it was dirty also but that was in 40 S&W IDPA loads. You can always try Auto Comp and see what you think. I use a timer and feel to find what best for me. The timer doesn't lie. Thanks, Eric

[Dannybot]

I run two set ups: JP bolt with carbine buffer and MFA modular bolt with H2 buffer.  Both use a carbine spring, both run light charges that make 126 PF in an 11" barrel.  My heavier set up is still 6 oz less mass than the one in question.  

 

The lighter set up is on a standard 16" upper,  the heavier in on a 11" SBR that I run suppressed frequently. 

[bmiller]

I tried the super heavy buffer a while ago, I did not like it. Your set up could be different, mine had excessive dot rise and dip with the heavy buffer.  I was not using mouse fart loads, but to me, I didn't see a a way get a soft shooting rifle with that setup.  

[TRUBL]

From our dealing with PCC......with pretty much any factory ammo, we've seen the sweet spot for total mass to be the 20-22 ounce range with a 223 rifle buffer spring. Now.......you have to have a buffer that will allow the rifle spring NOT to go solid.

 

Tim

[Cy Soto]

2 minutes ago, TRUBL said:

....you have to have a buffer that will allow the rifle spring NOT to go solid.

 

I'm not sure I understand. What do you mean by "not go solid"? 

[Steve RA]

Means not to "bottom out".  All air space gone between coils.

[Cy Soto]

Just now, Steve RA said:

Means not to "bottom out".  All air space gone between coils.

 

Ahh... Got it!  Thank you for the quick reply.

[gatortommy]

I've done extensive testing with powders in my PCC's and don't really notice any perceived recoil/dot bounce differences in fast powders vs slow powders so have settled on using fast powders for purely economic reasons. It takes me 30% more HS6 to make a given PF vs Titegroup. At one point, I hypothesized that the HS6 might make more gas to work the comp, but in testing I didn't notice a difference.

[Les Snyder]

Cy... if you are going to experiment with a bunch of different weight buffers, I found that it was easier to use a rifle buffer tube and rifle buffer ( I use an A1 Viet Nam era stock), and just fill the longer buffer with lead shot, different diameter brass slugs, solid poured lead... and in the end as TRUBL commented, came up with a stock 5.2oz rifle buffer (NFA modular bolt for a total of a little over 22oz) and .223 rifle spring for my 146 power factor loads... I do run a Miculek style comp as I found it helped reduce scope shake... I currently have the Enidine hydraulic in it from my 3 gun rifle for a match or two... good luck... if you need weights of various brass slugs it should be archived under my name

Edited June 19, 2017 by Les Snyder

[Aircooled6racer]

Hello: The magic buffer weight setup for me is in the 4.6-5.2oz range. KAK sell a kit you can change out buffer weights or just buy some of there weights for your buffer. The two buffers I am using now are 4.6oz and 4.8oz JP's with two different springs on them. They feel almost the same. Thanks, Eric

[blaster113]

I ran a Spikes ST-9X 9 oz buffer with a Wolff XP buffer spring and a CMMG bolt for a while with good results.  Barrel length is 16", no comp.  Dot movement seemed less than with the old combo of a CMMG 9mm buffer and carbine spring.  Function is also 100%.  Currently trying the MBX buffer with my reduced load.  load is a 125 grain BBI and Solo 1000 to make 135 pf.

Edited June 20, 2017 by blaster113
buffer