7" 5.56 SBR buffer weights?

[wally]

I've got a 7" chrome lined SBR in 5.56x45. What carbine buffer weights are suggested/available to try?

I weighted what I have on hand (g = grams):

"Standard M4" 9.84g 9.88g 9.45g

"H marked" 17.84g

"Spike's T2" 18.92g

"DPMS 9mm" 21.28g

Mine runs fine for 3-4 mags with the standard weight buffer and spring, but once its fouled a bit, I get ejection issues. My hope is a heavier buffer will slow things down a bit and reduce the fouling (empties out of the chamber, off the extractor, next round picked up but un-ejected empty stops the show). I'd like at least 6 or 7 mags without needing to clean it or squirt in Break-Free. My suppressor will be here soon, I expect this will make matters worse.

My plan was to try the heaviest, but the range was flooded today so I figured I'd ask what others are running since it'll be a week at least before I get another chance to try

 

[Gordon]

By acting as a muzzle booster the suppressor may very well make it runs well. An H2buffer works really well in my Noveske Diplomat 7" , maybe it is the muzzle booster device tho.

 

[wally]

My next question, what is the weight of an H2buffer? Or is its the "same" as a T2?

I'm sure it'll take some trial and error. Great excuse to get to the range

 

[Gordon]

Although I've heard some buffers weigh different from others do to tungsten alloy:
BUFFER WEIGHTS

Standard Rifle - 5.15oz

Standard CAR - 2.9oz

H CAR Style - 3.77oz

H2 CAR Style - 4.7oz

H3 CAR Style 5.6oz

9mm - 5.47oz, made of steel

Standard CMT carbine buffer - 2.9 oz.

CMT H buffer - 3.8 oz.

CMT H2 buffer - 4.1 oz.

Spikes ST-T2 - 4.3oz.

Armalite H3 buffer - 4.7 oz.

RRA 9mm buffer - 5.5 oz.
------------------------------------

Spikes 9mm buffers

ST-X SS 9mm buffer - 6.0 oz.

ST-9X SS Extended 9mm buffer - 8.5 oz.

ST-SST - 7.0 oz.


I think an H2 Colt Buffer as is in my 7.5 Diplomat should be enough and an H3 is really not necessary IMHO if the rest of the 5.56 DI is right.

 

[wally]

Hmmm, looks like a serious scale factor error in the reading of my scale as 1 ounce is something like 28 grams so weights look way off. I'll have to recheck.

Thanks for the list, it gives some options to look for should the ones I have not work out. I wish they were simply listed by weight instead of "codes".

 

[Dustin0]

H3 CAR Style 5.6oz

 

[wally]

The 9mm buffer ran great with both the 9mm upper and the 5.56. However it didn't help much with the 5.56 upper only running while clean issue -- after three or four mags I start getting ejection failures. No evidence of short stroking, I did lots of single rounds from a magazine and all locked back and ejected, but with rounds it the mag I had a high rate of ejection failures once things got dirty. Even loading only two or three rounds would sometime not eject the empty toward the end of the session. I used six different mags and even the P-Mag suffered the failures.

I'll compare the extractor to a known good one (or maybe just swap to see if the issue swaps).

Had zero issues with the 9mm SBR upper using four different mags and brands of ammo. Was happy to see my "sub-sonic" 147 gr reloads ran well.

Here is a quick photo:

The silver "E" clip above the bolt catch is so I can quickly remove the bolt hold open to remove/install the 9mm mag block. Ugly but functional and will do until my next SBR stamps come in so I can quit swapping uppers. The mag block is a Pro-Mag, despite my general bad results with Pro-Mag got this cheap enough to take a chance on and so far it seems to work well -- no feed failures and all mags locked back on the last shot.

I've also got a CMMG .22LR pistol (which will also be an SBR eventually) that I also use on the SBR lower from time to time -- it'll see a lot more use once my Sparrow suppressor comes in.

On the muzzle of the 5.56 is the quick mount for the Gem-Tech .308 suppressor that is also on the way. I also have the .5"x36 piston and spacer for my Osprey 45 suppressor, but that will have to wait for next time as this was the first time out with the 9mm upper and I wanted to keep it simple.

 

[Gordon]

I'll bet it runs good with a muzzle device.Course it will get dirty quicker , but not 4 mags worth.

 

[wally]

I'm thinking its got to be something with the extractor as all the empties are out of the chamber just not out of the ejection port. None are partially out the port either (no "classic" stovepipes".

I saw something similar many years ago in a 16" carbine where it was fine with brass cased ammo but stoved piped often with Wolf steel case, but these were almost always part way out of the port as a classic stovepipe. Turned out the extractor had too narrow a gap between the hook and the bolt face and wasn't fully fitting in the extraction grove. Something similar may be going on here, I'm about to get off the computer and check.

 

[rjrivero]

I built a 7.5" AR upper, and it was a filthy beast. She would be fine for about 100 rounds or so, but if you push the round count to 200 before at least running a bore snake and chamber brush on it, she would fail to eject. Cleaning the chamber would always "cure" the issue.

I just think pistol length gas is a filthy beast, and not really well suited for this DI operating system.

 

[wally]

You may be right, I didn't see any major issues with the extractor but the front was "thicker" on the stock one than on my replacement, perhaps not fully fitting in the extraction groove, so I swapped them.

The replacement also has bigger gaps along the side, it looked like gas was getting under the extractor, so perhaps it was prematurely removing it from the rim, now there is more space for any gas to escape. I also noticed the bolt rings all had their gaps nearly aligned, so I rotated them to make the gaps about 120 degrees apart.

I should get a chance to see if it helped this weekend, and I'll add a bore snake to the range bag in case its something I'll just have to live with.

 

[wally]

Looks like the issue was the extractor, maybe in combination with the gas ring gaps being lined up and perhaps letting gas under the extractor. The replacement extractor is thiner in the front to fit more fully in the extraction groove and narrower on the sides to make more room for any gas that might get under it to escape.

Ran 6 mags (180 rounds) with zero issues using the 9mm buffer. Ejection was about 4-5 o'clock (won't make the purists happy, but as long as the empties are out of there, I don't much care where they land!). I was shooting fast enough that it got uncomfortable to hold through my leather shooting gloves. Paused a bit and finished the last mag.

I'm a happy camper, its not often I go through more than six 30 round mags with a single rifle in a session. Not needing to swap the buffer makes switching between 5.56 and 9mm less hassle -- I'll have a dedicated 9mm SBR eventually.

 

[wally]

Ran another six mags through it today, so that's 360 rounds without cleaning, only a quick wipe down and return to the safe.

I really enjoy shooting this thing! Was also fun to swap in the 6.5" CMMG .22lr pistol upper to finish the outing with 100 rounds of cheap no recoil fun. My .22lr suppressor should be in my hands Saturday so I'm going to like the .22lr SBR a whole lot more real soon! (doesn't matter what buffer is in with the .22 as it never pushes it back, the CMMG pistol has a flat backing plug).