Broke an extractor

[tdbru]

FWIW, on my AR build I have 2 uppers, 20" and 24" both with RLGS and non adjustable blocks.

the lower has a full length fixed stock (long buffer tube), rifle buffer tube spring, and a heavibuffer (11oz vs std rifle of 5.xx oz).

with the extra mass in the buffer, the pressure in the barrel/case/gas tube is down quite a bit more than usual by the time the BCG starts to unlock the bolt and the gas key clears the tube. I have also done the radiusing on the extractor edges and removed the O-ring.

I've not had any extractor issues and don't expect to. cycling is slower than normal, pressure seems very low when BCG unlocks the bolt. as a benefit, to me, it seems, the action interior is pretty darn clean. very little amount of carbon blowback into the action. I think by the time the end of the gas key clears the tube, the pressure in the tube is quite low as compared to when running with the standard 5.xx oz rifle buffer. so less gas gets blown into the action, at least that's what I think is going on.

downside? on my light weight build the rifle has a little bit butt heaviness to it. on the bull barrel build, you can't tell, it's still barrel heavy.

functional reliability has been 100% so far, but it's a sporting rifle and leads a pretty pampered life compared to a GI service rifle. Brass ejects in very good condition. outside of the brass is pretty clean and doesn't have the burnt outside look. Case mouths get dinged a little. no extractor gouges on the rim at all.

you can tell it's cycling slower than other ARs but it's still ready to go before I can get the crosshairs back on target so no complaints about the slower cycling.

i'd read enough posts on this forum about the broken extractors and the likely cause that it seemed to me that if the bolt unlock got delayed a little longer, so the pressure in the case dropped down further, that extractor issues will go away. this is why I think the adjustable gas blocks are popular and useful. they can be adjusted to delay when the bolt starts to unlock as compared to a non adjustable gas block. but they can also have issues with becoming carbon fouled enough that they are no longer adjustable. So I tried a little different approach with delaying the bolt unlock. I used a standard non adjustable gas block for it's simplicity, and added mass to the reciprocating parts via a heavier (2x) buffer. This approach might not be for everyone. I've had no issues yet, but as i mentioned, I don't put my sporting arms to hard use like the service rifles receive. time will tell if this approach works well.

and I still picked up a spare extractor anyway. belt and suspenders you know.
-tdbru

[montana]

FWIW,
i'd read enough posts on this forum about the broken extractors and the likely cause that it seemed to me that if the bolt unlock got delayed a little longer, so the pressure in the case dropped down further, that extractor issues will go away. this is why I think the adjustable gas blocks are popular and useful. they can be adjusted to delay when the bolt starts to unlock as compared to a non adjustable gas block. but they can also have issues with becoming carbon fouled enough that they are no longer adjustable. So I tried a little different approach with delaying the bolt unlock. I used a standard non adjustable gas block for it's simplicity, and added mass to the reciprocating parts via a heavier (2x) buffer. This approach might not be for everyone. I've had no issues yet, but as i mentioned, I don't put my sporting arms to hard use like the service rifles receive. time will tell if this approach works well.

and I still picked up a spare extractor anyway. belt and suspenders you know.
-tdbru

According to the black rifle book, added buffer weight effects carrier velocity and has negligible effect on dwell time, especially with the random position of the loose weights and discs.

The Vltor A5 buffer system supposedly solves this problem with its internal spring design.

In any case, I find the heavier weight approach much akin to keeping the throttle down on a car while only using the brake. This is why I run the lightest buffer possible and adjust the gas to the system..This way will allow the softest perceived recoil and still be reliable.

With the Rifle Speed adj gas block, the problems associated with the other adj gas blocks are a thing of the past IMO.. The only down size is expense and matching the hand guard to the higher straight line gas tube..Some hand guards will not work with the straight gas tube..

[tdbru]

Montana,
the Heavibuffer has the rubber bumper on the back, like a normal rifle buffer, but otherwise is solid Stainless Steel. so no moveable weights inside. Yep the carrier is slowed down. I have no way to measure how fast everything is moving on the inside, but F=MA. if force stays the same and mass increases, then acceleration will decrease. the bolt carrier will not be moving as quickly. just physics. it will take longer for the gas key to uncover the gas tube. it will take longer before the bolt carrier moves enough to start to unlock the bolt. as I mentioned, I have no way to measure the difference, but you can feel it when you shoot the rifle. it doesn't cycle as quickly as it does with the standard rifle buffer.

And it may indeed be better to run an adjustable gas block rather than a heavier buffer in the long run. I don't have long run experience with this particular setup. So far it is 100% reliable functioning with no broken parts.

if I can shoot it enough to wear out both barrels, then I will have a better estimate of the reliability of trying to slow the BCG in this approach.
best to you,
-tdbru

[montana]

I understand the effect on carrier velocity, but dwell time is determined more by the port size/location, cam groove cut and the type of powder (pressure/burn rate) being used.

LMT created a longer cut cam groove for their enhanced carbine bolt carrier to increase the un-locking time process so the case would have less residual pressure during extraction. It worked as designed, but was rejected by the military because it would not work in rifle length gas systems.. The military didn't want two different types of bolt carrier groups in the supply system..
If increase in buffer weight was all that was needed to effect dwell time, then LMT would not have bothered with a re-designed cam tract for their enhance bolt carrier group and would have just increased buffer weight..

The increase in buffer weight has always been to reduce carrier velocity/cycle rate and prevent bolt bounce malfunctions on full auto, not effect dwell time..The original Edgewater buffer was replaced by the newer Colt designed buffer with the M-16. The new Colt designed buffer slowed carrier velocity (decrease cycle rate) and fixed the bolt bounce malfunction problem on full auto, but what it didn't do was have much effect on dwell time (even though it was almost 3 times as heavy) as the original Edgewater buffer..

I quote from the Black Rifle book page 202:
In the rifle, the new buffer did and didn't do several things.
First, because of the random position assumed at the end of each shot by loose-fitting internal weights and discs which compromised a large portion of the buffers mass, the effect of the buffers added weight on the rifle's "dwell time" or bolt opening cycle was negligible.

I understand the inertia forces of increased weight, but the actual effect buffer weight has on lock time has been way over emphasized IMO compared to gas regulation/port pressure/port location/ cam tract design. There is a happy medium with all things but I don't think I'm far off on my assessment..

[rickt300]

Interesting. I recently bought a heavy barreled 20 inch upper in Grendel with the original plan being to rebarrel to 6ARC if it didn't shoot. Well I have run 200 rounds through it since new, cleaned the barrel thoroughly before shooting it. I never took the bolt apart or cleaned much of the heavy sticky oil BCA uses out of it. Barrel is beautiful, not even noticeable fouling. Zero copper fouling! Bolt has gotten a bit dry and fouling was as expected. I removed the extractor to remove the O-ring and take a look at it to radius as recommended. No Oring found. Extractor already radiused and looks polished. So all is good.Load used is 120 gr. Barnes Matchburner powered by 29.5 grains of BLC2 popped with a Federal 205 primer. Accuracy and function have been excellent. Well I was taking the bolt apart as I typed this and lo and behold the gas key is loose! The bolts are "staked" but only enough to keep them from backing out.