Need some feedback from SME's on 12.5 barrel issue please.

[polydeuces]

Have a 12.5" CA barrel, which runs like a charm with any proper 5.56 ammo - soft and smooth as butter.

However - I like to shoot that dirty dank commie ammo - underpowered and all. So my quest is to get this upper to run reliably with Russian "underpowered" ammo.

Problem:
While feeding it WPA and TULA (62 gr & 55 gr), I tried this upper with a range of buffers (Car, H, ST-2 ) and springs (Sprinco Blue, BCM standard), but it keeps giving these failures depending on buffer/s[ring combination:
Failure to feed - most common with Sprinco blue and ST-2 buffer,
Failure to extract/double-feed (where the empty and the new round are competing for the same real-estate..) - most common with a regular spring and CAR buffer (weight at 2.8 oz.) but so far no cigar.

My relatively uneducated guess now is to get a reduced strength spring (Sprinco white), take one of the weights out of the CAR buffer - drop that weight down to 2.2 oz., and see what combination works best - if at all - as all else has failed.
Perhaps this simple combination will do the trick.

But after seeing these failures, started to wonder what part of the puzzle does what - what affects the feeding most, and what affects proper function most; extract/eject/feed, as it became pretty clear it is not as simple as just throwing in some random combination of buffer and spring & see what sticks.
Obviously one could keep on reducing buffer weight and spring power, but I'd like to know what function each has mostly - as they obviously work together (or not…and there probably is a limit - is there? What would be the lightest buffer, for instance?).

Big question: What part of the action is most buffer related, and what is mostly spring? Understanding it is not a black-and-white thing.

Obviously (as per Monty's suggestion) the next step would be opening the gas-port, but that I would consider the last resort and prefer not to, so until then I'd like to fix it the easy way.

I will post a review on this set-up once all is running how i want it to - should be interesting.

Thanks.

[RD62]

You get failure to feed from the heavy spring and buffer set up with under powered ammo possibly from short stroking (does the bolt lock to the rear on an empty mag with this setup?). Slow carrier velocity (gun runs too slow).

You get a failure to extract from the lighter spring and buffer because the lighter setup decreases lock time forcing extraction before the pressure in the chamber can subside more causing harsher extraction which if the extractor is worn may cause the issue you have (gun runs too fast).

Have you tried the standard spring and an H or H2 buffer?

I run the standard/H2 setup in my LMT 10.5 very reliably even with steel cased ammo (though I don't shoot it often).

I'm sure someone more knowledgeable will be along shortly to correct me if I am wrong though...

[polydeuces]

With the heavy spring/buffer the bolt would not lock back -indeed.

The lighter spring/buffer set-up not sure if the problem is considered extraction or ejection - the "old"shell sits on top of the "fresh" one, which is about 3/4 stripped out of the mag, both are stuck.
"Stove-pipe", or whatever one calls it.

Unfortunately I had no ability to take pictured. Perhaps this weekend.

Re: lighter - is it the spring or the buffer causing the issues in this set-up. Or both.....:( Or is this not something we can "quantify".....(doesn't this type of pondering require copious amounts of beer..........? :) )

[CoryCop25]

My best guess is that it is not a buffer/spring issue. It is a gas port issue. Many of the standard mil spec gas ports are much too small for the cheap under powered ammunition.
It is a trade off with high end 5.56 barrels. You get a smaller gas port for smoother cycling of hot 5.56 ammo and the inability to shoot any of the cheaper stuff.
A larger gas port will run the cheap stuff better but then you have an over gassed gun when you use the good stuff.

[TehLlama]

It IS a gas port issue - I wouldn't go any farther than running it extremely wet, and maybe a CAR buffer when you're running ultra cheap stuff - otherwise, IMI M193 isn't that much more expensive than wolf, and I wouldn't compromise the function of a solid rifle just to run really cheap ammo.

[polydeuces]

Thanks guys.
I am very much aware this is a gas-port issue, have built several rifles with CA barrels- at 16" though, which are extremely soft shooting - and will eat lower powered ammo.

However going to 12.5" and shorter this is where the gas-port at .069-.071 is no longer is sufficient to shoot (lower powered ) .223

Monty made this very clear to me and why they chose for that particular combination, and it makes perfect sense.
Quote: "That is the problem with SBR or pistol barrels in the AR platform it becomes more of a balancing act and harder to run a wide range of ammo.
We gear ours to run 5.56 only,(edit) if you try to make them to run both you can be over gassed in 5.56 and under in .223 they are enough other variables in the system. "

I have a DD 11.5" sbr which is like a trash can - shoots whatever i stuff into it-, but kicks like a mule compared to shooting Monty's 12.5" with 5.56 ammo.
This being one of the why's.

My goal here is to learn a bit more about how buffer and spring affect functionality, and what the limits are of what is reasonably possible - WITHOUT opening the gas-port (as stated in my original post).
Was hoping some could enlighten me a bit about the finer details of the working of these two parts.

Thanks.

[Scoby]

It IS a gas port issue - I wouldn't go any farther than running it extremely wet, and maybe a CAR buffer when you're running ultra cheap stuff - otherwise, IMI M193 isn't that much more expensive than wolf, and I wouldn't compromise the function of a solid rifle just to run really cheap ammo.


This is my opinion as well.

[Iraqgunz]

In my opinion the longer barrels would be more forgiving of firing crap ammo as opposed to proper ammo.

This shouldn't be of great surprise. If one looks at SBR's across the board there are only a few companies that produce SBR's that are reliable. None of them recommend using anything but MILSPEC ammo as far as I know.

[polydeuces]

In my opinion the longer barrels would be more forgiving of firing crap ammo as opposed to proper ammo.

This shouldn't be of great surprise. If one looks at SBR's across the board there are only a few companies that produce SBR's that are reliable. None of them recommend using anything but MILSPEC ammo as far as I know.

Absolutely - the same CA barrel/gas port in 16" shoots most any ammo reliable.
When going to 12.5 and less, things get interesting.

As mentioned earlier, going to try running a reduced power spring and remove some of the weight out of a CAR buffer, see what happens.

Apparently there is not really a minimum amt of weight the buffer should have?

[polydeuces]

Problem fixed - so far.....

Going to do some more testing with different ammo and buffer/spring combinations but so far the following set-up seems to run "reliable" (2-30 rd magazines, no failures and bolt lock on empty.)

Set-up: Regular BCM carbine spring, CAR buffer - factory weight at 2.8 oz, reduced to 2.2 oz.

Now I need to see how this set-up deals with 5.56 ammo.
Will report back with a write -up of sorts.

[TehLlama]

Run single round magazines - these usually manifest short strokes first as failures to lock back if it's just a lack of gas impulse. Should accelerate data gathering, unless you have drills to run on others.