View Full Version : Wont lock back on empty magazine with overgassed upper
SHERWINVILLARETE
03-05-21, 01:36
Im not getting a lock back on an empty mag with an overgassed upper. It happens when I use my older (about 4 years old) PMAGs. Works ok with newer mags. The rifle ejects about 2 oclock with brass cased ammo, 3 oclock with steel cased.
I swapped out the upper with a well gassed upper that ejects at 3-4:30 with brass and 5 oclock with steel cased. Still using the same lower, same mag, the only thing that changed was the complete upper, and the it locked back every single time.
Im guessing the bcg velocity is too fast for the worn out magazine?
Im gonna try a full auto bcg and a heavier buffer next time and see if that makes a difference.
Don't change too much at once. I'd start with a heavier buffer first as you mentioned. Next, try a springco blue spring.
BTW what buffer weight are you using and how old is the spring?
Are the gas rings and gas key in good shape on the problem bcg?
Whatever you do, only make one change at a time.
Inkslinger
03-05-21, 06:35
Maybe try some new magazine springs.
How about correcting the gas drive with the upper?
Also, what buffer is in there currently?
SHERWINVILLARETE
03-05-21, 09:10
Im using just a standard carbine buffer and flat wire spring.
The standard carbine buffer is worthless. I can't think of a set up where that thing is right.
As Clint said... Correcting the gas is step one. An H2 carbine buffer is where you want to be for almost every correctly gassed carbine set up. I don't mess with aftermarket springs.
SHERWINVILLARETE
03-05-21, 13:07
The standard carbine buffer is worthless. I can't think of a set up where that thing is right.
As Clint said... Correcting the gas is step one. An H2 carbine buffer is where you want to be for almost every correctly gassed carbine set up. I don't mess with aftermarket springs.
Hmm. A carbine buffer is right for well gassed guns or undergassed guns.
I dont think its the spring cuz the spring worked well for the longest time on multiple uppers.
Im no expert, but what weight buffers do the military use on their M4s?
Hmm. A carbine buffer is right for well gassed guns or undergassed guns.
A regular Carbine buffer would only work good on an undergassed gun. It's WAY too light, and has been very problematic on civilian/overgassed guns for years.
Im no expert, but what weight buffers do the military use on their M4s?
I think the currenty M4s come with H buffers.
JD Williams
03-05-21, 14:36
Current spec is an H buffer about 3.8 oz. I used a BRT insert to cure the same problem you are describing. Well gassed guns are glorious!
https://www.instagram.com/p/CIjxmThpzot/?igshid=19urqshx1b8gm
Unless you are controlling the gas at the source various and sundry other parts are at play.
ETA: H buffers are what I’m getting in my 6920s, sorry for the confusion.
#prettysurethatsbroken
Well gassed guns are glorious!
AMEN! I've had barrels in the past that were SO over gassed, they also outran the bolt catch. Absolute misery to shoot. I didn't even shoot my first SBR hardly ever because I just thought short guns were brutal.
The decades of idiotically spec'd ARs by morons in the manufacturing realm were tough times for the platform. It's how the AR piston stupidity got started.
Hmm. A carbine buffer is right for well gassed guns or undergassed guns.
No. It's too light. Some ARs thought to be over gassed are actually under buffered.
Im no expert, but what weight buffers do the military use on their M4s?
Military issue M4s have H2 buffers.
First, rid yourself of the notion that ejection angle is any kind of indicator as to how your upper is gassed. The change in angle using higher pressure ammo is more an indicator your extractor spring is weak. Test the problematic upper with just the BGC from the properly gassed upper and see what ejection angle you get.
Second, not locking back is an indicator that your gas system is leaking and is beginning to short stroke. Magpul has made several rolling changes to their mags over the years. Older mags may require the carrier to travel rearward more to lock back. (Lock back point also varies between different brands of mags.) Inspect for leaks, worn gas rings and worn gas tube.
Third, not locking back can also indicate the mag release is improperly adjusted. The button may need to be turned in a bit.
Fourth, how do you know your upper is over-gassed? Ejection angle isn't a reliable indicator. (If you don't believe me, get a barrel with an overly large gas port and an adjustable gas block and use ejection angle to tune it.)
Fifth, if the buffer is a carbine weight, you're wasting your time. Replace it with an H, or better yet, H2 buffer.
Sixth, replace the extractor spring with a Colt or Sprinco M4 spring. Trouble shooting with a weak extractor spring is a waste of time. Extractor springs are cheap.
Seventh, check the length of the action spring. If it's too short, it needs to be replaced. If it's been used a lot, it could have collapsed.
SHERWINVILLARETE
03-05-21, 15:36
Im gonna test with another bcg and use an H buffer.
titsonritz
03-06-21, 03:26
I think the currenty M4s come with H buffers.
H2 buffers.
titsonritz
03-06-21, 03:27
Hmm. A carbine buffer is right for well gassed guns or undergassed guns.
I dont think its the spring cuz the spring worked well for the longest time on multiple uppers.
Im no expert, but what weight buffers do the military use on their M4s?
Carbine buffers are shit. Current M4 use H2 buffers
titsonritz
03-06-21, 03:36
No. It's too light. Some ARs thought to be over gassed are actually under buffered.
Military issue M4s have H2 buffers.
First, rid yourself of the notion that ejection angle is any kind of indicator as to how your upper is gassed. The change in angle using higher pressure ammo is more an indicator your extractor spring is weak. Test the problematic upper with just the BGC from the properly gassed upper and see what ejection angle you get.
Second, not locking back is an indicator that your gas system is leaking and is beginning to short stroke. Magpul has made several rolling changes to their mags over the years. Older mags may require the carrier to travel rearward more to lock back. (Lock back point also varies between different brands of mags.) Inspect for leaks, worn gas rings and worn gas tube.
Third, not locking back can also indicate the mag release is improperly adjusted. The button may need to be turned in a bit.
Fourth, how do you know your upper is over-gassed? Ejection angle isn't a reliable indicator. (If you don't believe me, get a barrel with an overly large gas port and an adjustable gas block and use ejection angle to tune it.)
Fifth, if the buffer is a carbine weight, you're wasting your time. Replace it with an H, or better yet, H2 buffer.
Sixth, replace the extractor spring with a Colt or Sprinco M4 spring. Trouble shooting with a weak extractor spring is a waste of time. Extractor springs are cheap.
Seventh, check the length of the action spring. If it's too short, it needs to be replaced. If it's been used a lot, it could have collapsed.
^^^Listen to this guy. That pie chart is gabage I wish people would quit citing it. BTW, a carbine action spring should measure between 10 1/16" and 11 1/4", do not stretch it, cut it or any of that crap.
SHERWINVILLARETE
03-06-21, 09:05
Main reason why im running a carbine buffer is because i shoot a lot of weak ammo like steel cased through a BCM 14.5 middy which is considered super soft shooting by many.
Thanks for yalls input. I will do some testing and try to slow the bcg down and ill get back to you guys with an update lol
Main reason why im running a carbine buffer is because i shoot a lot of weak ammo like steel cased through a BCM 14.5 middy which is considered super soft shooting by many.
That's the ONLY set up I run with a lighter buffer than H2 carbine. H buffer is the sweet spot on my BCM 14.5 middies.
titsonritz
03-06-21, 20:16
I have an H2 buffer and Sprinco Blue spring in one of my BCM 14.5" mid-lengths, it runs great.
No. It's too light. Some ARs thought to be over gassed are actually under buffered.
Military issue M4s have H2 buffers.
For the first ten years they ran fine with standard weight buffers.
The official reports list reducing bolt bounce as the reason for the switch to the two tungsten weight buffer. There is no mention of excessive bolt velocity with the standard weight buffer.
Recoil is sharper with a carbine weight buffer. I experimented with an upper equipped with an adjustable gas block, suppressed and unsuppressed, with carbine, H and H2 buffers. After all the internet chatter about using different buffer weights to control over gassing, I was surprised fo find out all three buffers used the same gas setting. The difference was how recoil felt. Recoil with the carbine buffer was uncomfortably sharp. You can feel the reciprocating mass hit the end of the RE harder.
titsonritz
03-08-21, 11:45
Recoil is sharper with a carbine weight buffer. I experimented with an upper equipped with an adjustable gas block, suppressed and unsuppressed, with carbine, H and H2 buffers. After all the internet chatter about using different buffer weights to control over gassing, I was surprised fo find out all three buffers used the same gas setting. The difference was how recoil felt. Recoil with the carbine buffer was uncomfortably sharp. You can feel the reciprocating mass hit the end of the RE harder.
Translating into unnecessary abuse on your weapon.
Translating into unnecessary abuse on your weapon.
For the first ten years they ran fine with standard weight buffers.
There is no mention of any change in parts breakage between the early standard weight and later H2 buffer.
SHERWINVILLARETE
03-09-21, 09:04
From experience running the optimized gas port of the bcm 14.5, i find the lighter carbine buffer gives a smoother cycle, less harsh, faster follow up shots due to the lighter mass of the buffer. I think thats why some companies like JP make low mass bcgs etc. For their race guns.
Running a carbine and/or low mass bcgs on an overgassed gun can be a problem though which is the problem i might be facing now with a particular upper.
Failure2Stop
03-09-21, 09:07
I'm not saying that it's not the magazine, but you have to be running super fast to outrun a good condition magazine.
The M321 port firing weapon has a cyclic rate of over 1200 rounds per minute, which is about 200 rounds per minute faster than a rifle that would show issues with cleanly ejecting the fired cartridge (leading to intermittent "stove-pipes"). The Mk18 (depending on generation) runs at around 850-900 rounds per minute, which can bump up to around 1,000 rpm or more when suppressed, and magazines are *usually* not the failure point if they're up to snuff. If you are using PMags, you're probably safe up to 1500 rounds per minute, but you're likely to find the mechanical limit of the Stoner operating system before you hit the limit of the PMag.
I'm not saying that it's not the magazine, but you have to be running super fast to outrun a good condition magazine.
The M321 port firing weapon has a cyclic rate of over 1200 rounds per minute, which is about 200 rounds per minute faster than a rifle that would show issues with cleanly ejecting the fired cartridge (leading to intermittent "stove-pipes"). The Mk18 (depending on generation) runs at around 850-900 rounds per minute, which can bump up to around 1,000 rpm or more when suppressed, and magazines are *usually* not the failure point if they're up to snuff. If you are using PMags, you're probably safe up to 1500 rounds per minute, but you're likely to find the mechanical limit of the Stoner operating system before you hit the limit of the PMag.
The acceptable cyclic rate for the M16A1 was 700-900 rpm.
The M4A1 is 700-1025 rpm
The M231 was 1000 to 1250 rpm
I'm not saying that it's not the magazine, but you have to be running super fast to outrun a good condition magazine.
I've had it for sure. My first SBR (20 plus years back), there weren't many options on short barrels. I got a Sabre Defense 11.5 with a port over .080. This was so far back it was pre retard o-ring in the extractor patch for these nightmare ports.
I was probably running a carbine buffer to make things worse because heavier buffers were just starting to pop up. That gun was so brutal to shoot. It would regularly outrun the mag follower.
Colt 20 round mags have weak springs , right out of the box, FYI. Gen 3 Pmags in 20 rounders solved my problem one time in one such issue. And who knows with other no name mags. I cheat and run A5 buffer system and feel they are the holly grail of buffer systems. Probably overkill in many situations, but no downside other than spending $100 vs $35 or whatever.
PB
For the first ten years they ran fine with standard weight buffers.
There is no mention of any change in parts breakage between the early standard weight and later H2 buffer.
Yes. I've never had anything break because I was running a carbine buffer (but I suspect they cause premature extractor spring failures). But bloody hell! They hurt my shoulder!
Yes. I've never had anything break because I was running a carbine buffer (but I suspect they cause premature extractor spring failures). But bloody hell! They hurt my shoulder!
Well, the new extractor spring was introduced around the same time as the heavy buffer.
Failure2Stop
03-10-21, 11:33
The acceptable cyclic rate for the M16A1 was 700-900 rpm.
The M4A1 is 700-1025 rpm
The M231 was 1000 to 1250 rpm
Acceptance range and average performance are different things, and basing the cyclic rate on a full 30-round magazine (fixture dependent as well) will give a different implication of carrier velocity than directly measuring carrier velocity. Part of the issue is that people don't think about carrier velocity, so it's easier to base the observation/discussion on cyclic rate, since the average reader would basically need to mentally equate the relative speed.
I was giving general reference numbers with systems in current service.
The M4 ejector has issues if running over a relative 1,000 RPM.
Well, the new extractor spring was introduced around the same time as the heavy buffer.
I was referring to the extractor spring failures I personally experienced when I was still new to ARs. Some of my early configurations used carbine buffers and generic extractor springs. I suspect carbine buffers led to early failure of those generic extractor springs.
I cannot speak beyond that. I didn't intend to mislead.
SHERWINVILLARETE
03-14-21, 21:25
UPDATE:
Carbine buffer + comm spec bcg = no lock back
H buffer + comm spec bcg = no lock back
H buffer + milspec fa bcg = LOCKED BACK!
Milspec fa bcg 11.5oz
Comm spec bcg 11.2oz
I will try the h2 or h3 next time, test em and call it done.
Ammo:
m193 @ 1-2 oclock ejection
Wolf steel cased @ 3-4 oclock ejection
W/ H buffer + milspec bcg.
This upper actually ran fine with an H buffer and comm spec before. I noticed the lock back issue when i started using the Witt machine SME comp/blast shroud, overgassed an already overgassed upper i guess.j
Alaska3006
03-16-21, 09:04
I use the JP Enhanced Tuned Polished Spring.
I too suggest a H buffer to slow the bolt down.
OP, I had the exact same problem. BCM's are overgassed and it really shows when you suppress some of them, is that the upper in question?
And I had the problem with 20 round 'Colt' magazines (NHMTG), as mentioned in one of the responses, they maybe don't have the strongest springs (might be similar to your old/worn pmags)
Carbine is too light for nearly anything. It's cheap though, so a lot of people run it in their "good as" guns that are overgassed and under weighted and thus "eat everything" while beating shooter and gun to crap but hey at 200 rounds a year who cares?
Somebody mentioned Sprinco blue with H2 buffer. That is well worth trying, lots of positive feedback on that.
But really, Pappabear has it...go intermediate/A5 and never look back. They are in stock everywhere right now, even. Midway, BCM, Primary Arms, etc.
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