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 Barrel length effect on gas system 
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I have a dpms LR-308 that I had the barrel chopped down to 20" on. (was 24 to start with).

Last time I took it to the range, it seemed to be short stroking- the bolt would not travel back far enough to engage the bolt catch on an empty magazine.

I was thinking that maybe shortening the barrel has something to do with this- since the bullet is leaving the barrel earlier, there's less time for the gas system to be pressurized.

Is my reasoning sound? What should I try to fix this?


Sat Jun 01, 2019 10:38 am
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Oxblood wrote:
I have a dpms LR-308 that I had the barrel chopped down to 20" on. (was 24 to start with).

Last time I took it to the range, it seemed to be short stroking- the bolt would not travel back far enough to engage the bolt catch on an empty magazine.

I was thinking that maybe shortening the barrel has something to do with this- since the bullet is leaving the barrel earlier, there's less time for the gas system to be pressurized.

Is my reasoning sound? What should I try to fix this?


adjustable gas block may do the trick

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Sat Jun 01, 2019 10:59 am
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Oxblood wrote:
I have a dpms LR-308 that I had the barrel chopped down to 20" on. (was 24 to start with).

Last time I took it to the range, it seemed to be short stroking- the bolt would not travel back far enough to engage the bolt catch on an empty magazine.

I was thinking that maybe shortening the barrel has something to do with this- since the bullet is leaving the barrel earlier, there's less time for the gas system to be pressurized.

Is my reasoning sound? What should I try to fix this?


Yes, shortening the barrel results in less gas getting to the bolt carrier (shorter dwell time). The fix is to have the gas port opened up to supply more gas. (Not an adjustable gas block, that is to restrict gas flow on an oversized gas port, opposite problem from what you have.) I do not recommend just attacking it at home with a drill press, although some guys do that. If you do, at least use a brand new sharp high quality drill bit; you'll need to measure the existing port and step up in small increments in drill bit size until the rifle cycles correctly.

If your rifle has a heavy buffer in it now, you could try going back to the standard carbine weight buffer, but I wouldn't go any lighter than that. Be aware there are two different size buffers your rifle could use (308 buffer or AR15 buffer) and it depends which buffer tube is on your rifle.


Sat Jun 01, 2019 12:39 pm
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Sat Jun 01, 2019 6:16 pm
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MadPick wrote:
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Yeah! Someone link to the thread where this guy and someone else got into it about their barrel and gas dwelling and pig tails or whatever hahahahaha.

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Sat Jun 01, 2019 8:02 pm
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Not enough info to give any sort of good answer

What length gas system?

What’s the port width on the gas port?

What buffer tube setup ? Short/std ar15 tube , A5/armalite length, rifle?

What weight buffer ?

What buffer spring?

What kind of ammo?

What do you mean by short stroking?

Shoots a rd, then ejects but doesn’t pick up the next?

Doesn’t lock bolt back on one rd?


Sun Jun 02, 2019 1:07 am
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Options:
Lighter buffer
Lighter spring

You can buy different weights for inside your buffer, it takes some tinkering and testing to get it just right.
You can also buy reduced power recoil springs. Again, can take some trial and error.
Replacing buffer weights is pretty easy, finding the sweet spot requires gradually reducing weight until your timing is corrected to cycle the rifle, without reducing the weight too much.

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Mon Jun 03, 2019 6:42 pm
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