308 build

[Scrubbs15]

Hey y’all I am currently building an 308 with an aero m5 upper and lower. I want to run a 16 inch mid length gas barrel on it and want to know if I can run a rifle length buffer, buffer spring, and extension without problems. First 308 build and know that can be funny when it comes to reliability. I just want to educate myself before I spend money. Thanks. 

[Armed Eye Doc]

Welcome to the forum.  Hit up the intro section and let us know a little about yourself.

You can certainly use a rifle buffer system with a mid-length gas system.

[jtallen83]

You will be fine with the rifle length stock and buffer set up. 

[SgtDog0311]

Hey there JT, I'm just curious since I don't know any more (maybe less) than Scrubbs...    will that mean he'll likely want to tune the gas system with a rifle length buffer and mid-length gas system?   I ordered the Armalite 6 position but will be running a rifle length gas system.   I did order a Superlative adjustable so I'd be at least able to tune, but I've never been will clear on the likely necessity or not.

[jtallen83]

2 hours ago, SgtDog0311 said:

Hey there JT, I'm just curious since I don't know any more (maybe less) than Scrubbs...    will that mean he'll likely want to tune the gas system with a rifle length buffer and mid-length gas system?   I ordered the Armalite 6 position but will be running a rifle length gas system.   I did order a Superlative adjustable so I'd be at least able to tune, but I've never been will clear on the likely necessity or not.

Lots of variables but it should work fine without an adjustable block. There are many ways to "tune" these, buffer weight, spring rate, gas port size, weight of the BCG, etc. Most of the time manufactures have the gas length and port size set up to run both buffer systems. Sometimes they miss short requiring you to open the gas port up or lighten components. Most of the time they run on the high side of the gas required to get good reliability, these are the ones that can utilize an adjustable block if you want to play with it. Turning down the gas will lessen recoil but chances an increase in the failure rate. It's all about balance and carbine and rifle buffer systems in normal configuration have about equal weight in that balance so are interchangeable for function purpose allowing you to make that choice based on Ergonomics required. Many will disagree but after years of watching this forum and the problems that arrive here it seems clear the lighter, shorter DPMS carbine buffer system is too light, they account for a large number of the issues, at least swapping them for the Armalite carbine buffer system fixes them. 

[Armed Eye Doc]

29 minutes ago, jtallen83 said:

Lots of variables but it should work fine without an adjustable block. There are many ways to "tune" these, buffer weight, spring rate, gas port size, weight of the BCG, etc. Most of the time manufactures have the gas length and port size set up to run both buffer systems. Sometimes they miss short requiring you to open the gas port up or lighten components. Most of the time they run on the high side of the gas required to get good reliability, these are the ones that can utilize an adjustable block if you want to play with it. Turning down the gas will lessen recoil but chances an increase in the failure rate. It's all about balance and carbine and rifle buffer systems in normal configuration have about equal weight in that balance so are interchangeable for function purpose allowing you to make that choice based on Ergonomics required. Many will disagree but after years of watching this forum and the problems that arrive here it seems clear the lighter, shorter DPMS carbine buffer system is too light, they account for a large number of the issues, at least swapping them for the Armalite carbine buffer system fixes them. 

What he said.^^^

I was going to respond earlier, but JT said it better than I would have.

[98Z5V]

You need a 5.4oz buffer to run a run-of-the-mill eat-any-ammo .308AR in the DPMS or Armalite patterns.  That's the reason Armalite only uses 5.4oz buffers.  These aren't Race Guns that you need zero recoil on for your next timed follow-up shot, against the timer, against other competitors trying to take home series points or a trophy...   You start using lighter buffers, weaker springs, and you have to compromise the design of the gun to get it to run right.  Most guys with lighter buffers and weaker springs THINK the gun is over-gassed, because it's recoiling hard as hell.  Indeed, it is not over-gassed.  It is under-recoiled... They mistakenly "solve" the problem with an adjustable gas block.

.308 Rifle Buffers are 5.4oz.  They're 5.200" long.

Armalite AR-10 Carbine buffers are 5.4oz.  They're 3.250" long.

AR15 Carbine H3 Buffers are 5.4 oz.  They're 3.250" long.   (on this and the AR-10 Carbine buffer, you MUST use a carbine receiver extension that is 7 5/8" internal depth...  AR15 carbine receiver extensions that are 7.000" internal depth, or Armalite M15 Carbine receiver extensions that are 6 15/16" internal depth, will not work...)

KAK makes a heavy buffer that's 2.500" long, to use on a .308AR with the AR15 carbine receiver extensions.  It works.  It's 5.3oz.  Close enough for reliable operation. Run a Sprinco Orange Spring with that combination.  It was directly developed for that configuration.

This pretty much sums up the information on barrel gas port sizes and gas tube lengths, as well as buffers and buffer weight:

 

Here are known, verified Carbine Receiver Extensions that are a true 7 5/8" internal depth:

All AR15 and .308AR Rifle Receiver Extensions are 9 11/16" internal depth.  The aftermarket manufacturers very seldom screw that up.  AR15 A1 and A2 - use the exact same rifle receiver extension.  So do the .308ARs... 

Edited December 4, 2019 by 98Z5V

[SgtDog0311]

Thanks for the education fellas!