1st 308 Build - Complete Cycling Problems

[Dan Kotynski]

Hi everyone, apologies in advance if I use the wrong terminology.  I've build a M4 Carbine... no problems at all.  I wanted to do a LR308 (all DPMS) and purchased what I thought was a good set of parts to build.  It shoots fine, ejects spent rounds fine, but will not strip a round from the magazine and chamber it.  I'm hoping you guys can help me.  Here are the parts I've assembled:

* Aero Precision Upper

* Aero Precision Nitride BCG

* Faxon Firearms AR-10 18" HEAVY FLUTED, .308 WIN, RIFLE LENGTH, 416-R, 5R Rifling QPQ

* Superlative Arms .750 Adjustable Gas Block - Clamp On - Melanite - (now set at max gas)

* NBS Stainless Steel Gas Tube - Rifle Length

* AERO PRECISION - AR .308 M5 CARBINE BUFFER TUBE KIT

* B5 SYSTEMS -  BRAVO STOCK COLLAPSIBLE MIL-SPEC

I've double checked the gas block to ensure it an the gas tube are properly installed.  Still no luck.  Only other things I can think of are:

1) Is my buffer spring not right for a rifle length gas tube?

2) Using magpul magazines - have used two separate magazines - same issue

3) bad ammo?

Any help would be appreciated.. thanks.
 

[unforgiven]

I switched out the Aero recoil system for Armalite setup. Why adj. gas block?

[shooterrex]

How much does your buffer weigh?

It should be in the 5 1/2 oz range.

Does the bolt lock back on an empty magazine if you only shoot 1 round?

Do not confuse rifle length gas tube with the with what recoil system you need. It is all about reciprocating mass. BCG and recoil springs w/buffer have to work together with the gas pushing the BCG rearward.

Did you start test firing with the adjustable gas block wide open?

If it doesn't lock back on an empty magazine wide open your gas port is not large enough.

Drop by the introduction section and tell us a bit about yourself.

[Armed Eye Doc]

In addition to the questions Rex asked, will it strip a round from the magazine when manually cycling the rifle? 

What lower parts kit did you use?

Most specifically, put up the weight of your buffer.  It is likely 3.6 ounces or so and will likely need to be heavier.

This is a great thread to read to understand why buffer length and weight are important.

https://forum.308ar.com/topic/16799-gas-tubes-barrel-gas-ports-and-buffer-weight/

Edited August 17, 2021 by Armed Eye Doc

[98Z5V]

You mentioned nothing about what lower you were using, and that's the key component here, for determining the height of the magazine in relation to that Aero M5 upper - for feeding rounds.

Spilling the details on your lower, which is suspiciously absent from your parts list - well, that is key...

[98Z5V]

18 hours ago, Dan Kotynski said:

1) Is my buffer spring not right for a rifle length gas tube?

Like the other guys have already stated, your whole recoil system isn't adequate for a .308AR.  Not in the least. But that's a separate problem.  Your lower receiver details are the main problem here. 

[Black_Sheep]

My Aero M5 build was very similar and my experience the first time out netted the same result. Conventional wisdom says that you are under-gassed, which was certainly true in my case. After confirming proper gas tube length, gas key integrity and gas block alignment I enlarged the gas port and swapped the Aero Carbine buffer and spring for a much heavier buffer and spring package from heavybuffers.com based on rock solid advice from the forum's resident experts. 

More information is necessary if you want the correct advice for your specific combination. Check one of the "waterboarding" threads for what info is required... 

[Black_Sheep]

My Aero M5 build was very similar and my experience the first time out netted the same result. Conventional wisdom says that you are under-gassed, which was certainly true in my case. After confirming proper gas tube length, gas key integrity and gas block alignment I enlarged the gas port and swapped the Aero Carbine buffer and spring for a much heavier buffer and spring package from heavybuffers.com based on rock solid advice from the forum's resident experts. 

More information is necessary if you want the correct advice for your specific combination. Check one of the "waterboarding" threads for what info is required... 

 

My strangely similar thread: First time out with .308 build - major issues - General Discussion - 308AR.com Community