AR-10 vs. LR308 gas tube protrusion question

[George_cle]

I am working on an Armalite SASS with the finger-adjustable gas block. It's a rifle-length tube in Armalite's standard. The barrel was changed out with an 18" Proof Research, on the LR-308 standard. Since the LR-308 standard gas system is a little shorter (by about .365"), the gas tube protrudes further into the upper receiver, just past the cam pin recess.

The BCG closes like normal, and the gas tube is NOT touching the gas key or pushing the BCG back at all. Certainly if it was, the gas block/tube would have to be changed. But since it's not, is this setup good to go?

 

[msgriff]

Hard to tell for sure with your pic, but the condition of that gas tube does not look good (not talking about the crud). I am surprised that it didn't bottom out in the key. Even if it fits, the increase in tube to key engagement time may cause issues. Are you using the old ArmaLite bolt or did you change it to the DPMS spec, like your new barrel? Either way, I hope it's been headspaced.

 

[George_cle]

I am also surprised it didn't bottom out in the gas key. I was going to check headspace and test fire. This is the old Armalite BCG.

 

[bfoosh006]

That is to far into the gas key for me.

 

[MPD142]

Gas tubes are cheap, I'd use the correct length unit. Looks like you need the standard AR-15 Rifle length tube.

 

[George_cle]

It's too far for me too. The AR-10 BCG's gas key is set a bit further back than the LR-308. The photo below shows the Armalite on the left, and a Sharps on the right. The Sharps binds on the gas tube; the Armalite does not. The Armalite probably would work but I would be inviting other problems.

Headspace passed on the new barrel with the Armalite BCG. I'm going to replace the gas block and tube with a Seekins Select and a regular AR rifle-length gas tube.

 

[longshot2000]

Something's going on that's not quite right. It is clearly in too far. Now, whether that makes a difference, you will know. The big issue with AR10 / .308AR platforms is that every part can be different from different manufacturers. Well, maybe not that bad, but yes, it could. There is a different gas port length for Armalite AR10 verse DPMS, and you could have the wrong barrel or gas block or even extention.

 

[newguy2k3v2]

I had one of those rifles. If I remember right it’s a flare nut connection at the gas block so I doubt you’re going to find a shorter one on the shelf. You could probably trim it and re-flare it yourself. Good luck nailing the length.

Armalite uses a slightly longer than standard tube on their large frame guns. They did that so that the standard handguard and delta ring would work iirc.

Also I hope you got a bolt to match that barrel. Armalite bolt and dpms barrel equals excess headspace as I recall.