Pretty sure I'm building an AR-10. Looking for some advice.

[titanse05]

Ammo crate full of 308!!!

[RobertTheTexan]

Ammo crate full of 308!!!

Looks like some high quality parts you have there. I think it’s going to be an excellent build.


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[titanse05]

Looks like some high quality parts you have there. I think it’s going to be an excellent build.


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Yeah I don't buy junk....never really did. I'm excited about the build and can't wait to assemble it. I hope to have the ADM builders set in before the end of the year but I may not get it till early next year due to the Cerakote.

[titanse05]

Well I got the call from my FFL yesterday evening. Today after work I get to pickup my ADM builders set.

[titanse05]

Sorry for the crappy picture. Best I could do quickly since I can't do anything outside.

[Uffdaphil]

Okay, that makes me sit up and bark.

[titanse05]

Well I have it all assembled and went to attempt to test fire it today. The rifle will not fully chamber the round when using the bolt release.

Currently running a UBR 2 without the spacer with a carbine length spring and an H2 buffer. I'm not sure but I may need to swap to a rifle length spring. It just doesn't seem to have enough power to fully seat the round.

I am able to throw one in the chamber and the bolt closes fully and ejects fine with a pull of the charging handle.

[fledge]

You need a rifle length spring.

[titanse05]

You need a rifle length spring.

That is instantly what I thought.

[fledge]

But to know which rifle length spring I defer to those with more knowledge. I only have A5 rifle length springs and they don’t help my 308 cycle either. Too soft in that application. I’m still hunting for solutions.

[titanse05]

In looking at the manual for the UBR 2 it states that you are supposed to use carbine length buffers and carbine springs or A5 buffer/spring. I don't believe a rifle spring will work in my application.

[titanse05]

https://www.midwayusa.com/product/25...g-ar-10-lr-308

Going to order one of these to try.

[fledge]

In looking at the manual for the UBR 2 it states that you are supposed to use carbine length buffers and carbine springs or A5 buffer/spring. I don't believe a rifle spring will work in my application.

Does it specify a difference between platforms? What you describe is exactly correct for the AR15. You aren’t supposed to use a A5 buffer at all with an AR10. The CAR-10 buffer for the AR10 uses a carbine spring because the buffer is shorter than a carbine buffer and allows space for the carrier to cycle. A standard carbine is too long for the carrier to cycle with a carbine length tube. You need the longer tube and rifle spring with the carbine buffer (remove the UBR spacer).

[BoilerUp]

How long is the receiver extension / buffer tube on the UBR?

308 buffers/springs are a little confusing because the Armalite/AR10 is different that the DPMS/LR308 setup. If the UBR tube is more like an A5 extension in length, then you'll probably want to treat it like the Armalite which uses the same spring for carbine and rifle. While the AR10 buffer spring is longer it actually compresses shorter than an AR15 carbine length spring. This is probably what you want: https://www.rainierarms.com/armalite...buffer-spring/

If the UBR tube is the same length as a standard AR15 carbine tube, then you should be fine with the DPMS carbine length spring but you should also need the DPMS 308 carbine buffer (which is shorter). Since you are using a carbine length buffer with no issues I'm guessing the UBR tube is longer.

[fledge]

The UBR Gen 2 tube is A5 length. It comes with a spacer insert to shorten it to carbine length.