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New guy looking for help


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Hey all just joined. Looking for help on a aero m5 308. I can get it to run it is short stroking. 

parts used.   Aero m5 complete lower with UBR gen 2


complete aero upper 18” rifle length gas system

aero nibx bcg


So aero says this won’t work because it’s a rifle length gas system with a carbine/ubr buffer.  I believe that is a lie,but hoping to get some clarification. 



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Can you get a picture of the buffer tube internal depth?  If you are using the spacer, include that when you measure it.  8 - 8.25 inch is not a dimension that I know to work.

As you correctly surmised, Aero is incorrect and a rifle length gas system can definitely function with a carbine buffer system.  It just has to be balanced properly.  That aside, your buffer is too light.  You need a buffer that weighs 5.4 oz or very close to it.  At 2.5 inches, your buffer is designed for a standard 7.0 inch buffer tube.

Your recoil system is not correct as far as I can see from the numbers provided.  Get some pictures of the measurements and we should be able to get it corrected and functional.

There may be other issues to be addressed, but let's work on this first.

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It looks like your buffer tube is about 7 5/8 inches internal depth.  Is that correct?

It also looks like the back of your bolt is hitting on the receiver here...


That would be because you likely need a 3.25 inch buffer with your tube (assuming it is actually 7 5/8).  A standard AR15 H3 buffer will work with that size tube.  I would also change the spring.

This kit will get you both and a good buffer tube as well.  It will work with your rifle even though it is Armalite.


If you find it doesn't work for you, I will buy it from you for what you paid including shipping to you and to me.

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Was wanting to keep the ubr gen 2 buying anew tube would prevent that. Talked to Clint at heavy buffer and he suggested a new buffer and spring. Said he has had good luck with that.   In person it doesn’t appear to be hitting   What you are seeing in where they cut the threads. Really really don’t want to spend another 250$ on a new stock and buffer tube, etc.   

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9 hours ago, Target74 said:

Ubr buffer  tube is 8”-8 1/4 inside 

buffer weight 3.79 oz.  2 1/2 long

bcg weighs 18.02 oz

spring is 10 3/4” long.

ubr spacer is .745 

Buffer is too short.  The UBR 2 is designed for a 3.250" buffer when run on a .308AR.  The internal depth of the extension on the UBR 2 is 7 5/8".  You'll need an H3 buffer, the correct weight to run these things.  Any AR15 H3 Carbine buffer will work.  You'll also need either the Armalite EA1095 recoil spring, or a Sprinco Red spring.  That will solve any issue you might encounter with your recoil system.

Look at the ears on your lower, and see if the BCG was hitting it - it was, if you shot the UBR 2 with that 2.500" buffer in there.  Guarantee it.

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  • 3 months later...

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