AR15 Build Help

Posted by: MD0772

AR15 Build Help - 01/28/21 05:43 PM

So I decided to build my own 5.56 Ar15, ordered the parts I needed and after they came in I sat down and put it all together every thing looked good.. at least I thought so went to the range to test it out and it would fire one round eject the round but not reload.. did all the safety checks and reloaded and fired same result repeated several time but got the same result. So I decided to take the BCG out of my other AR and put it in the new build and just like that every thing fired correctly. So I decided to put the new BCG into my old AR to see if it would firer and everything worked as it should .. so I put the BCG back into the the original weapons they came out of and went to firer the new build with the original BCG it had in in and it would firer once eject round but not reloadÖ

Can any one give me any ideas on this seams out there to me any help greatly appreciated
Posted by: ChrisC

Re: AR15 Build Help - 01/28/21 08:12 PM

Are the bolt carrier groups identical? If one is slightly heavier, it may be the additional inertia that you need to cycle completely. Not sure if you are using a standard spring and weight, but I would check those to make sure itís not an H2 or H3 buffer. Or replicate the bolt carrier group that works, and make sure itís lubed well.
Posted by: RASAT

Re: AR15 Build Help - 01/28/21 10:08 PM

I'm not absolutely sure but I suggest you to Check and compare the Buffer, 2H works very good for AR Carbine 5.56, Regards
Posted by: ChrisC

Re: AR15 Build Help - 01/28/21 11:19 PM

Originally Posted By: RASAT
I'm not absolutely sure but I suggest you to Check and compare the Buffer, 2H works very good for AR Carbine 5.56, Regards


Usually, but with one BCG functional and the other not itís worth checking. I suspect itís under gassed and the alignment of the port and gas block should be checked, now that Iím thinking about it. That one BCG may be just a bit different in weight and overcoming it.
Posted by: Verylargeboots

Re: AR15 Build Help - 01/29/21 06:23 AM

Did you check the headspace? Lol
Posted by: MD0772

Re: AR15 Build Help - 01/29/21 09:42 PM

I will check these things out and get back to you all thanks for the help and suggestions
Posted by: Bcmgunfighter

Re: AR15 Build Help - 02/01/21 06:46 PM

Originally Posted By: Verylargeboots
Did you check the headspace? Lol


I was wondering this as well.
Posted by: ak66

Re: AR15 Build Help - 02/13/21 06:43 PM

Headspace would be a suspect. On AR-15s itís highly rare but can happen. Tell us more about the BCGs. Are they both standard full-auto M16 cut and the same weight/type? If both are identical from reputable manufacturers, check your buffer spring and weight - swap buffer and weight from your other AR and put it in new one. If still having issues - check gas block alignment, if itís adjustable open it completely, if still fails check buffer tube extension (make sure itís properly seated and staked).
Posted by: nvcdl

Re: AR15 Build Help - 02/14/21 01:40 PM

I'd suspect the new build has marginal gas and the finish of the swapped in BCG is slicker from wear/worn enough to make it work. I'd check alignment of the gas block as another poster suggested.
Posted by: siklonelinyx

Re: AR15 Build Help - 02/14/21 11:08 PM

Are the new rounds getting stuck where the feed ramps are? What type of rounds are you using? Steel or brass. If steel, your upper may not like it and have to test it with brass. If the your bcg isn't the problem since you tested out your new and old ones and they performed well, that may be the cause of the issue. Manually cycle your rounds. When the rounds gets ejected, are there any scratches on the actual bullet?
Edit: Just saw the og post date, not sure if you've fixed the issue or not.
Posted by: 2nd.amend

Re: AR15 Build Help - 02/16/21 08:51 PM

If you put the spring on the hammer wrong it can do this !
But not sure why it only dose with the one bolt may be a gas block problem

Switch the lowers that would eliminate the hammer spring
Posted by: jims59

Re: AR15 Build Help - 02/18/21 01:47 PM

I had a problem with my AR, It was doing the same thing. I took a mop that fit the chamber, put it on a drill and added a little Fitz to polish the chamber and it has run great ever since.
Posted by: shootergdv

Re: AR15 Build Help - 05/09/21 12:06 PM

Short stroking ? For grins , leave the bolt in place, swap the spring and buffer . If it works , compare the spring and buffer .
Just maybe one spring is slightly longer/stiffer -or buffer is different. The difference in weight of semi-full carriers as stated above could certainly work against you too .If so, the redneck fix would be to snip a coil.

You'll figure it out ! Part of the fun of DIY .