it's very difficult

by Miles , CIVITATES AMERICAE, Sunday, July 05, 2015, 13:28 (3369 days ago) @ rob

nothing personal, it's just that way.

Also unfortunate is that '.mil' troubleshooting doesn't deal with handloaded ammo and it's attendant peculiarities.

The list of things that could be causing the problem are:

The extractor is not holding the round tight enough & the case is coming loose from the bolt face before the ejector can do it's thing.

The buffer is too light causing the bolt carrier to travel too fast and open the gas path inside it too early, causing short stroking.

The buffer is too heavy causing the carrier to travel too slowly and not provide enough rearward thrust to overcome the action spring tension.

1 is unlikely as you say the gun works just fine with factory ammo, but problems with once fired cases you're handloading.
I assume most of these once fired cases you're handloading are from the factory ammo the gun had no trouble firing.
Also, an extractor problem is not usually a problem with 16" barreled, standard carbine length gas system semi-auto guns.

2 or 3 are what you may be dealing with with the particular components and powder load of that handload.
I've seen 2&3 both ways when using the different .mil rounds available being shot through different 5.56 rifles.

You buffer is unmarked, which means that it's probably the original standard weight.
So, the buffer being too heavy should not be the problem.

When Johnboy tagged along for range support, or tripped to the range for test firing after I'd worked on a gun, I always carried assorted spare parts.
$$ was not a concern to me, but is to you since what parts you can't use will just be sitting in a drawer.