All was well until I got bored....

[GIJOEL]

So, my 7.62x39 AR was running well in it's original configuration (A2 bushmaster upper). Then a friend offered a flattop upper receiver and a free float forend for a song and dance so I swapped. Took the carbine to the range and it stove-piped every 3rd-5th round, the only new things are the YHM receiver and the forend. The brass is ejecting with the same force as before (when it gets that far) so what gives? I figure either the brass is getting hung up on the ejection port or (a suggestion from the gun smith) I should get a heavy recoil buffer or buffer spring. If I thrashed the old buffer and now it needs to be upgraded or replaced does anyone have a suggestion? If I have a ejection port issue is there any harm in "flaring" the port?


16in model one barrel
YHM flattop upper
model one BCG
CAR gas system
standard carbine buffer and spring


Thanks for your wisdom High Roaders

 

[Rail Driver]

Well, if you flare the ejection port, the dust cover won't fit properly, if that's a consideration for you. I'd consider checking the headspace since you've switched uppers (check headspace even if the upper came fully assembled)

If it headspaces good, look into a new buffer and spring. Past that I really can't say without some research. *Edit to add: you could also be having ejector problems... Check your spring, plunger, and ejector key for damage and/or weakness and replace if necessary.

 

[longdayjake]

Make sure the gas block is still on straight and tight.

 

[GIJOEL]

The ejector and extractor are in good shape, I'll check the gas block, could the block have moved due to exessive pressure? I'm also thinking that the BCG needs to wear into the new upper?

 

[Omaha-BeenGlockin]

Easiest thing to try is to lube the bolt/carrier--with particular attn of working it into the extractor.

Break Free CLP----dripping

 

[Rail Driver]

Also, it's usually a good idea to get a new BCG when you get a new upper. If you've fired an AR (any caliber) for any length of time, that BCG gets "mated" to the upper due to minute differences between uppers... When you switch uppers, that BCG isn't gonna fit quite so nice anymore. I've heard of someone snapping off locking lugs after doing that.