SP1/M16 barrel with new M4 upper receiver?

[HeadDamage]

Is it a problem to use an old SP1/M16 pencil barrel with a modern M4 type upper receiver? The upper has feed ram cut outs that do not match the ones in the barrel extension of the old style barrel. Could rounds get caught in the gap that this makes?

Thanks.

 

[CarbineOne]

It's not recommended. The rounds can catch on the cut and damaged by the force of the bolt.

That being said, I shot two uppers with this type of config, and they were fine for 300 or so rounds combined. If it's just a table top range gun, it doesn't really matter. If you're doing matches or classes, get something that WILL work.

 

[HeadDamage]

That's what it looks like would happen hence the question. Dam it, I just when to assemble a new upper and noticed this. I don't think that I want to dremel the feed ramps on the barrel extension so I guess I'll have to try and find an upper receiver with out the M4 cuts.

 

[KevinB]

It will not work reliably with longer match rounds.