Best AR15 upper caliber

[etazelaar]

I have a question. What is the best (knock down power, cost per round, cost of complete upper) caliber/cartridge to go on an AR15 lower?

I've been looking at the mini 14 for over 20 years and now I have fallen in love with the mini 30.

So from my research I think the 7.62x39 would be best, although maybe biased. 1500 ftlbs, surplus ammo, $500 for upper complete.

What do you think? Don't forget pistol cartridges. Thanks.

 

[DnPRK]

Welcome to the site!

The drawback of 7.62x39 in an AR-15 is the lack of suitable magazines for the tapered cartridge. The top of the magazine has to be straight to fit into the AR-15 magazine well. This keeps the magazine follower from positioning the cartridge in a bullet nose-high position for proper feeding into the chamber.

And yes, I do have an AR-15 with a 7.62x39 upper receiver.