Another question on stripped lowers

[Les Gawlik]

I was thinking about a few stripped lowers before 10/1. Two questions- what do I lose by getting a lower that is labeled with a specific caliber, like .223/5.56? I don't think I've ever heard of someone getting an AR and worrying about putting a .300 Blackout Upper or a .458 SOCOM upper on their old lower, despite that it was marked .223/5.56 from the manufacturer.

Second, I saw some with a boron nickel coating. The ad said the resulting surface reduced friction. Is this surface coating recommended?

 

[RRHemi]

The caliber markings on the lower mean nothing as long as it is for the AR 15 platform. You could argue that the nickel boron coating will protect the parts better. This might matter if you were putting hundreds of thousands of rounds through the gun. I am running a nickel boron bolt carrier and after a thousand rounds the inside of my upper shows no signs of wear at all. I do run the BCG oiled. It is a great plating but imo not necessary on a lower.

 

[Boss94]

Well the .223 /5.56 does limit options like 9mm,.22 , 5.45X39, 7.62X39. Ect, ect.

Boron is a nice coating but some chemicals attack it. Also its not going to do much for friction fighting in a lower. A upper different story.

 

[mopar92]

The lower does NOT matter as far as markings. The UPPER and BARREL are what matters. You can take a 5.56 marked LOWER and slap a .50 BMG UPPER on it with no issues. As far as NiB on the lower Id avoid it. Extra cost, minimal benefit, and slippery a bad thing when your handling a gun.

 

[MDcompetition]

To answer your question, 5.56mm NATO is the platform to opt for and the ultimate reason is the ammo is highly effective up to 150 yards, plentiful and relatively inexpensive. If the SHTF you are not going to find much of those other caliber rounds available, it is hard to source them even now. I may get chastised for saying this but stay away from 5.56 62gr."Green Tip" ammo. It does not have the same ballistic characteristics as the 5.56 55gr. NATO round. If you intend on using your AR at any point for "Home Defense" the "Green Tip" does not tumble when impacting upon soft tissue, no, it will pass right through your intended target and may hit a "friendly". The 5.56 55gr. NATO round is designed specifically to tumble upon entering soft tissue, releasing significant kinetic energy and causing severe trauma. I just had to say what I know is true.

 

[gmkoh]

I think the OP's question was about labeling the lower with a specific calber vs "multical".

There are a number of uppers of different calibers that will fit on a standard AR-15 lower, (and whose mags are the same as the 5.56 mag, or at least fit the AR15 magwell), no matter what the lower is marked. (6.5; 6.8; 300 whisper, .50 beowulf et al).
There is an argument that if the commissars decide to ban, say the 5.56, then any lower marked 5.56 would be banned, but "multical" lowers would not, It's kind of a fine, esoteric point.