I have been looking into this kind of upper and just curious what others think. M1S seems to have pretty good reviews and I definitely like the price:

 

http://www.model1sal...category_id=287

 

I know the bolt has to be different (well, the extractor or ejector, I always confuse them) and I bought one a while back from midway on a whim (so that's not an issue at the moment), but I think I would want the low profile gas block instead of the stupid FSB (even though M1S does shave down the bayo lug).

 

Does anyone have an opinion about the target crown for this 20" barrel? It seems like that's fine for NJ and I wouldn't have to worry about getting a MB pinned/welded, but just wondering about the pros/cons since I'm used to my 16" 556 upper with the MB.

 

I have a lot more 762x39 than I do 223/556, so figured why not?

You will have the same ballistics with a 300 Blackout upper and uses same bolt and mags. I'm building one right now

 

 

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I don't know much about 300 Blackout, but it doesn't look like I can find any ammo in stock. I have like 10x the amount of 762x39 than I do 223/556 so that's why I was interested initially. Do you have the 300 blackout upper from M1S?

Colt used to make a 7.62x39 upper many years ago. The upper ran well but mags were somewhat problematic.

As I recall, there were several 'bandaid' type fixes for the mags, including building hybrid AK/AR mags.

 

If I were to consider one these days, I think think I'd have to go with the RRA version.

I don't have any personal experience with it, however, I have heard they run.

i am waiting for the lar-47 from rra. Im on the preorder list

I don't know much about 300 Blackout, but it doesn't look like I can find any ammo in stock. I have like 10x the amount of 762x39 than I do 223/556 so that's why I was interested initially. Do you have the 300 blackout upper from M1S?

 

No I build it up from scratch:

16" 1:8 Daniel Defense barrel

12" YHM float tube

YHM comp

JP stripped upper

JP bolt carrier group (backorder)

 

 

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If its cheap ammo your after the. The blackout is out of the running. You could also look at 5.45 upper?

Have a Colt MT6851DC upper (7.62 x 39), a 20 inch heavy barrel crowned muzzle with a rifle gas system and A2 front site. Works fine. Go for it if you want one. Need barrel and bolt to make it work. Magazine problem related to taper of shell. Required greater bend of magazine body to compensate cases. This caused feed issues. Smaller mags work great (Five or seven rounds).

I am considering a 5.45 upper but where the hell can you get NJ legal 5.45 mags?