what is needed for .40 ar

[G22inSC]

I built a 9mm sbr several years ago that a co-worker recently saw and then decided he wanted one also. Problem is, he wants a .40 caliber ar. If I remember correctly...I used a dedicated hahn block with 5.56 bolt catch, DPMS style hammer, 9mm buffer and complete RRA 9mm upper with the necessary 9mm mags. What parts would be needed to build a .40 caliber ar?

RRA sells complete .40 uppers but I have never seen .40 mag blocks and/or magazines. I would assume you would use the same 9mm buffer and DPMS style trigger, but what about the other parts? Thanks for any help and adivce.

[cj5_dude]

I just bought a 40 AR upper that was made by Olympic Arms. According to their website they still make them and they sell just dedicated uppers. They used to use custom modified Uzi mags but it looks like they now make a polymer mag that fits a standard magwell. I'd look at their website, might be the easiest route.

[alphadog]

how does the 40 cal perform on the ar platform?

[G22inSC]

I have no idea. I have my 9mm just as a training aid for my duty rifle to save on the ammo cost (back several years ago when I built it). I have never seen, much less shoot and actual .40 black rifle.

[Steel_Weasel]

Rock River has a .40 AR type carbine in development. It was supposed to be out 18 mos. ago but apparently severe magazine development issues have hampered the release. All things considered, you will probably see them by the end of the year.

[cj5_dude]

After putting a little over 100 rounds through my Oly Arms 40 upper I am very pleased with it. It's a blowback system and doesn't require any gas timing and gets rid of the complexity of that. It's really just a long barrel pistol, so it runs as you'd expect.

Oly Arms also seems to have switched from modifying hard to get magazines and is using home built polymer mags that seem to be the ticket (though I haven't used one).

So if he wants one I'd just buy an Oly Arms upper and run it, it's cool and fun and already available.