I just bought a complete bushy lower and I want to build a rifle with the pistol conversion ,ok here's the question.
I have looked at the Oly and the rock river uppers so what mags do you have the option of using with either upper?
Can you use the sten mags with Rock River?
I know if you go with the Oly you have to send them the mags and they perm attach the mag blocks,so what about the Rock River?
What mags can you use ?
And does the mag block get perm attached?
I also understand that with the oly there is no mod to the lower needed.
Jrzy

To answer your questions in order:
1)This is a toughie. I would say that the RRA is a bit better than the Oly. The only reason why I would say that is (I think) the parts for the RRA and Colt looks like it is interchangable.

2) Nope, the RRA 9mm system uses the Uzi mags like the Colt 9mm.

3) No need to modify the mags for the RRA upper units. Drop in mag block is used for RRA. The Oly system can use another mag block: the SOCOM mag well block.  It does not need permanent mods to the mag or rifle. It is a drop in system.

4) For the RRA-modified Uzi mags.
  For the Oly system-modified or non-modified STEN mags.

5) Only the Oly system requires the mags to be modify if only using their uppers without using any mag well blocks.

6) The big difference between the Oly and the RRA/Colt uppers is where the ejector is located. The Oly puts in the ejector in the upper which makes it self contained. The RRA/Colt has the ejector on the mag well block.

I own a Oly Arms 9mm and love it.

I use the SOCOM block and unmodified Sten Mags, all I can say is this setup is sweet.

I love the fact that I can swap from 9mm to 5.56 in a matter of seconds.  

Go with the OLY.  You won't regret it.

Max

I went with the Oly and it'll be here sat. morning,woo hoo!

I've got a Colt 9mm upper (same as the Rock River) and love it.

I buy Uzi mags for $12-$15 each. Two minutes with a Dremel and they lock up and feed perfectly.

I use STEn mags in my M11/9 and HATE them .... they are better than the factory M11/9 mags, but because they are single-stack, they are a pain in the butt to load. Uzis are double-stack and WAY easier, and that alone makes the Colt/RRA system much more attractive to me.

YMMV.

Remember Oly has the most flexiable magazine setup of any manufacturer.  Oly made teh first 9mm AR and also ahs the .40S&W, .45ACP and 10mm.

For magazine styles they have:

1) Oly one piece STEN mags

2) Oly magwell drop in from the top insert that then uses your pistol magazines that have a cutout for the mag release - yes they use the real M16/AR15 mag release.  Your pistol caliber magazine can be used interchangably between your pistol AND rifle! 9mm & .40S&W (Glock, SIG, Beretta, Browning, Taurus)

3) SOCOM block using $3 STEN mags - cheapest way to go.  Guys with FA usually go this route and it works very well.

Oly upper does not require any modification to the lower, like others do.

mark

My only experience is with my original Colt 9mm carbine and can say that no matter what a person decides they will have a ball shooting it. Since buying mine 4 years ago I've only put one 30 rnd mag thru my SP-1's, that was at the BRC to check out an orange thermold that I'd just converted/carved over in the campground with a pocket knife and 10 minutes of time.