I have a 9mm AR-15 from OlyArms. I am considering converting the rifle to a RRA (or similar) 9mm setup.

Is this easily done? I know I will need a new upper, bolt, mag, and magwell block. What else will I need?

I have heard of magwell blocks not fitting in some OlyArms lowers without gunsmithing. I have also heard of RRA/Colt mags not feeding well until the lips were buffed or filed down.

Should I even consider this conversion or am I getting in over my head?

What you are basically doing is no different than taking a .223/5.56 gun and converting it to a 9mm Colt setup.

If your lower is in spec, it shouldn't have any problem accepting a Colt style mag block.

As far as what else you will need?  You may need a different hammer, ramped bolt, KNS pins, different buffer.

If I were doing this, I would take a different route.

Sell the present rifle.

Buy a new RRA complete rifle or buy a RRA dedicated lower and RRA upper. Save some money. Converting will just cost a lot.

Also, CMMG has a dedicated 9mm lower.

The dedicated lowers are ready to go for mags without the magwell adapter that causes so many problems. Also, the dedicated parts are made to work with each other. Its also cheaper to just build it as a 9mm to begin with. I know.

I don't want to sell the rifle because it is in my name on a Form 1. How do I know if my lower is in spec? I know it is a forged lower, but that is all I know about it.... It was built around 2001 or so......

If all you're worried about is the magwell primarily, the hahnprecision website has the magwell dimensions that you can reference and compare to the actual measurements from your lower.  If you do get a block that is a tight fit, it isn't that big of a deal to take a few thousandths off here or there to make it fit your lower.

It's an SBR already, right? So, yeah, don't sell it.

You don't like the Oly style then? May I ask why?
The Colt system is only different; not better.

From everything I've read around here, Colt systems tend to be more finicky(sp?) as far as the positioning of the magwell/magblock/magazine are concerned. This is obviously less of an issue with dedicated carbines.

I've never heard someone post that they couldn't get a Sten mag to work.

If you want a Colt style then I would recommend a sell-n-buy like most other posters. But since you've already got one and parts are back ordered theses days, spend the money on a magblock and Stens.


Biased Oly owner.

ETA: Oh yeah, If a standard GI mag will fit the magwell, so will a magblock and a subgun mag(Sten). Remove the upper of course.

I have shot with a few guys that run Oly/Sten setups and they too can be problematic depending on the quality of the mags.

To counter your claims that Colt setups are more finicky based on everything you've read around here, keep in mind that the amount of "complaints" about finicky Colt setups is related to the influx of new vendors/parts into the Colt 9mm game - ProMag, CP, CMMG.  When it was primarily just Colt, RRA, Hahn, Colt/Metalform mags, modded Uzi mags, and such, there didn't seem to be nearly as many issues.  When folks stick to "known" parts, the Colt system can be nearly 100% reliable and not the least bit finicky.

Biased owner of multiple Colt style 9mm setups