I am looking at potentially buying a select fire AR-15 that has a Frankford Arsenal receiver that was converted by Olympic arms. I am curious to hear from those of you who own them what you think about them.

Generally speaking I try to avoid anything Olympic arms made or had their hands in like the plague. I have never been impressed with the quality of their products to include fitment issues on some of the full auto receivers they made in house.

The main concern that I hear from people with the Frankfurt Arsenal receivers is that they often will have tight magwells. I plan on running this with a belt-fed upper so I'm not so concerned about that.

My main concern above all is having potential issues with cracking in the receiver especially with the side to side vibrations from the belt feed mechanism on a belt fed upper receiver. I also have concerns about the potential for the attachment point for the receiver extension tube cracking. This comes to mind for me because of how many AR-15 receivers from the 80s and before were cast aluminum.

EDit/

If trying to avoid Oly, you're SOL on this one. Oly not only did the auto conversion on that one, they made the receivers for Frankford, originally, too, if I remember right.

1) The Lower was made by Oly, then converted by Frankford to full auto. There are a handful of companies that converted Oly lowers back in the day.

2) cast lowers are easy to spot, EA are the most well known cast lower and a five away is raised lettering. Forged lowers will always have letters stamped into the receiver.

3) yes, Oly arms lowers are notorious for being out of spec. They were cheaper than colts for a reason. This was the 1970s and 80s not everyone and their brother had a CNC milling machine that used 3D AutoCAD to produce Lowers with accuracies down to a fraction of a hair. The spec issues vary greatly from pins that are a little snug to lowers that will not accept modern mil spec uppers.

4) FWIW I have a Oly/Frankford RR.  I could not get uppers to close on it. I sent it off to USAnodozing, they milled down the upper shelf and rear radius, they also removed excess aluminum sticking out from the lower that was left over from the forging process, polished out some scratches, stripped it then re anodized it. It now fits all mill spec uppers with easy, and looks like a brand new lower right off the factory line. Cost around $500 round trip including shipping back in 2014.

5) can’t speak for belt fed, the MCR is in my bucket list but I have heard they are rough on lowers but can’t confirm that first hand.

6) if you are really worried about the durability of the lower and are making it a dedicated belt fed lower you might want to look into a RDIAS or RLL, as it would allow you to use custom lowers with a high cut mag well. The 100 round but sack hangs pretty low below the mag well and then 200 round box is basically unusable in the prone position unless you put extensions on your bipod.

I’ve seen two different versions of Oly/Frankford lowers, ones that were marked M16 with safe/semi/auto and other that were AR15 marked Safe/Fire.

As far as I know Oly did not do in house machine gun conversions, I believe the state of Washington does not allow it. They just made semi auto lowers and other companies did the conversions to full auto.

I grew up in Washington in the 90s and remember researching machine gun ownership in the state back then and what I recalled discovering was that machine gun transfers were legal up to 1994.

Btw the lower I'm looking at has safe, semi, auto markings for what that's worth.

I appreciate the info about US Anodizing. I have known about them for years but didn't know they offered machining services.

As far as getting a RDIAS I haven't seen them readily available since the late 2000s and now they are much more expensive than a RR to the point where they are are of my price range unfortunately.

Yeah they don’t advertise it well, it’s something they only offer for Transferable. I only found out about it as I was planning to have M60joe do the work and have them re-anodize and they said they have a guy who could do all the work in house.

Midwest tactical had a RDIAS right now for $33k, not a bad deal but if your price range is $20k or under then non-colt RR is the way to go.

RLL could be an option but would have to have the MCR BCG milled to match the SP1 dimensions

How durable are lightning link paddles? They look like a high wear part.

Ive heard to replace every 1000 rounds. They are cheap, like $10 a piece. Basically adds 1 cent to every round you fire.

FWIW, I have a Frankford RR since 1983 and it has been great. Many uppers and only a couple have been a tight fit. I have put many 10's of thousands of rounds through it in 556, 9mm, 9mm beltfed and yes, 22LR. I would love to send it to US anodizing but the risk of mailing it to get a nice finish seems too high to me.

If the RLL is set up and timed correctly, the paddles in my experience never wear out.   I have one of my links since 2004 and other than replacing the paddle after I bought it (original owner was using the wrong semi-auto bolt carrier type) I have been using the same paddle for 15+ years.

However, if you use the wrong type of and/or poorly timed bolt carrier, the link binds in the lower and can't actuate freely,  etc. than yes,  you can bend the shit out of the paddles in short order.

If you are having to replace the paddles on a regular basis than something is set up wrong.

Same...my dad has a FA from the 80’s...has never run all that great.   Biggest issue is the shelf is way high and won’t accept others uppers than the one it came with.  Probably should have sent it off to M60 joe, but that’s ship has sailed.  Will reach out to US Anodizing .

I have one, and most uppers fit no problem, the sear has been polished on the sides and a factory sear binds. Mine was painted by someone who did a crappy job, and I just need to send it off to US Anodizing and be done with it.  I have used it on a spikes .22lr upper and it runs most of the time, usually when I run out of light it doesn't something wacky and I put it in the safe until its time to pull it out and it works again.  I don't think its the lower, just the ammo I try to use.