Please.

Back in the last few years of the awb i bought this oly arms 40 was one of the very first ar15s I ever bought, i got the complete gun and a bushmaster 5.56 upper(post ban config) in the deal for $750. I bought a preban gun shortly after and well the pistol cal upper kinda got put to the side since mags were expensive and not easy to find and it's a fixed carry handle upper blah blah blah. But most importantly at some point along the way the lower got one of those pretty little special stamps and full time rifle upper and was 40 upper got neglected for something like 10+years only occasionally taking a trip to the indoor range.

Now after what feels like a lifetime I want to do something with the upper.

It was always in the back of my head to chop the barrel to 8 inches. Thats about the only thing I'm full decided on. And the only thing that worries me. This gun is pretty damn accurate as is at 25 yards and Its not something that's intended for anything more then around 50 or so but I still worry something might happen in the process to fuck the accuracy of this thing. anyway to more important things.

Its fixed carry handle and i plan to keep it that way. Fsb will have to come off, not sure if I want to keep the factory one and just slide it back or put one on the rail since the hg has to come off too but I like the standard fsb for some reason so this is still a toss up.

Yes at some point it's getting a can. It's more then likely going to inherit the aimpoint off another upper since my eyes are going to shit and its probably time to update the rifle optic from a compM anyway. Have not decided on a light or laser but both are mandatory items imo but thats for further down the road.

My main concern and biggest question is magazines.
My gun came with the old converted 41ae Uzi mag with the block welded to it to fit the Magwell. I've seen that you can send the old uppers to oly to have them redone to fit the new style magazines. Not sure I want to go that route as it doesn't look like I save any money on magazine costs. They are hard to find but when I see them the old style mag goes for about the same money. The only draw back to the old style mag that I ever really noticed was that fully loaded it was difficult to seat on a closed bolt. Would love to know if anyone has any experience with the re work and going from the old mags to the new ones. Was it worth it? Would you recommend a different route?

Have an Olympic 45 upper with 3 converted uzi mags and 3 black dog mags.
Runs great with all mags after they reramped it for the newer mags.
It's one of there older uppers, that's why they had to reramp it.
Buy some  of the newer full body mags, they also work to hold the bolt open on last round.

Why not buy a Glock pistol mag lower from Oly?

Will it work with the upper I have? I have no problem with that at all if it will work with the upper.

Something about those uzi mags that I just like idk what it is though.

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No problem... just get an AR Glock mag well adapter and modify it.  I found a basic one, took off the Colt style ejector.. and it works with my Oly 9mm upper on a regular 223 lower.

The adapter was made by Orion, but I think they went out of biz.  I was gonna buy a second block...

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Did you remove the ejector spring from the upper? I have a Oly 9mm upper which uses the proprietary poly mags but was thinking about using Endomags if possible.

No, I removed the ejector from the adapter block.  Most, if not all AR MAG well adapters are for "Colt style " blow back operation PCC.  

In the pic above, the slot is where the ejector in the adapter was.  The Oly. Ejector is visible in the pic.  This adapter is very basic & I noticed the leading edge of the magazine was close to the front (similar to the front edge on an old Oly Glock mag AR lower I saw.

The Oly 9mm was originally fed by unmodified Sten mags.  I have a Hahn sten block adapter.  And I also found some Sten mags with the spacer block welded on.  And so.eone sold a bunch of the newer generation Oly 9mm plastic mags on GB.  The Glock adapter just modernize the feeding and added another option to feed.  I thought I had a thread or replied to one in the last year with pics but can't find it.

I'd reach out to macon armory and get his thoughts on the matter. I think the best bet would be getting it set up for glock magazines. Adapter blocks and lowers are available, as are magazines.

I'd try modifying one of the glock mag inserts to work with the oly style upper.  If that failed I'd put it in the back of the gun cabininet for another decade.

double post.

Some more pics of my Orion modified Glock/AT adapter, Olympic Arms 9mm upper and a mag to give an idea.  With Orion gone (I think the seller John from Gunbroker passed away), the only option would be the ATI mag block.  Removal of the Colt style ejector looks easy enough & the height when installed looks ok.  Not sure about if the last round hold open would work or have to be removed...

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The ATI is about $100 to 150 depending on source.  Stern, might be too tall & the other manufacturer has a brace that gets in the way of the oem Olympic ejector

Also, the ATI when installed, sits flush (close to it) to the lower's upper edge where the upper meets.  The ATI looks to have more room between mag leading edge to barrel then the Orion.

I will probably pick up an ATI to mod for my Oly (spare).  I found the one by Mantador Arms but it sticks up... but I might get that for the feed ramp it has for my Colt style 357 Sig upper...