Oly Arms AR15 in .45 ACP. Finally got it put together!

[Corvus]

Here is the second installment of my Olympic Arms pistol caliber mid-magwell AR15 rifle project. The first installment--a 9mm setup using STEN mags, a two-piece Colt block, and the existing mag catch can be viewed HERE.

For this .45 project, I started out again with a two-piece Colt mag block. The front block looked like this:



And now it looks like this:



The rear block originally looked like this:



I modified it to look like this:



Notice that I had to mill a little trough to make room for the nipple on the back of the magazines I used. Which magazines did I use? Madsen .45 ACP mags. Here's a pic of one, notched and ready to use:



I found two dozen of these magazines at a gun show several years ago. I have never found any more since. (And sorry, none of the 24 I have are for sale.) The Madsen submachinegun was chambered in .45 ACP in Brazil from 1950-1953. It was also called the INA MB50 and the INA M953. A picture of one can be see on page 409 of Ezell's Small Arms of the World. The magazine is a double-column single-feed affair, and holds 30 rounds. Yes 30 rounds of .45ACP!

The Madsen .45 magazines are larger than the standard AR15 magwell by about 65 thousandths of an inch. So, I took my dedicated lower receiver, and had it hogged out to fit the Madsen mags. The lower magwell now looks like this (both sides are shown):





After milling, the thinnest part of the magwell wall can be seen in the picture directly above this text. The measurement at that thinnest spot was just about 40 thousandths.

I then installed the modified blocks into the lower. This is what the completed lower looks like:





Fortunately, I did not have to mill out the whole area (vertically), but was able to leave a reinforcing "lip" at the very top of the magwell--where the metal is thinnest even on an unmodified lower. You can see the "lip" in the pic below:



This lip does not only act as a reinforcement. It also acts as a stop for the magazines. They cannot be over-inserted because the lip stops them. I also installed the front block about 3/32" lower than flush with the top of the magwell, so that the little "ledge" on the feed ramp of the front block could act as a magazine stop as well. So the mags are being very securely held between the mag catch, the feed ramp ledge, and the magwell reinforcing lip.

Here is the completed and assembled receiver, showing the mag inserted with a round ready for stripping and feeding. As was the case with the 9mm STEN project, I found the extra distance the cartridge travels to get to the Oly Arms forcing cone to be a non-issue. Feeding has been completely reliable.





Needless to say, I am VERY pleased with how this project worked out. The followers in the Madsen mags even hold the bolt back!

[DaBunny]

Very impressive work, but you're still nuts.

[Charlie-2-6]

Thanks, that was a very insightfull post. If you have future projects, make sure to keep us informed.

[Corvus]

Finally had a chance to bring it out to the range this week. Worked perfectly!

[orionmkii]

[Stickman]

Very nice!

[Corvus]

[Thom]

This is exactly what I need to see for my current project, sorry for resurecting an old thread but you have provided much of the information I have been looking for.

Thanks Corvus!


Thom. . .

[gunslinger45]

That's one heck of a project you done there. Good looking workmanship also.

Ric