Not sure if this is the right spot for this topic (move if necessary) but here it goes...

I want to build (or buy completed) an ar45acp variant but can only find large frame lowers with glock pattern mag wells. Does anyone know where or who I can turn to in getting a lower that will accept something other than glock mags. Looking specifically for something that will seat FN 45acp mags.

Deathstroke,

Trying asking your question here:

https://www.ar15.com/forums/AR-15/Rimfire-and-Pistol-Calibers/15/

You will most likely get a response.

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Do an internet search on Macon Armory and get in touch with Rudy. If nothing else it’s a good starting point.

The 45 ACP world is a bit limited.  There are also Greasegun mag lowers, and Macon has their own mag and adaptor, but unless an FN mag will fit in the Glock magwell you are likely outa luck.  

I built a 45 ACP on an AR15 lower and use a customized insert in p-mags.  Capacity is limited by internal volume, but it runs great.  I am going to work on an insert for metal Grendel metal mags to increase capacity, if I ever find the time....

If you are willing to accept using a magwell adapter in a standard AR lower, in addition to Macon Armory, Stern Defense might have what would be acceptable for you in the way of a product that provides LRBHO capability.

Another potential product is the 1911 magazine pattern 'bolt on' magwell block sold by Blind Squirrel Enterprises.

A factor to consider that you might not be aware of is that the typically suggested preferred total weight of BCG plus recoil buffer (i.e., approximately the weight of the reciprocating parts) for a non-delayed (so-called "straight") blowback AR .45 ACP configuration is approximately 25 ounces or higher.  Use of a hydraulic buffer might be able to reduce the weight required somewhat.

In any case, as noted above, the Rimfire and Pistol Calibers Forum is the place to inquire.

Best of luck.

MHO, YMMV, etc.