Are they compatible? It looks like the pin holes may line up, but I’m not sure. It seems there really isn’t a standard yet on this double stack 1911 business.

The pin holes should line up. Is the RIA msh rounded at the magwell like a 2011 or flat like a 1911? I suspect the RIA uses a standard 1911 msh but have never seen one in person.

Well, the best pic I could find has the RIA MSH looking like this one:



A quick search of the 2011 MSH gave me (a jumbo pic) with this profile:



A popular 2011 manufacturer also lists a flat 2011 MSH but doesn't show a picture as it is listed.

I hope this helps.

Ugh. I had this long post typed out, then realized I really need to get all these pistols on the bench and really look at them with a set of calipers handy.
And probably post a pic or two of what I have and what I’m looking at.
FWIW, Dawson Precision has the arched MSH that I was looking at, guess I could contact them.
I do appreciate the replies.

Aren't the RIA's "Para" based guns? (mag/size wise)

Not that that answers your question, it just makes new ones.
But it might help in web search for the answer. Assuming my memory isn't off.

CAS; I think you are right. I know that Remington R1 19rd mags work in my full size RIA. The 22TCM/9MM combo is a little bit different story, apparently, as the Remington mags don’t feed well in it. I had to get more of RIA’s 17rd mags for it.

I decided to cut to the chase and just email Armscor support.

BTW: that full size, all steel, railed, double stack RIA is a heavy beast. Put 20 rounds of 147gr Lawman on tap, and my arms get tired before it’s time for a mag swap. But boy, does it shoot!

RIA is definitely a Para pattern gun. I still have no idea what msh it uses. Pretty sure it predates the STI pattern.

Finally got a reply from RIA support.
This is the link they gave me:

https://advancedtactical.com/i...ms-steel-arched.html

Any help from the braintrust?
I will admit to being new to modifying 1911, even though I have owned/shot them for years. In fact, the first firearm I bought, on my 21st birthday, was a Norinco 1911...sure wish I still had that pistol.

Post a picture or send me an email of the msh in your RIA and I will tell you what you need. As I mentioned previously, I doubt it uses a STI 2011 MSH.

This place never disappoints.
thanks to a couple of emails from tha1000, I think I have a starting point. Apparently the RIA double stacks (a Para Ordnance derivative?) uses a “standard” 1911 MSH. The magwell just widens from there to allow double stack mags. So I’m off to find a Main Spring Housing to my liking.
I know this is elementary to a lot of y’all, but I’m just getting into the 1911 platform to any kind of depth. I’ll try to post some pics as I go along.
Again, thanks to all of y’all.

Glad I could help