I have a new H&R upper receiver that won’t even come close to fitting my CMMG lower. It looks like the rear lug it too long or the lower shelf is too high. Do I need to find a low shelf lower to make it work?  I really do not want to dremel my rear lug to fit. Any advise is appreciated.

Lower shelf is too high, buy a low shelf lower. They are cheap and plentiful.

eta: I'd steer away from trying to dremel your existing lower.

Determine which is the problem component.  If it's the upper receiver, contact @mike_nds.

I have contacted PSA about possibly returning this upper, I have never encountered anything like this before and I have built dozens of AR rifles. The upper doesn’t even come close to mating up with my CMMG MK9 lower mostly at the rear. The H&R rear lug is too long to close the 2 together. I have tried several uppers of mine on the CMMG lower and they all fit fine. There is a considerable gap between the 2 at the rear and the rear takedown pin will not go in at all.

You only have the one lower to compare?  Do you have a friend who might have another you can try?

I only have the one dedicated 9mm CMMG lower, all my other ARs are 5.56 or 300BO. I will try the upper on all my other lowers and see what happens. The H&R upper in question is a clone of the Colt 635 slick side intended for building a Colt 635 copy. I really are not keen on using a mag block and converting a AR to 9mm. I have tried that with different mfgs; Colt, Hahn with less than stellar results, that is  why I like the CMMG MK4 lower that is a dedicated 9mm lower. It has been 100% reliable. The H&R might be out of spec: I could not even get a charger or 9mm bolt to go in it, it is very very tight. I really was set on this upper to work on my CMMG lower, but it doesn’t look promising.

"I have tried several uppers of mine on the CMMG lower and they all fit fine." Sounds like an upper issue to me. PSA will take care of you.

^^^^

Attached File


Looks like more or less a proprietary fit for the PSA PX9 lower. That's probably the issue.

@VillageGS

Mike_NDS is part of PSA management if that wasn't clear. You probably know given your join date but the way you mentioned contacting PSA, I wasn't sure if you realized you have probably the best person for the H&R line in the thread.

I assumed that it was common knowledge at this point. Maybe not?

https://www.ar15.com/forums/Industry/Mike-s-OFFICIAL-HandR-Retro-thread/301-301583/

So more like also compatible. Got it.

in for pics.

It’s not the lug, H&R uppers are just tight. I’ve had issues with them fitting on some lowers too.

They usually fit really nicely but occasionally you’ll get one that won’t fit on some lowers.

After several days of measuring and try fitting all my 12 AR rifles, I have concluded that some lowers won’t close and some fit like a glove. I don’t think now that the upper is out of spec but rather only fits on certain lowers. I have decided to keep it and fit it to a different lower other than the CMMG MK9 dedicated 9mm that I originally intended it to drop on. Six of my 12 lowers fit the H&R perfectly so if it is a no go with another dedicated 9mm, I will convert one of my 5.56 lowers with a Hahn dedicated mag adapter. Mike_NDS helped secure me a RA with PSA and I appreciate his assistance, but I have decided to keep the upper and adapt it to another lower. The bolt and charger issues are resolved, seems that it didn’t like my CMMG charger but accepted another charger no problem. My RRA and Spikes bolt work fine now because the H&R receiver was new and dry. It seems like it did not like my CMMG MK9 lower which is strange because it fit perfectly on another CMMG lower I have, a MK4 in 5.56.