To begin, I am a long-time lurker who (very) seldom posts. I’ve learned quite a bit from this site and am hoping someone here will be able to answer my question. I have previously tried Google and the M4C search engine, but no luck So here goes:
I am assembling an AR upper receiver group. Intended purpose is to shoot targets at the range, but I also wanted as quality and reliable a build as was possible. To that end, I purchased a LaRue Stealth Billet LT-007 A3 upper receiver to go with my (previously purchased) Green Mountain HBAR 20" barrel (I live in an AWB state); at the height of the pandemic the LaRue was the only upper receiver I could find that had rifle extension cuts (the Green Mountain barrel necessitated that feature) and from what I read, LaRue is a very well-respected company in the AR world (to say the least). In retrospect, perhaps I should have purchased a different barrel with M4 extensions, but this is where I am.
At this point in the build, I am searching for free float rail to mount on the rifle. I happened across an 18" Midwest Industries Combat 18" rail (MI-CRM17XR). (I am thinking of putting a bipod, hence the longer rail). However, there is a disclaimer on the MI webpage:
"IMPORTANT COMPATIBILTY NOTES!
Due to the many different dimensions in BILLET UPPER RECEIVERS on the market, please contact your billet upper receiver manufacture to insure fit of this handguard. This handguard is compatible with standard forged upper receivers."
Well, I contacted LaRue as MI suggested, but LaRue had not actually attempted to install this rail on to one of their LT-007 A3 upper, which isn’t surprising (I mean, why would they?).
So anyway, not to belabor this any further, does anyone here have any experience mating the LaRue upper receiver described with the MI Combat rail? Any and all help is much appreciated. Thank you in advance.
@DG23…that’s actually kind of interesting. A 3rd party vendor was selling the barrels and did not identify the make and model…some of the reviewers on said vendor’s website said it was a Green Mountain barrel. Sure enough, when I received it in the mail, there was the characteristic “G” marking on the barrel. However, there was no other markings such as caliber, for example. Just the letter G. A few months went by and I saw the same barrels on another website and the seller indicated that the barrels were manufactured for Colt by GM for a Colt HBAR model that never got produced. I can find no independent verification either way. The whole thing is a bit of a mystery.
@D_poynter, you are right of course about the measurements, but I do appreciate your response. I am not married to getting this MI rail and open to alternatives. Why do you not care for MI? Is there anything in particular you don’t like or just more of a personal preference kind of thing? I guess I will take a look at PA rails too.
@blacktail_8541 thank you! I appreciate the input. How do you like it so far?
I just realized the MCMR rails were made by BCM. One of my other rifles has a 13" Alpha Keymod (aluminum) rail…haha, I purchased it years ago when the Keymod vs MLOK battle was at its peak right before that report from the military came out comparing the two. Regardless, it is still a well-built rail and I really like BCM in general. That rifle in question was almost entirely BCM.
@Stick…the GM barrel had rifle cuts, not M4 feed ramps. Unless I got it backwards, didn’t that mean I needed an upper that was cut to accept non-M$ feed ramps? I bought the barrel over a year ago so it would be too late to return. Again, in retrospect, I probably should’ve held off on the barrel and went with another that actually had M4 , but hindsight is 20/20. Still better than my first AR purchase back in 2011…now that was a learning experience!
It is a rifle. You do not need M4 cuts. They will not hurt anything but in this case they are not needed at all.
If you decide you just ‘got’ to have those and want to sell that barrel I will gladly take it off your hands for what you paid for it. I would be willing to bet it is a tack driver and would be an awesome spare for my Colt 20" HBAR whenever I eventually toast it and go to swap it out…
You got a nice barrel. Nothing at all wrong with having a rifle extension on a rifle barrel.
If he wants to dump his barrel with the rifle cut extension to me and go to a barrel with an M4 extension and still use his upper that he has now - It will look like the last picture you just shared. Very bottom right hand side picture.
Since the OP question is answered I’ll diverge a bit.
So, curious what about the MCMR rail makes it appreciably better than the equivalent MI rail? The 17" rail he purchased is two inches longer than your $200 15" MCMR, thus more expensive. Longer = More materials = More expensive to produce = More dollars
The equivalent 15" MI rail isn’t $250, it is ~$200 as well, depending on what you call equivalent beyond MLOK.
Both material specs are exactly the same and both even come with a little piece of MLOK PIC.
I have a bunch of MI rails and find they are very high quality and easy to install.
