Update in this post

I recently ordered a CMMG RDB 9mm bolt and 8"-barrel combo.  I am now looking for parts for the rest of the build and I am considering the BCM MCMR handguard.  I only found one picture in the pic thread, but it wasn't the highest quality.
- Are there any more pictures out there?
- Are the BCM handguards no longer in fashion?  Any other recommendations?
- Do I need the 7"-handguard?
- Will it clear a suppressor or is it too close to the end of the barrel?

I got the 9mm CMMG RDB when they first came out and was really looking hard at the BCM MCMR rail but I didn't like how it doesn't have integraded QD sockets.
I really wanted the MI 8" Combat rail: https://www.midwestindustriesinc.com/product-p/mi-crm8.htm

I run these on my 9mm and .45 8" CMMG's now.

I have two 8" 9mm CMMG uppers using these rails:


The top upper is using a factory CMMG barrel and a typical 3 lug adapter.
The bottom upper is using a SS barrel that I had headspaced for the CMMG RDB bolt and the 3 lug adapter is threaded almost the entire length as seen in the picture below.


Kind of hard to tell from the angle of the picture but both barrels are the same length.

More info and pics on my site here: https://c3junkie.com/?page_id=280
Picture below shows how the Bixler suppressor nut goes in the rail.



I'm not clear what your suppressor mounting method is and what suppressor you plan on using.

Because of the barrel extension on the RDB barrel you can treat its length similar to that of a 5.56 barrel (vs a 9mm blowback barrel which is shorter and most often having an integrated barrel extension) for rail matching purposes.

MCMR is a pretty tight ID and will not fit a 1.37" (common pistol) suppressor body.  On an extended three lug mount like old SiCo mounts you will likely have some clearance for a slight tuck.  Get a 7" if you don't want to be concerned with clearance issues, BCM lists their exact lengths on their website.

-Google image search for pictures

-You need to decide what handguard you want....and then get the I.D. and length dimensions to compare to the suppressor

-You need to determine what length you want once you know what you want.

-You need to measure you suppressor to determine what handguards the suppressor will fit.


And once you know the suppressor dimension  .....look at the KVP KONZA and the Midwest Industries SP series handguards.




.

With the 1/2x28 piston and fixed barrel spacer there is about 1/8" from the back of the piston to the back of the body of the Osprey.  I would like to get a dedicated PCC/subgun can in the future, but have no idea how much room a tri-lug adaptor and can require behind them.

I've tried googling for images, but I apparently suck at google and get only non-relevant images.

If you want to sink that suppressor under the handguard you can grab a Strike Industries Strike rail. It has an ID of 1.57" if I remember correctly. It easily fits my Rugged Obsidian 45. Just be careful about placing things like handguard grips and such as the tolerances between suppressor and handguard are small. I unknowingly caused an endcap strike with Magpul MLok grip pads as they impinged on the suppressor ever so slightly pushing it out of line. $65 lesson learned the hard way. I wish I could post a picture but I am too new to posting on the forum.

Thomas

I can post your pic up if you want to email one.

The SilencerCo Osprey, which I mentioned above, is what I have now. It is an eccentric can that is 1.75" tall.  It will not fit inside any handguard small enough to grip.  I need to know if there is enough room beyond the BCM MCMR rail to mount it on an 8" CMMG 9mm RDB barrel.

I am sorry, I'm kinda off topic huh. Well I do hope you get it figured out and I hope it works well for you. Best of luck!

Thank you for the offer s4s4u I just posted a pic of it on the 9mm "show off" forum.

No problem.  You weren't the first and I wasn't expecting my post to be interpreted like that.  I guess I'll just have to wait and measure it myself once the barrel arrives.

It works!  There is about a millimeter of distance between the end of the rail and the shoulder for the threads.  The installed piston is the extended 1/2x28 from SiCo.  The short one won't screw down all the way for some reason.





In hindsight I should have ordered the 16" barrel and had it shortened to 10.5" to match the 5.56 I intend to put together.  There is very little room for my hand or for accessories (light, sling mount) on this length rail.

I am enjoying it so far.  I did find it doesn't like plinking ammo and a Geissle H3 buffer.  Other than that I've only had one jam.  Unfortunately that jam resulted in the round getting flipped over backwards and stuck in the magazine due to the Mean Arms' built-in feed ramp.