Hello

I'm thinking about converting my LMT MRP to a dedicated .22LR . However I am a NOOB when I comes to knowing exactly what parts I need in order to do it  

I'm gonna order the Spikes Dedicated 22LR MRP Berrel

But where I start getting lost is when it comes to the BCG.

I'd like to use the CMMG Right Handed .22 Evolution BHOAkit w/Anti-jam Charging handle and 25 Rnd mag

Right handed .22 Evolution conversion kit for AR15 rifles with forward assist adapter. Stainless steel, piston compatible, steel extractor pin, stainless steel firing pin captured spring, cotter pin in bolt retains firing pin, Drop-in forward assist adapter, buffer retaining relief cut, chamber adapter with improved live round extraction.
Includes:

Right Handed, Stainless Steel FA Equipped .22LR Action
BHOA Actuator
25 Round BHOA Magazine
Anti-Jam Charging Handle

What I'm not sure is when it come to the chamber adapter Am i correct in thinking that because I'm going to be using a Dedicated Berral I need to a Stainless steal .22 Collar instead.

And if so how does the Collar attach to the barrel ?  I've been searching the web and can't find any info on this part of the process.  

Any help is greatly appreciated

You'll need a Spike's or M1S collar, since the breech extension on Spike's barrel had a .500" nominal OD; thus a CMMG collar won't fit.
Atchisson bolts are by and large interchangeable, but the collar has to match the barrel. The collar replaces the chamber adapter used with .223 barrels,.
Piston compatible only has to do with conversions used in centerfire uppers.
You won't be putting a piston in a rimfire upper.
Your plan is about as sick as my MK12 Mod 0 .22.

Thanks for the help

I didn't even notice it said anything about being Piston compatible lol .

Do you have a link for the M1S collar ? I'd like to see it as compared to the spikes .  

Also how do you find the ID dimensions of a given manufactures Collars  ( Spikes, CMMG, M1S ) in order to figure out who's will fit a given barrel . Does this mean there is no industry standard when it comes to  breech extension OD diameters ?

Ohh and if I can't use the CMMG Collar do you think there would be any problems with the CMMG Receiver Plate Assembly lining up correctly to a different manufactures Collar.

I apologizes if these questions have been asked before, I just want to make sure i have a solid grasp and understanding before I start.  



Yeah I know i could buy   descent basic dedicated .22LR upper for what I'm gonna pay to convert my LMT . But I can't bring my self to do it . and this way i have it set up the way I want

CMMG is .460 but it also has a spring detent that snaps into a groove on the CMMG barrel. This keeps it from moving.
Spikes, M1 are .500 and a slip fit. Hope that it's a tight fit. If not, it can cause you problems.
The other collars will fit the CMMG rails. You won't know about the feed ramp until you try it.
I've used a Spike chamber adapter on a CMMG rail and it worked fine.
Dave

Ahhh ok i Understand now .

As for the Spikes Collar. If it were a loose fit on the breech extension do you think it would be possible to drill/ tap and install a set screw in order to keep it secure . I have 15 years in as a CNC machinist and have access to CNC Lathes. Mills and Bridgeports .

Sure, CMMG used to do the old style that way. What you have to watch is shooting them loose.

Cool.... good to know .

Thank you .

why dont you just use the spikes 22lr bolt, the one they designed to work with their barrel?

Mostly because I've been readying better things about the Cmmg BCG  than the spikes.


Also I want my Forward Assist to function and I don't believe that is even an option with the spikes bolt .

interesting, thats fair I guess. For what its worth my MRP 22lr conversion from Spikes (barrel and bolt) did need some minor fitting on the bolt, but since then has run 100% (not one malfunction in about 1500 rds so far). Really a fun toy.

Thank you for the info .

I haven't fully settled on all the parts yet, so I'll take all the information and help people are willing to give .  

But I'm leaning a lot towards these parts

Spikes MRP barrel
Spikes collar
Cmmg BMC w/forward assist
Cmmg Bolt hold open Actuator
Cmmg Anti jam handle
Cmmg Ejection Port Cover


Could you please tell me what minor fitting on the bolt you had to do ?

I had to change the radius on the rear of the 22 lr bolt so that the hammer was not hitting the rear of the bolt so square. Basically had to soften the angle between the contact surface of hammer and bolt under recoil if that makes sense.

I think the CMMG bolt is a good choice, however mine is not a dedicated 22, so I have no input on the other parts. That will be the sweetest 22 at the range...