SalorJ... I think it would be advisable to recognize there is a distinction between range shooters looking for short barrels or suppressors, and USPSA competitors not using an SBR'd lower but a full 16" upper... my carbine is for USPSA competition

the problems I encountered with my home build using CMMG barrel and bolt on a New Frontier billet lower were primarily that of magazine clearance...particularly with high capacity OEM Glock and ETS magazines ...at first I got caught up in trying to modify magazine lips for bolt clearance and whittling on the followers such that would allow the bolt to clear the follower when dummy rounds were hand cycled.... the unique sharp tooth profile of the angled locking lugs would drag on an empty follower and not run smoothly... simply lowering the magazine catch shelf in my case did not completely solve the problem, so I originally resorted to lowering and trimming the nose of the follower... I discovered that the MagPul Glock replacements mags would clear my particular set up without a problem... except that MagPul made only a 27 round mag... I had a 3D printed extension made, but it did not work reliably... you might look for producing a Taylor Freelance/Taran Tactical extension kit with spring to get the capacity up to 35+ for the USPSA shooters

currently I shoot a 40 round ETS mag, and allow the bolt to put slight scratches on the next to feed cartridge

at about 1200 rounds I started having weird double feed failures with a carbine that had up to that point worked 100%... pulling the bolt apart I discovered that the elastic plug in the middle of the extractor spring had hardened...consulting with other shooters on the Brian Enos Forum, a suggestion that I replace the extractor spring with a heavier duty Bravo Company spring with no O ring or plug... which I did, and for the last two matches have not had a problem... one of the members on this forum using a full auto/suppressed RDB has traced his problems to a weak ejector spring, which CMMG has replaced with a shorter spring for the 10mm conversions... at this point I have my OEM ejector spring in place...

good luck in your quest  Les Snyder L747

Spare parts would be great to see. Just the bolt itself and all the various springs (ejector springs in particular). Available separately. Currently you can get all of those from CMMG but only in an expensive bundle with a bunch of things you probably do not need a spare of like the carrier key for example. So just being able to get the high wear parts separately would be great.

Also the 10mm barrel and BCG kit

+1
The only place I've seen other than CMMG that sells the BCG repair kit is Optics Planet: https://www.opticsplanet.com/cmmg-inc-mkg-mkgs-complete-bcg-repair-parts-kit.html
...and they only have the 9mm and .45.  CMMG has a .40SW version but I don't see it anywhere.

They also have this kit but don't really need these parts often: https://www.opticsplanet.com/cmmg-inc-mkg-mkgs-bolt-carrier-maintenance-parts-kit.html


Although I did break one of their proprietary cam pins but attribute that to a barrel with excessive headspacing and they just replaced the barrel for me.

The biggest issue is the ejector spring and even then, you'd have to make sure you get the latest MK10 ejector spring.  Use that spring even for 9mm, .40SW, .45ACP and 10mm.  Since that spring will work in 'all' of them, I would hope CMMG would just use that and not have to question if you have the .45ACP ejector spring or what.

I say 'all' and intentionally left out the 5.7 as I don't have that one and presume a standard 556 ejector spring may work fine in that one...I don't know...or care really.

Good luck trying to get them to sell you the springs though.  I've asked several times and get the run around...Although I can't really complain as they have been replacing mine for free when they wear out.  I just like to have a bunch of spares....ultimate solution is to go to a fixed ejector setup like I did but that is another discussion.

ETA:  Glad to see some more dealer support for the CMMG RDB setup....and in FL too...too bad I gotta pay sales tax :)

SailorJ... a good friend developed the M16 bolt upgrade kit for SOCOM... it had a McFarland style continuous gas ring, the high temp O ring, and a high temp ejector spring... that spring had a bluish tint to the heat treat

what city are you located in?

@SailorJ

Thanks for the radial delayed sale.  Just ordered an 8in 9mm RDB bolt and barrel and a 3 pack of the Pmag conversions.  Looking foward to putting my RDB build together al a carte.

I'm glad you guys are available as a good resource for CMMG product. Thanks so much in advance. I'll be ordering more in the future as you guys have a lot of other great parts on tap at good pricing.

You may want to add any other .458 sized port door uppers you offer like the AERO XL one under the delayed blowack category unless you have some sort of agreement with CMMG to only place their specific product in that sub category.  I'm going to try my luck with a standard upper I already have here in my parts bin but if I find I need the larger ejection port door size I know where to find one ;)

Thanks again, you have the best deal I could find right now on the RDB bolt and barrel and being in stock.

No problem.
In a suppressor thread it was mentioned to buy from YHM based on the fact they have for the past few years been listening to their customer base and giving the people what they want.  You guys do the same and so I felt the same way to give business to those that sell you what your asking for, not something they want to push on you just because its in their inventory they don't want to be stuck with it.

Have a great day out there in FL today.

I don't think its that simple...CMMG's has been trying all different spring permutations....their latest MK10 ejector spring is supposedly made from some new material...
The .45 CMMG springs are also proprietary....but I don't recall them stating they were some new material.

See my website for some background testing I've done: http://c3junkie.com/?page_id=954

I've done all types of attempts...I even drilled out a 5.45 bolt and crammed a .308 ejector spring in there..: https://www.ar15.com/forums/armory/Full-Auto-CMMG-Guard-Tuning/23-494385/&page=3

The .45 springs are shorter than 556 but are thicker gauge than a standard 556 ejector spring...but they still died around 1K rounds for me.
I've killed a lot of ejector springs.  
I'm testing the MK10 spring now in .40SW in full auto and am at about 700 rounds now.  I haven't seen anyone else post any data on the MK10 spring.

There are some guys that say they have 3-4K on the original spring and no issues.  I've posted before that I believe the issue is inconsistent headspacing....discussed here:
https://www.ar15.com/forums/AR-15/CMMG-radial-delayed-system-ejector-spring-question/15-747732/

What about the 5" bolt barrel kit in 45 acp?

Also what about the kynshot buffers Amphibian has thoroughly tested and recommends.

And possibly magazines?

I'm going to test Amphibians recommended buffer spring combo this Friday. I'm running the 8" cmmg kit in a Angstadt Arms 1045 matched receiver set. I love this gun so much I just ordered two more Angstadt matched sets to build!

I'd also dd the parts Amphibian recommends for the "preferred" RDB setup.

VLTOR A5 buffer tube
Kynshott buffer RB5007
Tubbs 5.56 and 300BO flat wire springs

I'm just putting together an upper for use on a FA lower. I'd be happy to test springs, but I'd like to get a sense for the current CMMG spring first and test til failure. I'm in MI so pretty cold for shooting right now. :-)

Received my RDB parts from Right to bear. Thanks again SailorJ.

Looking forward to start my build and then see what needs tinkering depending on how she runs after the first outing.  Wish me luck.

Damnit.  You just cost me money.  Everyone else has this covered for the most part.  Maybe quality 3 lug adapters?

Just checked out the link and only saw the .45ACP lower.
Any plans to provide the 9mm lower (Glock mags)?

Any idea on price?

I myself am tempted to try Amphibian's A5 tube, Tubb spring, and 9mm Kynshot hydraulic buffer recipe.  So definitely if your considering carrying those parts at some point I'll just order from you guys instead of elsewhere. Call it the Amphibian RDB buffer kit and sell it as a combo

That's a good idea. It would honor Amphibians hard work and contribution to the RDB platform and make it easier to source the parts from one place.

Do it.  It's ridiculously good.  Outstanding in 5.56 full auto too.  Good idea to sell it as a package as well.

LOL...I'd be honored

I still haven't gotten over to the range to try mine out yet. You can definitely feel it is smoother though hand cycling it.

Dude I still cant get over how smooth your setup made my mk18 in FA.  I have an ssf trigger and it's not rated for blowback 9, so I haven't tried any pistol stuff until I get either an rdb upper or the new mean arms setup.

If you like that, you should really try a full auto 12.5 Mid gas 556....I don't shoot carbine gas unless I have to.

How about the CMMG 10mm lowers?  Word is the feed height is different than the 45?

What about some straight pull bolt action 9mm parts?

I know it’s a stretch

ETA - The same parts could be used for a DI upper.

I’ve been on the fence about building one of these.  Your parts prices have convinced me.  Thanks!