Converting to a Radial Delayed Blowback PCC Upper
- Thread starter calicojack
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Wait... Does the CMMG RDB setup not work w/ a Colt pattern lower? Was planning on getting a RDB kit.
I could swear someone was running a RDB setup at the last MDTCA event - which would have had to been on a Colt pattern (registered) lower.
It will run, but you have to file about .10" off the mag catch, or the Colt mag sits too high. Then you get play in the mag. The CMMG is designed to work with Glock mag lowers.
I had one, and got it to run, but it wasn't great in the Colt. The Scheel system is very nice. Not sure how it would run in full auto. You can borrow mine and find out, if you want.
Ammo Jon
Ultimate Member
- Mar 3, 2008
- 20,985
Yeah, you and countless others around here.
You’re welcome
Yeah - speaking of which - I need ammo.
Sounds like in Mar this year, CMMG updated the RDB barrel to work w/ they MK9 Colt pattern. Sounds like the barrel is different. Marked "9mm Luger" vs "9x19 Nato" for the older version. I can't see how a different barrel would make a difference (but maybe it's the whole system and just the barrel is the part that's marked.
Teratos, Why did you have to shave down the mag catch? The bolt carrier hitting the feed lips? Would think you'd be able to just machine a little off the bolt carrier instead? (I've heard people doing that for Glock carriers before. Or was it the opposite - narrowing the carrier to fit between Glock lips. I can't remember...) I'll ask Matt who was running that CMMG system last event so I can ask for more details.
Teratos, Why did you have to shave down the mag catch? The bolt carrier hitting the feed lips? Would think you'd be able to just machine a little off the bolt carrier instead? (I've heard people doing that for Glock carriers before. Or was it the opposite - narrowing the carrier to fit between Glock lips. I can't remember...) I'll ask Matt who was running that CMMG system last event so I can ask for more details.
Yeah, the lower lugs would also mar the ammo. It worked if you drop the mag a little. I didn’t want to mill off the lower lugs, since they function in the delay system. I didn’t know CMMG made a version that works with Colt. I bet the lower bolt is modified. I really like the Scheel system sitting on my Colt pattern gun now. Gotta get it out and really shoot it. Only about 150 rounds through that.
This is how I "save" money. I start with "I don't want to spend $300 on a roller delayed blow back accessory for a 9mm PCC that already runs well" - so I'll just get a whole new 8" 45 APC Radial Delayed Blow back PCC. Wait - now I am spending $800+ And that's even with using a bunch of spare parts lying around!
You know what - totally worth it. I'll start with a braced pistol and then figure out how to get it to an SBR length later.
You know what - totally worth it. I'll start with a braced pistol and then figure out how to get it to an SBR length later.
In fact the cheapest 9mm PCC CMMG makes now is RDB and uses Colt 9mm mags. They eliminated direct blowback from their lineup to focus solely on RDB for PCCs.
It’s a good system, and a hydraulic buffer makes it even better.
Which hydraulic buffer are you using?
This one:
https://www.brownells.com/aspx/search/productdetail.aspx?sid=230885&pid=124983
Cool part is that it’s fully compatible with 5.56 uppers if you’re running an A5 length buffer tube.
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