CMMG's radial delayed blowback may be a game changer for pistol caliber AR's

drypowder

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https://www.cmmginc.com/shop/rifle-mkg-45-drb2-45-acp/

CMMG has a .45 ACP PCC with its radial delayed blowback mechanism. The delayed blowback reduces pressure before the bolt moves fully rearward, so they are able to use just a H buffer instead of the very heavy buffers typically needed for proper functioning of a pistol caliber AR. This should result in significantly reduced felt recoil. They also have built in a supposedly reliable LRBHO mechanism, which has been a challenge for Glock mag AR designs.

If this works well, I'm sure they'll expand into 9mm since the AR-9 market is many times larger than the AR-45 market.
 
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Question is why didn't they start with 9mm? How many 45 PCCs are there out there? I'm gonna guess that they tried and it didn't work on 9mm...
Good question. Could be the lower pressure of .45 ACP was easier to work with. Maybe what they learn from this will allow them to design the bolt for 9mm.

Edit: CMMG will be releasing this in several calibers over the next several months, so I have to imagine that 9mm will be one of the calibers. Also, they will have complete rifles/pistols, complete uppers, and bolt/carrier/barrel kits. The availability of complete uppers and bolt/carrier/barrel kits suggests that a proprietary CMMG lower is not necessary for proper function, which is appealing for those with existing SBR and pistol lowers.
 
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Probably some of the same reasons the Kriss was originally 45. Primarily the felt recoil of the 45 is far greater than that of the nine so a significant reduction will be readily recognized and far more apparent than in a 9.

And 9mm in a rifle platform has very little recoil to begin with. And as Joe said, the lower pressure of the 45 makes it easier to work with.
 
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And 9mm in a rifle platform has very little recoil to begin with.
In the designs that use a heavy buffer, whether it's the various AR-9's or the Keltec Sub-2k, you can feel that buffer cycling. Much more so than in 5.56.

I think a big part of the appeal of CMMG's design will be the reduced pressure pushing the carrier and buffer rearward (and thus allowing for lighter cycling mass), which should make for a smoother shooting firearm; as well as a lighter weight firearm - 9mm AR's are deceptively heavy for their typically short-barrel configurations. And if their LRBHO for Glock mags is reliable, that will help seal the deal for a lot of folks. Though CMMG will definitely make you pay a premium for it; but if this design is everything they are promising it to be, it should help drive prices of other AR-9 parts even lower.
 
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If Sig can make a gas operated 9mm, anything else seems silly.

I have a 45ACP Olympic arms AR15 and it uses a standard weight AR15 buffer.
No H buffer needed or recommended.

I think CMMG is just recycling old bell bottom jeans.
Does Oly arms have a 9mm upper for which they recommend only a carbine buffer?

What buffer are you using in your AR-9?
 
My AR9 uses a JP SCS.
Prior to that I used a Slash 9Q.
Ditched the heavy buffer & bolt weight and it changed into a different gun.

Oly arms 9mm upper also uses (used) a standard carbine buffer.

You should try out a 9mm AR with the bolt weight removed and a SCS buffer.
Shoots very flat with very little bounce.
 
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As long as they make a 9MM that uses the Colt pattern mags. I wish they'd do a .45 that used grease gun magazines. My biggest "gun" mistake was not ordering 1 or 2 HK USC carbines back in 2011 before they stopped importing them. Buds had them as low as $1,000 or less. At the time, it would have been pretty easy to be a Navy lower and stock, as well as have the barrel shortened to do a complete UMP conversion for around $2,500.
 
As long as they make a 9MM that uses the Colt pattern mags. I wish they'd do a .45 that used grease gun magazines. My biggest "gun" mistake was not ordering 1 or 2 HK USC carbines back in 2011 before they stopped importing them. Buds had them as low as $1,000 or less. At the time, it would have been pretty easy to be a Navy lower and stock, as well as have the barrel shortened to do a complete UMP conversion for around $2,500.

Oh man, that would make a great thread.
"Biggest gun mistakes"

Personally, I've no interest in any of those UMP style HK carbines.
No decent triggers available, limited optic mounting choices, limited aftermarket support etc.

These days it's all about options and the AR platform cannot be beat, in that regard.
 
Oh man, that would make a great thread.
"Biggest gun mistakes"

Personally, I've no interest in any of those UMP style HK carbines.
No decent triggers available, limited optic mounting choices, limited aftermarket support etc.

These days it's all about options and the AR platform cannot be beat, in that regard.
Agree with you on the limitations of the form factor, but still when you consider the package you could create around a .45 for $3K (with a nice optic) it is appealing between the history, function, and sex appeal.

uk-ump-usc-conversion.png
 
but still when you consider the package you could create around a .45 for $3K (with a nice optic) it is appealing between the history, function, and sex appeal.

uk-ump-usc-conversion.png

Until you shoot it and realize it's all show and no go!
Crappy cheek weld, no mag funnel, narrow recoil pad, lame grip angle, it chews up brass, has a crappy safety, does not allow a grip forward stance and generally reeks of HK snobbery!

(I jest...but only a little)

There is a reason you never see them in PCC matches and price isn't it.;)
 
Until you shoot it and realize it's all show and no go!
Crappy cheek weld, no mag funnel, narrow recoil pad, lame grip angle, it chews up brass, has a crappy safety, does not allow a grip forward stance and generally reeks of HK snobbery!

(I jest...but only a little)

There is a reason you never see them in PCC matches and price isn't it.;)
Well what do you expect from a 30 year old design and something made by Germans!
 
In the designs that use a heavy buffer, whether it's the various AR-9's or the Keltec Sub-2k, you can feel that buffer cycling. Much more so than in 5.56.
Yep, a Sub2k in .40 is not all that fun to shoot due to the heavy buffer mass slamming your shoulder. By contrast shouldering my Roni housing a G22 and 9" barrel (essentially a .40 PCC) is a pussycat due to the delayed action vs the Sub2k's blowback.
 
By contrast shouldering my Roni housing a G22 and 9" barrel (essentially a .40 PCC) is a pussycat due to the delayed action vs the Sub2k's blowback.
This raises the point that something like the Micro Roni might be the best option, in many respects, for a 9mm SBR.
  • Takes Glock mags
  • FAR less expensive at ~$200 + stamp vs $400 on up for an AR-9 upper + buffer
  • No fiddling/tweaking required to get it to run properly
  • reliable LRBHO
  • folding stock, so very compact
  • soft shooting compared to run-of-the-mill blowback 9mm AR/rifle designs
Downside is it's ugly as sin compared to all those sexy AR-9's.
 
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This raises the point that something like the Micro Roni might be the best option, in many respects, for a 9mm SBR.
  • Takes Glock mags
  • FAR less expensive at ~$200 + stamp vs $400 on up for an AR-9 upper + buffer
  • No fiddling/tweaking required to get it to run properly
  • reliable LRBHO
  • folding stock, so very compact
  • soft shooting compared to run-of-the-mill blowback 9mm AR/rifle designs
Downside is it's ugly as sin compared to all those sexy AR-9's.

I don't know. I think they look kinda cool. If I was going to SBR a GLOCK though, I'm just get the Fab Defense stock and foregrip. Much more compact and true to factory design. Cheap too...

I like the KPOS better than the Roni though. It seems much less bulky...

10693288_1518613271718430_1430707127_n.jpg
 
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This raises the point that something like the Micro Roni might be the best option, in many respects, for a 9mm SBR.
  • Takes Glock mags
  • FAR less expensive at ~$200 + stamp vs $400 on up for an AR-9 upper + buffer
  • No fiddling/tweaking required to get it to run properly
  • reliable LRBHO
  • folding stock, so very compact
  • soft shooting compared to run-of-the-mill blowback 9mm AR/rifle designs
Downside is it's ugly as sin compared to all those sexy AR-9's.
Not as ugly as a sub2k, or high point carbine!
 
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Also the Roni is at least as light as the sub2k if not lighter, and there is no comparison in that department with a 9mm AR. The only real downside I see to my Roni is with the 9" barrel I doubt it would run with a can on it. Good, now I don't have to buy a .40 suppressor. :)
 
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This raises the point that something like the Micro Roni might be the best option, in many respects, for a 9mm SBR.
  • Takes Glock mags
  • FAR less expensive at ~$200 + stamp vs $400 on up for an AR-9 upper + buffer
  • No fiddling/tweaking required to get it to run properly
  • reliable LRBHO
  • folding stock, so very compact
  • soft shooting compared to run-of-the-mill blowback 9mm AR/rifle designs
Downside is it's ugly as sin compared to all those sexy AR-9's.

Also a large aftermarket for Glocks, more or less the AR of handguns
 
Ah yes, of course this would be offered with a brace. $300-$350. Not cheap enough to sway me from an AR-9 pistol. $200 would be a lot more compelling.

I've thought about the 16" PCC like you posted, if I had a 45 cal can, I'd probably get one.

I've got a couple guns I want, and couple I might sell.
 
I've thought about the 16" PCC like you posted, if I had a 45 cal can, I'd probably get one.
16" PCC? Me? No way. Now that we have braces (and especially for those who have SBR lowers), 16" barreled PCC's are a niche market, IMHO. I would have zero interest in one.

If you're referring to the link in the OP, that's just what they rolled out first. I'm sure there will be shorter uppers and bolt/carrier/short barrel kits in various calibers. Something a lot shorter than 16" would be much more suitable for a can.
 
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CMMG now has the Guard in 9mm; takes Glock mags. Does have LRBHO.

This thing ticks a lot of boxes: softer shooting than direct blowback AR-9's, 8" barrel, Glock mags, LRBHO (not sure if it's reliable).
Pricey, but CMMG will eventually be rolling out complete uppers and maybe bolt/barrel kits.

 
The pistol variant in .45 AC s near the top of my list of must buy in 2018.

My H&K USC is fun but nowhere near as fun as the .45ACP will be in the AR-15 platform.
 
Looked at these pretty heavily and seems nice. I’ve heard lots of talk about them not cycling hollow points. That’s a deal breaker for me.


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CMMG now has the Guard in 9mm; takes Glock mags. Does have LRBHO.

This thing ticks a lot of boxes: softer shooting than direct blowback AR-9's, 8" barrel, Glock mags, LRBHO (not sure if it's reliable).
Pricey, but CMMG will eventually be rolling out complete uppers and maybe bolt/barrel kits.


Shoot my AR9 with either the 4" or 8" barrel and the JP SCC setup and let's see how much softer you need it to be. Here's a hint, if you need softer, maybe let your boyfriend do the shooting!

Edit: the CMMG system still looks fantastic. Interested in hearing more on whether the .45 cycles HPs though.

Edit 2: since I doubt CMMG will make them, wonder if they'd sell just the uppers, and if they'd work with a Bazooka Bros lower or other lower that takes grease mags?
 
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Shoot my AR9 with either the 4" or 8" barrel and the JP SCC setup and let's see how much softer you need it to be. Here's a hint, if you need softer, maybe let your boyfriend do the shooting!

Edit: the CMMG system still looks fantastic. Interested in hearing more on whether the .45 cycles HPs though.

Edit 2: since I doubt CMMG will make them, wonder if they'd sell just the uppers, and if they'd work with a Bazooka Bros lower or other lower that takes grease mags?
As @Slacker noted earlier, the JP SCS made his AR9 shoot completely different. I think CMMG was going after the broader AR9 market - the folks using the heavy 9mm bolt + heavy buffer (like the Slash buffer). But going with the JP SCS may be more cost effective than the CMMG route; though we'll have to see what these sell for once they've been out for a bit.
 
^^totally. I see it's pretty much proprietary, so I may be back to trying to build an AR45 using QC10 stuff.

Edit. Dang, QC10 doesn't have a .45 grease gun lower! Thought they did!
 
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As @Slacker noted earlier, the JP SCS made his AR9 shoot completely different. I think CMMG was going after the broader AR9 market - the folks using the heavy 9mm bolt + heavy buffer (like the Slash buffer). But going with the JP SCS may be more cost effective than the CMMG route; though we'll have to see what these sell for once they've been out for a bit.

In the interest of full detail disclosure, in addition to the JP SCS, I also removed the pinned in weight in the CMMG 9MM BCG.

All conventional wisdom says the weight is required or your carbine becomes an atomic bomb.
Losing the pinned bolt weight made a noticeable reduction in "dot dip" and cycle speed aka smoothness.
I have yet to experience any issues, and my carbine has seen at least 5k rounds of my reloads.

IIRC, my CMMG bolt with weight removed still weighs more than the FACTORY JP 9mm bolt that they use in thier badarse 9mm AR game gun.

FWIW, with the heavy 9mm buffer/weighted bolt setup, a 147gr heavy 9mm felt smoother.
With the current SCS/no bolt weight, 115GR @ max load of titegroup is smoother shooting.

My carbine has a 7" barrel. I can't speak to what effect a 16" tube will have.
 
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Ryan I removed the weight out of my CMMG too when I did the JC setup. I probably have 400 rounds down the pipes between my 4" and 8.5" upper. I have a 16" upper built other than flash hider/comp (gimmick on AR9s, I know), so I will be shooting it with the JC setup as well.

I forgot, I also bought the Brownell's Gen 2 9mm BCG (which has to be a Faxon, they look identical other than logos) and removed the weight out of it as well. Have yet to shoot it but I expect nothing but excellent results out of it as well.
 
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I also removed the pinned in weight in the CMMG 9MM BCG.

I’m gonna try that today, thought that doing so would cause all sorts of problems. Given the lower mass did you need to increase the spring to get it to chamber reliably?
 
I’m gonna try that today, thought that doing so would cause all sorts of problems. Given the lower mass did you need to increase the spring to get it to chamber reliably?

Mine has had no problems. But I used the JP SCS short version intended for the Maxim CQB stock because I am running the LWRC Ultra Compact stock kit.
 
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