Anybody running a CMMG RDB Radial Delayed Blowback 9mm?

[sigstroker]

Regular straight blow back is on sale direct from CMMG for $142.46.
https://cmmg.com/lower-receiver-sub-assm-mk9-smg

Good price.

[beanz2]

Regular straight blow back is on sale direct from CMMG for $142.46.
https://cmmg.com/lower-receiver-sub-assm-mk9-smg

Add $80 for the RDB parts kit:
Colt mags: https://cmmg.com/parts-kit-mk9-9mm-r...metalform-mags
ASC/ C-products mags: https://cmmg.com/parts-kit-mk9-9mm-r...k-asc-cpd-mags

It seems that the link is for back ordering either version.

I had no idea Colt magazines are different from ASC / C product magazines!

[ar15barrels]

NO.

They have completely different barrels and bolt groups.

Traditional blowback has the breechface 1/8" outside of the barrel where the bolt stops against the rear face of the barrel.
There is no separate bolt and carrier in a traditional colt blowback setup.
The bolt and carrier are all one piece.

Radial Delayed Blowback uses a rotary locking bolt sliding/rotating in a bolt carrier that engages locking lugs inside the barrel extension and the beech face is 3/8" inside the barrel.
The bolt lugs lock into the barrel.
The carrier rests against the back of the barrel extension.
This lockup of the bolt is what "delays" the unlocking.
Hence the "radial delayed" in "radial delayed blowback".
The spring between the bolt and carrier as well as recoil impulse of the gun causes the carrier to move rearward a little which ends the "delay" from the bolt lugs being locked into the bolt lugs. Once the bolt lugs unlock from the extension, then the pressure in the barrel can then "blow" the bolt group the rest of the way back until the buffer and spring returns it forward again.

A traditional blowback has NO locking feature of any sort other than the mass of the bolt/buffer trying to sit still.
In traditional blowback, the pressure in the barrel pushes the case out the back of the barrel which makes the bolt and buffer move to the rear until the energy is used up and the spring is so compressed that the spring pushes the buffer and bolt back forwards.

[ar15barrels]

I had no idea Colt magazines are different from ASC / C product magazines!

Colt mags seem to have better followers and springs that better actuate the bolt catch.

[ysr_racer]

Ain't this a pickle.

The Lead Star upper is RDB compliant, but not the lower. However the Juggernaut lower is RDB compliant, but not the upper

CMMG for the win.
.

[beanz2]

Well, we just don't know if the supplied buffer and spring have very specific weights or rates to "fine tune" the gun to the RDB BCG. Unfortunately when I got mine, I threw them in a box with a bunch of AR15 buffers and springs without labeling them as I'm using something else. Wish I had taken the time to look at them closely.

[ysr_racer]

My buddy runs a buffer with the weights removed in his RDB. Says it runs great.

[verdigris]

The bolt for the CMMG also comes with 3 different weights to add to the bolt to fine tune it at well. They are added in the back of the bolt carrier.

[ysr_racer]

The bolt for the CMMG also comes with 3 different weights to add to the bolt to fine tune it at well. They are added in the back of the bolt carrier.

Mine didn't, just barrel and bolt/bolt carrier.

[verdigris]

Mine didn't, just barrel and bolt/bolt carrier.

Ill take some pictures of mine when I get back home tomorrow and post.

[ysr_racer]

This is what I ordered, and what I got. I don't quite get adding weight, don't you want the lightest bolt carrier group you can get?

My buddy runs a 1oz buffer, and it's really soft.

[verdigris]

I just pulled this off the website. I run the 5 inch barrel vs a 16 inch so added 11 inches probably softens it up as well. Don’t know how to post without attachments but here are a couple screenshots below. Mine came with it didn’t pay extra maybe it’s just a separate item now.

[ysr_racer]

Interesting, mine didn't come with that.

[sigstroker]

Did you order the El Cheapo version?

[ysr_racer]

Ok the difference between an AR9 RDB lower and an AR9 blow back lower is twofold.

You need to remove the ejector on the AR9 blow back lower, and the mag needs to sit .020-.030 lower in the RDB lower.

Easy enough to do, just take .020 of the top of the mag catch. But since some AR9 blow back lowers use the ejector as a mag stop, you need something to keep the mag from dragging on the RDB Bolt.

The CMMG lower has a built in stop, as does the Juggernaut.