9mm CMMG OAL

[RickT]

I have my CMMG running 100% on all loads, but I think I'm going to have to ream the barrel throat (have a 'smith do same).  Had been running Bayou 115gr at 1.105", but their new profile which is shorter and stubbier will probably need 1.075" or so.  The shorter rounds feed and 2.8gr of SP barrel dents the space, but I've never had to load this short before.  Bayou says the new profile is more accurate and I have no reason to doubt, but I'm shooting SC.  Anyone else experienced this with the CMMG barrels?

[Salsantini]

I'm using the Bayou 124 gr.  I had them at 1.145.  Too long for my chamber.  I backed them down to 1.125 and it seems to have solved the issue

[mrd]

I haven't tried your bullets but I have the CMMG and it needs the shortest OAL of my 9x19's. It's ridicolous. After all the sloppy QC in my CMMG rifle I will hesitate to buy again.

 

I tried a Clymer reamer but that did nothing to the throat, only wore on the reamer. Barrel is nitrided, tell the gunsmith about it before so he's prepared. He'll probably need a carbide reamer.

[RickT]

I've got a couple of things going on I believe.  The CMMG OAL is, for example, reduced from what I can run in my 9mm 1911, but it may also be that I've got some cases that spring back (CBC comes to mind) that may be created out of spec rounds.  I had this happen in spades with these cases and 147gr FP bullets and even the 115gr need to be seated pretty deep.

[Halo09]

I’m running the  CMMG Rotary bolt with their barrel, bolt, and lower, all paired into a Gibbz upper.  I’ve put a lot of federal 130 PCC ammo through it with no issues.  I’m not 100% sure what their OAL length is, but it is a saami spec round so I don’t think they are loaded long.  

[RickT]

On 4/22/2020 at 12:02 PM, Salsantini said:

I'm using the Bayou 124 gr.  I had them at 1.145.  Too long for my chamber.  I backed them down to 1.125 and it seems to have solved the issue

I found this bullet could usually be loaded to a greater OAL.  I'm loading my CMMG with the new 115gr Bayou bullets to 1.08".  In the end it really doesn't matter as long as the gun feeds well and using just a dash (2.8 - 2.9 gr SP) I'm hardly compressing the powder.  The Redding micrometer seater is so repeatable that OAL changes are really ho-hum.

Edited April 25, 2020 by RickT