CMMG BHOA and BDM Magazines

[brassburnz]

After reading their literature and watching their youtube video, I purchased two Bolt Hold Open Actuators from CMMG. I have both the old and the newer X-form BDM mags with replaceable feed lips. I have one X-form mag with the steel feed lips and the others have plastic feed lips.

After several hours of trying to get the BHOA's to work, I gave up. I did manage to get the BHOA to work manually, so I can at least lock the bolt open without a mag inserted. This is with a Rock River Arms lower, a RRA flat-top upper, CMMG M4 profile dedicated .22 barrel and a chrome CMMG bolt. Only the BDM X-form mag with the nylon feed lips will fully seat in the mag well with normal pressure. All the mags will seat normally without the BHOA in place, but with the BHOA inserted, the older mags and the X-form with the steel feed lips won't seat.

The BHOA will not fit in my other dedicated .22. It is a pre-ban Palmetto Armory billet lower made by SGW which is now Olympic Arms. This lower will not accept the older BDM mags. The upper I purchased from UXO2 and I'm not sure of the make, but it has a CMMG parkerized bolt.

I found UXO2's post regarding the Catch22 unit. I ordered some S&W 15-22 mags the other day. If they fit in the second lower, I'll take a serious look at this solution.

http://www.arcatch22.com/

I also need to get my hands on a CMMG mag to see if it will work. Now I know why I'm seeing the CMMG BHOA sold on Amazon for less than suggested retail.

[uxo2]

I gaved up on mine.

BlackDog mags are the standard.

as for the catch22..I love.
The lower I have it on is strictly a .22
Works great with 15/22 mags

[nrakid88]

I really want the BHOA... I wonder if the CMMG mags are any good. Ive only ever tried BDM

[brassburnz]

I gaved up on mine.
BlackDog mags are the standard.
as for the catch22..I love.
The lower I have it on is strictly a .22
Works great with 15/22 mags

The CMMG unit should not be advertised as something that just drops in. It needs to be fitted to the lower and the upper.

I can see why the CMMG BHOA doesn't work in my lower, but I don't want to take the time to fix it right now. I need to take a considerable amount of metal off of the BHOA to get it to fit properly and it will probably only work with that particular upper and lower.

The Catch22 may be my only solution right now.

[thatsteveguy]

I gaved up on mine.

BlackDog mags are the standard.

I had the same experience and decision too.

[uxo2]

The CMMG unit should not be advertised as something that just drops in. It needs to be fitted to the lower and the upper.

I can see why the CMMG BHOA doesn't work in my lower, but I don't want to take the time to fix it right now. I need to take a considerable amount of metal off of the BHOA to get it to fit properly and it will probably only work with that particular upper and lower.

The Catch22 may be my only solution right now.

Couple of things..

Redi mag makes a adapter with BHO
but it only works with 15/22 mags and you cant
use BD mags.
It is also readly removable.

Catch22
Is pinned on.
It works as a LRBHO with 15/22 mags
or simply as a BHO with BD mags.
Benefit..Both mags can be used.
Bolt is locked back for RM inspection.

I have 2 catch22's and very happy with them
becuase I can use my preban cieners
or use 10rnd S&Ws.

Or when I visit family in AZ I can run hicap
15/22s or run my BDs back to back.

[shadow65]

Go with the Redi Mag and S & W mags. Best option for bolt lock back.

CMMG dropped the ball again with the BHOA and Gen ll mags.
I did have some success with them but it takes a lot of tweaking and is not reliable, just like the mags.

The Gen l CMMG worked great but would wear out the feed lips after 8k.

Dave N

[SOAR79]

I thought that the bold hold open feature only worked with their EVO mags? I could never find them in stick so I have no experience with them

[shadow65]

BHOA worked with the Gen ll grey mags and the Evolution mags, or was supposed to.
Dave N

[brassburnz]

When this project started, I was just looking for a way to lock the bolt open using the standard bolt-catch. During cease fires at the range, I don't like placing an empty .223 case in the action to show clear. Also, mags don't drop free because the bolt puts pressure on the follower.

Ideally, I'd like to have my dedicated .22 rimfire AR operate like a centerfire AR in every respect except the round being fired. I thought I could accomplish this with the CMMG BHOA, but it's not working out that way for me. I may just go ahead and fix this thing just because of the challenge.

[shadow65]

If you just want the ability to manually lock the bolt back, which is what I use the bhoa for, it's not difficult. Unless the spec is way out of tolerance by now (which is very possible with CMMG) minor to no fitting is needed.
The rule of thumb is the frame should not hang in the upper receiver when installed and the upper and lower are opened up.
I adjust the set screw in the bhoa, while moving the bolt back and forth, until the bolt rubs and starts to hang on the bhoa. Then back of 1/2 turn.

The trick to bhoa operation with the bhoa mags is the bolt catch spring. I clip a couple coils off mine. CMMG also started providing a reduced power BC spring with the BHOA.
The mag spring has to overcome the pressure of the BC spring.
Dave N

[brassburnz]

With the upper I'm working with, the BHOA won't fit in the upper. When installed, the BHOA won't let the upper and lower close enough to engage the rear takedown pin. Consequently, the BHOA protrudes into the lower just enough so a magazine won't seat far enough to engage the mag catch. If I force the magazine into the magwell, it will catch, but then it's a bear to remove.

I purchased two BHOA's, and both will work in another dedicated .22 AR, but not the other. I ordered a Catch22 and some mag adapters for the S&W 15-22 yesterday so hopefully that will solve the problem.

I have an M261 .22 conversion and another CMMG conversion I run with a 5.56 upper. I'll have to see if the CMMG BHOA works with that rifle. I have about 10 more days of vacation time, then it's back to work and all these little projects will have to just sit in the garage for a few months.

[uxo2]

.

I ordered a Catch22 and some mag adapters for the S&W 15-22 yesterday so hopefully that will solve the problem.

I have an M261 .22 conversion and another CMMG conversion I run with a 5.56 upper. .

Just give up and sell the thing. ""CMMG conversion""

As for you decision to buy the catch22.
You will not regret it.

15/22 mags or your Blackdog mags

2 different mags in one gun.

[NorCalDustin]

Go with the Redi Mag and S & W mags. Best option for bolt lock back.

CMMG dropped the ball again with the BHOA and Gen ll mags.
I did have some success with them but it takes a lot of tweaking and is not reliable, just like the mags.

The Gen l CMMG worked great but would wear out the feed lips after 8k.

Dave N

yeah... the BHOA takes about 30 minutes to properly fit where it will work 99% of the time... I've actually started doing it for guys when i go to my local range. I've probably fitted at least 50 at this point. CMMG acts like minor fitting is required... its more than minor.

As for the Gen1 mags, the 10rnd mags were horse **** because they had an area that the channel would wear out in within 300 rounds and the follower would get stuck.

I do like the Gen2 mags (the new ones)... Meh.

[brassburnz]

Just give up and sell the thing. ""CMMG conversion""

As for you decision to buy the catch22.
You will not regret it.

15/22 mags or your Blackdog mags

2 different mags in one gun.

When the Catch22, mag adapters, and 15/22 mags arrive, I probably will just give up on the CMMG BHOA and move on to a different project.

I have two Thompson Center Contenders that need a little tweaking to get everything running right. I have a Super 14 in .223 and a 10 inch bull barrel in .22 rimfire I plan on shooting a little more.