I had a CMMG stainless rimfire kit and just acquired a new Echo 2 that runs with an M16 bolt.  I had asked about this before and it seemed nobody had tried this before.

I bought the auto sear trip kit and weight from CMMG and went to the range for some disappointment.  I knew it would have issues, because dry fire testing was also failing.

Fostech sells the CMMG kit, so one would assume it works.  I looked closely at the photo on the Fostech website and see it comes with a different coil spring for the trigger lock assembly.  I emailed Fostech and they said they also grind the tabs off the CMMG sear trip bar.  Their photo shows these things:



I am awaiting their response to acquire the spring.  Their mail message alluded to other things possibly needing work to get the rimfire kit running.  I will keep the thread updated as I progress with this project.  Please post your experiences with this if you have been down this road.

I am adding a photo of the trigger too:



Rifle is an Armalite M15 and has a Spikes ST-T2 buffer and standard spring. (edit to add that this isn't relevant.)

This photo from Fostech shows two springs...................

I have a 22LR CMMG Banshee upper that I run with a Fostech Echo.

Before I bought the auto sear trip and anti bounce kit from CMMG I emailed them and told them what I was planning on doing. Their service department said that I would need to buy the kit from Fostech, so I did. The kit from Fostech does come with the tabs ground down and have an extra spring. The extra spring is provided in case the one that they cut to size is giving issues. I did not have to use the extra spring.

I have no issues with the Fostech trigger on my 22LR build but I have found the extra kit to be a PITA. I’ve purchased a Franklin Armory BFSIII and it should be here today. I’m going to use that trigger on my 22LR and use the Echo strictly for centerfire.

I just got an email and had a phone conversation with Fostech.  An extra power spring is sometimes needed for the actual CMMG kit.  They also send one modified trigger lock reset spring and one stock spring.  If the mod spring doesn't work, you use the stock type and just cut a coil until it works.

The three springs with shipping were $14, because I already had my CMMG kit prior to buying the Echo triggers.

They also said that sometimes it works better without the anti-bounce weight.

When they arrive, I will update this thread.

I tried mine tonight and can't get the damn thing to run proper. In echo I'll get the first pair of shots but then the trigger is rock solid, sometimes if I beat on the forward assist I can get 2 more shots otherwise I have to charge it. This is with the Fostech shortened spring. The BFS 3 works great in my buddies spikes tactical .22 but I wanted to avoid the hammer follow issue. So now I have a bunch of money invested in this crap

I have the springs and installed the heavier action spring in the CMMG kit.  I also filed off the tabs on the auto thingy.  The gun function dry-fires fine now, which it didn't before.  I will try to get to the range before the end of the week for testing.

I'm looking forward to your report!

Just back from the range.  This one seems to be so close to working.  I had the extra power spring in the CMMG kit and started with the stock spring in the part they call the trigger lock.  It was not going fully into battery most times, but did work a few times.  I tried one of the trigger lock springs that Fostech sent me, but neither of the two looked any different than the stock spring.  Results were the same. eta: (I looked at the Fostech photo again and it clearly shows two different springs for the trigger lock.  Something is fucky with the springs I got. I sent Fostech another email)

I am thinking that if I cut a coil or two off the trigger lock spring, this may run just fine.  I didn't have a cutter with me and I was sweating balls.  It is also, probably time that I run a scrubber in my CMMG chamber.  As touched upon by another poster, I could hit the forward assist and kick it into battery and it would fire. So damn close...........

The indoor range swamp coolers are the low buck variety and it was approaching 106 outside, so the temp differential sucked ass with additional ass sweat humidity.

I was using CCI Mini Mags and Aguila Super Extra copper bullets during this evolution.

The bottom line is that I think you can probably shoot a SD3G trigger as fast, or faster than this kit with an echo.  I may change my mind if I get it running, but that is what I am thinking here.  Maybe just stick to the 5.56 with the Echo as designed.  Fostech selling CMMG kits may be false hope...............

After an email from Fostech, I cut about 3 coils off the trigger lock spring.  I ran 8 mags through the gun with several 10 round strings that ran well.  I think another coil or two may do it.  I didn't want to fiddle with the spring at the range and risk launching it.  I will give it another try soon.  I think I may be close.....

I am damn glad I bought that mag loader.

eta:  This project is now on hold because this Echo is now in my CNC .45 lower for testing.  When I get that Echo back from repair, I will resume this effort.

Fostech received the trigger Friday 8/17.  A tech/engineer just called me a few minutes ago (9/20) and a replacement trigger is being shipped today. 

I am going to use one of my lowest buck builds for the next testing.  It has a crappy milspec trigger in it now.  I expect this trigger will live in that build for quite some time.  I will run it with .223 first and then try rimfire again. 

I run the BFSlll in mine with a Taccom .22 BCG and a CMMG.
Never had to run an anti bounce kit, change springs or any modifications.
I wonder why the Fostech is so much harder to run.

Dave N

I ordered the CMMG kit from Fostech and it works fine. I didn't even change the spring. The do sell a charging handle that is supposed to eliminate some feeding problems. My conversion kit even works when your messing around with it out of the gun and its in your hand. I have a hole in my ceiling to prove it.

Fostech replaced my trigger and did so very quickly.  I just ran it at the range with .223 today in a different rifle, a 16" M4 A2 type clone.  Ran great.  I will try it with rimfire soon.

This one is a bit different.  I have to have the safety in the echo position with the hammer forward when I push the trigger lock forward in order to hinge the gun closed and push in the rear pin.

My county range masters had a problem with me firing binary today.  They say no full auto and no binary, yet it isn't in the rules anywhere. Rules are posted on a sign board and they make all shooters read them before shooting.  I even checked on the way out to make sure they didn't add an extra line on the rule board. It is like the unwritten rules list or something.  I called the parks/rec director, but had to leave a message.  It tends to be difficult to follow unwritten rules.  It is like playing Calvin ball.

I guess they haven't noticed it before when I was shooting suppressed or pistol caliber stuff in the binary mode.

Popped in a BFS3 in my 15-22 and have had no issues with it.

Finally finished this project.  Been busy.  I cut somewhere between 4-6 coils from the trigger lock coil spring.  I was using my new warranty replacement trigger tested with 5.56 already.  I put in the CMMG kit and put a quarter between the buffer and the kit.

7 mags burned through like a raped ape on crack.  I was in and out of the range very quickly.  I sure am glad I bought that squeezy mag loader.

I was running Aguilla Super Extra Velocity 40 grain plated ammo.

I function tested it with the stock trigger lock spring before I made any changes.  The bolt would not go into battery at all unless I used the forward assist.

Even with the stiffer action spring on the CMMG kit, the bolt doesn't have enough mass to overcome the trigger lock spring.  This is the device that prevents hammer follow, which the Franklin doesn't have.  After reducing the spring length/coil count on the lock spring, the bolt was cycling manually, and then ran perfectly at the range.

Now that my County range doesn't allow binary triggers, being able to use a PCR or a rimfire kit at the indoor range is a good thing.  I will just tuck the unmodified lock springs into my grip storage compartment for an outdoor non-managed range situation.