CMMG FTE

[Tom Freeman]

On 5/12/2020 at 5:02 AM, RickT said:

My upper is a complete CMMG unit so there should be no question of headspace (which frequently gets raised in the context of ejection issues).  FWIW I've had some spectacular fails with two Gen2 CMMG-branded mags.  Haven't seen this with the Endomags using Gen 3. (That picture wasn't staged!  That's what they looked liked after the stoppage.  Can't imagine how that happened)

 

I always insert a full mag with an open bolt and the next round definitely gets beat up by the bolt passing over it including scratching through the coating on that round.  Some folks have smoothed out the lower lugs a bit, but I don't think this behavior is necessarily relevant to the ejection issues.

 

 

 

If your reloading, be sure you seat your ammo a little on the short side to be 100% sure they are not dragging on the inside of the EndoMag insert.  I had the same problem and seating 5 thou deeper fixed it.

[RickT]

11 minutes ago, Tom Freeman said:

 

 

If your reloading, be sure you seat your ammo a little on the short side to be 100% sure they are not dragging on the inside of the EndoMag insert.  I had the same problem and seating 5 thou deeper fixed it.

I'm down to 1.08".

[RickT]

The take of the CMMG runs full circle.  Despite my not having made any changes since I first received a bolt parts kit from CMMG (installed ejector spring and extractor/sring in the original bolt) and despite my have test with factory ammo every combination of bolt/upper/lower in my possession I ran >200 rounds through the gun in practice without a failure of any sort.  This included reloads ranging from 3.6 to 3.2 grains of SP behind 115gr Bayou bullets.  I'm baffled, but please despite the mystery.  I did an ejector spring replacement more recently, but both bolts had been test following that replacement.  I'll be shooting between 200 and 400 rounds/week so we'll see how it goes.

[MoRivera]

Barometric pressure, maybe.  

[Tom Freeman]

On 5/13/2020 at 4:53 PM, RickT said:

I'm down to 1.08".

 

Crap.  That rules that out.

[RickT]

11 hours ago, MoRivera said:

Barometric pressure, maybe.  

I'll take success wherever I can find it.  It's unfortunate that I lost track of the identities of the two new bolts, but I suspect the successful tests and practice session involved the bolt that was found to have the shortened ejector spring which I replaced.  Match today so we'll see how an additional 100 rounds works.  I'll generally shoot the rifle 250+ rounds/week so I'll have plenty of opportunity to see how this goodness holds up.

[RickT]

My #1 upper continues to run flawlessly.  I'm waiting for a replacement bolt for #2 and in the interim I've been experimenting with a bolt I had on hand.  With the Mk10 ejector spring and a BCM extractor spring I get strong ejection, but the case hangs up every 10-15 rounds.  It appears the BCM spring with helper plug may be hanging onto the case too long.  I'll try taking out the helper plug and see what happens.  Also will try a standard ar-15 extractor spring which is what CMMG recommends.

[MoRivera]

So an update....

 

I was getting a bunch of FTE's and hangups, ejector seems pretty strong but took out the extractor and this is how the spring looked....an extra-strength Sprinco unit tat I put in there a while back.  Sorry the the camera phone pics are blurry but I think they still show....

 

 

Spring is kinked/compressed.  I don't know how many rounds but would estimate around 1700-1900.  This was part of a 3-pack of extra-power springs that came with both the center plug and o-ring from Springco.  Also emailed CMMG if to ask if they could send factory recommended replacements, but for now (as I have a few shoots coming up), I'm wondering if I should run one with the o-ring since I ran it with just the spring before.  What do y'all think?

 

 

ETA: I just put the spring in without the o-ring.  But man, there's essentially no movement on the extractor when I get the pin back in, like the spring is compressed all the way.  Wondering if I should clip a coil.  I also installed with the 'fat' side on the bolt so it wouldn't bind in the 'keeper' hole on the extractor.

Edited November 22, 2021 by MoRivera