That's not a machining error, or at least not an accidental one.  CMMG changed the collar spec so new collars look like that on older barrels.  Even worse, using an old collar on a new barrel can result in the ramp snapping off.

It's as if they were bored by things working smoothly for too long.

That's even worse if it's intentional.

After a lot of pressing on the customer service rep, he finally forwarded my photos to engineering.  The response I received afterwards had a dramatic tone change from dismissive/apathetic to urgently needing my upper to be shipped back without any delay.  They also attached photos of what a chamber is supposed to look like:




These photos are what my 22mag looks like and what I expected the 22lr to look like.  I'm thinking now that this was a QC issue and they probably released a significant number of bad barrels and word finally got past customer service and back to the people who should have caught this before shipping.  I hope this is reason enough for them to look through all the remaining barrels they have in stock (look at the bins full in the background!) and remove the bad ones.  If you have a BCA rimfire upper, check your chamber and brass and if that cut goes into the chamber at all, send it back out of caution.  

I'm glad they do not have an unsupported chamber by design, or at least revised it to be supported.

I am glad that they got back with you and also admitted that there is a problem with some barrels. Lemons will slip out now and then, but it is how a company rectifies the issues that matters most.

Yep.  I would have preferred it didn't take 10-12 emails to finally get the photos forwarded to someone who was able to say "oh, crap, not good" and address the issue in a straightforward manner, but I'm pleased I'll be getting a good unit.  I'm sure it'll probably even be inspected before shipping this time!

As an aside, I also have one of the CMMG 0.675" stub barrels, and one collar to fit it, while the rest of my uppers are the 0.700" stab/collar.  I had left that upper at my parent's farm and forgot that the barrel was the short one.  With the BoreBuddy extractor and titanium firing pin, the rounds were being held firmly enough to set them off with 100% reliability and no ruptures, so until I picked up some brass, I didn't notice the headspace issues:



A perfect little 0.025" ring on every fired case.  I think I'll probably sell off that barrel/collar and replace it with one of my spares that have the correct stub/collar length.

This is an opportunity to get a Walther Lothar barrel to go with the short collar.

L-W is out of the rimfire game, unfortunately!  My issue is more that I have a stack of bolts/barrels and a bag of collars of the 0.700" variety and only one collar and barrel of the other, and where that short collar went is anyone's guess.  It's probably mixed in somewhere since it works on the longer barrel stubs (until the feed ramp cracks off, at least).

I wish I hadn't ground down my long collar; I'd have swapped with you.

I have a short collar on the first bolt I purchased from Right to Bear, the barrel ordered at the same time had the long stub. Second bolt I ordered came with the long collar. Probably have 17-1800 rounds thru the short collar no problems yet. Have seen a picture of the ramp sheared on short collar long stub gun.

Just tonight, I realized that my only long collar came from RTB as part of a package with a barrel with a short stub.  Only when responding to RM did I realize that if the barrel that came with the long collar had a long stub, maybe I shouldn't have ground down that long collar.  I get the bolt and collar that came with that barrel and put them together and turns out the original barrel is still a bit short for that collar, a collar I trimmed when I had problems getting it to work with a Lothar Walther short stub.

I'd complain if it didn't work so well.

BCA expressed a replacement to me, and the chamber looks a lot better:

the difference between the 2 pics isn't jumping out at me.  what am I supposed to be seeing?

I kinda wished someone would just come up with an upper that took 10/22 barrels and bolts.

Go to the bottom of page 4 for the "before" pics.