Thread: Trim length

While reading up on the dreaded carbon ring. I came across an article sighting that some of the problem is caused by the gap between the end of the case neck and start of the lead. This person's idea was that the bigger the gap, the greater the area for carbon to settle and form a ring. Obviously he recommended that measuring this gap and reducing it would help to stop the carbon ring from starting.
His theory was to make a brass plug that fitted into a 100thou shortened and sized case, with a portion slightly wider than the case mouth outside diameter by a 1-2 thou. The rest the same size as the internal case mouth. Load the round and close the bolt. Thus pushing the tight fitting plug back into the case when it contacts the end of the chamber. His suggestion after measuring this length , was to trim by 2thou and that would be ideal for that chamber.
With thought I see at least one problem with this method.
1st you need to make sure your measurements are accurate and are measuring to the right place.
2nd if you shoulder bump by 3thou and your neck has only 2thou clearance. Then you're in for problems. I would have thought his recommendation was -2 + shoulder bump. So -2+-3=-5.
My question is. Is having only 2 or 3 thou from neck to end of chamber going to cause pressure or other problems? As an example by doing this, my necks on one rifle can grow another potentially 20thou past maximum length.
Is it actually going to help stop carbon rings? Or potentially cause more problems than it solves. I've never heard of this method before.
I will say I did have a wet day, small piece of brass, and was looking for an excuse to play on the lathe to fill in time instead of housework.

Sent from my SM-A145F using Tapatalk

I can, and do, check that gap between the end of the neck and where the leade starts with my borescope. I chamber an empty case, close the bolt then insert the borescope down the muzzle. Easy to see ths gap. Only thing is I can't measure it but it does let me see when I need to trim a batch of cases.

Couldn't you just measure a tight one, the trim say 0.005" and check if the bolt closes, repeat etc

That sounds like a lot of work. Are you having issues, or have you had issues with carbon rings?

You know you can clean a carbon ring out if it becomes problematic.

The SAMMI and CIP specs are based on a couple of hundred years of research and experience but some poeple persist on trying to put their own personal stamp on things. What you are trying is a bit like filling your car sump up with vegetable oil because really, the manufacturers don't know much . . .