Question....had a thought

[jwrowland77]

I've read and read that when bumping the shoulders on a bottleneck case you should bump them around .002.

Well, I was looking at the headspace gauge put out by Hornady. I got to thinking I wonder if I can use my OAL comparator and and measure about halfway down the shoulder by putting in a larger insert.

Well, I did this and measured halfway down a FL resized case (.308) and it measured 1.663. Then I measured a case fired out of my Rem 700 and it measured 1.665. Total difference was only .002.

Does this mean I have a tight chamber? With the difference being this small, would it make a difference whether I FL resized or neck resized? Is my brass going to be able to last a bit longer since they aren't stretching that much?

Just some thoughts I had today.

 

[Longhorn 76]

After a few times neck sizing only, the cases will get a little hard to chamber.

 

[blarby]

Generally when you fireform- you do it to a specific chamber.

If you use fireformed brass from gun A in gun B, and it moves around again, it kinda defeats all the purpose of measuring and fireforming it to chamber A in the first place.

Fireforming is as much about minute accuracy gains from consistent pressure as it is about case life- and you kinda pitch both out the window when you unform it by putting it in another chamber.


With that said and on to your actual question, machining is all about tolerances.

SAAMI and other governing bodies provide standard dimensions for sporting arms and ammunition machining specifications. Unless you have a heisenberg compensator, and a machinist and machine capable of using it, you are going to have slight variances in any machined product.

Sometimes that difference is held to exacting standards- for example, nosler requires its machinists to be able to hold standards of .000001 of an inch one millionth of an inch! ( as of their last posting for looking for machinists) if you want to be able to wrench on their bullet jacket equipment.

Thats pretty dang precise.

Chamber specifications don't have to be that precise, and every company is different- but .002 of an inch variance is well within standards.

Now you know why factory ammo is so dang small- it has to fit from the tightest end of the tolerances allowed, to the loosest- and everything in between.