Brass Growing Too Much?

[Mikemci]

6mm Remington AI brass growing .006" - .008" with each firing.
This seems excessive, what could be the causing this?

 

[gunsandgunsmithing]

6mm Remington AI brass growing .006" - .008" with each firing.
This seems excessive, what could be the causing this?

If you're referring to the trim length growing, that's typically due to the die sqeezing the diameter down too much. You either need a smaller chamber or a bigger die.

If you're referring to the shoulder being blown out that much between sizing and firing, that's in the die adjustment, as in bumping the shoulder too far. It can be a combination of both, too.

The more you move the brass, the more it will flow and the life of the brass is reduced.

 

[Mikemci]

I'm referring to trim length.
The die is a custom die, made from 3x fired brass (Whidden).

 

[M-61]

Have you been bumping the shoulder?

 

[Mikemci]

Yes, I have been bumping the shoulder .001"

 

[DiffEQ]

What brand?

 

[Mikemci]

Norma Brass.

 

[whatsupdoc]

OK, how are you setting up the resizing die?
Are you measuring the shoulder ? If so how?

You need to supply details. How do you expect people to help without information?

 

[M-61]

Yes, I have been bumping the shoulder.

Bumping was required (bolt stiff or not closing)?
Bumping the shoulder ( MY OPINION) is not part of sizing brass. When hard to close bolt occurs then the shoulder may need 'bumping' back. In doing so that brass you move has to do somewhere. It is done to correct a fault so to speak.
I might suggest NOT bumping, resize and reload as you do, and see what is happening to the OAL of the brass.
I don't reload your particular cartridge but I have some 222's and 30BR's that have upwards of 20 + reloads on them and I have never "HAD" to bump. I do not consider it a normal step in reloading as I said. Done out of necessity. I really try to work the brass as little as possible. This technique has not effected accuracy at all. In a rifle used for hunting I would cycle each round through the rifle to ensure all is OK.
The above is strictly my opinion and I can shoot in the 2's and when all is great, in the 1's
But then again, I only de-burr a flash hole once when the brass is new, never change the angle on the flash hole, and Never change its diameter, and I only chamfer the neck after the case needed trimming. Maybe different than some folks but it works for me in my rifles.

 

[Doom]

To be clear, you are referring to trim length growing by .006” after resizing from one firing to the next?

 

[Mikemci]

To be clear, you are referring to trim length growing by .006” after resizing from one firing to the next?

Exactly.

 

[Metal God]

As you describe everything , there is no way your brass should need .006 to .008 trim . This leads me to conclude , you think you are doing what you say but you are not or your die is not properly cut for your chamber .

I don't need to trim that much off my AR brass and I bump those shoulders .003 and several have nato spec chambers . No , there is something not accurate in the way you think you are sizing your cases . I thought I knew for sure what the issue was until you said custom die . One thing that comes to mind is that the three cases you sent in were not actually fully fireformed to your chamber . Resulting in a tighter cut die which in turn results in a smaller sized case . Any chance the cases you sent in were only fired once using a pretty light load ?

 

[Mikemci]

As you describe everything there is no way your brass should need .006 to .008 trim . This leads me to conclude either you think you are doing what you say but are not or your die is not properly cut for your chamber .

I don't need to trim that much off my AR brass and I bump those shoulders .003 and several have nato spec chambers . No there is something not accurate in the way you think you are sizing your cases . I thought I knew for sure what the issue was until you said custom die . One thing that comes to mind is the three cases you sent in were not actually fully fireformed to your chamber resulting in a tighter cut die which in turn results in a smaller sized case . Any chance the cases you sent in were only fired once using a pretty light load ?

I agree with you.
This is actually an issue that my Brother in law is experiencing. He is shooting these in a Blauser and he has 2 barrels, chambered in the same caliber. He thought that he could swap barrels and shoot the same, resized brass interchangeably. I think that he is not keeping his brass segregated.
I just wanted to see if there may be other causes, that I had not considered.

 

[Mikemci]

Thank you all for your helpful responses.
Looks to be operator error.

 

[gunsandgunsmithing]

You can answer you own question by seeing "when" the growth is occurring. Measure your fired brass, then measure the bump and the oal on sized brass. Fire it and measure again. When did the stretch occur? I'm betting it happens after sizing...custom or not. If you want to get a little more in depth, I look for no more(between firing and sizing) than about .0015- .002 smaller sized at the shoulder/body junction and about .0006-.0007 smaller sized at the web/.200 line....preferably a tad less. If the die is yielding more than this, it's sizing too much and that brass is flowing forward during sizing it. By far, this comes from the sizing operation most often. This being an AI chamber makes it even more likely because the straight wall and sharp shoulder tend to not flow upon firing as much as most cases. Really excessive pressure can do it in the chamber but you're way up there if it's not in the sizing op.