Tomorrow I will be shooting my .270-7mm-300WM! Yippe.
So your wandering what I'm up to? I'll tell you. My 7mm-300 WLM is built with a tight neck chamber. I have to turn/machine my case neck to a precision fit to the chamber.
What I had tried was to take a stock 300WM case, anneal it and neck it down to 7mm. This worked, except in the necking down process the necks were no longer concentric to the body of the case. That's BAD for accuracy!
So I was trying to straighten all the neck by hand.. it was SLOW and not perfect. Then when I turned the necks- the neck walls were not perfectly uniform in thickness all the way around- UGH!
It would be nice if I could just fire form them but I can't. The neck diameter in my chamber is .312"
If I load an unturned neck with a bullet I get this: the neck wall thickness on this brass I'm working with is about .0145" thick so:
.0145 neck wall on one side plus
.284 bullet diameter plus
.0145 neck wall on the other side equals
------------------------------------
.313" neck diameter for the loaded round.
So theoretically an unturned laded case will not fit in my chamber- not to mention your supposed to have at least .003" clearance on the neck for safe bullet relief.
So I can't fire form unturned cases. Crap.
Or can I?
The minor bore diameter of a 7mm bore is about .276 -.277.
Hmm... .277 is a familiar number thinks me- oh yeah the good old .270 winchester bullet is actually .277 dia...
So I ran the math:
.0145 x 2 for wall thickness Plus
.277 dia bullet equal
---------------------------
.306 neck dia for a loaded round!
So yep I loaded up all my brass with ultra el-cheapo 270 deer bullets and am headed to the range tomorrow. The .270 will just barely drag the riflings- not even enough to get a great gas seal. But my brass will fire form perfectly- then I can turn the neck perfectly- and make perfect 7mm-300WLM ammo.
And the nearly "slip" fit of the bullet in the bore shouldn't add wear to the barrel.
Fun fun. In all my days I have never shot a "wrong" bullet in a gun. I feel like a mischievous little kid.
So your wandering what I'm up to? I'll tell you. My 7mm-300 WLM is built with a tight neck chamber. I have to turn/machine my case neck to a precision fit to the chamber.
What I had tried was to take a stock 300WM case, anneal it and neck it down to 7mm. This worked, except in the necking down process the necks were no longer concentric to the body of the case. That's BAD for accuracy!
So I was trying to straighten all the neck by hand.. it was SLOW and not perfect. Then when I turned the necks- the neck walls were not perfectly uniform in thickness all the way around- UGH!
It would be nice if I could just fire form them but I can't. The neck diameter in my chamber is .312"
If I load an unturned neck with a bullet I get this: the neck wall thickness on this brass I'm working with is about .0145" thick so:
.0145 neck wall on one side plus
.284 bullet diameter plus
.0145 neck wall on the other side equals
------------------------------------
.313" neck diameter for the loaded round.
So theoretically an unturned laded case will not fit in my chamber- not to mention your supposed to have at least .003" clearance on the neck for safe bullet relief.
So I can't fire form unturned cases. Crap.
Or can I?
The minor bore diameter of a 7mm bore is about .276 -.277.
Hmm... .277 is a familiar number thinks me- oh yeah the good old .270 winchester bullet is actually .277 dia...
So I ran the math:
.0145 x 2 for wall thickness Plus
.277 dia bullet equal
---------------------------
.306 neck dia for a loaded round!
So yep I loaded up all my brass with ultra el-cheapo 270 deer bullets and am headed to the range tomorrow. The .270 will just barely drag the riflings- not even enough to get a great gas seal. But my brass will fire form perfectly- then I can turn the neck perfectly- and make perfect 7mm-300WLM ammo.
And the nearly "slip" fit of the bullet in the bore shouldn't add wear to the barrel.
Fun fun. In all my days I have never shot a "wrong" bullet in a gun. I feel like a mischievous little kid.