7mm Rem Mag. Inside neck diameter?

isanchez2008 · July 13, 2010, 10:58 PM

Heres the story. I have recently started loading for a 7mm Rem. Mag. I prepped my cases just like any other rifle case. The issue I'm having is that when I seat my bullets they are being "shaved" of their outside diameter. My brass has been chamferred plenty and when being seated the bullets are lined up VERY straight. I am not getting the half circle slice of copper that can happen from a sharp case mouth against a bullet that is not lined up properly. I measured the inside neck size on my sized cases and it comes back at 0.279". Anyone know if this is normal? Did I maybe get a defective die or am I missing something?

Kawabuggy · July 14, 2010, 12:14 PM

That's a .005" difference between bullet O/D & your I/D on the case neck. I'd say that is a bit excessive. Try a different die. I've heard that .003" is about right for I/D of the case neck before seating the bullet and that would put you at .281.. You'd think that the extra .002" would not make a difference but I bet if you try another die your problem will be solved.

wncchester · July 14, 2010, 01:11 PM

7mm = .284"

The determining factor isn't the die, it's the expander ball. Mike your's. If it's smaller than .281" or .282" you need another expander.

I'd suggest getting a Lyman "M" expander die. It's a single purpose die that has a dual diameter expanding plug which, when properly used, insures no damage to bullet heels during seating.

An ideal neck size for both the best bullet grip and straightest seated bullets is .001" less than bullet diameter but few loaders are comfortable with that so .002-3" less is normal.

isanchez2008 · July 14, 2010, 09:17 PM

Thank you very much. When I get home from work I will measure the expander. It's a brand new die so it should be easy to get midway to take it back.

July 13, 2010, 10:58 PM	#1
isanchez2008 Senior Member Join Date: October 13, 2008 Location: WA Posts: 344	7mm Rem Mag. Inside neck diameter? Heres the story. I have recently started loading for a 7mm Rem. Mag. I prepped my cases just like any other rifle case. The issue I'm having is that when I seat my bullets they are being "shaved" of their outside diameter. My brass has been chamferred plenty and when being seated the bullets are lined up VERY straight. I am not getting the half circle slice of copper that can happen from a sharp case mouth against a bullet that is not lined up properly. I measured the inside neck size on my sized cases and it comes back at 0.279". Anyone know if this is normal? Did I maybe get a defective die or am I missing something?

July 14, 2010, 12:14 PM	#2
Kawabuggy Senior Member Join Date: April 25, 2008 Posts: 224	That's a .005" difference between bullet O/D & your I/D on the case neck. I'd say that is a bit excessive. Try a different die. I've heard that .003" is about right for I/D of the case neck before seating the bullet and that would put you at .281.. You'd think that the extra .002" would not make a difference but I bet if you try another die your problem will be solved.

July 14, 2010, 01:11 PM	#3
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	7mm = .284" The determining factor isn't the die, it's the expander ball. Mike your's. If it's smaller than .281" or .282" you need another expander. I'd suggest getting a Lyman "M" expander die. It's a single purpose die that has a dual diameter expanding plug which, when properly used, insures no damage to bullet heels during seating. An ideal neck size for both the best bullet grip and straightest seated bullets is .001" less than bullet diameter but few loaders are comfortable with that so .002-3" less is normal.

July 14, 2010, 09:17 PM	#4
isanchez2008 Senior Member Join Date: October 13, 2008 Location: WA Posts: 344	Thank you very much. When I get home from work I will measure the expander. It's a brand new die so it should be easy to get midway to take it back.