300 win mag headspace?

[uncleduke]

I'm new to shooting belted mags and was curious how much the shoulder will move forward normally. I've been reloading for rimless cartridges for many years and have never seen the headspace this far forward. After comparing a fired round to an out of box round I'm seeing .0150 in growth. I know the belted mags headspace off the belt but this seems exessive. Any opinions are appreciated.

 

[bozo699]

I'm new to shooting belted mags and was curious how much the shoulder will move forward normally. I've been reloading for rimless cartridges for many years and have never seen the headspace this far forward. After comparing a fired round to an out of box round I'm seeing .0150 in growth. I know the belted mags headspace off the belt but this seems exessive. Any opinions are appreciated.

UncleD,
I don't know if I have ever measured before and after cases for the .300wm doesn't matter though, after you fireform to your chamber set your die up to give whatever shoulder bump you feel necessary as you will be headspacing off the shoulder now, I set the shoulder back about .001-.0015 on both of my .300wm's I have had zero problems best of luck to you.
Wayne.

 

[X Ring Accuracy]

What wayne said he beat me to it.

 

[Robert]

I'm new to shooting belted mags and was curious how much the shoulder will move forward normally. I've been reloading for rimless cartridges for many years and have never seen the headspace this far forward. After comparing a fired round to an out of box round I'm seeing .0150 in growth. I know the belted mags headspace off the belt but this seems exessive. Any opinions are appreciated.

Uncleduke,
I think it would be important to make sure first the chamber is correctly headspaced?
R.G.C

 

[jscandale]

Its not really that critical how much the shoulder is blown forward if you plan on using the same brass for that rifle all the time and set up your die accordingly, however the shoulder dimension is a set distance from the belt which leads me to believe that there is excessive head space. I would pick up a set of headspace gages and check it out. I would bet that you will be suprised. You can use headspace gages for any of the belted magnums bases off of the Holland and Holland design (.300, .375...).

JS

 

[lloydx2]

When fireforming belted mags Especially when chamber is long (bolt face to shoulder datum) its best to start with new brass and load into the lands. Faster and more even blow lenght. With long chamber it may take several fireing to get there. And what happens is case tends to headspace off belt. you dont want this. Bolt may become hard to close and your not out to shoulder yet. .015 is long. But its doable. More room for powder. Sorry I have edited this post. The terminology was wrong in the original posting.

 

[fullersson]

If you have excessive headspace the round shouldn't fire unless you're jamming the lands with your bullet or if your rifle has a control feed head. If I were concerned about it I would get a smith to check the headspace. Brian Brown.

 

[memilanuk]

I recently got a new .300WM chambered up... my first belted magnum. The work was done by a quality gunsmith, barrel was headspaced using commercial Forster gauges. Even so, virgin Winchester brass is blowing out 0.015" (give or take a bit) on the first firing. As one person I talked to called it: .300 Win Mag Improved!

I know from long experience that Winchester .308 brass is grossly undersized in about every possible way; looks like their .300WM brass is as well.

 

[Rustystud]

Monte:

Remember uncle SAAMI. The have to fit everybodys gun. Easier to put one -.0015 smaller than one +.0015 larger. Not .015

Every belted case headspaces off the belt. Dies should be set for just bumping the fire formed case.

Nat Lambeth

 

[bozo699]

Monte:

Remember uncle SAAMI. The have to fit everybodys gun. Easier to put one -.015 smaller than one +.015.

Every belted case headspaces off the belt. Dies should be set for just bumping the fire formed case.

Nat Lambeth

Nat,
so after the initial firing of the new brass you set your dies to just bump the shoulder and you don't bother with the belt anymore,...correct? I always wondered why then with a custom we don't have the reamer ground to .002 or so short of new brass ( from base to shoulder ) so we don't stretch the cases so far during initial fire forming?
Wayne.

 

[memilanuk]

Seems like it'd a waste of an awful lot of case capacity to me.

I know virgin cases are supposed to fit in any given chamber, but 15 thou under size on headspace is just ridiculous.

 

[kendog]

The belt was originally designed to control headspace on the 300 H&H, which has a very slight, long shoulder. It is almost useless in a cartrige with a more defined shoulder like the 300 Win Mag. Like others have posted, just set your die up to bump the shoulder back 1-1/2 thou and go. Treat it like any other modern bottleneck case.

 

[Rustystud]

A reamer cuts a chamber one size and hopefully it never grows. You don't want to work your brass. Fire form it once and bump it .0015- .002. Your dies should be cut to prevent the shoulder from causing any contact with the die.
Nat