Sako 300 Win Mag chamber concern

[ratbuster]

I have had a Model Av 300 Win Mag for 30 years that I have never hunted with and shot only a small number of shots with factory ammo. Out of curiosity I recently measured factory ammo vs. fired cases using a Hornady comparator at the shoulder datum. I was very surprised to find the case had lengthened .018" with Federal Premium ammo and .023" with Winchester Super X.

I am planning on an Elk hunt next year and would like to improve the accuracy over the factory ammo which is 1 MOA at best. My concern is reloading these fired factory cases. They have stretched a long way.

The primers have not backed out like you would expect to see from excessive headspace.

From what I have read the cartridge is headspaced at both the belt and shoulder. Does having the belt reduce the chance of case head separation? I suspect the stretching is occurring somewhat uniformly from the belt to the shoulder but I don't know for sure.

Is it safe to reload these cases? One person suggested to create a false shoulder with virgin cases and fire form them.

What say you?

 

[shortgrass]

Belted magnums are headspaced off the belt. Sounds like you already have fire formed cases. Reload 'um. For a hunting rifle 'bump' the shoulder enough for reliable feeding, but not more then is necessary . Many belted magnum chambers have a longer body even though they were headspaced off the belt when the chamber was cut. Don't sweat the small stuff, this is a common occurrence.

 

[ratbuster]

Thanks Mr. Shortgrass!

 

[Riesel]

Be sure to keep an eye on the cartridge overall length, the bullet seats deeper than one might think.

 

[jepp2]

The primers have not backed out like you would expect to see from excessive headspace.

That is because the belt is holding the case head near the bolt face. Just don't set the shoulder back more than you would on a bottleneck case. You get 1 free stretch, the next one can be problematic.

 

[boltfluter]

I used to create a false shoulder for the first firing of new brass back when I owned a .300 Win .Mag. Brass lasted virtually forever . Just something to keep in mind if you run into trouble.

Paul

 

[GenePoole]

I am unfamiliar with this 'false shoulder' thing. How does that work?

 

[ratbuster]

Thanks to all for your responses!

 

[Cloudrepair]

I am unfamiliar with this 'false shoulder' thing. How does that work?

Neck up to a larger diameter then neck back down to correct diameter with shoulder in right location so that shoulder has a slight crush fit when the round is chambered. Like a 30-06 necked down to 280ai with shoulder in right place

 

[m249b]

I have had a Model Av 300 Win Mag for 30 years that I have never hunted with and shot only a small number of shots with factory ammo. Out of curiosity I recently measured factory ammo vs. fired cases using a Hornady comparator at the shoulder datum. I was very surprised to find the case had lengthened .018" with Federal Premium ammo and .023" with Winchester Super X.

I am planning on an Elk hunt next year and would like to improve the accuracy over the factory ammo which is 1 MOA at best. My concern is reloading these fired factory cases. They have stretched a long way.

The primers have not backed out like you would expect to see from excessive headspace.

From what I have read the cartridge is headspaced at both the belt and shoulder. Does having the belt reduce the chance of case head separation? I suspect the stretching is occurring somewhat uniformly from the belt to the shoulder but I don't know for sure.

Is it safe to reload these cases? One person suggested to create a false shoulder with virgin cases and fire form them.

What say you?

I have a sako Trg M-10 in 300 mag. It has the exact same chamber dimension issue. As suggested, I now set a false shoulder and fire form all new factory brass. Problem solved.

 

[Dusty Stevens]

What die are yall using to bump these shoulders on a belted magnum? Ive never had one thatll size the base above the belt and come close to the right shoulder. I swore off belted magnums years ago for any accuracy work just because of this. A 375 h&h is the only belted magnum in my bag of tricks. Too many shoulder headspaced fire breathers out there to worry with a belt and shoulder anymore

 

[GenePoole]

I use the Redding Body Die:

https://www.midwayusa.com/product/420044/redding-body-die

I don't have any statistics on case belt/shoulder data so I can't say much about what's going on. I only have one 300WM, but I use the same type die for all my reloading calibers. I typically take a once-fired case that is hard to seat and adjust the die in very slight increments until it seats with little or no resistance. Then I lock it and mark it for the specific rifle for which it will be used. For the necks, I use a Lee collet die. It sizes the necks without affecting any other case dimensions and does so without unnecessary working of the brass.

 

[JRS]

What die are yall using to bump these shoulders on a belted magnum? Ive never had one thatll size the base above the belt and come close to the right shoulder. I swore off belted magnums years ago for any accuracy work just because of this. A 375 h&h is the only belted magnum in my bag of tricks. Too many shoulder headspaced fire breathers out there to worry with a belt and shoulder anymore

Larry Willis (Innovative Technologies)