Question about chambers

Trubkir17

Trubkir17

Hammer Time Executive member
I was reading about the 7mm Practical on Nathan Foster's Ballastic Studies website. He states that the chamber for belted magnums should be cut deep enough so that the bolt will almost close or close with some resistance on the No Go gauge. I think his reasoning is he gets better brass life, but I don't truly understand why he says this. Does anybody else do this?
 
Trubkir17 said:
I was reading about the 7mm Practical on Nathan Foster's Ballastic Studies website. He states that the chamber for belted magnums should be cut deep enough so that the bolt will almost close or close with some resistance on the No Go gauge. I think his reasoning is he gets better brass life, but I don't truly understand why he says this. Does anybody else do this?
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My GUESS would be to make sure the case is headspacing on the belt and not the shoulder…🤷🏻‍♂️
 
It’s my understanding if you set the bolt to close on a No-go, it’s a longer chamber…
 
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LightTheTower said:
My GUESS would be to make sure the case is headspacing on the belt and not the shoulder…🤷🏻‍♂️
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To my way of thinking the cartridge would headspace on the shoulder and there would be some amount of free space in front of the belt.
I am pretty sure after reading that section a number of times that his theory is he gets better life from his brass. He also claims he gets better accuracy.
 
Trubkir17 said:
To my way of thinking the cartridge would headspace on the shoulder and there would be some amount of free space in front of the belt.
I am pretty sure after reading that section a number of times that his theory is he gets better life from his brass. He also claims he gets better accuracy.
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Hmm🤔🤷🏻‍♂️
 
My dad said that when he was shooting Belted Magnums many moons ago, he would bump the shoulder like any regular cartridge and didn’t have any issues with brass life. This was in a 7-REM Mag.

This conversation came about when discussing the pros and cons of the 7mmPRC.
 
I forgot that the 7mm Practical is a wildcat so he is fireforming his brass and then neck sizing only. Sorry for the noise.
 
There's no reason, in my little mind anyway, that you can't headspace off the belt AND the shoulder with a little trial and error. It still makes me smile and shake my head that after over 100 years of successful belted magnum cartridges somehow the belt has become as issue with a seemingly growing number of folks.
I also intend to build a 7mm Practical one day. I think it might be the perfect compromise between the 7 mag and the 28 Nosler. JM2C

Regards
 
Trubkir17 said:
I was reading about the 7mm Practical on Nathan Foster's Ballastic Studies website. He states that the chamber for belted magnums should be cut deep enough so that the bolt will almost close or close with some resistance on the No Go gauge. I think his reasoning is he gets better brass life, but I don't truly understand why he says this. Does anybody else do this?
Click to expand...
Did you not read this part?

Note that your go gauge is -5 thou while your no-go guage is +5 thou. Please ream forwards until the bolt is either able to almost close or is able to close on the no-go gauge but with a measure of resistance. This will set the chamber forwards of its mid headspace point. The customer can then fire form and headspace his brass at the shoulder. The shoulder will stretch well before the case head is able to move forwards. This will make reloading easy and saves a great deal of headaches. A common problem for example, is rifles being returned to the smith after the customer has stretched cases during initial case forming operations (such as extruding the case by accident over an expander button). This and other belted case reloading dramas can all be avoided by letting the case breathe. And as suggested, this approach is optimal for belted magnum accuracy.
 
Yes, I did read that. I read that many times, but I am missing or not understanding his point.
 
Mountainman said:
There's no reason, in my little mind anyway, that you can't headspace off the belt AND the shoulder with a little trial and error. It still makes me smile and shake my head that after over 100 years of successful belted magnum cartridges somehow the belt has become as issue with a seemingly growing number of folks.
I also intend to build a 7mm Practical one day. I think it might be the perfect compromise between the 7 mag and the 28 Nosler. JM2C

Regards
Click to expand...
I find this amazing as well. The pendulum has swung away but I am thinking in the near future Hornaday will come out with the new 7mm Super Tits. It will have a belt and will be the new big thing.
 
There are a few strategies to help a belted mag be friendlier to those minimum sizing and running pressures we do now.
He's simply giving it a few more thou of headspace from go gauge zero. I redid my 300 win reamer years ago but gave it a little more room just ahead of the belt in diameter but then keep the headspace at .002. This lets you get .0005 of resize right in front of the belt when running hot and min sizing and it keeps it going without a Willis die.
Pertersons long brass is one of the best best gimmicks for a few extra pennies I've ever seen as it was literally a solution looking for a problem and an easy extra few cents a case. The real solution would be a correctly spec'ed sizer die that lets you size to the belt at .002 shoulder set back.
 
I am going to have to go back and look at the SAAMI drawings because I am not understanding something basic about when the belted magnum is "in battery".
 
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