Finally got my hands on a model 70 in 300 win mag. In my limited research so far I’ve learned that these magnum chambers are really long. Therefore “bumping” the shoulders a few thousandths of an inch seem to be the preferred amount. Otherwise the cases fail quickly. My question is how do you full length resize the body while also controlling the amount you bump the shoulder?

https://www.amazon.com/Bushing-Replacement-Compatible-Checking-Bottlenecks/dp/B09V7C51B7/ref=sr_1_5?keywords=hornady+comparator+kit&qid=1668839242&sprefix=hornady+com%2Caps%2C224&sr=8-5

You can use a tool like the one above to check how much you're moving the shoulder.  As long the sized case chambers in your rifle, the body is OK.  Annealing the brass will help extend it's life.  For calibers that use expensive brass I keep the brass segregated and only shoot the formed brass out of the same bolt rifle and then neck size.  When I start to get resistance when chambering - I'll push the shoulder back a couple of thousands. 

https://www.amazon.com/Bushing-Replacement-Compatible-Checking-Bottlenecks/dp/B09V7C51B7/ref=sr_1_5?keywords=hornady+comparator+kit&qid=1668839242&sprefix=hornady+com%2Caps%2C224&sr=8-5

You can use a tool like the one above to check how much you're moving the shoulder.  As long the sized case chambers in your rifle, the body is OK.  Annealing the brass will help extend it's life.  For calibers that use expensive brass I keep the brass segregated and only shoot the formed brass out of the same bolt rifle and then neck size.  When I start to get resistance when chambering - I'll push the shoulder back a couple of thousands.

I should have clarified that I will be developing these loads for hunting. The accuracy will be secondary to reliability for my application. Therefore I need to be able to chamber the rounds from a magazine and from what I understand the fire formed cases are not reliable enough in the field while hunting. I guess my question is more about whether or not I will be able to fully size the length of the case (to get back to factory specs) while also controlling how much shoulder bump I give the case. I hope that makes sense 

I think you still need to use the tool to measure the length of the case before firing and then how much you're setting back the shoulder as you adjust the sizing die to get the shoulder back to factory.  As far as the body, you can use a 300WM case gauge - if your sized case freely drops into the gauge it should reliably chamber in your rifle. 

I think you still need to use the tool to measure the length of the case before firing and then how much you're setting back the shoulder as you adjust the sizing die to get the shoulder back to factory.  As far as the body, you can use a 300WM case gauge - if your sized case freely drops into the gauge it should reliably chamber in your rifle.

Awesome I will be checking out that gauge    mahalo!

You could use a body die then a collet neck sizer. RCBS makes a gauge to determine shoulder setback. https://www.rcbs.com/case-processing/measuring/precision-mic/564.html

You could use a body die then a collet neck sizer. RCBS makes a gauge to determine shoulder setback. https://www.rcbs.com/case-processing/measuring/precision-mic/564.html

Mahalo!

Get a case comparator as mention above. After your first firing fl size your case just like any other shouldered cartridge. Measure your fired case and set the shoulder back .002-.003”.There is collet sizing die for belted magnums that will get down to the base of the belt but I never had an issue or need for one when sizing 7rem mag using Norma and nosler brass.