headspace help

got my new barrel and also headspace gauges. kinda unsure so needing some technical support. these are ptg gauges and are simply a cylinder with the rimmed portion on the bottom. i was under the assumption that the top of a headspace gauge was taperd like the case of a cartridge toward the end. these gauges i received are labeled go and no go and o.a.l is the same. ptg numbers 156824 and 137065. they are belted magnum gauges for my 300 win mag. the difference i found is .003 at the base with a micrometer. being they are cylinders and square cut on the end where or how will my barrel hit them for space. do i have the right headspace gauges

The chamber will rest on the shoulder of the headspace guage.

Belted magnums headspace off of the belt not the shoulder. Measure from the front of the belt to the base and you will find the difference.

so i got the right gauges the question is do you prefer a tight lockup on the bolt or just snug but still in compliance with the gauges and why

I would headspace using the go gage as per normal.

However, if you want a tighter fit try one of these options;
1) Adjust your headspace during resizing by adjusting your resizing die.
2) Headspace on a fired and full length re-sized case. Using this option you may not be able to use factory ammo.

So all good advice except for first response (BigBlue forgot you were doing a belted cartridge).

Most factory belted magnum chambers will have a LOT of room in the sholder area when you chamber a factory round. When you fire it, the shoulder moves forward quite a bit. Then when you F/L size the brass it moves the shoulder back to the factory ammo position. This isn't good for brass life (or best accuracy).

So after setting headspace with the gauge you can do three things -

Leave as is and have the same situation most factory belted mags have (not a big deal if you aren't a handloader).

F/L size a piece of brass fired in your rifle with your dies and reset the headspace on this brass (a compromise to get it a bit better).

Size your brass so as to just barely bump back the shoulder ("partial F/L size") - this is probably the best option and you can find lots of info on how to set your dies to do this here and other places.

Quote:

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F/L size a piece of brass fired in your rifle with your dies and reset the head space on this brass (a compromise to get it a bit better).

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This is how start to head space all my magnums. I prefer to head space off the shoulder rather than the belt.
Good article here. http://www.larrywillis.com/headspace.html