How do i check headspace?

You need a set of "go" and "no-go" headspace gauges for the .303 British-approx $60 with postage. Best bet would be to take it to a 'smith. Most have the proper gauges and it is a quick check to do.
 
Good call Mikeystew. There are so many out there that buy ammo and head straight to the gun range without knowing "is this gun safe?"
 
The distance from the face of the barrel to the face of the bolt should ideally be no more than .064". Up to .074" was acceptable, but case life is dramatically reduced. If you measure the thickness of the case rim, and know the thickness of the shims you are adding, you might be able to come up with a fairly accurate measurement. You would have to use a light touch - the camming action of the bolt as it closes will tend to compress the rim plus shim.
A quick and dirty method is to fire a primed case. The primer will back out of the case, and case rim thickness plus primer protrusion will give you an idea of the dimension.
Accurate measuring equipment is needed. A $15 Canadian Tire digital caliper would not be the instrument of choice.
Best bet would be to either have a gunsmith check headspace with gauges, or get your own. For one job, it doesn't make sense to buy gauges.
 
"...how does one go about checking/measuring headspace..." Headspace is checked with headspace guages. It's a rifle manufacturing tolerance that allows ammo made by all makers to be used in a firearm. Brownell's, Stateside, sells 'em. About $30US each.
The set consists of a Go, No-Go and a Field. They don't measure anything though. They just tell you if the headspace is within tolerance. The bolt should close completely on a Go. It should not completely on a No-Go, but if it does, you try the Field. If the bolt completely closes on a Field, the headspace is excessive and the rifle is not safe to shoot with any ammo.
It's best to remove the extractor, put the guage in the chamber and gently close the bolt. It can be done by putting the guage under the extractor and closing the bolt.
 
I got a related question as well. I recently got a set of Go, No-go and Field guages in .303 and checked all my Lee Enfields and P-14s. The P-14s where good as they closed only on the Go, but my No1MkIII closed on Field. So I got out my spare bolts and bolt heads and tried a few combinations. I did messure the lengths of each as well. The only combination that would not close on Field also would not close on Go. Could this lead to excessive pressures? It does feed rounds just fine without any excess force needed.
 
If the gap between the boltface and breechface is too small to accept a .064" Go gauge, it might or might not be possible to close the bolt on a round. If the bolt closes, fine. This does not affect pressure.
If you are swapping bolts, it is not enough to just find a combination that gauges. Both the bolt lugs need to engage the locking shoulders in the receiver.
 
looking at my brass closer it appears that my primers are flat which is leading me to believe it was excessive pressure to blame, is that even possible in old factory ammo?
 
There are many causes of flat primers. Pressure, the metal in the cap, excess headspace. Flat primers are one of the least reliable indicators of high pressure. If primers are becoming noticeably flatter as handloads get hotter, they are sending a message though.
 
tiriaq said:
If the gap between the boltface and breechface is too small to accept a .064" Go gauge, it might or might not be possible to close the bolt on a round. If the bolt closes, fine. This does not affect pressure.
If you are swapping bolts, it is not enough to just find a combination that gauges. Both the bolt lugs need to engage the locking shoulders in the receiver.
Click to expand...

The bolt does close on all of the different rounds I have on hand. From ww2 dated DA, dominion, privi, winchester, federal and remington.

The lock-up is very positive but the matching bolt to the reciever will close on Field regardless of the bolt-head used. I have 4 bolts and around 8 bolt-heads.
 
Put some marker on the lugs, and see if it is scraped off when the bolt is closed. If only one lug is making contact, shooting will probably be affected.
 
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