In an effort to obtain acceptable groups with a post 64 Mod. 70, 300 Win Mag., I discovered one bolt lug was contacting only about 65% and the other about 20% or so. I lapped the lugs, stopping @ approx. 95% and 70% contact since I do not have a headspace gauge. I would guess that no more than a couple of thousandths removed from lugs, but have no way of measuring.

I have fired Remington 150 grain factory loads with no primer setback or cratering both before and after lapping lugs.

My handloads are sized to produce very slight resistance as the bolt is closed the last 1/4", thus headspacing off the shoulder, not the belt, and my Wilson adjustable case gauge set so that a sized or fired case is flush with the maximum headspace ledge of the gauge.

Now for the problem. I purchased a box of Winchester 180 grain Failsafe factory ammo, which I assume is loaded rather warm, to use as a base line to measure case head expansion compared to my handloads. I dropped one of these cartridges in my case gauge and was surprised to note that it measured .028" under minimum headspace. I then checked a new unprimed Winchester case and it measured .022" under minimum. Since the Wilson gauge measures "headspace" off the shoulder, not the belt, it really gives you no idea of your rifle's headspace.

I then miked a piece of masking tape @ .005". It took two layers to produce friction as the bolt was closed. Measuring thickness of the tape revealed it had compressed to .009" on the Failsafe and .0075 on the unprimed case.

My question is, is .009" too much headspace to fire the failsafe ammo in this rifle?

Thanks for your ideas on this.

regards,
hm

I think that nominal headspace on a belted case is .220, all chambers being larger and all brass being smaller. I've measured brass that was down to around .213/.214 and seen chambers that were bigger than the .224 "no-go" gage. That is why a lot of us dislike belted cases. If you use your regular dies and headspace on the shoulder you will likely see a second, small "belt" on the cases just ahead of the belt.
I like .404 Jeffrey based cartridges for the lack of a belt and still plenty of capacity. Opinions...

The headspace is supposed to be .220/227. Cases vary all over the place as John Ricks pointed out. The written tolerance on cases is .220 -.008 so a maximum chamber (headspace) could be .227 and a case could be 212 which is .015" in theory.

Jay,Idaho and Savage99:

Thanks for the information.

I had never measured belted cases (just assumed they were .220 like the book says )but just measured a few and see what you mean about case-case variation.

Guess my .007-.009 would not be considered excessive then.

Regards,
hm

Don't take any measurments of the shoulder of the case.

I "swear" that factory Magnum ammo is purposely made to have the shoulder set back farther than it should be. This is just so that it will always chamber, as it headspaces off the belt anyway.

Actually, you should get a no-go gauge and be sure you have not set the lugs back too far.

If you really want it snug, have the barrel set back a turn, and then rechamber it so that the bolt will close on a virgin case, but NOT close on the Go gauge. I regularlly do this, and find that it is amazing how much space there really is in there.

Hi Terry:

"I "swear" that factory Magnum ammo is purposely made to have the shoulder set back farther than it should be. This is just so that it will always chamber, as it headspaces off the belt anyway."

That is exactly what I suspect!

I have been thinking about having barrel set back anyway because, IIRC, ammo loaded to max. magazine length has a .170" bullet jump to lands.
Suspect the long throat may be a contributing factor making this rifle so finicky to various loads.

By the way, sent you a PM a few days ago. Thanks for the help.

Regards,
hm

How I cheated on my .300 Win PSS barrel. I found that new ammo in my chamber was blowing the shoulder ahead quite a bit more that I thought was needed. So I removed the barrel and set it back an amount that just makes the new cases snug AT THE SHOULDER. To do this, I had to use a boring tool to move the belt counterbore forward. Worked very well. To use a .300 Win. reamer would mean that I would have had to set the barrel back enough to get a new complete neck 'cause factory necks are also bigger than needed.