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Harry Bonar
November 13, 2005, 06:41 PM
Shooters:
I traded for a factory new (had been just hunted with) Savage 111 from a friend and it is in 300 Win Mag. I also bought an adams and bennet 416 taylor bbl for it and fitted it with a .220 headspace guage I made myself - aok!
But, I noticed the 300 mag cases had the primers slightly flattened on the factory cases.
As you know, the bbl nut on the savage is easy to loosten, so loosten it I did. With a new factory cartridge in the chamber I could turn the bbl 1/4 turn until I felt the head.
Then with the .220 go guage in the bbl chamber I still had to turn it 1/4 turn farther in till I made contact!!
As you all probably know the belt is supposed to be .220 long! And, if memory serves correctly the British used a .220 go guage, and a .222 no-go guage. Now, SAAMI gives .220 go and, a .227 max.
The SAAMI dm's show for a cartridge .220 -.008! For the chamber it gives .220 - .227 max. So, you could have with a minimum case (.212 long) and a maximum chamber (.227 long) a total headspace of about.015 which is .009 over max for centerfire rifles. Not only that but think of the unsupported case right in front of the belt!
When I fit a bbl to an action with a belted magnum I ALWAYS fit to a .220 guage! Hope this provokes thought
Harry B.

Unclenick
November 13, 2005, 11:12 PM
Harry,

Yikes! That is a fairly astonishing set of numbers. I thought everything but the Weatherby's and the Van Horn rounds were .220 off the belt. But -.008 for the brass?!! My first thought is that a bottle-neck case will end up headspacing off the shoulder before the belt touches down. Maybe you should chamber it that way on purpose as insurance if the manufacturers are that loose?

Second thought: since the Savage headspace is so readily adjustable, maybe you're better off buying all the brass you're likely to use in it at once, from the same lot. Then set the gun up for that lot. What a nuisance. An not knowing if a commercial cartridge would be able to chamber afterward is unsettling. Can you carve a hollow in th butstock to carry the nut wrench with you? ;)

Nick

Harry Bonar
November 15, 2005, 09:11 AM
Dear shooter:
That's a good idea! I guess factories think that the SAMMI specs are O.K.
Most cases (belted mags) actually measure about .216 from belt to case head. I really think the British were right in making the Dm, .220 go - .222 no-go!
If the ammo makers actually produced belts of .220 and the mfgrs. used the British system of .220 go - .222 no-go we'd be O.K.
In rechambering for .458 Lott, some smiths make the mistake of cutting the belt area in too far - results on firing are stupendous! The belt cutting area on the reamer ought to be "non-cutting" then it wouldn't cut in too far.
Your right about headspacing on the shoulder; but, if that exposes too much of the area in front of the belt then we've got a problem!
I don't like belted magnum cases - the reason the British used it was with pretty much straight walled cases.
Harry B. Thanks UNKLENICK

James K
November 17, 2005, 09:55 PM
OK, I am confused. A belted case is supported (headspaced) on the belt; the shoulder is pretty much irrelevant, just as it is in a shouldered rimmed case (.30-40, .303 British, .30-30). Why try to use the shoulder anyway when there is no need to do so?

Jim

cntryboy1289
November 18, 2005, 12:51 AM
Jim, I like to neck size my 7mm Rem mag only because they will headspace off the shoulder this way. It just seems to help with accuracy. The belt will allow the case to not sit concentric with the bore at times by allowing a case to move about in front of the belt.

This is why Winchester and Remington spent so much time finding the right cases to use for their short magnum cases. Most of the time the belt doesn't add much to the case as far as strength anyway so it makes good sense to me to want to cut a chamber to headspace off the shoulder like so many other cases do.

Harry Bonar
November 18, 2005, 09:23 AM
Dear Shooters & Jim:
The max allowable headspace is usually no more than .006 from the "go" guage. I like to set my headspace using the gauge and also, a new Federal, Winchester or Remington case. I like to actually feel the bolt close with absolutely NO clearance with a new case or, as preferred, a slight resistance.
I you set your sizer die to bump the shell holder and then go i/8th turn more, supposedly you're sizing the case to factory dm'! But, if you do after several loadings you will, in rifles with max acceptable headspace, notice some incipient case head stretch! If you headspace, or size, correctly you won't. The trouble with the belted caee is that by resizing so that the shoulder is your "datum" then the head can't stretch the possible .010 - .015 as with the die mfgrs' directions - as a matter of fact, now, many loading books recommend using the shoulder on belted mag cases to headspace off of - of course the weapon must be in spec as regards the guages!
I know this seems complicated and I apologize if I've been Confusing!:D
Harry B.