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Reloading 7mm Rem mag

 
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  #15  
Old 07-24-2012, 02:44 PM
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Join Date: Dec 2005
Posts: 2,114
Re: Reloading 7mm Rem mag

Quote:
Originally Posted by Clark View Post
And if brass manufacturers ever make any brass longer than .215" to the belt, they will be ready for it
I've had Winchester brand .338 Win. Mag. brass with belts headspacing at .218". SAAMI spec's state headspace is .212" to .220", but if sized cases headspace off their shoulders, then belt headspace doesn't matter. Especially if you somehow size the body diameters immediately in front of the belt back to virtual new case dimensions.

I find it amazing that new .30-.338 Win. Mag. cases (.300 or .338 Win. Mag. ones sized down in a .30-.338 FL die to hold 30 caliber bullets; longer necks with .300 cases) with shoulders back far enough that when the belt stops against the chamber headspace ridge and its shoulder's back a few thousandths from the chamber shoulder, fairly straight ammo will shoot well under 3/4 MOA at 1000 from SAAMI spec chambers. Brand new .300 Win. Mag. cases have also done as well.
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  #16  
Old 07-24-2012, 03:31 PM
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Join Date: Oct 2006
Posts: 484
Re: Reloading 7mm Rem mag

Bart, I am sure you know more than me about anything that has to do with shooting.
Your standards for accuracy are sometimes so high, that some of your extra efforts do not apply to me, but I always appreciate your posts.

I have found that all the brass in a bag is likely to measure close to the same.
Here are some measurements from different bags.
I could see I had enough brass to last me all my hunting days, and stay under .215"


7mmRemMag
.215" WW
.213" RP
.215" RP
.215" WW

264WinMag
.213" RP

300 WinMag
.217" SuperX Nickel plated
.215" SuperX
.210" RP
.215" RP
.213" Win Super
.216" FC 07
.212" RP
.211" DWM
.211" FC
.210" FC

338 Win Mag
.215" WW
.211" WW
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  #17  
Old 07-26-2012, 01:54 PM
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Join Date: Oct 2008
Posts: 98
Re: Reloading 7mm Rem mag

"I've had Winchester brand .338 Win. Mag. brass with belts headspacing at .218". SAAMI spec's state headspace is .212" to .220", but if sized cases headspace off their shoulders, then belt headspace doesn't matter. Especially if you somehow size the body diameters immediately in front of the belt back to virtual new case dimensions."

Bart B, it's amazing to me how many people don't understand this, resize your belted cases exactly the same as you do non belted cases by bumping the shoulder back a couple thousandths and the belt is a non issue.
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  #18  
Old 07-26-2012, 02:30 PM
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Join Date: Oct 2006
Posts: 484
Re: Reloading 7mm Rem mag

On another forum I saw a thread locked over controversy when it was suggested that adjusting the die down to bump the shell holder is not best for bottle necked cartridges.

I started researching every Bart Bobbitt post I could find in 1997 when I read this
https://groups.google.com/forum/#%21...ns/iL7zv-cktJc

Quote:
Leafing through my copy of the May 1997 issue of Precision Shooting, I
encountered an ad for Krieger Barrels, Inc. that showed an actual-size
copy of a 20-shot group shot at 800 yards by "Bert Bobbit [sic] with
his Krieger Barrelled PALMA rifle." Now this group has a .942" mean
radius, with an extreme spread of 3.325. If it were a 5-shot group,
you'd say, "Somebody else has shot that well at 1,000 yards." But a
20-shot group? God!!
At first I wondered if this was rec.guns's own BartB because of the
spelling in the ad. Then I realized the odds against having two superb
riflemen with such similar names were almost as great as having
obtained a 20-shot group that small through chance and chance alone.

All I can say is, if BartB and any other poster ever disagree about
anything having to do with shooting, I'll know whom to believe.
I had read lots of Bart's posts before 1997, I did not catch on until then that he was the answer book.
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  #19  
Old 07-26-2012, 04:37 PM
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Join Date: Dec 2005
Posts: 2,114
Re: Reloading 7mm Rem mag

Quote:
Originally Posted by apexmtnman View Post
"I've had Winchester brand .338 Win. Mag. brass with belts headspacing at .218". SAAMI spec's state headspace is .212" to .220", but if sized cases headspace off their shoulders, then belt headspace doesn't matter. Especially if you somehow size the body diameters immediately in front of the belt back to virtual new case dimensions."

Bart B, it's amazing to me how many people don't understand this (setting fired bottleneck case shoulders back a bit), resize your belted cases exactly the same as you do non belted cases by bumping the shoulder back a couple thousandths and the belt is a non issue.
Best thing about doing this is those belted (and rimless ones, too) will center perfectly up front in the chamber regardless of how much clearance there is around the case body behind the shoulder and around the case neck.

It's best understood without pictures by noting how rimless bottleneck head space gauges fit the chamber. When the bolt closes on them, the shoulder on the guage matches the shoulder in the chamber fits and centers perfectly in the chamber at the shoulder when the bolt's closed and headspace is a bit short stopping the bolt from closing all the way. The center of that gauge up front doesn't have a neck, but if it did, the neck would also be perfectly centered.

If one can imagine a .243 Win., .260 Rem., 7mm-08 and a .308 Win. case all being chambered in the same .308 Win. rifle. When the spring loaded ejector in the bolt face pushes them forward until their shoulders stop against the chamber shoulder, the necks on each one is perfectly centered in the chamber neck. Lots of room around the .243 and less as neck diameters get larger. When the firing pin strikes the primer, each case will be driven harder into the chamber shoulder; if the in-line ejector doesn't center the case shoulder in the chamber shoulder, the firing pin smacking the primer will. The primer detonates after the case shoulder's hard against the chamber shoulder. So a .243 Win. live round's bullet will start out dead centered, straight down the bore in a .308 Win. chambered barrel.
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