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Old March 28, 2001, 12:14 PM   #1
imq707s
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What is the velocity of this load? 7mm Rem Mag,64gr. of H-4831 behind a 139gr. Hornady SST bullet. Is this faster or slower that a factory 140gr. round? Thanks
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Old March 28, 2001, 01:25 PM   #2
bergie
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Velocity of that load should be close to 2950 fps. Hornady manual doesn't list H-4831, and Hodgdon's basic manual that I have doesn't show that bullet, but does have a 140 gr with a "do not exceed" load of 64 gr H4831 at the 2950 velocity I mentioned. Winchester catalog has factory loads with a 140 grain bullet, either the FailSafe or the Ballistic Sivertip are listed at 3150 or 3100 fps respectvely.
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Old March 28, 2001, 03:53 PM   #3
KilgorII
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It depends on temperature, seating depth, barrel length, primer type, chamber dimensions, rifling type and twist, and other things.

The only way to know for sure from your rifle is to chrono some from your rifle.

Chronos aren't that expensive. You can get a decent F1 shooting chrony for $65 brand new if you look around.

Bergie's data should get you close though. However, when running a max load like that, it's a good idea to know what it's really doing lest your pressures be spiking.

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Old March 28, 2001, 04:06 PM   #4
imq707s
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My Lee Reloading manual says that 67gr. is the max load for a 139gr. bullet and H-4831 powder. It says that the starting is 62.8gr. of H-4831. I've shot the 67gr. (max load in lee manual) without any problems at all, but 64gr. is more accurate.
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Old March 28, 2001, 09:13 PM   #5
Johnny Guest
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2950 or 3100? So what?

imq707s--
I have zero experience with loading for 7 mm Rem Mag but I've loaded a bunch of centerfire rifle and carloads of pistol ammo.

I believe you have a good handle on the situation already:

I've shot the 67gr. (max load in lee manual) without any problems at all, but 64gr. is more accurate.

If you know your load is accurate and have confidence in it and your ability to hit with it, what difference could another 100--150 fps make? I understand the wish to know the true velocity, if for no other reason than to make intelligent use of the drop tables. Sorry I can't help on that score.

Best of luck--
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Old March 28, 2001, 10:04 PM   #6
Gewehr98
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Johnny, I think it has something to do with the fact that the big belted magnums are supposed to go oodles faster than their smaller, non-belted caliber mates. To slow down a magnum just for the sake of accuracy (not to mention extending barrel life) would rub some folks with Magnumitis wrong, and just plain **** off folks running such monsters as the .30-378 Weatherby. Not that I'm much better, I'm building a 6.5-300 Weatherby for a flatter trajectory way out there where my 6.5-06 runs outta steam...
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Old March 29, 2001, 12:04 PM   #7
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I can understand the desire for assured performance. Using a magnum for reduced loads wastes powder. Sorta like using a CART racer for commuting to work.
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Old March 29, 2001, 06:38 PM   #8
Johnny Guest
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MAGNUMITIS!

G-98, Poodleshooter---

I can understand that syndrome. I used to do it with a .338 myownself. And Elder Son has surely done it with a .300 WinMag--

But, if you have a good, ACCURATE load that's already running well into the Mangl'em realm, who sacrifice the accuracy just to be able to say the bullet's traveling at Warp six?

My .338 notwithstanding, my problem has more often been the opposite--I found that the more IMR 4350 I crammed into a .257 Roberts case, the better and tighter my 100 gr PSP bullets shot. I finally got scared and quit ootching it upward.

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