7 Mag & 45-70 Chrony Data Here !!

J

jrslate

New member
Gentlemen,

I finally got a chance to get out with the new chronograph and try a few of my loads....some good news, some real surprises

Here are the results and some comments...

Weather 45 degrees F and cloudy

7 MM Rem Mag-Ruger M77 MkII, 24" barrel

1.) 175 gr. Nosler Partition, Fed 215 primer, 62.5 gr. Reloader 22

5-shot average of 2744 fps, Nosler claims 2970 fps from the same load, this is a difference of 226 fps...hmmm, why is this? Any help would be appreciated

2.) 175 gr. Speer GS, Fed 215 primer, 61 gr. Reloader 22

5-shot average of 2740 fps, Speer claims 2834 fps, a difference of 94 fps.

3.) Remington Core-lokt 175 gr. Factory load - 2807 fps. R-P claims 2860 fps.

45-70 Govt. Marlin 1895G 18.5" Barrel

1.) 405 gr. Lazer-cast, 51 gr. Reloader 7, Fed 210 primer

8-shot average of 1952 fps. This is a good load, probably close to Max. Good accuracy too.

2.) 350 gr. Hornady FP Interlock
52 gr. Reloader 7 - 1938 fps average
52 gr. Reloader 7 - 1969 fps average

Why did it take 50 gr. less bullet weight and 2 gr. more powder to barely exceed the cast bullet load?

Any help would be appreciated

Joel Slate
Slate & Associates, LLC
The Safari Specialists
www.slatesafaris.com

7mm Rem Mag Page www.slatesafaris.com/7mm.htm
 
Seeing lead outpace the jacketed bullets, given similar powder charges, is fairly common in .45-70 and other large bore, medium to low velocity cartridges. The lead bullets, being softer, deform more easily to fit the rifling and are often sized a bit larger than factory jacketed ammo. Less of the powders energy is used in obdurating the bullet to the bore, and the lubricated lead alloy bullet slides more easily down the barrel than the copper jacket of the conventional JHP. There are internal ballistics factors from the heavier projectile accelerating more slowly down the bore allowing more burn time and compression of the gases, increasing the efficiency of the powder and giving a more even pressure curve. More push for less powder at lower peak pressures.
 
I haven't found a 7 Mag. load yet, factory or handload, that lives up to its claimed velocity. In fact, my son's 7-08 is only about 75 fps behind my 7 mag with 140 gr. bullets. Plus it is much quieter and kicks considerably less. I suspect that the 7 mag quoted velocities are from rifles with some throat erosion. If I could do it again, I would buy my 700 LH in .270! Just my $.02.

David
 
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