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Adventures With The .45-70.

Even though it was new in 1873, the .45-70 remains popular. It was the cartridge used in the old 1873 "trapdoor" Springfield rifle and the last blackpowder cartridge issued in this country. It was replaced by the .30-40 Kraig at the dawn of the smokeless powder age.

In its original configuration, the cartridge was loaded with a 405 gr. .45 caliber lead bullet backed with a charge of 70 grs. of blackpowder. All you have to do is look at a round to realize that there's a lot of powder space there. Unfortunately, when you want to use smokeless powder to duplicate the pressures of the old ammo, there's a lot of space left over.

Bad things have happened to people who didn't recognize the potential for disaster caused by that excess space. One of the myths explains the catastrophes that have befallen .45-70 shooters is that small charges of smokeless powder detonate with explosive force. There's only one problem with that story: it cannot be duplicated in the laboratory.

Powder and reloading authorities tell me that true detonation simply cannot occur with the relatively small quantities of smokeless powder used in any handloads.

Well, if it didn't detonate, what blew up those guns? Let me be the first to say that I don't know if the things we have seen with .45-70s are caused by the theory I'm about to report, but it is certainly plausible. Metallurgical examination of some guns that were destroyed doesn't show evidence of detonation, it shows that the failures were due to high pressure, but powder charges were relatively small. How could that be?

When gunpowder burns it produces gas under pressure to move the bullet. As the bullet moves down the barrel, the volume of the combustion chamber increases. If the volume increases at a rate greater than the rate of gas production then the bullet can slow down or even stop in the barrel.

If the bullet stops, it becomes, in effect, a bore obstruction. To paraphrase Mr. Newton's law: bodies at rest want to stay that way. And they don't care even a little if that behavior happens to make your gun blow up.

If it weren't for the fact that the volume of the combustion chamber (cartridge case and bore) increased to reduce the pressure, a relatively small powder charge could wreck almost any gun, but usually it takes a combination of bad things happening to do it. The .45-70 is a potential candidate because of all that extra powder space.
 .45-70 LITE LOADS

Bullet Powder Charge Velocity
Remington 300 gr. JHP Reloder 7 31.0 grs. 1,194 fps
Remington 300 gr. JHP Reloder 7 33.0 grs. 1,254 fps
Remington 300 gr. JHP Reloder 7 35.0 grs. 1,419 fps
Remington 300 gr. JHP 2495 BR 40.0 grs. 1,460 fps
Cast 405 gr. LFP 2495 BR 36.0 grs. 1,279 fps
Cast 405 gr. LFP MP 5744 25.5 grs. 1,171 fps
Cast 405 gr. LFP MP 5744 27.0 grs. 1,292 fps


All loads were assembled in Remington cases using Remington large rifle
primers.
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Article Details
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Author:PETTY, CHARLES E.
Publication:Guns Magazine
Article Type:Brief Article
Geographic Code:1USA
Date:Aug 1, 1999
Words:524
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