Ballistician's Notebook: The .45-70 Government
January 04, 2011
Any cartridge that is nearly 140 years old and still popular gets my attention and my respect.
Handloads for lever-action .45-70 rifles must closely observe the industry overall length spec and be firmly roll-crimped. This one is just under the maximum of 2.550 inches.
Any cartridge that is nearly 140 years old and still popular gets my attention and my respect. The .45-70 is the longest serving centerfire rifle cartridge in the sportsman's arsenal. There was a period between the 1930s and the 1970s when it appeared to be headed for obsolescence, but rifles like the modern Marlin 1895 and the Ruger No. 1 renewed interest. It is also a widely handloaded cartridge, a tribute to its flexibility and good manners. This column looks at some of the factors the reloader needs to respect.
The industry set the .45-70's maximum average pressure (MAP) to 28,000 psi. When we tested blackpowder loads at Speer, we found the highest pressure we could generate with 500-grain bullets was about 21,000 psi. Interestingly, I'd found out years before that at least one big ammo company did not load higher than 21,000 in deference to the Model 1873 Springfield--the famous "Trapdoor" that so many .45-70 shooters still use.
We ultimately divided the .45-70 data for the Speer manuals into three sections. In addition to a Trapdoor section, we had one for current lever-action rifles and modern single-shot reproductions at the industry max of 28,000 psi. We included a section for the most modern falling-block single shots and converted Model 98 Mausers that we loaded to 35,000 psi.
If the Ruger No. 1 can handle cartridges that rate a MAP of 65,000 psi, why cut the .45-70 at 35,000 psi?
The reason is the case. If a case needs to hold a fair bit less pressure than 28,000 psi when factory-loaded, there is no compelling business reason to add more costly brass to strengthen the case for use at 50,000 psi. Three brands of .45-70 cases I weighed averaged 191 grains; the newer .450 Marlin case, rated for 43,500 psi, averaged 215 grains. A .45-70 case may be fine for the first shot at high pressure, but regardless of how many times the case was--or wasn't--fired, you can't change the fact that its design criteria were centered on confining less than 28,000 psi.
Believe me, you can produce plenty of .45-caliber "ouch" at both ends of the rifle at 35,000 psi. If you need more than that pressure level delivers, look to the very nice .450 Marlin.
The rifling pattern can make a difference in whether a .45-70 rifle will shoot cast lead bullets as well as jacketed ones.
That Darned Case Cannelure
If, like me, you have a stash of older .45-70 cases, some may feature a deeply rolled cannelure. It was done when the case was made, not after it was loaded as was more common. It allowed the base of the old 400-grain softpoint to "perch" to avoid being deep-seated by recoil in a tubular magazine. If you loaded a bullet that sat deeper in the case than the factory bullet, you quickly found that the cannelure stopped the bullet as effectively as a steel plate. Fortunately, the company that did this has seen the light and eliminated this superfluous feature from its unprimed .45-70 and .38-55 cases.
People have built tools to remove this cannelure, but I find it as easy to fire-form the cannelure out of the way. I load either an Ideal 300-grain or an RCBS 325-grain cast bullet with a modest charge of IMR-4759 or Accurate Arms 5744; the cannelure irons out nicely with little additional stress to the case.
Bullets & Rifling
The .45-70 started as a lead-bullet cartridge, and old barrels were rifled with a pattern of lands and grooves aggressive enough to engage fairly soft lead. When new rifles appeared in the second half of the 20th century, jacketed bullets were the norm, and rifling reflected that. Barrels were mostly button-rifled (swaged) with a multi-groove pattern having shallow grooves. They shot great with jacketed bullets but often failed to accurately shoot cast lead bullets.
Cowboy action shooting has influenced many riflemakers to revert to "cut" rifling with a pattern that works well with either jacketed or cast lead bullets. If you have a rifle with the shallow groove pattern and want to shoot cast bullets, the only workable out that seems effective is to cast the bullets very hard--linotype hardness seems to work best. You will probably find that loading a little lighter helps the bullet stay in good contact with the rifling. Plinking loads in the 1,200- to 1,400-fps range will usually not stress cast bullets regardless of the rifling style.
Older unprimed .45-70 cases, as with the .38-55 cases shown here, can have a deep case cannelure that needs to be removed by fire-forming before seating long bullets.
Like many straight-wall cases that evolved during the blackpower days, the .45-70 excels with many of the propellants you would load in the .223 Remington. If you're loading light, keep an eye on airspace. The .45-70 is not too picky, but very low-volume propellant charges may show larger ballistic variations than you want. Fortunately, the word "flexibility" I used before to describe this cartridge translates to "being forgiving." Still, consider bulky cast-bullet propellants like Accurate Arms 5744 or IMR-4759 when loading low-velocity loads.
Cartridge overall length is important for .45-70 lever-action rifles. They require a length that falls between 2.490 and 2.550 inches for reliable feeding. Most .45-caliber bullets designed for the .45-70 will have crimp cannelures that are positioned to fall between those values when loaded and crimped. And remember: All bullets to be used in tubular magazines must be flat-tipped and their cannelures must be designed to prevent the bullet from shifting deeper in the cases under recoil. The .45-70 has plenty of recoil to accomplish this if you fail to do your part.
Bullet profile can't be ignored. The industry cartridge drawing for the .45-70 shows no leade, or "freebore"--the rifling origin is at the end of the chamber. Early lead bullets accommodated this by having a reduced-diameter step where the bullet's nose and bearing surface met. This feature is harder to achieve i
n jacketed bullets. A number of the "reborn" rifles had some freebore, so a lot of 1970-vintage jacketed bullets for .45-70 were profiled to fit existing rifle chambers, not the drawing. When some of the rifle companies reverted to a strict standard chamber without any freebore, bullets that worked in older rifles failed to fit new ones.
Before loading a bunch of ammo, make a few dummy cartridges with the bullet you want to use and make certain that they chamber without interference. If loading for a lever rifle, test how they cycle while you are at this stage. It will save you a lot of grief later.
I think I've said that before!