Found this while searching for information about loads and limits to consider for my 45-70. Great read, full of information - a primer of sorts for learners new to the caliber.
Posted by Murphy on Jan 24 2006
All this talk about the 45-70 as an all-round rifle makes me wonder about the role this old cartridge is now being asked to play in the hunting fields. Oh, donít get me wrong I think itís a great old warhorse, but if a hunter were out to acquire a new rifle for general river bottom duties, there are better choices. Much has been written, here and elsewhere, about the prowess of the 45-70 as a hunting rifle, all good comments, but I think some are misleading. Before I step on too many toes let me say that I agree with the general concept of the 45-70 here of late but I think the analysis doesnít go far enough.
First of all, if an individual will set out to find the best do-it-all rifle caliber, I canít see the reasoning for the 45-70. Great to add to the battery but if it were the only one, I would consider myself ill equipped, except in some few circumstances. Now if we have only a 45-70 and would like to make it work for every thing, weíll do the best we can, thereís plenty to work with, but we canít make into a dragon slayer. The decision for the 45-70 is based, in part I believe, on the recent modern loadings for the caliber and published loading data that indicate very high energy levels due to higher velocity of light for caliber bullets, specifically 300 and 350 grain. These would also have the added advantage of flattening the pumpkin ball trajectory that has become the accepted norm for the caliber. The light for caliber loading for the 45-70 some 130 years ago was a 405 grain load, the 500 grain being standard until the cavalry wanted something lighter to keep the mounted soldiers on their horses after firing the heavy loads.
Energy figures touted by ammo manufacturers today make for a wonderful marketing agenda but unfortunately donít tell the whole story and are not necessarily supported in actual field performance. You mileage may vary and some models donít fit all tracks! Kinetic Energy is formulated as Ĺ the Mass times the square of Velocity. Well this certainly gives the edge of 8 to 1 odds to velocity. Mass is not the weight of the bullet, it is the weight of the bullet in pounds (grains/7000) divided by the static acceleration of gravity (about 32 ft/sec). We then multiply this tiny number by the square of the velocity to get the energy figures. (You can try this at home) This gives a big number and looks more impressive on the back of the ammo box. What is not mentioned is a more meaningful concept called momentum. (Mass x velocity) We learned in Metallic Silhouette shoots that it was the momentum of the bullet that pushed the rams over, not the d***ling energy figures.
The light for caliber projectiles for the 45-70 certainly make it a quicker getter of game in the deer and caribou class and connecting on longish shots an easier task but are not the ticket when a much more massive animal rears his majestic head across a wide drainage. For a bullet to do its work it must reach the vitals and destroy them, and to do that, several factors must be met. I will list them in no particular order except to say that the first is always first.
3. Bullet Construction
5. Impact Velocity
6. Bullet Stability
We arenít going to discuss number one, for obvious reasons, except to say that of all the animals Iíve missed, this was the cause. Number two is a big one and really the subject of this dissertation. We will discuss number three in more detail later but for now I will say the bullet must stay together and not expand so much as to limit penetration. It must be matched to the animal and impact velocity. The next three, along with the bullet construction, are all so inter-related they must be discussed together.
Back to the 45-70 cartridge of the 21st century, a large caliber by most standards, and impressive looking. Whether loaded with a 450 grain LBT style bullet or one of the new 350 grain JHPís, it looks as if it can get the job done. But can it? What is more important, velocity or bullet weight? How can we be sure a bullet will penetrate? Why are some calibers better in the game fields than others? Whatís so great about the 30-06 or the 375H&H? The 30-06 and the 375, along with a few others have been around almost as long as the venerable 45-70 and like it have a great reputation as a hunting caliber. It is my position that the 45-70ís reputation, though well deserved, is from a more specialized style of hunting than the other two as they are more generally accepted as universal calibers and more versatile. This style of hunting is very respectable and quite demanding, often requiring more skill than the 400 yard cross-canyon shot. This is spot and stalk and get up close to deliver the goods. A task at which the 45-70 will be well suited with most loadings, but it is not suited nor should not be used for the long cross-river shot on the big bull, just before he slips into the alder thicket. Even with the new loadings of 300 grains at 2300 fps from the Marlin. Here is the problem. Penetration or the lack of it. I promised weíd talk about it.
Penetration is a product of caliber, on the negative side, and bullet weight and impact velocity on the positive side. And of course bullet construction, which can make or break any deal, but for the purposes of this discussion, will always be perfect, not magic but perfect, no matter the velocity or the toughness of the beast, it will always work for us.
I said caliber on the negative side meaning the bigger the caliber (bullet diameter) the harder it is to push it through any thing. Always sharpen you spear correctly. I also said bullet weight and velocity on the positive side. (Velocity is important?) The bullet weight/bullet diameter relationship is already well compensated for with what we call sectional density. It is the weight of the bullet in pounds divided by the square of the diameter. (More math) So this is getting simple already, just two things Sectional Density (SD) and Velocity, specifically impact velocity. How much of each do we need? The answer would surely be how much penetration do we need? The skull of an elephant is about 14 inches of spongy shock absorbing bone and when taking a frontal brain shot we need lots of penetration. Ok, weíre not hunting elephant, but you get the idea. How about a black tail deer? Not much needed. How about moose and other big brown furry things? Well, obviously we need a lot of penetration. Before we penetrate any further into this subject (pun intended), letís talk a bit more about bullet weight. Well, I said 300-350 grain bullets are light for caliber bullets. They are short and have low SD. If its diameter were less for the same weight penetration will be better. Or, if it was heavier and of the same diameter, it would penetrate more, always, given equal construction and velocity. The ďmagicĒ number for Sectional density is .300, or there about, thatís what we shoot for. Bullets with SD numbers .300 and above are rarely ever recovered. They pock mark the country side beyond our target, for through and through penetration. Two holes, always better than one. For a bullet that cannot fail and a given SD, velocity will determine penetration, the faster the deeper. Now if this seems too simple just remember, we have a perfect bullet. Caliber is listed as number 4, so how does it help to destroy the vitals. Bigger bullets make bigger holes.
Letís delve into those other factors and see how they relate to penetration. Bullet construction and impact velocity must both be considered when selecting hunting bullets and calibers and they must both be matched to the intended quarry or at least for a certain group of animals. Since I have written reams on this subject I will summarize it now by simply saying; the higher the impact velocity, the stronger the bullet must be and impact velocity should be considered as muzzle velocity for bullet selection purposes because we donít know where we will stand when we need it. There are many very good, proven bullets available, we have no excuses. This brings us to velocity, specifically 45-70 velocities. There are volumes of data for hand loading and many custom loads available from varied makers that claim to be as good as it gets to wring every ounce of killing power from this old veteran. Buffalo Bore, Cor-Bon and Garrett are all very popular and of good quality. These range from a 300 grain JSP at 2350 fps to a 500 FMJ at1625 fps, for Buffalo Bore, and they are further labeled, penetrator load and expander load, to avoid confusion I guess. There 430 grain LBT hard cast (solid) penetrator load is listed at 1925 fps and Iíve chronographed these from an 18.5Ē barreled Marlin Guide Gun and obtained a very consistent 1818 fps. So it is my guess that these and all velocities are taken from a rifle with a 22Ē barrel, not 18Ē. Now, even the highest velocity is low by modern smokeless powder rifle standards, but letís assume that these velocities will be the same in our gun and go from there.
This range of velocities, from about 1200 fps to about 1800 fps is what I call puncture wound velocities. I call it that because for a projectile to do damage at this velocity, it must just penetrate from momentum because expansion cannot be depended upon to add any tissue destruction. For a bullet to expand at these velocities it would have to be so lightly constructed that it would destroy itself upon impact with all but the most thinly constructed of targets. This is high performance handgun velocity, and in some cases can make large surface wounds but cannot be relied upon to both penetrate and expand, such as a Swift a-frame bullet would from a 300 Win mag. This leaves the 45-70 right on the edge where the next level begins. This is the 1800-2250 fps range. This is stopping rifle velocity. This is the velocity of the many proven Nitro Express calibers that are still used today to stop charges. But at this velocity expansion is considered a problem rather than a benefit and it would only serve to reduce penetration, so solids or very strongly constructed and always heavy for caliber bullets are used, when dealing with nasty stuff. 500 grain 458ís, 570 grain 470ís and 900 grain for the 618 bore of the 600 Nitro express and with SD of .340, .368 and .337 respectively. When we push the 45-70 to its limit it will be in this category with heavy hard cast bullets, but only at up close charge stopping distance. Actually all the NE calibers have a muzzle velocity of 2000-2100 fps, so when compared to them it is still wanting. Expansion is not a reliable characteristic at this velocity and rather than depend on it, we try to eliminate it when dealing with the tough guys. This is the slot the 458 Win mag was intended for but was found lacking when factory ammo didnít achieve the required velocity. And the 45-70 is not a 458 Winnie! In order for the 45-70 to effectively enter this category of stopping rifles it would have to be fired from the strongest rifle available for it and that is the Ruger No. 1. That would be at more than 3 times its original pressure levels. I have fired the 450 grain LBT style bullets at 2150 fps from my Rugers 22Ē barrel and I donít want to do that. That is very hard on the brass and the rifle. The Ruger is a heck of a lot stronger than Marlin 1895 so Iím sure we wonít try that in the Guide Gun. To use the 45-70 to fill a niche that it was never intended to fill is not going to work well. It is an up close gun; donít try to flatten the trajectory to reach out yonder, which makes it less effective up close. An LBT style bullet of 400-450 grains at 1800 is about it in the Marlin guide gun and it will be at its best.
Now, briefly, for number 6, Bullet Stability, as most know is produced by the spin the rifling imparts to the bullet as it goes down the barrel. True, but how much is enough?
This is a function of surface feet per minute (sf/m), as the bullet rotates, the distance it would be traveling if rotating on a flat surface each minute. It is not rpm but sf/m. So the larger bores will stabilize at lower rpm than smaller bore. Also the longer a bullet the more sf/m it will need to stabilize, this is a length thing not a weight thing. Also a pointed spitzer requires more sf/m than a round nose or flat nose of the same length. (Even though the RN/FN is heavier) It is easy to stabilize a bullet in the air, but to keep it stable when it runs into grass, twigs, trees or a dumb animal is another chore entirely. Yes a bullet must be stable after impact in order to penetrate in a straight line yes it must be straight or it doesnít count. (Remember number 1, we pointed it at the vitals.) Spitzer bullets, particularly fmjís are notorious for veering off course (yaw) due to loss of stability on impact. Many controlled expansion spitzer bullets that fail to expand for what ever reason will do this. So, stability is aided by bullet weight (energy of rotating forces, flywheel effect), blunt configuration, tough, (retains shape) and bullet diameter, the bigger the better. So a good bullet must be chosen and will still be a compromise. For the 45-70 to perform at its best, meaning get the most horse power out of the old war horse, it needs heavy, high sectional density, hard cast, (basically solids) LBT style bullets at achievable velocities, about 1800 fps. Put them in the right spot at ranges of about 100-150 yards and you will see good results.
Weren't this fun. Good shootin'.