The Firing Line Forums - View Single Post - Cartridge Length

Archie · September 28, 2008, 05:00 PM

Consider that any number of specifications generated by SAAMI or any other source are for commercially manufactured ammunition intended for use in any commercially manufactured firearm. Over all length is an assumed guideline, a starting place if you will. They are not wrong or to be ignored, but they are somewhat arbitrary.

Some of the following should be self evident upon reflection and some may not. Please feel free to use that part of it with which you feel comfortable.

Loaded cartridges have to be short enough to fit into magazine, cylinder or cycle through action (think lever action rifle).

Loaded cartridges have to be long enough to properly function through action (think semiautomatic pistol or lever action rifle).

Loaded cartridges have to be short enough the bullet doesn't hang up on the rifling or chamber leade and keep the loaded round from chambering fully.

Then... the depth of seating of a given bullet changes the internal volume of the combustion chamber. A larger internal volume will - all other factors being equal (bullet, powder and charge, primer, case structure) - give less pressure and therefore less velocity. Some of my handloads run at book maximum (which varies from book to book, as many of you may have noted) but don't deliver the same velocity. Sometimes, they run a little over and I back off.

This partially explains, by the way, how it is my four grain load of Bullseye with a 300 grain bullet outruns your exact same load by 100 fps. I seat mine deeper for some reason. Not to mention in reality there is no such thing as 'exact same'. (Above paragraph has numbers picked at random for illustrative purposes - do not use as load data.)

So, my standard operating procedure (SOP) is to fiddle with a dummy round until I get something that works in terms of paragraphs one through three above, then work up a load using standard references and a chronograph. (Sometimes a peak pressure meter, too.) Most of my handgun loads these days are for accuracy, so I don't worry too much about top end, whole hog, 'max' loads. On the other hand, I do have a couple magnum handguns and a Super 38; if they don't run fast and hot at need, there is no point in having them.

Hunting rounds are similar. Usually they don't require 'max' loads, but a good healthy load delivering accuracy.

September 28, 2008, 05:00 PM	#2
Archie Senior Member Join Date: May 27, 2000 Location: Hastings, Nebrasksa - the Hear Posts: 2,209	Couple of factors at work. Consider that any number of specifications generated by SAAMI or any other source are for commercially manufactured ammunition intended for use in any commercially manufactured firearm. Over all length is an assumed guideline, a starting place if you will. They are not wrong or to be ignored, but they are somewhat arbitrary. Some of the following should be self evident upon reflection and some may not. Please feel free to use that part of it with which you feel comfortable. Loaded cartridges have to be short enough to fit into magazine, cylinder or cycle through action (think lever action rifle). Loaded cartridges have to be long enough to properly function through action (think semiautomatic pistol or lever action rifle). Loaded cartridges have to be short enough the bullet doesn't hang up on the rifling or chamber leade and keep the loaded round from chambering fully. Then... the depth of seating of a given bullet changes the internal volume of the combustion chamber. A larger internal volume will - all other factors being equal (bullet, powder and charge, primer, case structure) - give less pressure and therefore less velocity. Some of my handloads run at book maximum (which varies from book to book, as many of you may have noted) but don't deliver the same velocity. Sometimes, they run a little over and I back off. This partially explains, by the way, how it is my four grain load of Bullseye with a 300 grain bullet outruns your exact same load by 100 fps. I seat mine deeper for some reason. Not to mention in reality there is no such thing as 'exact same'. (Above paragraph has numbers picked at random for illustrative purposes - do not use as load data.) So, my standard operating procedure (SOP) is to fiddle with a dummy round until I get something that works in terms of paragraphs one through three above, then work up a load using standard references and a chronograph. (Sometimes a peak pressure meter, too.) Most of my handgun loads these days are for accuracy, so I don't worry too much about top end, whole hog, 'max' loads. On the other hand, I do have a couple magnum handguns and a Super 38; if they don't run fast and hot at need, there is no point in having them. Hunting rounds are similar. Usually they don't require 'max' loads, but a good healthy load delivering accuracy.