Cartridge Length - Book vs. Practical

[Fox1]

I'm loading 9mm, 115 gr MagTech or Rainier bullets at 4.2 gr.

The Hornaday book calls for a C.O.L. of 1.100" but it comes out pretty short. Very noticeable when placed beside factory loads.

I measured some Winchester factory rounds and their C.O.L. is 1.160".

I realize that the depth of the bullet can vary internal pressures but what should one do in a situation this extreme?

I have been loading them at 1.135" then testing them in my magazine and they work just fine. They also shoot fine as well.

Do I just stick to 1.135" from here on?

[Archie]

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.

[TEDDY]

best post archie:gives them somthing to think about.

[Smaug]

Originally Posted by Archie

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.

300 gr. bullet in 9x19? That is either a typo or a very risky, compressed load. Please confirm.

[rg1]

A difference in bullet shapes causes lots of questions about overall length in pistol and rifle. 9mm 124 gr. FMJ bullets I've used vary in their tip shape. Winchester has a more sharply tapered round nose and is why the factory seats them longer. MagTech round nose I've seen are a blunter shorter taper. Remington and Speer 9mm bullets have a little different shape too. That's one reason you see overall length variations in pistol and rifle.
Winchester .223 55fmj's and military 55fmj's are sharper pointed that most others and overall length for the sharper tipped bullets are 2.250" while other less pointed 55 fmj's recommended length is as short as 2.200".
One thing I've played with is using a factory cartridge to set the seater die just to see the outcome. I've put the factory cartridge in the press and screw the seater stem down to just touch the factory bullet. Then I try one seating different same weight bullets just to see what the overall length comes out to. As the seater stem touches the bullet on the ogive or taper of the bullet, you'll get different oal's and sometimes the oal matches the book for the bullet you've used. Feeding reliability in your pistol is the main concern plus you don't want to use max data and seat bullets deeper as pressure will increase.

[keys85]

How much velocity loss would you lose, say, per .010" you seat longer?

[Bogie]

For handguns, I generally load as long as possible, and still have adequate function - ie., the bullet doesn't stick out the front of the cylinder, or the case doesn't hang up on the feed ramp, or the bullet doesn't get jammed by the lands.

For single shot rifles, I usually jam slightly into the lands. For magazine fed rifles, I go the longest that will fit in the magazine and feed.