Loading manuals and bullet velocity

[eflatminor]

I'm wondering if it's just me or is anyone else not able to obtain the velocities listed in loading manuals without more grains of powder than are indicated? Stated another way, whenever I use a certain amount of powder, my velocity is anywhere from 100 to 300 or more feet per second slower than what is indicated in the manual. I've noticed this with both of the rifle rounds I load (30-06 and 22-250) from three different bullet makers and their respective manuals: Sierra, Barnes and Hornady. To date, I've simply used more powder to get the velocity I'm looking for, all the while watching for signs of too hot a load. So, are the manuals wrong or am I doing something wrong?

 

[Grandpa Shooter]

Unless you are using exactly the same rifle or pistol, and are shooting under the same atmospheric and weather conditions you won't get exactly the same results. You are doing what all of us do. Working up your own load using their data and altering it to fit our expectations. Just be careful not to overtax the action on YOUR firearm!

 

[USSR]

So, are the manuals wrong or am I doing something wrong?

No, you're not doing anything wrong. All the reloading manual are vetted by their lawyers (can't have any lawsuits now, can we), so even in a worse case scenario, there is no way you can blow up your rifle. By knowing what velocities are safely attainable with your rifle/load, and carefully working up your loads by running them over a chrony while looking for high pressure signs, you are doing exactly what you should be doing.

Don

 

[Steve C]

In .357 mag I generally get a little better than the manuals by Speer and Hornady with a 6" revolver, Sierra is almost always right for a 4" revolver though their data comes from a 6". The powder company data from Hodgdon is usually a lot faster than what I can get though they're usually taking velocities from a 10" or longer Test barrel. Winchester data published by Winchester gives me the same velocities as their factory ammo. Alliants listed velocities are usually over stated.

I'm shooting in a warm climate (AZ) and over 1000 ft elevation. My 4" velocities are

 

[Ol` Joe]

It depends on the data and the firearm. In my 45acp and 6.5x55 I get very close to the book.My 30-06, 708, and 223 give lower velocities then the book. Then there is my 270 Win that gives the book max velocity with from 3 to 4 gr LESS powder then the books calls for.
The chamber/bore volume, components used and temprature, ect must match or you will get different then the book. The SAAMI spec chambers and bores are normally much tighter then the ones we get from the factory and make for a lot of variation. changing powder lots, primer type, ect adds to the difference. If you use the exact components listed, and load to the COL recommened, and test at the books test temps, you should be fairly close to book velocity.

 

[brickeyee]

There are a huge number of variables that all play in the final velocity.
Every machined part has a tolerance.
If the manufacturer uses pressure barrels, they tend to be at the tight side for chamber size (produces higher pressure).
Add in the lot of powder may not be the same (even burn rate has a tolerance), primers, bullets, case capacity, bore roughness, etc.