Loads for different bullet types

[syh]

This might be a really novice question, but something I never put much thought into before now.

Looking through load data, there are differences between FMJ, jacketed HP, plated, etc.

Why?

Also, I'm loading some Frontier "CMJ cast". Should these be treated any differently than than FMJ?

Thanks ahead of time!

 

[Marlin 45 carbine]

jacketed slugs produce higher pressure due to friction than cast slugs.
generally speaking cast slugs will begin to 'lead' the barrel and cone (on revolvers) after about 1100 fps most barrels and loads. good lube and sizeing to bore with good powder keeps this to a minimum.

 

[helg]

In addition to friction factor, which is mentioned by Marlin45, different bullets differ in length. Longer bullet is seated deeper. This reduces volume, where powder starts to ignite. Same amount of powder in smaller volume means higher pressure. This is the nature for load adjustment.

 

[1SOW]

+1 on the previous replies.
A large number of variables come into play.

friction/heat
bullet overall length-ogive determines length contacting the lands
bullet dia.,weight & composition
YOUR Gun: Bullet nose shape vs chamber tightness and proximity to the lands may drive your gun's Max. OAL which again effects pressures and powder loads you can use
All (And more) drive the pressures and powder speed needed to safely fire the bullet.

In 9mm: 124 gr JHPs may need to be loaded with x.xgrs of win231 at 1.09" OAL to get 1065fps.

124 gr FMJs may need x.y grs of 231 and an AOL of 1.13 for the same 1065fpm

The plated bullets may need to start using loads for lead bullets.

etc, etc,etc

Published load data gives you safe starting loads to work up to the bullet performance you want in your gun.



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