Powder charge for longer bullets

zZ_denis

zZ_denis

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I have some 155 grain bullets that i want to load in .308, but they are SIGNIFICANTLY longer than the typical 155 gr J4 bullet that the loading manuals have data for.
To keep the OAL the same (2.800"), the bullet would be sitting MUCH deeper in the case.
How much would the maximum powder charge differ in a load with the same bullet weight, but approx 30-40% longer bullet?
 
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2.800" is AOL for feeding from a magazine. Seat them .020" off the lands and fire them single shot just like the Target Rifle and F Class boys do.
 
46.0 gr of Varget with a 155 is the load many Palma shooters use. I use this load with 155 gr SMK's, Nosler's, Berger's and Lapua's.
 
Like Maynard I don't change my powder charge, when switching to a different brand of the same match grade bullet weight, for rifles only.
One time I switched from a 155 Berger to a 155 Lapua scenar and I found it was more accurare with 1/10 of a grain less, but at the same OAL. All this in my 308.
 
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You don't mention the powder, the bullet, the case, the load you have been using, or whether your existing combination results in a compressed load.
In general, if you are changing something, it is a good idea to reduce the powder charge, and work back up.
 
Bump.

I want to be able to use these loads in a semi auto (with a mag), so the OAL can not exceed 2.800"

Perhaps you guys misunderstood me. Its not just the brand of the bullet that is different. I got some old surplus bullets that are A LOT, ( like 30%) longer than typical 155gr bullets, yet, they weigh the same (155gr). Would the bullet sitting 30% deeper in the case increase pressure to dangerous levels?

Tiriaq, these are plinking loads for semi-autos. I use whatever cases/powder i have on hand. I usually load "plinking loads" exactly half way between min and max charges recommended in the manual. With the bullets in question, most powders i use would be compressed. I dont know what the bullets are called exactly. They are old, pulled .308 mil surplus, 155gr FMJ
 
What part of "In general, if you are changing something, it is a good idea to reduce the powder charge, and work back up." don't you understand? A bullet that is 30-40% longer that normal goes beyond "in general" and you should start over and work up.

"Generally" the length of a standard bullet does not have that dramatic on an effect on case pressure in a rifle as compared to a handgun cartridge. A compressed powder charge is not necessarily a bad thing, unless perhaps you were heavily compressed with the standard bullets.

There is no magic formula for longer than average bullets. Don't forego proper load development, especially with non-standard components, to save a few bullets or a few grains of powder.
 
If two bullets are the same caliber and the same wieght, but one is significantly longer than the other, it must then have a shorter bearing surface and and therefore would produce less pressure, so there would be no need to reduce your powder charge,in fact you might find that you have to slightly increase it to keep the same velocity. Seat the bullet as long as your chamber will allow, best accuracy is most often with minimal jump to the lands anyway.
 
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