.308 win. case trimming lenght

GhillieShooter

GhillieShooter

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Hi all, I am wondering, if variation in "case trim" will affect accuracy/pressure/muzzle velocity etc?

Generally I see a recommend "trim to" length of .308 being 2.005", will a batch of 308.win. cases varying from 1.995" to 2.000" be ok to safe use? i Did 40 round norma case like that...Was planning to put some Sierra 168gr. HPBT on them.

Thanks
 
Safe to use, yes, but you'll have varying OAL due to the bullet being seated to different depths. Trim 'em all to the same length, then chamfer and deburr. It's one of the important steps when loading match grade ammo. I'd load your Norma brass with a less expensive bullet and shoot until you can get the 2.005". A thou or two plus or minus will do as long as you can get 'em all the same.
 
Do you, guys, see a difference with a .002" variation on the lenght of the case when shooting out to 300 meters?

Which is the tolerance on that?:confused:
 
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sunray said:
Safe to use, yes, but you'll have varying OAL due to the bullet being seated to different depths.
Click to expand...

If you leave your die at the same spot, your OAL will be the same for all of them, just some will have a couple thou more bullet sticking out. The case does not touch the die, or go further into it due to a shorter length.
 
GhillieShooter said:
Do you, guys, see a difference with a .002" variation on the lenght of the case when shooting out to 300 meters?

Which is the tolerance on that?:confused:
Click to expand...

As stated I trim mine to 2.000", Then I batch them by weight into 1 gr batches. Some cases may get fired 2-3 time more than others. Some cases may get neck sized while others in the same weight batch might get FL sized. (which by the way will stretch the case more than shooting it).
So I might end up with some cases .010" longer than other in the same box, but all the same weight. I shoot these out to 1000 yards and see no difference in accuracy.

When seating bullets the seating depth of the bullet is not effected by the length of the case. If you mic the length of match bullets you will see they are not all the same, don't worry about this. The best way to make sure the seated is to the proper depth is by seating so the ogive is the same.
 
maynard said:
As stated I trim mine to 2.000", Then I batch them by weight into 1 gr batches. Some cases may get fired 2-3 time more than others. Some cases may get neck sized while others in the same weight batch might get FL sized. (which by the way will stretch the case more than shooting it).
So I might end up with some cases .010" longer than other in the same box, but all the same weight. I shoot these out to 1000 yards and see no difference in accuracy.
Click to expand...

Maynard at what stage in the reloading process do you trim your brass. I have learned that for consistancy to trim my Brass AFTER I have neck and FL size then sort them by weight. I seem to get more consistancy this way.

To ghillieshooter

the short answer is yes to all three the question is how much and is it noticable. For short distances 300 or less you may not see a noticable difference in your group size. However the further away you shoot the more pronounced the difference in trim length will be.
Just for Sh$t and giggles differences in brass length will have a larger affect if you jump or soft/hard seat your bullets into the lands. Jumping will show a greater variation in velocity then if you were to soft/hard seat them.
If you don't want to trim the brass to the shortest length an alternative solution would be to simply shoot the 1.995 together and then the 2.000. Take notes when you do and see if you notice a difference in vertical between the two brass lengths
 
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Trevor60, I use a Gracey trimmer so in order the get a consistant trim length the brass should be FL sized. Brass can grow more by FL sizing than by shooting it, so I usually just neck size.
When I rebarrel is usually the time I trim to length. If I start out with brass at2.000" it takes a quite a few reloadings to get too long.
If the ammo I have loaded ends up being shot from one of my other target rifles, I will FL resize and check the length, trimming when needed.
Just to clear up one thing that may not be clear in my previous post. Each MTM box of ammo either FL sized or neck sized stay in the same box, they are not mixed.
 
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