Sometime in the past, I did a test on the effects of seating depths on accuracy, and frankly, saw very little difference.

I used match bullets.

Some members have been saying they get better accuracy with mono bullets if there is a jump to the rifling.

This jump seems to vary according to the source.

I am running an experiment to see what the results are.

Rifle is a Kimber 8400 PATROL TACTICAL HB.

Bullets are original BARNES 180 XBT.

Load is 36.0 VVN 540.

I just looked in the book, and added the minimum recommended charge to the maximum and divided by two.

Started off with cartridges loaded to 2.800 inch, which the maximum for the 308 Winchester.

1. 0.596
2. 1.233
3. 1.058
4. 1.250
5. 0.985

Average 1.0244

2.770"

1. 1.611
2. 0.741
3. 1.426
4. 1.428
5. 1.167

Average 1.2746 inch.

I will continue shooting with each increment 0.030 shorter.

Have fun guessing the results.

I will post all targets once I am done.

The rifle does foul quite a lot.

I am cleaning the barrel between each batch.

Comparing one rifle to another is just nuts. There are too many variables to consider. How long is the lead? What type of rifling? Where is the origin of the rifling? Bore size? Brass used and trim length? And on and on.
I do crimp. Not crush. A measured pull of 18 pounds is used. This way, all rounds fired have the same force needed to get the bullet moving out of the case. All I shoot is long range and my loads have won many matches. I load as per the specifications of the cartridge design. This being all bullets will jump into the rifling.
Thanks for your data. Obtaining ballistic data is fun.

quote:

Originally posted by Rapidrob:
Comparing one rifle to another is just nuts. There are too many variables to consider. How long is the lead? What type of rifling? Where is the origin of the rifling? Bore size? Brass used and trim length? And on and on.
I do crimp. Not crush. A measured pull of 18 pounds is used. This way, all rounds fired have the same force needed to get the bullet moving out of the case. All I shoot is long range and my loads have won many matches. I load as per the specifications of the cartridge design. This being all bullets will jump into the rifling.
Thanks for your data. Obtaining ballistic data is fun.

Agree that each rifle is a law unto itself.

But, there have been several people saying they get better accuracy if the bullet has a jump.

Some go as far as stating that this jump should be of certain distance.

I think some manufacturers reported as saying certain seating depths are required for best accuracy.

With normal match bullets, in my past experiment, there was no discernable difference.

I seated bullets jammed against the rifling, to them just barely held by the neck.

I am trying to satisfy my own curiosity.

With specific match rifles and ammo, one does need to go to extremes to eliminate any variables.

I have a heavy bench rest rifle, built by my friend Dwight Scot, who has built many rifles that have won championships in the bench rest matches.

I have shot groups with it that are actually impossible to measure!

That is not the case with hunting rifles shooting hunting bullets.

I agree all rifles are different and I think seating depth can make a difference, with Barnes TSX and TTSX, anyway. They both seem to shoot a bit more accurately in my rifles seated between .030” and .050” from rifling. My son has a Win M 70 in .375 H&H, identical to mine but his shoots 40-60 fps faster than mine with the same load and his is more accurate with these bullets seated .025” from rifling. This is with .375 and down, I’m not man enough to be able to tell the difference in .416 thru .505

I know from experience that Berger bullets are particularly sensitive to seating depth.

I understand it has everything to do with the bullet’s secant ogive.