Anyone accurately tested the effects of seating depth

[si-snipe]

Hi guys

Has anyone (keeping all of the variables the same) tested the effect of COAL on accuracy? If so what did you discover? I know that many people seat the bullets well out to COAL in excess of 2.30" but many stick to factory length too both seem to have accurate results. So I am interested to see how many people have found variations in accuracy with different seating depths?
Can you please specify group size at specific COAL and rifle used.

Many thanks,
Si

[acloco]

My factory chambered 204 prefers 0.050" off the lands....which is longer than standard COAL.

[Hotshot]

I tried .020 off the lands on my first 204 w/39 gr SBK's. I now have three 204's and I've had two others. They all had slightly different distance to the lands as measured with a stoney point. I've never changed my seating die setting because all the rifles shot very well with the same load. Several friends have also shot my ammo with very good results. Magic COAL is 2.303 for me. No scientific testing to back that up except nine rifles liked it and none didn't. If I found a rifle that didn't like this load, I'd try .010 longer and shorter to see if it made any difference, because so many rifles have shot the load so well. If that didn't work, I'd probably trade off the rifle.

[Jim White]

I have test under those conditions and have found it does matter. However, there are trade off's. With the 204 I don't do it because there is so-much jump to the lands and that creats less neck tension for me.

For my 223 80 SMK/AMAX and 75 AMAX, 6mm (105 AMAX) and 308 175 SMK, I do it. For my 6mm with the 105 AMAX it makes that rifle a single shot because the rounds are to long to function as a repeater. The same goes for the 223.

HTH,

[si-snipe]

Thanks guys.
Jim - what would be the down side to a reduced neck tension in the .204?
Cheers,
Si

[Jim White]

In my case, the chamber has a lot of free bore. Couple that with the short neck of the 204 round there isn't much neck left to adequately seat the bullet if I wanted to get out close to the lands. So I just do the MAX OAL 2.260 IIRC and have loads that shoot real good.

[rfurman24]

Both of my 204s are very sensitive to seating depth and both prefer different seating depths. Groups will go from .25 to over 1" in my Cooper with different seating depths.

[Codeman]

With my rem 700, I can't reach the lands (not without basically zero neck grip). I have tried many seating depths varying from factory to 2.355. All shot good in my gun. I finally settled on 2.300 just because I shot the best group of my life with it.