Home Forums Reloading Big Game Rifles Why/How does.280AI bullet seating depth affectd accuracy?

In trying to work up loads for my 280AI I couldn't get groups less than 1.5" no matter what bullet/powder/primer combo I tried. Finally I tried seating .020 off the lands instead of .010 and the groups shrunk to 1.25". Then I went .040 off the lands and the groups went to 1.0". Next time I go to the range I will try.060 off and see what happens. I have never experienced this before. I have two questions in regard to this:
1. Why does seating this far off the lands help accuracy?
2. Is this a situation that comes up from time to time, or is it rare?
Thanks

No telling with each rifle. Had an '06 that did best with almost a .250" jump.

Whatever works

Mine is reamed for SMK's so in effect has a free bore for everything else lighter or shorter. Shoots sub MOA but still working on it so don't know ultimately what it will do.

I would say it is a little unusual but not that uncommon. I would also bore scope it to check for tool marks or anything that might affect the seating.

I my experience every rifle is little different. I have many that like .001" bullet jump after the case is fire formed. I have a very few that work best with a bullet jump nearly .01". Some of my old Weatherbys have so much free bore that is not possiable to even touch the rifling with the bullet. Even with the old Weatherbys I can group well under 1/2 inch, it just takes time. I had a 7mm STE built up and during barrel break-in I had seated the bullets out to the rifling loading them one at a time, but in practice the bullets had to be seated nearly a 1/4 inch shorter to function through the action. In this case the accuracy was the same it still shot about 1/2 inch at 100, not bad if you consider it is a lever action designed over 100 years ago. In your case I feel the .280 AI caliber has nothing to do with the seating depth vrs accuracy, it is this case in many rifles regardless of the caliber. Good luck!
Good shooting!
Marcus.

My 280 AI shoots 3/4 inch at 100 after breaking barrel in. nosler custom brass 140 acubond .030 off lands also 140 barns ttsx .040 off lands IMR 4831 pwdr starting load 56GR 2880 velocity. I am confident the group will get better.

Mulepacker,
59gr IMR4831 is giving me about 3150 with a Sierra 140BT in a 24" Shilen tube. Your 3/4 group sounds real good to me! Tomorrow I will try this load seated .060, .080, and .120 off the lands to see if the accuracy improves. IMR4831 has been my most accurate powder. These 280AI's seem to have a mind of their own as mine HATES RL-22 and Accubonds. Go figure. I have yet to try the TSX's but probably should as they shoot lights out in my 338Win Mag. I'll post the results of tomorrows shoot tomorrow I hope.

I shoot 140BT just .010 off the lands that will shoot minute of chicken egg at 200 yds. with great consistancy! I have seated them out to .020 that did not shoot as well. Rifle bbls. are all different and will require different loads. Keep working up your load and seating depth for the best accuracy.

Kingmanguy,
If I can get 3150 with 59gr out of my pac nor 24" tube I will be happy. I also have a 338 that shoots TSX's SUB-MOA. The past few years loading the lighter 185TSX and 210TSX have proven to be both accurate and mortally efficient. 225gr and 250gr are probably more standard loads for the 338 but its been fun playing with the lighter less recoil.....grin.

Lets talk 280AI and 338 somr time PM me with a phone#

Wade