Effect Of Bullet Seating Depth On Accuracy

We have always been made to beleiev that bullet seating depth affect the accuracy of the particular load. So we deided to try a test of our own, and see how this works.

We selected a Remington 40X rifle in 222 Remington. It is a standard factory rifle, and the only thing done to it is that we replaced the factory stock with a synthetic stock. The rifle has a 20 inch, heavy stainless steel barrel.

We did not try to find a particularly accurate load for it. We picked a starting load in the Vihtavuori manual, using VVN 130 powder. The bullet we picked is the Bill Brawand 52 grain match bullet.

Brass was from SAKO, originally was from factory ammo. 140 cases were used, we full length sized them after each firing, and we trimmed them after 4 firings.

According to the book, the maximum over all length for this cartridge is 2.130 inches.

With thsi bullet, we found that at a length of 2.310 inches, the  bullet is jammed into the rifling by at least 0.010".

We shot 5, five-shot groups with this load, and shot 5, five-shot groups of loades that have been reduced by 0.020" for each lot.

We continued this until we got to 1.930", then decided to load a last lot of 1.870"

Our bullets were molly coated, and we cleaned the barrel every 100 shots. The barrel was very easy to clean

The results are listed below.

The Remington 222 40X used in this test. It has a Leupold 6.5-20X scope.

On the left is the longest loaded round we could use 2.310 inch. This one is jammed into the rifling. The middle one is loaded to the maximum specs of this cartridge, 2.130 inch. The one on teh right is the shortest round we tested. This one was 1.870 of an inch.