[Unclenick]

Markr,

Alas, there is no way to tighten the brass from the outside without indenting the bullet as the brass tends to spring back from applied pressure. The slight indentation is needed to give it a "hook" to hold on with. If you pull a bullet successfully crimped with the Lee die and mark the side with a Magic Marker, then pull it along a flat surface like a pane of glass, you will the marker remains where the crimp was because the bullet has, indeed, been narrowed where the die touched it. If it hasn't, you didn't have the die adjusted to give you a very serious degree of crimp.

The above was the basis of the advertising "feud" that went on between Lee and Sierra for a few years back in the early 90's. Sierra didn't want their carefully uniformed bullets indented for best accuracy, while Lee claimed accuracy was improved by their crimp which improved ignition consistency. In the end they were both right under the right set of circumstances. Under some conditions, like extreme long range shooting, the indentation's effect on ballistic coefficient made its consistency and uniformity extra critical and it could become a dominant error term over a long flight. Guys with benchrest chambers who were making perfectly uniform ammunition with good case fill could introduce bullet tilt and other issues with that crimp that a gun grouping in the tenth inch range can reveal.

On the other side of the coin, if a fellow was shooting in a wide range of hunting temperatures, the extra start pressure from increasing bullet pull could improve ignition consistency enough to get better accuracy. If he had a gun with a whippy barrel, that improved consistency could keep the bullet exit timing closer to the same phase of muzzle deflection every time. If he had a self-loader, like a service rifle, that tended to push bullets in or tip them, the crimp could help prevent that irregularity.

So, the bottom line is you have to try it in your gun. As a general rule, I think you'll find that if your gun's best groups without crimping are no better than about 1 moa, the crimp may provide help. If your best group without crimping is under 1/2 moa, it may make it worse. This happens because of the trade-offs involved.


hhunter318,

As to neck tension, generally speaking, Mr. Guffey has it right: more is better from the starting pressure and ignition standpoint as long as it's consistent. Military match ammo in a number of instances has been found to be more accurate than the same components loaded at home, and that's been traced to the military pitch seal gluing the bullet in and increasing start pressure. Apparently that can be more consistent than neck tension alone.

If you want to get fancy, RSI sometimes will do a run of their Load Force instruments, which measure to the nearest pound the force used by a press to seat each bullet. If you sort your loads by seating force, it can indeed get you another increment of precision on your target. It's another one of those things that probably won't help if you have a load shooting much over an moa to start with, but which can help make an moa or less get a bit smaller.