We all know that case length can be important, esp. if there is too much. However, assuming that it is not so much so as to effect pressure, how does it effect accuracy? If there is a variation of, say .020', there will be a difference in neck contact with the bullets. That would affect bullet pull. Does anyone have any idea of the effect on accuracy? Any bench comp. guys here?

Chambers can be a good bit longer than brass.
You might measure your chamber by expanding a longer case. After measureing your chamber you will know the exact maximum lenght of case your can use.
If you want to know the details PM me.
I have formed many military cases and I normally make them the lenght of the chamber.
For example most military Mausers and Mannlichers are about .040 (1mm) longer than the specification for maximum case lenght.
I usually make the cases the maximum length to fit the chamber. When they are fire formed the first them the usually get a little shorter.
Once they are resized they may reach maximum lenght. At this time I trim them about .002 less than the chamber. After the next firing I trim to .005 short and pretty much do not have to trim again for a long time.
With jacketed bullets I see effect on accuracy.
With cast bullets I want to leave the case only about .001 to .002 short. This prevents the cast bullet from upsetting and forcing a ring of lead ahead of the case into the gap on each shot.

quote:

Originally posted by Brice:
We all know that case length can be important, esp. if there is too much. However, assuming that it is not so much so as to effect pressure, how does it effect accuracy? If there is a variation of, say .020', there will be a difference in neck contact with the bullets. That would affect bullet pull. Does anyone have any idea of the effect on accuracy? Any bench comp. guys here?

Uniform case length is one of the factors in case uniformity, along with total case weight, neck thickness, etc., etc. Presumably, the more uniform the case, the more accurate the load.

I don't recall any studies comparing the effect of mixed (but not excessive) lengths of cases on grouping. I would think such effect would be small enough that it would only be identifiable in very accurate bench rifles. It would probably exist to the same degree in a .75-1.50 MOA hunting rifle, but would likely not be measurable within the accuracy limitations of such a rifle.

By the way, some reloaders are anal-retentive about the uniformity of the weight of their cases. However, the weight means nothing if the cases are not first trimmed to a uniform length.

Thanks for the comments. Stonecreek, I agree accuracy variance due to case length differences of .010-.020 or thereabouts probably would be undetectable in this rifle. A problem I'm having is that the fireformed R-P cases for this 257 AI are too short to provide for decent seating of 100 gr. bullets. That is, not enough bullet in the neck. I like to use high quality cases, such as Lapua, but I doubt they are available in 257 Roberts. I also agree about case weight. I do weigh cases, but only to identify those that are way out at the ends of the bell-shaped curve. Excess runout, on the other hand, can significantly affect accuracy.

SR4759: Thanks for the offer. I'll take you up on it.

You won't notice the difference on a hunting rifle, but would on a bench rest gun that shoots into one hole.