I have full-length sized 50 cases of 300 Winchester Magnum brass. The brass were all once-fired but in two different rifles (some of them may have had different powder charge too). After resizing, I am noticing that the case length (to shoulder datum, measured using Redding Dial-Indicator tool) is not the same for the resized brass. Some are sized to "standard chamber - 0.005 inch". Some other are sized to approximately "standard chamber - 0.002 inch". I wonder what causes this variation:

a) normal tolerance of the reloading press
b) that the brass were fired in two different rifles (but the sizing operation should have eliminated any original difference in length (?))
c) any other factor such as me pressing the handle not with the same force all the time, lubrication issue, etc.

?

I appreciate your feedback and experiences.

Thank you,
-Omid

Think about it for a moment. 0.003 of an inch variation is almost nothing. It's quite literally less than the average thickness of a human hair.

You also fired it in two different rifles.

And yes, any variance in methodology could be sufficient for this small variance.

My first guess is the different rifles. Did you keep the cases from the different rifles separate? Lower pressure charges can also cause a difference that would be most noticeable in long chambers. If you were reasonably consistent in you resizing then slight differences in lube or handle pressure is the least likely cause.

If the brass starts out with different sizes before resizing this can also be a culprit. When shooting different powder loads you will have different expansion of the brass especially when new. Brass springs back. So cases that start larger stay larger than cases that start smaller because it is trying to spring back to it's original size. At least this has been my experience.

I have the redding competition die set. I know what my maximum case expansion is. But I might use 3 different shell holders to get all my brass back to the same size. Well at least within .001.

Thank you for your comments guys! Very helpful, so this is not a problem and could have been due to the "original" size of the fired brass being slightly different.

I should mention that I have found it hard to distinguish between brass fired once in my three 300 WM rifles. All seem to have nearly the same size which is Minimum chamber + 0.000 to Minmum Chaber + 0.002 inch (again measured using Redding tool).

I have been thinking buying the Redding competition dies set (the bushing model) but I have so far resisted the temptation Would that improve my accuracy by any discernible measure? I make loads for hunting and general shooting at the range, not for competition.

Thanks again

I load for four 7 Rem mags. I don’t have time or patience to keep the brass separate. I full length size the cases. All four are sub inch with one of the Sakos almost a one hole rifle. As long as I’m an inch or less I’m fine for hunting. I load all the same length.

If necks aren't lubed sufficiently,you can pull the shoulder coming over the expander. Just a thought.

When brass is work hardened at different rates (2 rifles) the springback will not be consistent when bumping shoulders.

If you were to anneal it would greatly improve the consistency when sizing.

I'm glad you are getting the results you are. I reload for multiple .30-'06, 8x57, .300 Savage, .32 Winchester Special, and .30-30. I used to mix brass between the rifles but have had better results since I stopped.

Thanks again for your helpful comments. I have marked the sized brass in two groups so I can test if this slight difference in case length will make any difference. I am expecting that it should make no noticeable difference in accuracy.

This^^^^^^^

It also gives you higher variance in neck tension as well.

MM

The size difference is moot due to the belt. For hunting loads tuning neck tension has usually not helped accuracy that much for me it does for others. Concentricity is number one and for hunting loads I go to the Lee Collet dies before bushing dies as they are inexpensive and simple and they work.

But the competition dies if set up well do produce concentric loads. The bullet seater can be a source of alignment woes and the types that support the bullet like the competition seaters usually hold run out to a minimum. But anymore I just don't worry about that last quarter to eighth inch of accuracy. I have become the load and go type.

This would be my first guess. Try taking the expander ball out of the die and resizing some of the mismatched cases then see if the shoulder datums are the same. I'll bet they're a lot closer than they are now.

hmmm.. does this imply that one could use a precise neck-sizing die and then run the cases in a "body-die" to get consistent FL-sized brass?