Go Figure this

[Mr Peabody]

I got a load for my CZ-75 that shoots well enough you can keep all your shots in a 3 inch circle at 15 yards; all day long. Yesterday I loaded 50 rounds with new W-W brass. The group I shot this morning looked like a shotgun pattern, using what was already loaded in the many times fired brass got me back to my regular group. What gives?

[tsubaki]

I have never been an advocate of sorting brass for accuracy but others swear by it.
Now that you have some legitimate tests to perform, see if there are discrepancies between the two groups. Such as the case volume, flash hole diameters and over all length.

[tsubaki]

This is all assuming that you loaded the different groups the same. Such as the same batch of powder, primers and projectiles.
And also shot under the same weather conditions.
Again others will argue the fact of temperatures and barometric pressure.

[runfiverun]

I would be more inclined to think about neck tension and case length.

[303Guy]

Perhaps it's just the fact of them being new cases. Reload them and see what happens.

[.22-10-45]

Thats why the benchrest shooters fireform all their brass a couple of times before trusting it to an important match.

[mr surveyor]

I got a load for my CZ-75 that shoots well enough you can keep all your shots in a 3 inch circle at 15 yards; all day long. Yesterday I loaded 50 rounds with new W-W brass. The group I shot this morning looked like a shotgun pattern, using what was already loaded in the many times fired brass got me back to my regular group. What gives?


did you chamfer and deburr that new brass?


jd

[country gent]

The new brass may be slightly diffrent than the old in composition of brass making for softer or harder cases with diffrent springiness or tension. It may be lightly thicker or thinner than the old making for a change in case volumne. case head inside of case may be slightly diffrent making for change in volumne. Brass cases can and do vary from lot to lot. Check some of the old brass for volumne by sitting on a scales and with a syringe fill case with water to case mouth level do this on 5-10 cases and average. Do the same with same numbr of new cases and average this will tell you how much diffrence there is between the to batches. (have fired primers in the cases for this) This test will also give an idea which way to go with powder charges.

[Mr Peabody]

I sat looking at things yesterday and found one difference. The new cases had ever so slightly high primers. I really think it's a matter of grip. The new cases have a different amount of it. I got to looking to see when I bought these cases and I found a date of 06/2001. The other cases I'm using are a little newer. Length seems to vary about the same regardless of brand, though all are short. In fact the new W-W cases were close to minimum length where the others were shorter. I reloaded some more unfired cases with a different brand of primer and some of the 1x fired cases too. Using Federal primers got me below flush where the CCI's had been high. We'll see.

[Mr Peabody]

I went out today and shot some more. The once fired cases I had from the last session were used as well as more unfired cases. The once fired did better than the unfired and the many times fired did the best. I think that using a boolit I size at .357 needs a lighter grip than the new cases are giving. Which works for me just fine knowing that the more I use a case the better it get's:-)