Up until now I have been full length re-sizing for my .300 win. I have run thru about all my brass, so now all the brass I have has been shot thru my rifle. I was going to try and just neck size the next loading. Do I have to drop a few grains of powder? Am I going to get different pressures with the brass being tighter in the chamber? If this doesn't have a positive effect on accuracy, I will go back to FL re sizing. Thanks Guys

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I was going to try and just neck size the next loading. Do I have to drop a few grains of powder?

In my opinion, NO

The unsized brass acually gives you a "larger" chamber if you disreguard the brass in its fully expanded form. The load should be fine as is as long as it was safe in your FL sized cases. Sizeing isn`t an issue.

Thanks Guys. I was thinking that if the brass was tight in tighter in the chamber with less expansion room the pressures would be greater.

No, untimately all full pressure rifle loads (modern of course, no black powder here) expand the brass to fit the chamber...by neck sizing you are just leaving the brass at that fully expanded state. It is the ultimate volume of the combustion chamber that you are concerned with...and it's the same at the end whether you FL size or neck size the same piece of brass.

That makes perfectly good sense to me. I should have thought of it. Thanks

You will just have 30-50 fps more velocity with the NS'd cases given all other aspects of the load are the same. Accuracy may improve also. The reason is it takes more energy to expand the FL sized cases than the NS'd ones. That energy comes from the expanding gas of the burning powder. Since that energgy is not used expanding the cases it pushes on the bullet. I've measured the effect many times with the chronograph using many different cartridges.

Larry Gibson

I am hoping for the accuracy to improve, of course. Also I would think it would extend case life.

CDH is right, the brass expands to near chamber size the first firing. New brass can be much smaller with a lot more headspace but once it is fired it is within .002" of being too tight in the chamber to cycle well. Each subsequent firing hardens the brass and reduces springback until usually by the 3rd or 4th you will have to push the shoulder back.

After you start pushing the shoulder back, it is best to have a gauge so you don't push it back so far that you are overworking the brass. I use the Stoney Point Head and Shoulders Gauge and push the shoulder back .0015" for Partial Full Length Resizing.

Maintains your accuracy and doesn't overwork the brass.

quote:

Originally posted by chain:
Up until now I have been full length re-sizing for my .300 win. I have run thru about all my brass, so now all the brass I have has been shot thru my rifle. I was going to try and just neck size the next loading. Do I have to drop a few grains of powder? Am I going to get different pressures with the brass being tighter in the chamber? If this doesn't have a positive effect on accuracy, I will go back to FL re sizing. Thanks Guys

No, you don't have to reduce the powder charge-if anything the fire-formed case will take a little MORE, but in any case, you sure can use the same charge.....