260 Rem with 243 cases better groups?

[Roberto]

Hi Guys, I recently sized 243 cases up to 260 and found that my overall groups with the 243 cases are shooting tighter and higher at 100 and 200 yds. I loaded the same powder in the 260 cases IMR 4350 with 44 grains with 120 spitzers. I also annealed all cases before reloading. I shoot with a Remington cdl 260 with 24 inch s/s barrel with 1 in 9 twist. Any idea why my groups are different?

Cheers

 

[RT2506]

I have no idea why your groups are different but my buddy found out the same thing. This was when Remington first came out with the 260 in a 700. He got the SS with a 24" barrel. You could not hardly find any ammo much less cases at that time. He did find ONE box of ammo and was using these cases to reload and work up loads. There was not any load data then either. He was using H4350 and Sierra 120 and 140 gr bullets. He had a new bag of Rem Nickle 243 cases so he decided to neck up a few and try them. His groups went down to bug holes and he still has never went back to 260 cases.

 

[elkaholic]

I have no idea why your groups are different but my buddy found out the same thing. This was when Remington first came out with the 260 in a 700. He got the SS with a 24" barrel. You could not hardly find any ammo much less cases at that time. He did find ONE box of ammo and was using these cases to reload and work up loads. There was not any load data then either. He was using H4350 and Sierra 120 and 140 gr bullets. He had a new bag of Rem Nickle 243 cases so he decided to neck up a few and try them. His groups went down to bug holes and he still has never went back to 260 cases.

Are you using the same brand of brass? Brass being equal, about the only difference I can think of is you will thin the neck somewhat by necking up the .243 which could cause a different POI. You might also shorten the brass length a little as well? As far as accuracy goes, it just might make a difference in what your particular chamber likes?..........Rich

 

[Roberto]

Hi Guys,

Thanks for the info, I am going to measure the case capacity and compare volume of the different cases.

Cheers

 

[djtjr]

Different brass has different wall thickness which translates to different internal volume so with the same powder charge and different case capacity there is a different amount of presure and therefore velocity that your gun could like more. Also perhaps the brass is more uniform and or consistent where neck tension is better and again more consistent which is perhaps why your gun likes it better. There are a lot of variables that could make this load better but at least you found it.
Best,
D