Encore 260 Remington...Weird results

[Rol Page]

I have been working on load development for my Encore 260 Remington Rifle and today I had some weird (to me) results.
 
The brass that I was using was once fired reformed Lapua 243 brass. Nosler 130gr Accubond bullets, IMR 4064 powder, Rem. 9 1/2 Primers.  I am basically neck sizing the cases per suggestions from a Nosler Tech. and seating bullets just short of the lands.  I have a bump comparator to check my sizing die to insure minimal or no shoulder adjustment and a bullet comparator to insure consistent bullet seating depth.
 
100 yd group from a bench was 2.973" while just for giggles I put a target @ 200yds and the group was 0.80"....  With the same loads.
 
I have resorted to using Sweet's 7.62 Solvent to clean my bore between shooting sessions but only use a dry patch between shots at the range.
 
Has anyone had a similar experience?  When I spoke to the Nosler Tech. his parting suggestion was "Don't give up on that bullet, (Nosler 130Gr Accubond) until you try it @ 200yds."
 
Needless to say, I will be putting together some duplicate loads to confirm or dispell the results.
 
Thanks in advance for any and all suggestions.

[Larry L]

I can relate a circumstance I had with a 30/338mag that I had the same issues with. I could not get a decent group at 100 yds regardless of all of the tricks I knew. But the same loads would shoot under 1/2" at 200 yds. I finally called the Sierras folks to ask why I was having the problem and the tech asked if I had any of the targets handy. I got them and we went over all of them at 100 yds. My targets were showing a real light wisp of black to the top side of the bullet hole on the paper. According to the tech, I was pushing these bullets so hard that the core was not a solid when it left the barrel. With the heat generated and the pressure combination, the bullet core was semi liquid when it left. It would not stabilize until the core went back to solid and that was the problem. I solved my problem by going to a heavier bullet for close range shooting but still use the 168 Matchkings for the longer ranges. The real long range stuff I'm using a custom Winchester made 190gr HPBT at 2700'ps and it shoots TIGHT at 600 yds and at 1000yds.
I can't imagine that you're turning up that much pressure with the 260 but it's something to consider. IMR4064 gets pretty warm with max loads in my 7-08 and at night you can see the base of the bullet appearing to look like a tracer from the heat. The bullet is the Speer 115gr HP. Might try changing to a different powder like Varget or AA2520.

[gbjeep]

I have the same problem with my 6.5 grendel. It has been explained to me that the bullet does not stabilize until after 200 yds. I almost pulled my hair out during load development, but now just start at 300. I am using 120/123 gr matchkings. I don't know how much of what i was told was true, but it sure explains a lot. My 1.5 moa 100 yd groups are .5 moa at 400 yds so i just go with it.

[AtlLaw]

I had the same thing happen quite a while back.  Unfortunately I can't remember the rifle or cartridge.     Being senile is no fun... 
 
Anyway, I did some research at the time and came up with the stabilization theory that gbjeep eluded to.
 
Doesn't the long range crowd call that something like the bullet "going to sleep" at a certain distance?