Does a half of grain of powder make that much difference?

[tcob68]

I have a Cooper 22 MVT in 6.5-284 that I took with me to an NRA summer course in precision bedding taught by Speedy Gonzales. After getting it ready to bed the bases Speedy looked at the mounting holes on top of the receiver and said "look at this". The mounting holes on the rear of the receiver were so far out of line you could see it with the naked eye. We drilled them out to 8-40 and then bedded the bases. I can't say for sure if it shoots better but it does seem to be more consistent.

 

[pills]

I had the same exact problem I started my cooper m52 by shooting 140 accubonds with 2 different powders at several different loads...I would get a 1/2 group then1 1/4 and another 1/2 etc...tried everything I could think of shorter, longer etc...then my shipment of 140 Berger Vld hunting came in. 1st group .25" no bs and no problem being under 1/2 MOA with every group so far out to 400....I'm not saying you have to shoot bergers but I would try different bullets.

 

[deertroy1]

This is from Cooper Site

The now famous 1/2" at 100 yards Cooper Firearms of Montana, Inc. accuracy guarantee for center fire rifles began in 1998 with the introduction of the "Varminter" in Models 21 and 22. Soon after, the Montana Varminter became an instant classic.

Don't they send test target and I'm not sure of the yardage but why don't you call them see what they shot?

They shoot 130gr Sierra MK with an unspecified charge of IMR 4064. They use to specify the charge weight and I believe it was 39grains.

 

[deertroy1]

I had the same exact problem I started my cooper m52 by shooting 140 accubonds with 2 different powders at several different loads...I would get a 1/2 group then1 1/4 and another 1/2 etc...tried everything I could think of shorter, longer etc...then my shipment of 140 Berger Vld hunting came in. 1st group .25" no bs and no problem being under 1/2 MOA with every group so far out to 400....I'm not saying you have to shoot bergers but I would try different bullets.

That's what I'm doing. I have some 140gr Bergers I will try. Does your M52 have a long throat?

 

[pills]

No . I measured the OAl to the lands to be 3.044 with the 140 accubond. Tried from there shorter without getting good results. I even called Cooper who told me they got their best loads with RE22 and a 142 SMK seated to an OAL of 3.000. I know its a different bullet but if figured I would give this OAL a shot with the accubond. Still no good. I got ahold of some 140 bergers and I made the 1st loads with the dies set the same as I had for the accubonds. I knew due to the profile this would be longer but should be the same distance off the lands. They shot great at this length so I didn't mess with it anymore. I think the OAL is 3.100. I see that berger manual and also nosler list the OAL to be 3.228 if I remember right. I could not come anywhere close to this with the accubond. Cooper told me they have "tight" chambers and that I should not necksize only. also told me not to use Blackhills ammo in the 6.5x284 because it would be too hot.

 

[deertroy1]

Just set up with the Inter-bonds. The best I can do is 0.077" from the lands and still fit the magazine. That seems like a big jump!

 

[deertroy1]

No luck with the Inter-bonds. Shooting 45.5, 46 and 46.5 grains of IMR 4007. The groups measured 1.6", 2.2" and 1.1" respectively. That was shoots 27 through 35 and this thing is still Copper fouling like crazy.

 

[pills]

What caliber are you shooting

 

[deertroy1]

7mm-08 Rem

 

[pills]

I am not surprised that the factory ammo shot 1"+ thats about the norm. If I were you I would try different bullets first.