7-30 Waters

[ammo.crafter]

Using a Thompson Center (old style) in 7-30 Waters with a 23-inch heavy barrel.

Extremely accurate combo...when switching from 120gr to 139gr the poi shifts 2-inches to the left...rather than a height differential as one would think....and yup the scope is mounted correctly.

Any ideas?

 

[Magnum Wheel Man]

I think it has to do with the rotation... I don't always see an elevation change with different weights, some times ( actually quite often ) I see an angular change...

 

[ammo.crafter]

change

Actually the change was some what angular as you noted.
This is the first time I have experienced such a drastic poi change (left and right) due to bullet weight.

 

[Magnum Wheel Man]

2" sounds like a lot though... do you know how much of a velocity difference difference you have between the 2 loads ???

BTW... my 7-30 is a Contender also, but a 14" barrel

 

[ammo.crafter]

7-30

2500=120gr
2300=139gr

 

[Magnum Wheel Man]

so... were your 139 grain loads as accurate overall, as the 120's ??? I haven't loaded for or shot that barrel reciently, but have gotten really good accuracy out of mine in the past ( I'm actually due to reload for it again to replenish my supply of ammo, some time probably this next year )... I'm not sure about the 7-30, but alot of the older Contender barrels were on the slow side of the twist rates ( the 223 for example, I made up a cusom barrel with a faster twist, as my old barrel didn't stabilize even 55 grain bullets well )

 

[GeauxTide]

If they're accurate, adjust your scope.

 

[ammo.crafter]

7-30

Both loads are extremely accurate...not unusal for hole-in-hole. I'll check the twist but the bbl is only one year old.
As for adjusting the scope, well of course. The question posed was one of curiosity as one would imagine the heavier bullet to hit low not right or left.
THX

 

[oneoldsap]

Barrel harmonics change with every load change , The shift in POI can move in any direction . It depends on where in the rotation of the barrel the bullet exits !