243 bullets shooting quite different.

[grouse]

Never experienced this.
Shooting 87 grain sst into tiny groups from a tikka 243. Moved up to some 100 grain and the groups were 4-6" to the right. I've experienced a different poi with different ammo but not usually this much horizontal change.

 

[LVJ76]

I have the same issue with my 7mm-08. With my rifle sighted in with the 139gr SST bullet, the 120gr Ballistic Tip will impact 5" to the left. Both group Sub Half MOA groups but POI is completely diferent

 

[LVJ76]

When I asked I was told it was barrell harmonics

 

[degreen]

When I asked I was told it was barrell harmonics

Different bullets go down the barrel at different velocities especially different grain bullets. Which in turn changes where the barrel whip is when the bullet leaves the barrel.

 

[LVJ76]

Different bullets go down the barrel at different velocities especially different grain bullets. Which in turn changes where the barrel whip is when the bullet leaves the barrel.

That makes sense, thanks degreen

 

[LVJ76]

Grouse, dont let that stop you from using the other bullets, all you need is the right load for them and done.

 

[Dosh]

If there's tiny groups, perhaps I could live with adjustments to the windage.

 

[grouse]

Yeah. The 87 grain are very light recoiling I was just hoping to drop down weight for a youth hunter and then back up again. I've seen poi change but not by that much

 

[busdriver989]

http://www.varmintal.com/amode.htm

 

[catamountsierra]

The NEF Handi-rifle I used to have shot great, close to half MOA with 100gr Partitions and about 3/4 with 70gr NBTs; at 200 yards, however, the 70gr bullets were around a foot higher POI. 400fps doesn't account for that, but barrel harmonics definitely can.

 

[adrexco]

The 243 twist rate is too slow for heavier weight bullets. 100gr is where you'll start to see issues. Some shoot ok, others not. That's the benefit of the newer cartridges like the 6mm CM, faster twist rates.

 

[emp1953]

my vote is for a combination of twist rate, barrel length and barrel harmonics. The 100gr bullet is quite a bit longer than the 70 gr. The twist rate that makes the 70gr shoot great doesn't like the longer heavier bullet. I've had it happen to me with a Remington Model 7. Shot light bullets to one point and 100's to another point. Still was a nice group. So I learned to live with the windage / elevation adjustments when switching from varmints to deer. A change to a powder with a different burn rate also helped tighten the groups with the heavier bullet. Additionally freebore had to change for the heavier longer bullet. For all intents and purposes I worked up an entirely different load. Every rifle has its own personality even if they are the same manufacturer and sequential serial numbers.

 

[DavidleeCole]

I have the same problem with 100 gr. From my .243 win model 70 with 1:10 twist even the 95 gr. Win silver tips. But with 80 gr. Nos ballistic tips no problem good to go. I have tried to speed up and slow down the 100's with several powders and still no good so I stay with the ole trusty 80'S

 

[adrexco]

here too, Winchester M70 .243, doesn't like 100s. Heaviest it likes is 85gr.