6.5 A MAX New and Old

[Dave in Idaho]

I was looking at some boxes of 6.5 140gr A MAX's last Saturday and saw that the box listed the 140gr's "for 1-7 twist only". Is this new? I have a 2 year old box that doesn't specify this and they shoot great in my rifle (8 twist). Did they change the bullet in some way to cause the 7 twist designation? I fought the urge to buy some until I could pose the question to the board. I think they should be fine, but I want to know for sure.
Thanx. Dave.

 

[Guest]

Several issues are in play that the bullet companies can not control, so they error on the fast side of what actually is needed for twist rate.

1) All barrels are not created equal, cut rifled barrels tend to be more accurate on the helix. A button rifled helix can vary significantly just from one lot of steel being slightly harder or softer than the last.

2) A bullet that will not stabilize in a 12 twist .223, may easily stabilize in a 22/250. Keep in mind twist rate does not stabilize a bullet, RPM will in relation to a couple of other things. The faster you shoot the more RPM the bullet is spinning.

A bullet company wanting to avoid problems will pick the slowest cartridge they think the bullet will be popular in, and then choose a slightly faster twist rate to compensate for Barrel differences across a range of manufacturers.

I shoot the 140 Amax out of a one in nine twist LILJA Barrel, and out of a one in eight twist LILJA with no problems. Anyone who sells you a one in eight twist that will not stabilize this bullet perhaps needs to look hard at how they measure the twist rate of their barrels. You will find very little difference in the RPM necessary to stabilize either design, the old or the new.

 

[Guest]

Howdy Steve,

I would like to see a comparison of the 8 and 9 twist based on horizontal dispersion, and then seperately vertical dispersion. Do you have any old targets that you could take independent measurements on?

I have found both capable of 1/4 MOA at short distance and the 8 twist showing a little advantage in higher winds at longer distance. I would like to do more testing under a variety of conditions before drawing any hard conclusions.

 

[Steve Shelp]

David,
Agree with S1. I to shoot Lilja barrels and my 9 twist Light Gun class BR rifle is a hummer with these bullets. I've got a 8 twist Lilja 3 groove for my switch barrel Heavy Class rifle also. You don't need a 7 twist for the average 6.5 capacity case.

S1,
Have you noticed any difference in 100yd accuracy in comparing the 8 to 9 twists 1 for 1? The reason I ask is that my 8 twist barrel using the Hornady's, I have to slow them down under 2800 to get them to shoot the same accuracy as the 9 twist with the same loading components. I've been able to repeat this test. I understand the RPMs of the 8 is going to be more and they should have to slow down to equal the 9 twist RPM equavilent. My 9 twist will shoot like a house-a-fire at 100yds (w/ 1000yd loads) but the 8 twist won't touch it at 100yds. But they are 1 for 1 at 1000yds the best I can tell. Not done fully shaking down the 8 twist loads yet.

Just an observation on my part and curious if you've seen anything along the same lines?

Steve

 

[Dave in Idaho]

Thanx for the replies. I guess I will buy several boxes the next time I get a chance. I appreciate the input.
Dave.

 

[Steve Shelp]

S1,
I'll have to go back and look at my targets. I think I still have them from my intial testing at 100yds.

I'll screw the 6.5 barrel back on my HG as soon as I have time the play with it and keep track of the difference of vertical and horizontal. I record this for all of my 1000yd targets but not recorded for 100yd stuff.

Steve