Twist rate and bullet stability at 900 yards

Brent · #8 10-25-2003, 11:21 PM

Final proof was in setting a target closer at just 30 yards away. Result was a bit of a jagged hole and some dark gray smudge just under the bullet hole.

Len, would you expand on what you mean by that a bit more?

Interesting...

Len Backus · #9 10-26-2003, 05:12 AM

Brent

The hole looked normal going in but not clean and round on the backside of the target backer. This material is a piece of that honey-comb stuff that normally takes bullets very cleanly.

Darryl Cassel · #10 10-26-2003, 07:25 AM

len

The jackets on the Hornady bullets are very thin.

We tried them in our 7/300 Weatherbys but found that the 168 Gr Sierra MK worked MUCH better and gave better groups in the 9 to 9 1/4 twist barrels.

We ran them at 3250 FPS with great success on animals in a 30" barrel.
Later
DC [img]images/icons/smile.gif[/img]

dbhostler · #11 10-26-2003, 07:59 AM

Len,

I've been running the same bullet at 3280fps and haven't had a problem. I moly coat these A-Max bullets, but that shouldn't make a difference. 96grn Retumbo lit by a 9 1/2 M. Interesting though...

db

Len Backus · #12 10-26-2003, 09:58 AM

Darryl

I will never, ever, have your wind reading skills so I am trying to work with higher BC bullets.

.625 vs somewhere near .500 for the SMK.

#13 10-26-2003, 10:44 AM

[ 10-26-2003: Message edited by: Crispin Goodall ]

Brent · #14 10-26-2003, 11:51 AM

Len,

The reason I asked, and I was wondering if you were thinking they were unstable at close range (30yds) and that's why they might be exploding down range, but this is how I understand it, correct me if I'm wrong tho:

When the bullet leaves the muzzle it can be upset by the blast, and also MV and spin is high, but as the bullet heads down range, velocity decay is much greater than spin rate decay, so now bullet spin is able to better dampen yaw. I'm really not sure the bullet becomes "more" stable down range as a result, but it seems if slight key holing is present at close range, even 100-200 yards, that does not necessarily mean the bullet will not stabilize completely soon after this and never go unstable until it's near subsonic speed or even after that.

I know many people that don't recommend shooting groups any closer than 200 yards for this reason only.

It's not a 7mm, but close, but dad's 6.5WSM has pushed the 140 Amax over 3250 and they've never came apart in his 9 twist, sounds strange they come apart down a lot lower too. Maybe Hornady could sort out the problem for you, maybe they'd like to even have some bullets back to analyze???

I'm fixin to move up and try to hit 3500-3600 fps with the 178 Amax in the 30-338 LI so I'm wondering if they'll even make it at that speed now. All 9 hit the paper at 3400 fps or so at 300 yds the first time out with them.