Rate of twist - bullet stability?

[sabinajiles]

I recently purchased some Cutting Edge Bullets(CEB) 44 cal 250 gn Maximus bullets. They are CNC machined, controlled fracturing bullets. CEB says they are for 1 in 24" twist or faster and claim a .311 ballistic coefficient. I have range tested them out of my Accura MR, which is only 1 in 28", using a smooth green Harvester sabot and 120 gn of BH209 in order to keep the velocity as high as I can to aid stability. At 100 yds, they are dead nuts accurate and are punching clean holes and appear to be stable. Our late winter deer season starts Thursday and I would like to use this bullet. From my blind, any shot opportunity will more than likely be under 120 yds but there are a couple of lanes that could present up to a 185 yd shot. It's going to be way to windy here the next couple of days to get a good range test of the Maximus bullet at longer distances so my question to you long range shooters is this. Since I'm not spinning these bullets as fast as preferred for best stability, can I expect them to lose stability over the longer distance as velocity decreases and avoid any shot over 100 yds or do you think stability would hold up to 180 yds? I haven't had a chance to shoot them through a chronograph yet but with 120 gn BH209 I would guess they would be a bit over 2000 fps. I ran the numbers through a ballistics calculator and with the high bc, they would still be going around 1600 fps at 200 yds. Would the spin at this velocity, out of a 1 in 28" barrel be enough to keep the bullet stable? I've attached a photo of the bullet to show it's profile. The 250 gn Maximus is on the left. A .430 265 gn FTX is in the center and a .430 300 gn XTP is on the left.

 

[Grouse]

You have nothing to worry about, the bullet is either stable or its not. A non boattail bullet will become unstable at either 400 or 500 yards i forget. Thats were a boattail has an advantage to keep the bullet stable at long long range.

 

[Confederate rifleman]

Look up Greenhill's formula for rifling twist. All copper bullets will be lighter for length than lead or cup and core designs. Its the length of a bullet relative to diameter that determines the required rate of twist. A 165 grain .30 caliber doesn't need as fast a twist as a 165 grain 6.5 mm.When you get close to minimum twist rates, then velocity can play a useful role.
If you're grouping well, chances are you're good to go.
Nasty looking bullet btw.

 

[a1smokepole]

Just start backing down on your powder and see if they keyhole that will tell you if it will stablies. like down to 80grV at 100yds.

 

[sabinajiles]

Thanks for the replies. I did run the numbers on the twist calculator on the Berger bullets site and these bullets came out as marginally stable for the 1 in 28" twist. I have only shot about 20 rounds with this bullet and it is grouping quite well at 100 yds, less than 2" and that's with a full power load of 120 gn BH209. Since it's only a 250 gn bullet the recoil is not at all bad and is easily manageable. It is a nasty looking bullet. You can't see it in my photo, but there are 4 groves machined into the side of the hollow point cavity for the controlled fracturing of the petals. Hopefully, I will get to check out it's terminal performance this weekend. The company also has several other muzzleloader bullets, including .430 210 gn and .451 250 gn versions of this same bullet I'm shooting which are better suited for the 1 in 28" twist. I plan on range testing them after my season is over.

 

[52Bore]

Your bullet seems to shoot well for you. I saw a 40/240 CEB shoot very well in a local match this fall.
Since you know what it does at 100, great time to test again is when it's windy. You might learn more about what the bullet does, than on a calm day - plus you'll have the range to yourself.
Your correct as it slows your accuracy will diminish, usually at a exponential rate..
Just me maybe, but I don't think it's right to shoot something that you don't have the confidence.

I have shot with multiple rifles with different twist at 1000 yards over the last two decades - twist is most certainly is critical factor in bullet stability. I have a 45 1:24 twist gun that shoots well out to 5-600 (won quite a few silhouette matches at Friendship, 220-500yds), but it has never done well when shooting matches that go to 1000 - seems the group is always a random 8-12' circle inside or around the 6' square target frame, those to do connect on paper are still head on - no evidence of yall/tilt. I made bullets from 400-550, varied powder charges and none have done well at 1000 - I've concluded that it just will not shoot because it's rotation has slowed to the point of loss of any reasonable accuracy.