Have a 458 Winchester Mag. These rifles had barrels designed for the 500gr. bullet. Been shooting 350 grains but find the groups to be very poor. Since the OAL of the bullet decides whether or not it will cycle through the action I'm assuming the longer bearing surface should stabilize the bullet in its travel through the barrel. With the Speer 350gr the crimped bullet makes a jump of about an 1/8th " to the lands - this would more than likely make the bullet enter the barrel off center. A longer bullet be it lead or jacketed should correct this problem. Am I correct?
Bullet bearing surface ?
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saskgunowner101
CGN Ultra frequent flyer
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- near Prince Albert
Superscout, I don't have the answer,but I have a few thoughts.If I'm wrong,I'm sure to get schooled by fellow cgn'ers.First,I seem to remember reading something about european target rifles??And they had a bit of free-bore(I think it was)before the rifling,might have been to do with pressures or accuracy,more uniform,I can't say.Second,the rifle was made to eat 500 grain bullets,so the rifling is probably optimum for them. You're now using bullets that are 150 grains lighter,and obviously shorter,which is only 70 percent of the original weight.Didnt early m-16's have a problem with bullets tumbling when they changed weight??but I think they went heavier,not lighter.And if this wasnt helpful at all,just know it took longer to type it than for you to read it!Good luck with your problem.
In regards to the M-16's, I have heard two very different versions on why they were having a bullet tumbling in flight problem.
#1. The us army changed the powder they use in their 5.56 rounds which caused a massive muzzle flash and this led to bullets tumbling off with no accuracy. The army then changed their barrels to a 1 in 12 twist (from a 1 in 14) to spin the rounds fast enough to stabilize them.
#2 The M-4 with it's shorter barrel was not providing enough velocity, which would actually cause a lack of penetration. This led to a heavier bullet, which in turn caused the bullet tumbling issue. Same cure was listed for this problem (increase the barrel twist).
I know there are many black rifle guys who are going to clean this up before long!
I have a friend who reloads for a .458 win mag, I will ask him tomorrow what he does. I can tell you now his first answer will be to shoot 500grn bullets, but their are other solutions too. Can you simply seat the bullet out farther to take up more of that space? You might want to compare the length of a 500 grn bullet to the length of a 350 grn bullet too, and then have a look at how much barrel twist you have. The problem could be caused by a shorter bullet with not enough spin leading to bullet yaw in flight. Someone wrote a mathematical formula to determine how much twist you should have in relation to your bullet length, but I can't remember who it was offhand.
#1. The us army changed the powder they use in their 5.56 rounds which caused a massive muzzle flash and this led to bullets tumbling off with no accuracy. The army then changed their barrels to a 1 in 12 twist (from a 1 in 14) to spin the rounds fast enough to stabilize them.
#2 The M-4 with it's shorter barrel was not providing enough velocity, which would actually cause a lack of penetration. This led to a heavier bullet, which in turn caused the bullet tumbling issue. Same cure was listed for this problem (increase the barrel twist).
I know there are many black rifle guys who are going to clean this up before long!
I have a friend who reloads for a .458 win mag, I will ask him tomorrow what he does. I can tell you now his first answer will be to shoot 500grn bullets, but their are other solutions too. Can you simply seat the bullet out farther to take up more of that space? You might want to compare the length of a 500 grn bullet to the length of a 350 grn bullet too, and then have a look at how much barrel twist you have. The problem could be caused by a shorter bullet with not enough spin leading to bullet yaw in flight. Someone wrote a mathematical formula to determine how much twist you should have in relation to your bullet length, but I can't remember who it was offhand.
- Location
- Somewhere on the Hudson Bay Coast
Are you crimping the shorter bullets? Crimping will uniform the bullet pull weight, something that is built in when a bullet is seated very close to or touching the rifling. .458 Winchester ammo can be fired in rifles with Lott chambers, and I've never heard about any accuracy issues when doing so, although pressure will be lower, so bullet jump, in this instance, does not seem to impact accuracy in a real practical sense when bullets are crimped.
If you were shooting lead bullets, I would say that better accuracy could be realized with longer bullets because the longer bullet with a long bearing surface better stabilizes relative to the center line of the bore (it's less prone to wobble or yaw in the barrel), but I don't believe this follows with jacketed bullets. Target shooters however, who choose VLD's have more difficulty getting those bullets to shoot than they do standard match bullets, so there must be a point of diminishing returns when the bearing surface becomes very short relative to the overall length of the bullet. In the case of the 350/.458, there is a very long bearing surface relative to it's length. Perhaps you just need to experiment with different loads or powders to find the sweet spot for those 350's. Choose a powder with a medium burning rate (3031, 748, RL-7 etc) and if you are trying to drive the bullet very fast slow it down a mite, and conversely if you are driving the bullet very slowly, try speeding it up.
If you were shooting lead bullets, I would say that better accuracy could be realized with longer bullets because the longer bullet with a long bearing surface better stabilizes relative to the center line of the bore (it's less prone to wobble or yaw in the barrel), but I don't believe this follows with jacketed bullets. Target shooters however, who choose VLD's have more difficulty getting those bullets to shoot than they do standard match bullets, so there must be a point of diminishing returns when the bearing surface becomes very short relative to the overall length of the bullet. In the case of the 350/.458, there is a very long bearing surface relative to it's length. Perhaps you just need to experiment with different loads or powders to find the sweet spot for those 350's. Choose a powder with a medium burning rate (3031, 748, RL-7 etc) and if you are trying to drive the bullet very fast slow it down a mite, and conversely if you are driving the bullet very slowly, try speeding it up.
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A slight jump to the rifling is common in guns with magazines which limit OAL. as well as lever guns and i don't think it will cause drastic accuracy problems. Most likely the twist is too fast or the rifle just doesn't like that bullet, i would try others, especially heavier and cast as well. It may just be that the bearing surface is too small for the twist/bore dimensions.
- Location
- Somewhere on the Hudson Bay Coast
My experience is that the accuracy of light bullets does not degrade with a fast twist. My 1:8 .308 shoots 168's quite nicely, and my 1:7 .222 used to shoot 52 gr MK's extremely well. While I will concede that my experience might not be universally true, I have had greater problems from slow twist barrels not stabilizing heavy bullets than from fast twist barrels not shooting light bullets.
Well - how does it shoot with other bullet weights? I've had rifles shoot just fine with a relatively large freebore, I wouldnt consider it to be the principal culprit, without knowing more about the general performance of the rifle.
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