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Muzzleloader bullet spin rate
Discussions related to Guns and Firearms

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iowafarmboy
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PostPosted: Fri Jan 08, 2010 4:04 pm    Post subject: Muzzleloader bullet spin rate Reply with quote

Has anyone ever figured out if the bullet spin rate has anything to do with accuracy? Especially if using a sabot where the centrifugal force opens up the petals the instant it leaves the barrel. I have a 1 in 28 inch twist and a muzzle velocity of 2066 fps. Am I correct in saying that at the muzzle the bullet is spinning at 885 rpm. As the bullet slows does the spin rate drop with it? I had a 25/06 and I calculated that bullet spin rpm at 4,067 with a 1 in 9 twist.

I have noticed that the Barnes TMZ sabots (4 petals) open up uniformly and drop off quickly. The Shock Wave E-Z sabots (2 petals) almost always just drops one petal that breaks off and the other remains intact in it's original position. On virgin snow you can see where the E-Z sabots hit the ground at very high speed and much farther out from the muzzle.

At least in my rifle, the TMZ's are more expensive but they are the most accurate. I have never seen any distortion in a Barnes sabot base but often (especially in warmer weather) i see it with the E-Z sabots. Instead of an "O" shape they are an "0" shape. These are summer pictures. The winter E-Z sabots don't seem so distorted and the Barnes sabots are opened up a full 90 degrees.



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summer sabots
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summer sabots
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chambered221
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PostPosted: Fri Jan 08, 2010 6:54 pm    Post subject: Re: Muzzleloader bullet spin rate Reply with quote

Your correct with 885 but it is RPS (revolutions per second) multiply that by 60 to get RPM’s, in your case that’s 53,100 RPM.
Your 25-06 looks about right but you didn’t give the velocity and that’s also RPS not RPM.

Spin rate has everything to do with accuracy !!!
The twist of the barrel and velocity determine the spin rate, if to slow of a twist is used then you will not have enough spin rate to stabilize the bullet.
Think in terms of a spinning top.

When it comes to sabots I was always told broken petals and distorted bases meant you were getting blow by (not sealing) or you running more pressure than what it was designed for. (back down on the powder)
About 5 or so years ago I ran into this when I switched to Triple 7.

The higher temperatures of summer is most likely the cause for more damage to the sabot. (your creating more pressure) I’m assuming your using the same amount of powder in both summer and winter.

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chambered221
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PostPosted: Fri Jan 08, 2010 7:18 pm    Post subject: Re: Muzzleloader bullet spin rate Reply with quote

iowafarmboy wrote:
As the bullet slows does the spin rate drop with it?
Forgot this part !!! oops !!!

Yes it does but at a slower decent and usually not enough to affect stability.
Somewhere in the neighborhood of 600-1,000 yards seems to be where long range shooters start being concerned with adding a little extra twist but this is of great debate without any definitive answers.

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iowafarmboy
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PostPosted: Fri Jan 08, 2010 9:18 pm    Post subject: Re: Muzzleloader bullet spin rate Reply with quote

That's AMAZING! No wonder the sabots open so nice. I forgot one thing. The summer sabots were fired in the old barrel. It was about .004 undersize from the breech to about 8 or 10 inches out. That's why I got a new barrel. The breech plug leaked so bad I'd hate to guess how much pressure was lost. So I'm starting over. I'm trying some different sabots with different bullets and powder loads to find a good combination. In the old barrel I had the best luck with 300 grain bullets. I think it's that the bullets are just a little longer. I'm hopeing to get good results from 250 grain bullets with the new barrel. The numbers look slightly better with 250 grain bullets plus they shoot just a little flatter. Thanks for the info.
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