Does a higher twist rate slow down the muzzle velocity? I've read where the twist rate was increased in the newer Marlin rifles. It seems to me that a higher twist rate would mean more drag, at least until the spin was picked up by inertia. Does that make sense or am I crazy? Or is it possible that it does make sense and I'm crazy anyway?
To some degree. From a text book point of view the total work done on the bullet is computed by multiplying the force on the bullet by the distance travelled down the bore. This work increases the energy of the bullet by giving it linear velocity and angular velocity. The more twist, the higher angular velocity it gets, and thus the lower the linear velocity, all things being equal.Originally Posted by NashvilleMike
Now the real world tends to be a bit more complicated than that, with friction, non-constant forces, etc.
I'd say you'd have to measure it to be sure of what really happens .
in 1998 Marlin® INCREASED the twist rate from 1:38" to 1:20" in the 444 Marlin. 45/70's have always been w/a 1:20" twist, whether Microgroove™ or Ballard rifled. The 450 Marlin® has always been w/a 1:20" twist. When the XLR series came out the 30/30 was DECREASED from 1:10" to 1:12". (All other 30/30 Marlin® rifles retain the 1:10" twist Microgroove®). When the 308ME and 338ME were introduced they have 1:12" twist. The 35 caliber Marlin®'s have ALWAYS been 1:16" twist.Originally Posted by NashvilleMike
The only way to know for sure would be the pit a 1:10" and 1:12" 30/30 against each other, all else being equal. A sharper comparison, I feel; would be between two 444 Marlin®'s, pre & post 1998 - 1:38" Microgroove vs 1:20" Ballard, w/22" barrels. Shoot say five Hornady® 265gr FP Light Magnum™rounds through each gun. This will allow you to ascertain your theory much more accurately. The Light Magnum™ rounds advertise 2325fps on the box. Shooting them in my 1988 22" barrel 1:38" Microgroove™ - I averaged 2265fps.
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You must remember, the longer, heavy bullets need more twist to stabilize. A slower twist rate may not have as much drag and with lighter shorter bullets it will suffice. The old Black powder rifles had longer and slower twist rates because a round ball or a maxi ball were short enough to stabilize. Then came the buffalo hunters with long heavy bullets, they needed a faster twist rate to keep the bullets from tumbling and have better accuracy at long distances.
There is a good reason for the twist rate, if it weren't then we would still be using smooth bore muskets.
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Twist rate should corralate with bullet length and velocity both. Wrong bullet length for twist rate and the bullet will not stabalize and it will tumble. Velocity to high for twist rate and the bullet will slip and still not achieve the correct spin to stabalize. It is a balancing act between all three to find a good bullet weight(which correlates to length) and push it at the maximum velocity at which it will still grip the grooves in the barrel and spin without slipping. All of this as stated is not an exact science. A few variables are bullet diameter, bullet hardness, jacket ( paper or copper), smooth sided bullet or grooved bullet, width of grooves, number of grooves. Long story short, if it was easy everyone would shoot well, and if you are not crazy now, by the time you finally find the correct combination for your gun you may be.
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I have no idea, I'm just yapping here. Your question does make sense though. More resistance could be expected from a tighter twist. My guess though is that it's a purely academic question, in practical terms I think there would have been a lot of sqwawking years ago if it made a difference in the field. The idea of testing it out using the 444 is a good one though.Something to do for someone with a lot of time and a bunch of ammo on hand. Also one of each twist rate rifle. Now there is a reason to buy a rifle if you don't have both types. In the name of scientific exploration. Let's see if you can get that to fly with your wife. You'll make the sacrafice in the quest for knowlege.
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At extremes it would matter but I really doubt theres any noticeable difference between 1 in 38 & 1 in 20 let alone between 1 in 12 & 1 in 10. If rifling twist produced signifigant differences in resistance to a bullet moving down a bore then I think it would be noted in loading data too.
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Thanks all. Good, interesting info.
A special thanks to mudpuppy, that's the answer I was looking for
Don't necessarily slow it down but it does help with longer heavier bullets.
The faster rates produce more pressure for a given bullet wgt for equal powder charges in cals with a slower rate.
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