I am sure this question highlights my ignorance but if you have a 1/7 twist barrel, all else being equal, does it mean lower velocity than if the barrel was a 1/9 or 1/12 twist? So for example does 62 gr ammo come out of a 1/7 twist tube at the same velocity as a 1/9 twist tube? I looked this up a couple times but my google-fu is weak. I realize one is spinning a lot faster but I am talking about linear muzzle velocity. Any numbers to clarify the issue? Thanks!
1/7 twist 5.56: does it reduce velocity vs 1/9 or 1/12
- Thread starter mshootnit
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No. It doesn't reduce velocity...just increases spins.
W.E.G.
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How did you come up with that notion anyway?
MIL-DOT
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I actually sounds quite logical to me. The more the round is forced to spin, the more "ground" it has to cover, and the more drag it would be exposed to. It's kinda like when a car with two pasengers is driving through a tight curve, the passenger on the outside seat is actually traveling ( a tiny amount) farther and faster than the passenger on the inside seat.
Exagerate the premise and the spin,hypothetically, say to 1/100 rather than 1/12. I suspect THAT would cause a discernable reduction in velocity, making the OP's question valid, IMO.
Exagerate the premise and the spin,hypothetically, say to 1/100 rather than 1/12. I suspect THAT would cause a discernable reduction in velocity, making the OP's question valid, IMO.
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Simple question, looking for facts, lets keep the thread on track. And thanks for the replies
Thanks Mil-dot I think you clarified my reason for asking as well or better than I could have.
You might have an increased moment of inertia, but this could be offset by higher pressure peak possibly?
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MIL-DOT
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No worries,bro, glad to help. This is interesting,I'm still pondering this one, but as jmr40 concured, I think there has to be some, admitedly minute, loss of velocity.
beatledog7
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When a bullet is fired through a rifled barrel, energy is spent developing the rotation, rotation that can only be accomplished by resistance against the forward energy, redirecting it into torsional energy.
I don't know how much it slows forward acceleration, and I suspect it's little enough as to not matter in the real world. But it has to be more than zero.
I don't know how much it slows forward acceleration, and I suspect it's little enough as to not matter in the real world. But it has to be more than zero.
I admit, I don't know the answer. But the explination I heard is that the faster twist caused more resistance in pushing the bullet through the barrel. At first that seems plausable, almost as if you were shooting a slighly heavier bullet because of the faster twist. But smokeless powder will just generate more pressure when met with more resistance and often generate more speed.
I'm not proposing an answer, just relaying something I've heard. And this is something I only heard about farily recently so I'm looking for definitive answers as well.
I'm not proposing an answer, just relaying something I've heard. And this is something I only heard about farily recently so I'm looking for definitive answers as well.
stubbicatt
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I know the Palma guys tend to shoot 13 twist barrels that are 30" long because they believe that the faster twist decreases velocity. Stands to reason, although I really don't know how to cipher on it.
silicosys4
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Rifling does decrease velocity to some degree. Energy from velocity is sacrificed as friction, to cause bullet twist. Tank main guns are a prime example of this. There was a large movement away from rifled barrels to smoothbore in the late 70's and early 80's, starting with the Soviets (to wide derision), the widely copied. As far as I know, at this date, there is only 1 main battle tank using rifled barrels, the British Challenger tank; and only then to maintain the ability to use high explosive "squash head" rounds which are very effective against concrete structures in urban combat.. Which the British would expect to see a lot of in any scenario taking place on the island. Pretty much everyone else uses a smoothbore main gun. This is for a number of reasons....to maintain barrel life, and the ability to fire missiles or flip-fin rounds from the main gun tube....but velocity was a large reason as well. High velocity, depleted uranium core penetrator style sabot rounds use a smooth bore for maximum velocity, as velocity is the only delivery of energy onto target; no explosives. Penetrator style rounds also don't functionally work out of a rifled barrel...When it hits, the tip stops rotating and remains stationary as it penetrates, while the body and tail are still trying to twist...resulting in poor on target performance, and instances where the penetrator literally flies to pieces against the target as it torques apart.
In small arms though I'd expect the difference between smoothbore and rifled barrels to be negligible, and the difference between 1:7 and 1:9 to be almost unmeasurable by your average sportsman.
In small arms though I'd expect the difference between smoothbore and rifled barrels to be negligible, and the difference between 1:7 and 1:9 to be almost unmeasurable by your average sportsman.
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tryshoot
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More twist, more friction. More friction takes more energy. More energy to move = less velocity. Real world no diff, but very good ?.
barnbwt
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I thought rifling "cheese grater's" the bullet a tad as it first engages and is subject the maximum torque to start spinning. "Overrifling" would seem to either shave excess material from each round fired, fouling quickly and even affecting accuracy. You can also theoretically overspin the bullet, causing it to fragment or deform under its own centrifugal force (unlikely in sane calibers/loadings, supposedly).
I'll bet neither of these situations occurs anywhere near 1:7" in .223 loadings, though
TCB
I'll bet neither of these situations occurs anywhere near 1:7" in .223 loadings, though
TCB
Sport45
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beatledog7 said:
^^This.
The chemical energy in the propellant charge is converted to potential energy as chamber pressure. That energy is converted to kenetic energy in the form of velocity and spin. Spinning the bullet faster means less energy is available to make velocity.
But like he said, I doubt it's very much velocity loss as it doesn't take a whole lot of energy to spin a relatively light and small diameter bullet.
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Pete D.
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Chrono
It seems to me that there are a whole lot of variables that could account for the differences as stated.
I wonder if this type of difference is detectable by the average Sportsman's chrono and outside of laboratory conditions. I don't know that it isn't or that that data is incorrect or that the test as stated may have been done in a lab. I did, however expect that the difference would be yet smaller than that.
It seems to me that there are a whole lot of variables that could account for the differences as stated.
While this is one interesting observation, I wouldn't come to any conclusions based on one example. I handload 30-06 rounds for myself and family members. Altogether my loads are shot through 7 different rifles with barrels ranging from 20"-24". All have 1:10 twists, but are made by Ruger, Winchester, Remington and Weatherby. All shoot to very different speeds. The slowest barrel is a 22" gun that actually shoots 130 fps slower than another 22" gun. One of the 20" guns will match it, the other comes close. The 24" gun is less than 20 fps faster than the fastest 22" gun, but almost 150 fps faster than the slowest 22" gun.
There is simply too much variance between individual barrels to draw any conclusions from 1 example. Not saying this is incorrect, just that if 100 people were to chronograph loads, and if we see a trend, then the numbers are more valid.
wanderinwalker
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I see jmr40 made the point I was going to about different barrel chronographing different speeds.
I will say in Highpower competition, the general concensus from the shooters I shoot with is a 1-8" twist MIGHT allow a bit more speed, but the 1-7" MIGHT be a bit more forgiving for shooting at 600-yards and out. That said, my rifle has a 20" 1-7" barrel and it shoots faster than the 20" 1-8" barrel that was originally on it. So...
I will say in Highpower competition, the general concensus from the shooters I shoot with is a 1-8" twist MIGHT allow a bit more speed, but the 1-7" MIGHT be a bit more forgiving for shooting at 600-yards and out. That said, my rifle has a 20" 1-7" barrel and it shoots faster than the 20" 1-8" barrel that was originally on it. So...
W.E.G.
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Where did you hear that?
Do you REALLY think the Palma shooters are shooting any twist rate other than the one that gives best ACCURACY for the Palma bullet?
Certaindeaf
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I think the highest velocities have been attained with smoothbores.
firesky101
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Maybe... I have heard gain twists last an extremely long time, so perhaps the initial engagement of the rifling is very hard on the barrel. If would certainly be less friction with slower twists.
jakk280rem
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I have a hunch that with the velocity variations present in two identical barrels and variations from cartridge to cartridge, the difference would be statistically insignificant.
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