RockyMtnMT
Official LRH Sponsor
I am going to try and give some clarity to twist rates needed for projectiles. With the need for high bc bullets for long range shooting, people think if the bullet just gets longer we will have higher bc bullets for our favorite rifle. The thing is, our favorite rifle very likely will not have enough twist for this great bullet. Remember the caliber/diameter of a given bullet must stay exact. So the only way that a bullet can get heavier is to get longer. Remembering that weight is function of bc. Lighter reduces bc, heavier increases bc. The lighter a bullet is for a given length the more twist it requires to stabilize. The heavier a bullet is at the same length the less twist required to stabilize it. So if we take a bullet and profile it down to super pointy fantastic drag profile it will get lighter, and require more twist for its length. It will also lose some bc due to less mass. The hope is that the increased drag profile overcomes the lack of weight. Getting off the subject a bit now, but you see the point.
Back to twist rate. We just finished designing .25 cal. Hammer Hunter bullet for a 9"twist. This bullet weighs 103g and is 1.202" long. This design will need a faster twist than factory rifles have in order to function to it's full potential. It was pointed out to me that we should make a higher bc bullet for 10" to 12" twist rifles because that would make more sense when it comes to sales and marketability. Problem is, it is not possible. So I started doing some calculations. I used the same length of 1.202" as a constant for comparison purposes. If I take this length of copper with no profile at all. Visualize a .25" cylinder square on each end 1.202" long. This "no profile" bullet would weigh 140 grains. Minimum recommended twist rate would be 1-10". Wow! So then I thought what if I did the same thing using the heaviest material we have to make bullets out of. Pure lead, no jacket, same straight cylinder design. This would be the heaviest possible projectile that could be created at a length of 1.202". It would weigh 179.2 grains and require a minimum twist rate of 1-11.5" for proper stability. Holy cow!! This heavy weight would still not stabilize in some factory .25's.
The other thing that happens with required twist from caliber to caliber is as the diameter of a bullet increases the required twist decreases. So if you compare a .25 cal. bullet of the exact same length and weight to a .308 cal., the .308 would require significantly less twist. To make sense of this I will have to make an imaginary .308 bullet from some imaginary material. Here we go. I have made a .308 dia. bullet that is 1.202" long and weighs in at 103 grains. Everything the same as our .257 103g Hammer Hunter except the dia. The imaginary .308 bullet would have a minimum required twist of 1-10.3" compared to the 1-9" for the .257.
The summery of this comes down to the fact that the original design of different cartridges in factory rifles is what it is. The .25's were designed to run little bullets really fast. The .264 cal. rifles that are hitting the market now are designed for longer range shooting. Most of them are in 1-8" twist rates. The 1-10" to 1-12" factory twist rates for .257 rifles is extremely slow.
By the way, I am not picking on the .257's.
Steve
Back to twist rate. We just finished designing .25 cal. Hammer Hunter bullet for a 9"twist. This bullet weighs 103g and is 1.202" long. This design will need a faster twist than factory rifles have in order to function to it's full potential. It was pointed out to me that we should make a higher bc bullet for 10" to 12" twist rifles because that would make more sense when it comes to sales and marketability. Problem is, it is not possible. So I started doing some calculations. I used the same length of 1.202" as a constant for comparison purposes. If I take this length of copper with no profile at all. Visualize a .25" cylinder square on each end 1.202" long. This "no profile" bullet would weigh 140 grains. Minimum recommended twist rate would be 1-10". Wow! So then I thought what if I did the same thing using the heaviest material we have to make bullets out of. Pure lead, no jacket, same straight cylinder design. This would be the heaviest possible projectile that could be created at a length of 1.202". It would weigh 179.2 grains and require a minimum twist rate of 1-11.5" for proper stability. Holy cow!! This heavy weight would still not stabilize in some factory .25's.
The other thing that happens with required twist from caliber to caliber is as the diameter of a bullet increases the required twist decreases. So if you compare a .25 cal. bullet of the exact same length and weight to a .308 cal., the .308 would require significantly less twist. To make sense of this I will have to make an imaginary .308 bullet from some imaginary material. Here we go. I have made a .308 dia. bullet that is 1.202" long and weighs in at 103 grains. Everything the same as our .257 103g Hammer Hunter except the dia. The imaginary .308 bullet would have a minimum required twist of 1-10.3" compared to the 1-9" for the .257.
The summery of this comes down to the fact that the original design of different cartridges in factory rifles is what it is. The .25's were designed to run little bullets really fast. The .264 cal. rifles that are hitting the market now are designed for longer range shooting. Most of them are in 1-8" twist rates. The 1-10" to 1-12" factory twist rates for .257 rifles is extremely slow.
By the way, I am not picking on the .257's.
Steve
I have read that moving the center of gravity of a bullet forward also reduces required twist rate (don't actually no if it is true). So if more weight means better BC, more pointy tips means better BC, shorter bullets require less twist rate, and moving center of gravity forward reduces required twist rate (maybe). Then here is the thought. You said that lead is the heaviest thing we can make bullets out of... well I don't know anything about what is legal to make bullets out of and what is not BUT... tungsten is 1.7 times the weight of lead (roughly). Has anyone seen the alco ULD bullets? My totally hypothetical question is, what if one were to make a mono bullet (like your hammer bullets) but rather than having a hollow point, it would have a pointed tungsten insert in the tip (kinda like alco's aluminum tip) that would go about half way down inside the core of the bullet? I understand that this would be a labor intensive design which could be cost prohibitive, but just for grins what would happen if someone would do this?
