reloading new 243.
- Thread starter Flat Tire
- Start date
Jim Watson
New member
The .243's 10" twist was meant to handle up to a 100 grain flatbase spitzer; Berger says ok for a 90 grain boattail.
Up to. Which your rifle shoots BEST will be determined only by shooting the gun. Lots of .243s do very well with 87 grain bullets.
Up to. Which your rifle shoots BEST will be determined only by shooting the gun. Lots of .243s do very well with 87 grain bullets.
A mate of mine has a Tikka T3- 243 he shoots the 55 grain bullet a bit, with velocities hovering around 3900-4000 fps But that little 55 gr bullet slows up pretty quick.
The 243 with a 55 gr pill has got similar powder volume and speed as the 220 swift, but he said accuracy was better with heaver bullets from 70 to 90 grains. I guess because it’s a 1 in 10 twist. The 70-grain bullet would be the go in the 243 your still getting 3620 fps with a stiff load of varget.
The 243 with a 55 gr pill has got similar powder volume and speed as the 220 swift, but he said accuracy was better with heaver bullets from 70 to 90 grains. I guess because it’s a 1 in 10 twist. The 70-grain bullet would be the go in the 243 your still getting 3620 fps with a stiff load of varget.
The fomular to determine the twist is:
CE/(L*C)*C
CE = Col effic. (or 150 for a jacketed Lead core bullet)
L = Lenght
C = cal
So: 150 devided (the lenght devided by the cal)
multiply that number by the cal.
So basicly measure the bullet you want to use, devide that by .243
Devide that number into 150
Multiply that number to come up with the recommended twist.
Now you just have to work backwards until you come up with the bullet you need.
CE/(L*C)*C
CE = Col effic. (or 150 for a jacketed Lead core bullet)
L = Lenght
C = cal
So: 150 devided (the lenght devided by the cal)
multiply that number by the cal.
So basicly measure the bullet you want to use, devide that by .243
Devide that number into 150
Multiply that number to come up with the recommended twist.
Now you just have to work backwards until you come up with the bullet you need.
Flat Tire,
Kraig gave you the Greenhill formula for bullet stability. Notice that what matters to it is bullet length. Weight and velocity don't even enter into that simple equation. So your question should have asked what bullet length is best? Weight, especially at long range, also matters because it affects ballistic coefficient (BC). So figure optimal stability will give you best accuracy in dead still air and BC will tell you which bullet is least affected by wind at 500 yards? You really need a combination of the two for long range, so I would suggest you pick the bullet with the highest BC number that is still stabilized well in your gun.
Most bullet makers don't publish that length number. You have to measure it or to guess it from a photo. This is not to say weight has nothing to do with stability—it does; so does velocity and air density, which are also missing from the Greenhill formula—it is just that they are not as significant to stability as length.
So, then, how do you decide you have acceptable stability for a given bullet? There is a more modern, complicated and expanded version of the Greenhill formula worked out by Don Miller that was published a few years ago. It does take velocity, bullet weight, and also temperature and barometric pressure (for air density) into account. It is too complicated to write out here, but if you have Excel or the Calc spreadsheet program in the free Open Office Suite, you can use either open an Excel file I made that does the calculations for you. You just fill in the blanks. It is called the Bullet stability and twist estimator. You can download it free from my public file repository here. It will tell you the best twist for an entered stability factor (1.4 to 1.5 are considered ideal by a couple of good sources, so I use 1.45 myself) and it also tells you the stability factor you get with your existing twist. Just enter the numbers.
Kraig gave you the Greenhill formula for bullet stability. Notice that what matters to it is bullet length. Weight and velocity don't even enter into that simple equation. So your question should have asked what bullet length is best? Weight, especially at long range, also matters because it affects ballistic coefficient (BC). So figure optimal stability will give you best accuracy in dead still air and BC will tell you which bullet is least affected by wind at 500 yards? You really need a combination of the two for long range, so I would suggest you pick the bullet with the highest BC number that is still stabilized well in your gun.
Most bullet makers don't publish that length number. You have to measure it or to guess it from a photo. This is not to say weight has nothing to do with stability—it does; so does velocity and air density, which are also missing from the Greenhill formula—it is just that they are not as significant to stability as length.
So, then, how do you decide you have acceptable stability for a given bullet? There is a more modern, complicated and expanded version of the Greenhill formula worked out by Don Miller that was published a few years ago. It does take velocity, bullet weight, and also temperature and barometric pressure (for air density) into account. It is too complicated to write out here, but if you have Excel or the Calc spreadsheet program in the free Open Office Suite, you can use either open an Excel file I made that does the calculations for you. You just fill in the blanks. It is called the Bullet stability and twist estimator. You can download it free from my public file repository here. It will tell you the best twist for an entered stability factor (1.4 to 1.5 are considered ideal by a couple of good sources, so I use 1.45 myself) and it also tells you the stability factor you get with your existing twist. Just enter the numbers.
Last edited:
42769vette
New member
i have a prohunter with 1-10 twist and 28 inch barrel i shoot a 80 gr barnes ttsx sub .5 moa on my first load. i haven't started to fine tune the load yet but it shows some promise.
I have an old Remington 788 that will put three FACTORY Federal Premium 85 gr. BTHP's into .300". On the other hand, it will also shoot Hornady Custom 100's into one hole. Other brands and styles shoot 50 cent groups, and the bearing surface on those short 55-60 grainers will not stabilize well IMHO. Let us know what you come up with. -7-
