Twist rate - Basic Question


Well-Known Member
How do barrel twist rates influence the flight of a bullet given it's weight? I often hear about such and such a twist rates suits such and such grain weight, but what is the common rule?

And, secondly, I have had a look in my instructions for the Styr Pro mountain I have in 243 but it does not mention it's twist rate, I cant get onto the Styr's website thanks to work firewall, does anyone know what it is??




Site Staff
Get yourself a cleaning rod that turns nice and freely in the handle, then draw a line along the rod, fit the jag with a tight fitting patch, push the rod into the barrel, when the line is on top put a mark on it then push the rod down the barrel until the line re-appears then mark it again. Remove the rod and measure between the two marks that will give you your twist rate.

Alternatively, fit the patch and push the rod into the barrel, mark the rod top then withdraw the rod, when the mark re-appears on the top, mark it again and the distance between is your rate of twist.

I forgot to say mark it in the same place, I usually use just where the rod disappears into the chamber. I know you would do this anyway but I thought I would mention it in case my wife wants to do it :eek: :eek:

Hope it makes sense.



Well-Known Member
Just so as you know Jerry, it doesn't actually mention the twist rate on the website...bit of an omission on their part.


Well-Known Member
Drew said:
Just so as you know Jerry, it doesn't actually mention the twist rate on the website...bit of an omission on their part.
Too true!!

Will do the manual measurement mentioned above!


Well-Known Member
have a look at one of the reloading manual's I think the vitavourhi manual explains everything. but basically the twist rate effects the stability of the bullet as it travels to the target, if the bullet is over stabalised (twist rate to fast) it fly's like a rubgy ball with to much spin and will not hit the target point first but may enter the target slightly sideways and upright if the twist rate it to slow then the bullet will look pitch and yaw as it flies towards the target and not be to accurate.

in short try to get you hands on a copy of the vithavouri reloading manual and it will explain all, be prepared to be train spottered as it goes into the magnus effect, ie:- why and how wind effects the path of a bullet.

I think the Styer pro mountain has a twist rate of 1in 9.


Well-Known Member
Twist rate Basic Question

Sanders, This might help. I found it on an American site re. the 6.5x55 Mauser


"The twist required in calibres equals 150 divided by the length of bullets in calibres."
1) Divide the length of the bullet in inches by the calibre to get the length in calibres.
2) Divide 150 by the number from #1
3) multiply the number from #2 by calibre to get the required twist.

So, for my new favourite .243 bullet, the 85gr Sierra HP BT, this is what we need to do:
Bullet length = .946
so a 1:9.5 twist would be required.
Neat, huh?


Well-Known Member
Very neat, I assume I can get bullet lengths from the ammo maker's web sites?

Cant check from work as such sights are banned.... :evil:


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Had a bit a practise session today and ran a selection of ammo through my 243

The conclusion was : 100gr shoot better than 55gr.

Sako, cheap but wont group.
Norma, not bad grouping but not as good as I hoped.
Federal, the best groups and I think I will stick with them.

Weather was not great, a bit blowy and wet at times but at 100yards I did manage to put three shots into just over an inch with the Federa 100gr.

I will stick with those for now.


Offroad Gary

Account Suspended
try RWS T mantel - not cheap but my pro mountain loves them. they hit 1" higher than 100gn federals and have a bit more legs. £26 a box though!