A twist checker is attached to a suitable cleaning rod. The one below is used on a .22 rod with a 4mm metric thread. It engages positively in the grooves of the rifling to eliminate any slippage that usually occurs, when a jag and rag or a brush is used to measure the twist rate of a barrel.
We used to make them in dedicated sizes such as these, but now do them in a universal style that is easier to make and fits a number of calibers.
For once off use, one can fashion the hooks from a paper clip and super-glue it to a cleaning rod. A paper-clip is well polished and it can be removed from a cleaning rod with no damage to the cleaning rod thread.
Old style checker above and the new universal one attached to a cleaning rod.
By compressing the legs of the spring, a wide variety of calibers can be measured.
The new style checker is easy to make from a short length of spring wire and a 5mm tube with a 3mm hole in it. See the diagram with dimensions at the bottom of the page.
To measure twist, you need a cleaning rod, a small spirit level (any straight edge will do in a pinch), a pen or pencil, a measuring tape and a small ball of sticky putty (crazy putty, presstick, whatever you call it in your part of the world). It is also useful if there is a rifle to measure.
Attach the spirit level to the cleaning rod.
Compress the spring and check that it engages positively in the grooves of the rifling.
Push the rod into the barrel until the spirit level is...... level
Mark the position of the rod at the muzzle
Push the rod further into the bore, while watching the spirit level, for one full rotation.
Mark the cleaning rod at the muzzle again.
Remove the rod from the barrel and measure between the two marks to find the exact twist of your barrel.
Here are the two parts of the twist checker. Spring wire around 0.65 to 0.75mm works well. The tube can be made from aluminium or copper. Once the tube is threaded internally over about half its length, the spring is inserted at the opposite end and the tube is crimped in a bench vice to hold the spring in place. This diagram is for a twist checker that fits a cleaning rod with a 4mm metric thread. Obviously, any thread that will fit your cleaning rod can be used, as long as dimensions are compatible with the outside diameter of the tube and the bore of the rifle.
GS Custom Bullets, situated in Port Elizabeth on the East Coast of South Africa, manufactures solid copper, turned, monolithic bullets for hunting and sport shooting. These bullets are used by hunters on several continents, hunting from the smallest of antelope to the largest of dangerous game, using the smooth HP bullet, as well as the more popular HV, FN and SP bullets with the patented drive band concept. GSC bullets are configured for the highest possible ballistic coefficients. SP bullets are mainly used for sport shooting. All GS Custom Bullets are coated.