September 26th, 2021
Erik Dahlberg illustration courtesy FireArmsID.com. Sometimes a barrel won’t stabilize bullets as you would expect based on the stated twist rate. A barrel might be stamped with a 1:10? It might be stamped on the side, but it is actually a 1:10.5? twist, or even a 1:19.5?. Bartleins and Kriegers are cut-rifled barrels that hold to the specified twist rate. Due to the nature and process of the rifling, there is a greater chance for a slight variation in twist rate with buttoned barrels. Factory barrels can also be slightly off-spec. Before you begin load development, it is important to determine the true twist rate after you have purchased a new barrel. You don’t want to spend a lot of money on expensive bullets only for that to stop working. Sinclair International offers a simple method to determine the twist rate of your barrel. Sinclair’s Simple Twist rate Measurement Method
You can measure the twist rate of your barrel in a matter of minutes if you are not sure. A good cleaning rod with a rotating handle, and a jag that is very tight fitting are required. If you’re going to access the barrel through the breech, or the muzzle end, you will need a rod guide. Under load, ensure that the rod moves freely in the handle. After a few inches, you can stop the patch from being inserted into the barrel. Place a piece of tape near the handle of the rod to mark it. You can measure how much of the rod is still sticking out from the rod guide. You can measure from the rod guide, muzzle guide, back to the flag, or to a spot on your handle. Continue pushing the rod in until you reach the mark or tape flag. Measure the amount of rod remaining in the barrel. The same reference marks were used for the second measurement. Next, subtract this measurement form the first measurement. This is the twist rate. If the rod has 24 inches left at the start, and 16 inches after one revolution, then you have 8 inches of travel. This is a 1:8? twist barrel. Empirically determining barrel twist rate
Twist rate refers to the distance in inches that the rifling takes for one complete revolution. A 1:10 would be an example. Twist rate. A 1:10? A barrel with rifling that makes one revolution per 10 inches of barrel length has a ratio of 1:10. Manufacturers of standard rifles usually publish twist rates. Custom barrels can be ordered by caliber, contour, or twist rate. If you need a custom barrel chambered, you can ask the gunsmith for the twist rate.
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