Now for the practical airgun barrel twist testing!
Here’s some practical results that the HAM Team have found so far. Plus we’ve added another twist to the discussion (groan)…
Barrel Twist Rate Testing
Well, it turns-out that it’s not so difficult to test your airgun barrel twist rate. All you need is a cleaning rod, plus a jag or brush for the appropriate bore diameter, plus some painter’s tape and a cable tie.
For this HAM testing, we used cleaning rods manufactured by Bore Tech. These include a convenient, simple system of markers to simplify determining one complete rotation of the rod.
In addition, we used cleaning brushes of each appropriate airgun caliber. That’s from .177 all the way to .30 caliber. Fortunately Bore tech includes a .20 caliber brush in their system, so that enabled us to include this less-common caliber.
The test methodology should be simple. Just pull the brush-fitted rod through the barrel until it has made a full, 360 degree rotation. Measure the length of rod between the start and finish points of the full rotation. That length in Inches is the barrel twist rate.
We found it easier to judge the rotation of the rod by adding a cable tie in place around the rod, as shown here.
This YouTube video shows the basic concept.
But, we found that there are some “wrinkles” that will make things easier…
First, the gun needs to be securely held in place, or held by another person while the measurement takes place. That’s really important!
Next, we found it’s much easier to measure the twist rate of a breakbarrel than it is for a PCP.
Our technique was to just break the barrel, but not cock it, of course!
Then run a cleaning rod through from the muzzle.
Next, attach a brush of the appropriate caliber.
Then add a piece of blue painter’s tape around the cleaning rod at the muzzle.
The next issue is that airgun barrel twist rates are relatively long. This means that it may not be possible to rotate the rod a full turn before the brush comes out of the barrel.
So – in many cases – we need to measure the length of half a rotation of the rod (180 degrees).
After either a rotation of 180 or 360 degrees, stop and measure the distance from the tape to the muzzle. Obviously it needs to be doubled if the rotation was half a turn. This is the twist rate in Inches.
For PCPs, it’s a little more difficult if you’re using a rod and brush. This is because the brush is pushed first all the way down the barrel to the magazine.
As the brush and rod is pulled back out of the barrel to make the measurement, the bristles of the brush need to reverse their orientation. This can require considerable effort!
For PCPs, we have found that it’s easier to use a jag and patch, rather than a brush at the end of the rod.
It’s even easier if you can remove the barrel from the gun before measuring it!
Either way, that’s the basic technique for measuring the twist rate of an airgun barrel.
Now Let’s Add Pellet Weight To The Discussion
While it’s true that just knowing the airgun barrel twist rate can be an interesting academic exercise, I want to add a practical application to it…
Part of the thinking behind this exercise is to see if barrel twist rate is – indeed – related to the accuracy of our airguns. If it is, then it should be possible to derive approximate recommendations for pellet weights to try – or avoid – when searching for “the right” pellet for a particular air rifle.
We’ll do this by matching airgun barrel twist rates against the most accurate weight pellet that is found with that barrel through actual shooting experience.
Yes, I know that there’s a ton of other factors to take into account in finding “the right” pellet for your air rifle. However twist rate is one aspect that I believe has not been previously accorded sufficient attention.
Let’s see…
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