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Determining Rifle Barrel twist

Whisky Tahoe

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A question on twist rate came up in another thread, so we have done the right thing and moved that topic to it's own thread.

The number of inches of travel to make 1 complete revolution is called the twist rate. There are several published charts on twist rates for various rifles, some of them are even accurate! However there's no guarantee that a published twist rate applies to your specific gun barrel. Knowing the twist rate is important for selecting cartridges or components that will shoot well out of your particular barrel.

Determining your twist rate is pretty easy for bolt actions but you need a few things:
Bore Guide
Cleaning rod (preferrably 1 piece coated)
Jag tip
Patches
masking tape
Pen
Tape Measure

Insert the bore guide
put a small strip of masking tape on the rod near the handle. You want it on the rod so it revolves.
Mount the jag tip on the cleaning rod and pierce a patch off center
you are going for a smooth fit enough to rotate the rod but not one so tight it requires lots of push resulting in start/stops.
Insert the rod, jag, patch into the board guide and into the barrel just past the chamber. This is where the rod will start turning due to the rifling.
Mark the tape with line at the top like 12:00.
Measure from the end of the bore guide to the end of the tape. You don't have to be exact but pick a place because you will use that place again. That is your X distance
Push the rod slowly toward the muzzle while the rod it turning and stop when the mark comes back to 12:00.
Measure the distanced from the bore guide to the end of the tape using the same place you measured to before. This is your Y distance.
Subtract Y from X and you have the distance your barrel takes to make 1 revolution.
You will probably have to round up or down a little but some barrels do have fractional twist rates like 6.5:1 so consider rechecking and when comfortable your measurements you have determined your twist rate

20 or more years ago, twist rates that favored lighter bullets were common. Today, it is more common for higher twist rates as the popularity of heavy bullets has increased. Several bullet manufactures offer tools to determine ideal twist rates.
I like to use the tool at Berger, Twist Rate Stability Calculator
which lets you calculate what twist rate is optimal, marginal, or not recommended.

My Rem 700 223 only has a 1:12 twist rate which limits my bullet choices to 65 gr, though my ARs have either 1:9 or 1:7 allowing a heavier bullet. There is a condition where having too much twist is not recommended for some bullet weight/Velocity combinations. That is why the stability calculator is handy to help you avoid sub-optimal situations. When using the berger tool for non berger bullets, realize that other bullets are likely constructed differently so there's no guarantee the data is valid. Reasonable place to start though if your chosen bullet manufacturer doesn't provide twist rate recommendations.

No Bad Days...
 
Last edited:
OP
Whisky Tahoe

Whisky Tahoe

Messages
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Is that a question or statemento_O
Maybe both? My post was posted prematurely necessitating an edit. Not sure what you saw. Mea Culpa on a possessed touch pad. Today was better than some, usually it selects chunks and waits for you to type and replace your hard work while laughing demonically.
 

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