View Full Version : Twist rate in barrel?
April 19, 2011, 12:24 AM
I just bought a Turkish Mauser that has been re barreled into a 6mm Remington. I also put a Bold trigger on it. Im trying to work up a load for it but I need to find out how to determine the twist rate so I can decide what bullets to push through it. I have shot about 20 rnds of 80 grain speer SP through it and it wasnt getting very good groups, around 2'' average. I shot IMR 4831 and IMR 4060 both with the 80's. It seemed to like lighter loads better. So how do I determine what twist rate is the barrel?
April 19, 2011, 12:56 AM
Put a jag on a cleaning rod and wrap a piece of masking tape around the rod near the handle.
Put two patches on the jag and apply the bore cleaning solvent of your choice. (Why waste a trip through the bore, eh?)
Start the jag about 4-6" into the bore. Stop and measure the distance from the back of the receiver to the cleaning rod handle. (Measurement 1) Put an index mark on the masking tape with a pen or magic marker.
Tap the cleaning rod through the bore until your index mark indicates the rod has made one full turn. Stop and measure the distance from the back of the receiver to the cleaning rod handle. (Measurement 2)
Measurement 1 minus measurement 2 is the inches per turn for your rifle.
April 19, 2011, 12:52 PM
Awsome, thanks for the help
April 19, 2011, 01:31 PM
The tape on the cleaning rod works well for discriminating 12" twist from 10" twist, but it is problematic in telling 9.25" from 9.5" twist.
April 19, 2011, 01:49 PM
True, but any ordinary bullet will have trouble telling the difference, too.
April 20, 2011, 09:28 AM
I know from shooting 75 gr Vmax in a 6mmBR with 14" twist, that at 2900 fps, the bullets may make a 0.1" group at 50yards, but keyhole at 100 yards.
So my fear with 7mmRemMag and 180 gr VLD bullets is great groups at 100yards, and keyhole at 500 yards.
And 7mmRemMag rifles come in baby steps between 9" and 10".
I realize this academic with 6mm barrels, that usually come in bigger twist increments.
April 20, 2011, 02:02 PM
Ok well she has a 1 in 10 twist. That should stabilize 100 grain boolits just fine shouldnt it? I shot some 100's out of it this morning and I was getting about 1'' groups. But the 80's I shot were about 1/2''. Also only about 100 rnds have been shot through this barrel, how many rounds will it take to completely break it in? And will my groups improve after it does? The first 20 rnds I put through it I ran a patch through it after every shot.
April 20, 2011, 02:25 PM
The 10 twist was originated by Winchester for 100 grain flatbase bullets in the .243 Win. I think late model .244 Remingtons were also 10 twist. Factory 6mm Remingtons were typically 9 twist.
Of course your Mauser has a 10 twist because that is what the builder wanted to put on it. Maybe all that was available at the time, if it predates the modern fascination with ultra high BC bullets in fast twist barrels.
Berger shows their 90 grain boattail (not VLD) as suitable for a 10 twist.
A 95 grain Sierra MK has no warning on a twist requirement faster than standard, but their 107 does.
But in the end, the barrel must tell you what bullet shoots best.
I think that after 20 shoot-clean cycles and 100 rounds total, I assume with regular cleaning, your barrel is well broken in.
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