Do You Know Your Rate of Twist? Really?????

[Old School 611]

 

Well all shooters match their bullet to their rate of twist or should.

 

Sometimes I like to shoot the heaviest bullet I can, Like I shoot 69gr 224 in a 1:9 Barrel.

 

Well that I consider the max weight for that twist BUT they shoot very well.

 

So for kicks and giggles I measured the rate of twist...Not 1:9 at all it's 1:8.5 which makes a difference.

 

Now my Savage 12 bolt gun is supposed to be 1:9.25 Well that's not right either it's 1:8.75

 

So the take away? Not all barrels are what they are stamped and if you measure you may have more bullet flexibility.

[vjf915 456]

Interesting.  How did you measure?

[Old School 611]

Put a tight patch on a cleaning jag. Take a reference point Mark the rod and push it in one revolution and measure the distance between your reference Marks. That will be your rate of twist

 

 

Sent from my iPhone using Tapatalk

[Krdshrk 3,878]

Sinclair’s Simple Twist Rate Measurement Method
If are unsure of the twist rate of the barrel, you can measure it yourself in a couple of minutes. You need a good cleaning rod with a rotating handle and a jag with a fairly tight fitting patch. Utilize a rod guide if you are accessing the barrel through the breech or a muzzle guide if you are going to come in from the muzzle end. Make sure the rod rotates freely in the handle under load. Start the patch into the barrel for a few inches and then stop. Put a piece of tape at the back of the rod by the handle (like a flag) or mark the rod in some way. Measure how much of the rod is still protruding from the rod guide. You can either measure from the rod guide or muzzle guide back to the flag or to a spot on the handle. Next, continue to push the rod in until the mark or tape flag has made one complete revolution. Re-measure the amount of rod that is left sticking out of the barrel. Use the same reference marks as you did on the first measurement. Next, subtract this measurement from the first measurement. This number is the twist rate. For example, if the rod has 24 inches remaining at the start and 16 inches remain after making one revolution, you have 8 inches of travel, thus a 1:8 twist barrel.

[Old School 611]

Here you go!

[djg0770 481]

So you are assuming ZERO slip in the patch, huh?  I have some issues with that.  The bearings in a cleaning rod are not "precision bearings" designed to rotate under an axial force per se.

 

While I think the basic method above will get you close, I believe there's a margin of error which you have not accounted for.

[Old School 611]

So you are assuming ZERO slip in the patch, huh?  I have some issues with that.  The bearings in a cleaning rod are not "precision bearings" designed to rotate under an axial force per se.

 

While I think the basic method above will get you close, I believe there's a margin of error which you have not accounted for.

Dan - I use a good Tipton rod and a tight patch. There is NO slippage. The rifling engraved on the patch is proof of that.

[Vlad G 345]

I'd think patch slip would result in a longer measured twist, not a shorter one?

[Old School 611]

I'd think patch slip would result in a longer measured twist, not a shorter one?

That's true Vlad. If there was that kind of slippage you'd never be able to clean your barrel down into the grooves.

 

Rods, jags and patches are made to engage the rifling. I could see something undersized slipping like worn out brush.

[almiz111 26]

Let's say all you say is good and correct.

 

The question is: what"s the diff?? 9 vs 8.75?? Are you shooting National Match at CMP out in Ohio?

 

What is the group size improvement? Just curious.

[Old School 611]

Let's say all you say is good and correct.

 

The question is: what"s the diff?? 9 vs 8.75?? Are you shooting National Match at CMP out in Ohio?

 

What is the group size improvement? Just curious.

Allows you to shoot a bullet that you may think is marginal for your twist. Just allows you more options to experiment with.

[tattooo 220]

What do you all feel is an optimal bullet weight for an 1-7 18" .223/.556 barrel ? I use 55 grain for practice but i know a heavier grain should more accurate for the twist

 

[Krdshrk 3,878]

What do you all feel is an optimal bullet weight for an 18" .223/.556 barrel ? I use 55 grain for practice but i know a heavier grain should more accurate for the twist

 

What twist rate is your barrel?  1/7?  1/9?

 

[tattooo 220]

I am sorry 1 - 7 thought i put it in my question

[Parker 213]

A good read on bullet twist, RPM, and a twist rule formula:

 

http://www.accurateshooter.com/technical-articles/calculating-bullet-rpm-spin-rates-stability/

[T Bill 649]

You might find the 70, 75 and 77 the most accurate at any speed but that would have to be proven on the range as barrels vary by manufacturer, lot, and construction (steel types and build specs).

[Old School 611]

A good read on bullet twist, RPM, and a twist rule formula:

 

http://www.accurateshooter.com/technical-articles/calculating-bullet-rpm-spin-rates-stability/

Yes RPM is what stabilizes the bullet.

 

But rate of twist has a greater effect on RPM than does velocity.

 

And velocity is limited by the available limits of pressure.

 

Thus we change the twist rate to increase RPM and rely less on velocity.

 

All that being said. I drive 69gr bullets in a 1:8.75 twist as fast as is safe to obtain max stability and accuracy and it appears to work.

[Krdshrk 3,878]

I am sorry 1 - 7 thought i put it in my question

 

Oop I see it now...

 

It really depends on your gun and what you're trying to accomplish.

 

I've been looking at the MK262 round lately - 77gr OTM Sierra HBPT MatchKing w/ Cannelure...  If it works for the US MIlitary for DMR Applications, I'll take it.

http://www.shootingtimes.com/ammo/special-forces-to-civilians-black-hills-mk-262-mod-1-review/

[tattooo 220]

O.k thanks...... ill read up on that round