Wind deflection

[Ross308]

I've read a few articles lately stating that a .22 cal. with a tapered bore will shoot in the wind with less deflection than a barrel with a straight bore. I believe the barrel mentioned was a Benchmark two groove barrel. If this true, what's the science behind it. That would be a real advantage when shooting rimfires at a hundred yards where the wind always seems to blow. Thanks for any info.
Dan R.

 

[searcher]

I have read many times that "choked" barrels do produce better results and a Krieger barrel I had put on a Stiller action supposedly came choked. It is interesting to understand how any tapering or choking could affect the bullet in a deliberate manner to resist wind. Personally, I don't understand the science (wouldn't be my first time)- so not really sure I buy into it. Tony Boyer makes mention in his book about barrels that produced less drift for him. No science mentioned - just personal experiences.

 

[10rita]

Anschutz match rifles from the factory have achieved a choke in the end of the barrel by leaving the end a couple of inches slightly larger in diameter. You can feel this if you push the lead from a round through the bore.

I discussed this with Karl Kenyon many years ago and Karl said he had never seen an Anschutz barrel that wouldn't shoot better if you removed that choke. He did that to one of my rifles by counterboring the muzzle with a 5/8 inch bore the length of the knob and then re crowning it inside that counterbore. The rifle did shoot better. This is similar to what Rimfire benchrest gunsmiths are doing to Sporter barrels today for the purpose of tuning.

Whether the choking made them less wind sensitive is still in question.

 

[patriot]

Just a theory...

The sooner a bullet stabilizes the lower the drag, which results in less wind drift. Some claim to have measured tune by shooting through paper to see where it stops wobbling. I have not repeated the test, but most of us feel a rifle in tune is less wind sensitive. But does a choke or taper help it to stabilize earlier?

Mark

 

[searcher]

Glad you posted that Patriot. That makes sense to me.

 

[LHH]

Could it be these barrels generate more drag so the bullet leaves the muzzle at a slightly lower speed? The same might be true for really long barrels.
BC increases as a bullet slows down, so wind drift might be slightly less.

http://www.exteriorballistics.com/ebexplained/22rimfire.cfm

Wind drift at 100 yards for a muzzle velocity of 1080 FPS is 2.4 inches, but at 1040 FPS drift is 2.0 inches.
Not saying the difference is 40 fps for these barrels, but even a 20 fps difference is .3 inches at 100 yards.

At least this explanation has some science behind it.

 

[searcher]

I think you are saying the slower the velocity - the better the wind resistance? There is science to that - which goes against the idea that faster velocity = less time affected by the wind. I can understand the unstabized bullet creating more drag - even at the same velocity as an unstabilized bullet.

 

[patriot]

Yep, slower in these velocity ranges has less drag and less wind drift. Another theory is that longer barrels produce more consistent velocities. My 30 inch mini-palma 40x Lilja tight bore shoots very well; as long as you are not moving when you break the shot. If I get bored someday I'll run a two chronograph test measuring velocity at the rifle and at 100 yards. Unfortunately many of these improvements are so small they are lost within the margin of error; not measurable.

Mark

 

[Ross308]

Patriot-LHH;
I believe you are right on. Anything beyond 16 inches of barrel will start to slow down the round. A choked barrel would do the same. That's the science I was looking foks r. Now does anybody have a good idea what the absolute lowest velocity would be the sweet spot for the least wind deflection. Don't want much do I? But that would make a lot of difference in the barrel length compared to the stated velocity of this high priced ammo we're using. Just a thought. Anyway thanks for your interest and quick feedback.
DanR.

 

[patriot]

If the JBM ballistic calculator is correct and I didn't make a mistake, for 100 yards it is between 800 and 900 FPS muzzle velocity.

Mark

 

[Ross308]

Patriot,
Thanks for the follow up. Something else to think about. I wonder how close you could come to that velocity with a choked barrel with a little extra length to it. Guess I'll have to borrow my buddies chrono. and see what this Norma Match checks out at compared to his Anshultz. Thanks again.
Dan R.

 

[dickn52]

I have found that MOST bullet deflection happens in the first 2-3 yards of the muzzle. Placing a flag at the target is worthless since everything bad that can happen has already happened. IF I put out two flags on a 50 yard course, one is close and the other maybe at the 20 yard line. After that the trajectory is set pretty much.

 

[patriot]

The wind force at the target has a longer impact, but deflection depends on the condition. It could be still at the target and roaring down range. In general I agree with the flag placement, unless the wind is from the target in which case one down range will give you advanced warning.

 

[LHH]

Dickn52 is correct.
A small wind deflection at the muzzle turns into a much larger deflection as you progress downrange.
For rimfire, BC increases as you progress downrange slightly decreasing the effect of wind and any deflection has a shorter distance to widen.
A small deflection with 25 yards to target will be much smaller than a same deflection with 100 yards to the target.
Any ballistics program will confirm.

 

[patriot]

It is a good rule of thumb, but it is only correct if the conditions are uniform and they are rarely uniform. Chattanooga is a good example. At the state championship on Saturday the wind was running in a channel behind the target then rotating the opposite direction in front of the target. Reading the wind at the line was nearly useless.


Update - Here is a calculation (1072 MV)
3 MPH Left wind 1st 50 yards = .3 inch deflection to the right at 50
9 MPH Right wind 2nd 50 yards. At 80 yards the .3 deflection has been negated - back to 0. The last 20 yards the bullet drifts .5 inch left.

 

[Eric Leonard]

the 2 groove will leave less grooves on the bullet for wind to grab it,,maybe reducing drift

 

[patriot]

... unless the groves are within the boundary layer; like the tail wheel on a ME109.