Re: Sleepy Bullets VS Sleepy Arrows(Archery)
I would agree with most or what Kolbe wrote in his article. In fact there was not much in there that was not exactly what I have been saying.
What points in his article do you feel I do not agree with?
The only theory I may question is the precession theory but he knows more about that then I do for sure so I would never challange him on that, to be honest, this is only theory anyway.
I do disagree with him about teh problem seating VLD bullets away from the rifling producing in barrel "yaw". THis may happen in a poorly chambered rifle built to mil specs such as the 308 match rifles he is referring to.
In my custom chambers and throats in my extreme range rifles, there simply is no where for the bullet to get out of alignment with the axis of the bore as I generally cut my extreme range throats 0.0002" over bullet diameter. This is very tight, 0.0001" on each side of the bullet only. In fact you will get rub marks on the bullet body when you chamber a round, there simply is no where for the bullet to cant.
What I have seen with VLD bullets seated off the rifling is that teh thin jacketed bullets get horizontal velocity built up before then start rotating. The heavy, long bullet then engages the origins of the rifling and the front of the bullet begins to rotate because of the rifling.
The middle and rear of the heavy bullet has enough inertia to resist this rotational force very a slight period of time.
Because the bullet has a very thin jacket, this jacket can not control this "wringing" action and the bullet is twisted. Finally, enough of the bullet has been engraved by the rifling to have total control over the bullet and everything begins to rotate.
The problem is that this Winging out has weakened the jacket/core bond and as a result, when the bullet is released from the crown, this weakened bond is inconsistant and results in shifting and expansion which results in variations in flight.
This is nothing different then a very cheap made bullet with inconsistant jacket thicknesses and such. The bullet will now rotate around an axis point that is off dead center of the bullet and consistancy will suffer.
Now, if we take the same bullet, same velocity and seat teh bullet so that the bullet is touching solidly into the rifling. The bullet simply can not go forward without beginning to rotate.
Also, the horizontal velocity is still very slow at this point and the thin jacket will handle and control the stresses of getting the entire bullet rotating much better then when the bullet has gained velocity before spinning.
Basically, it is just easier on the bullet and thus allows the thin jacketed match bullets to survive higher velocities and fast twist barrels.
I have tested this in several rifles, the latest was one of my V-Block rifles chambered in the hot 22-6mm AI. It was fitted with a 1-8" twist Lilja 3 groove barrel of 30" in length.
Testing the Berger 80 gr VLD bullet over RL-22. I started with the bullet seated 0.050" off the rifling and at 3300 fps the consistancy of this bullet on target dropped off dramatically.
At 3500 fps, the bullets were not reaching the target.
I started the process again but seated the bullets +0.020" into the rifling, hard into them. Velocity topped out at 3600 fps with groups in the 3/4" range at 500 yards.
I also tested this with the 75 gr A-Max and it resulted in similar results.
With the 80 gr Sierra Mk the results were different. Seated off the rifling, the Sierra bullet still reached around 3600 fps but groups at 500 yards were in the 1 3/4" range.
Seated hard into the land the load work up showed they topped out at nearly the same velocity but groups were in teh 1" range.
The reason, the Sierra Mk has a significantly thicker jacket then the Berger or Hornady match bullet. This thicker jacket in my opoinion, controls the Wringing effect and does not result in a weakened jacket/core bond.
One othe rtest was with the 55 gr Hornady V-Max and the 55 gr Ballistic Tip.
Using Rl-22 again, I started with the V-Max bullet. At 3800 fps this bullet let loose, did not matter if it was into the rifling or not.
The 55 gr Ballistic Tip shot into 2" roups at 500 yards from 3800 fps up to a max of 4300 fps. It also did not matter what seating depth was used either.
The difference in the two bullets, Jacket thickness. The Hornady has a traditional thin cup jacket and the combination of the 1-8 twist and the extreme velocity was far more then this bullet would handle.
The Ballistic tip with its heavy solid base had no problem with consistancy up to 4300 fps even at the extremely high rotational velocities in this fast twist barrel.
That is really the only area I would not fully agree with Dr. Kolbe on. The reason is because I have tested this in many rifles and it nearly always stays true to form to some degree or another.
Other then that we believe very much the same.
Again, he knows vastly more then I on the subject and would not disclaim anything he says, I just have another theory to explain the same happenings.
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