Meplat Uniformity Accuracy Effect at Short Range

[Joe Woosman]

Bryan,

Can you add anything on this subject? I suspect real measured effects are too small to be practically measured. It seems to me a meplat not uniform with a bit of an angle on it would cause a center of pressure imbalance leading to some amount of dispersion. Does this hold water with you?

 

[Bryan Litz Ballistics]

I've tried several times to observe this effect, but haven't seen anything to indicate that a ragged looking or tilted meplat causes bad groups. In fact, there's an argument that trimming them flat may imbalance the bullet. Think about it this way; assuming the jacket is concentric, if you cut material off one side and not the other, you have a mass imbalance which is very bad for bullets. Good thing is the affected mass is near the bullets axis of rotation, meaning it will have less impact than if it were on the outer edge of the bearing surface.
In my testing, I would separate the 'best' (flatest) meplats from the worse (most tilted) and shoot groups. With 1/2 MOA rifles, I see no difference. It might be interesting to do the test with a sub 1/4 MOA rifle to see if you can tell a difference at that level.
-Bryan

 

[Joe Woosman]

Thanks for the input Bryan.


Could you elaborate on the argument that trimming them flat may imbalance the bullet? I haven't come across that concept before.

I'm sure any short range accuracy loss due to meplat imbalance would be very small, otherwise, the short range BR crowd would be all over it.

My thought behind the question was not pertaining to a mass imbalance but a pressure imbalance relative to the axis of rotation. Accepting that a wind force is applied at the center of pressure and the bullet is turned about the center of gravity, it seems to me the same force and moment would apply. IF - a bullet could be stable and not rotating, and IF a bullets CP was slightly off center due to an angled tip, the bullet should drift. Being that real bullets are spinning, maybe this pressure imbalance would average out and not cause angular dispersion? In theory, could this cause a continuous yawing motion? If so, would this not effect BC and wind drift values - if only slightly?

 

[Bryan Litz Ballistics]

Joe,

The idea is that; assuming the jacket is perfectly balanced before forming into a bullet, if you form the bullet, then remove metal from one side, it would un-balance the bullet. Note that meplat trimmed bullets shoot very precisely and no precision issues have ever been observed (to my knowledge) from trimming, so the idea of un-balancing the bullet by trimming is likely not valid or too far in the weeds to show up.

On the center of pressure (CP) being off center, you hit the nail on the head: the bullet is spinning so any 'steering' effect is averaged out meaning it doesn't cause any net deflection.

The high RPM's of a bullet are a great source of dispersion, but this is a case of the rotation nulling out a source of dispersion.

-Bryan

 

[DocBII]

Bryan,

I've found meplat uniforming to be helpful with a number of calibers and distances. If uniforming unbalanced the bullet, would the difference be large enough to show up when tested on a Juenke machine? I don't have access to one, so I haven't been able to run the test myself.

Thanks,
DocBII

 

[DocBII]

Good day,

Anybody out there with a Juenke (sp?) machine to test the unbalance theory? I'm ready to put it into internet theory category. Trimmed, with or without pointing, bullets perform more consistently for me.

Thanks,
DocBII