Shot Dispersion & Evaluation
The only shot evaluation targets I have seen are for pistol shooting.
I have not seen any of these target charts for position shooting or benchrest shooting. They may be out there, but I have not seen them.
From what I know about position shooting with smallbore and highpower rifles: My best advice to my students, when I was coaching: “Learn to call your shots”.
For benchrest where we are able to subract a lot of the human error: Vertical dispersion can be caused by the stock sticking on the sand bags and not moving back from recoil the same from shot to shot. We use baby powder or spray silicon on the bags to made the stock slide more uniform on the bags.
Horizontal dispersion can be cause by WIND. And: Pressing the trigger to the side rather than straight to the rear.
Dispersion on all directions can be causes by not managing the recoil EXACTLY the same from shot to shot.
Barrel vibrations come in all sizes and all directions. They can give us horizontal or vertical groups. We can change those vibrations in centerfire rifles by changing powders, charging powder weight, changing primers and seating the bullet at different depths.
In rimfire we don’t have as many options. We can calm the galloping vibrations by testing different brands of ammo until we find one that the barrel likes. AND: We can put an adjustable tuner on the muzzle of the barrel. Browning has a patent on tuners for centerfire. Buy a Browning or a Winchester if you want an adjustable BOSS tuner on your centerfire.
In both rimfire and centerfire, free floating the barrel or putting upward pressure on the barrel at the forend can change barrel vibrations. We can also make changes in barrel vibrations by changing torque on the guard screws, or by gluing the action into the stock. Guard screw torque is measures in inch pounds. For glass bedded wood stocks, torque range should probably be between 15 and 30 inch pounds. More may crush the wood. For pillar bedded stocks you might go higher, but not more than about 40 to 45 inch pounds.
These is a lot more to this subject, but I don't have the time this afternoon to write a book.
Rimfire E-Mail Benchrest Match Coordinator
Last edited by Joe Haller; 08-08-2003 at 05:41 PM..