Recent content by Jim Boatright

Interior Ballistics: One approach to minimizing the variation in muzzle exit speeds for groups of shots is to make sure that your bullets obturate the bore completely as soon as they engrave the rifling into their bullet shanks. We routinely saw extreme spreads of 2-4 fps in 5-shot group testing...

Thanks, Nik H. Here is a new paper I am writing about the importance of minimizing initial bullet yaw and yaw-rate in long-range rifle shooting. It is based on seeing the results of many runs of my (available by email) Excel spreadsheet calculating recoil induced, vertical plane muzzle motions...

My 6.5 and 338-caliber LAW muzzle brakes were custom designed by Mic and me for hard-mounting Magneto-Speed chronograph sensors. The bottom groove is for clearance of the shop-made offset sensor front-mount, and the top groove is for symmetry. The top plane of the inductive sensor must be...

I have not touched base with Mic McPherson since COVID-19 began. I would recommend a simple little high-evacuation-rate brake on the straight walled 45/70, no matter how hot you might load them. I used bulk packed Remington 300 grain JHP bullets at 2300 fps for plinking from Winchester high-wall...

IIRC the guy from the Houston warehouse said that 21.75-inch barrels were most accurate for IBS/NBRSA short-range centerfire benchrest (Sporter and HV classes). That article was much discussed in Precision Shooting Magazine during the 1990's when I started writing articles for them.

Your feeling that that bullets having smaller axial inertia values would spin-decay faster is correct, Max, all else being equal. Where you are mistaken is in thinking this would be a large effect. The radius of gyration (kx) of a bullet about its spin-axis varies much more with caliber and...

Just out of the muzzle, the initial spin-rate ω0 of the bullet in radians/second is given by: ω0 = 2π*V0/Tw = 2π*12*V0/(n*d) where V0 is the muzzle velocity in feet/second, the twist rate Tw is given in feet/turn, n is the number of calibers/turn, and d is the caliber in inches. Thereafter...

When your rifle and loads start producing very uniform bullet speeds just out of the muzzle, it makes sense to use Extreme Spread (ES) for a group of shots as your performance metric instead of Standard Deviation (SD). We found in our development of monolithic copper ELR bullets that, by...

Yes, that is a pretty good analogy. Transonic flight through air is often described as "turbulent" for planes as well as bullets. Long-nosed supersonic rifle bullets tend to become unstable when they fall into the transonic speed range even though their gyroscopic stability is very high (Sg >...

Some notes on crosswind sensitivity for 22LR rimfire: As was formulated by DeDion in 1859, air drag causes wind drift "downwind" across the target which is proportional to the actual time-of-flight with air drag minus the hypothetical time-of-flight to the target at the undiminished launch...

I've heard everything from 9" to 16" of barrel length for max bullet speed with different types of 22LR ammo. I would estimate about 12" of bullet travel for match ammo.

By minimizing the vibrational connections among the four parts I mentioned (barrel, action, stock, and scope), the vibrational effects on the muzzle at bullet exit time are more predictable; i.e., not affected as much by variations in support and hold.

You got it, Brianf. I pillar-bed some "action screws" into the bottom of the barrel-block. Be sure the trigger does not contact in the stock or trigger guard. There really is no need for a recoil lug with 22LR, but the bedded rear face of the barrel-block handles even heavy recoil loads. I...

Yes, the short barrel length in front of the bedding block is much easier to tune at the muzzle than a long barrel. The clamp-on bedding block should ideally not stress the barrel at all. I find that a scope rail cantilevered from the top of the barrel block is also a good idea for minimizing...

Yes, I did that with a "Ruger" 10/22 in a laminated stock. Would be a winner in IR 50/50 if it were legal. Imagine being able to shoot all 25 record shots in one wind condition.