Mach Trimming for Handloading Nerds
 

Regards sub-sonic shooting accuracy. Cliffs - Vertical group spread is cut in half by loading for a velocity average matching the speed of sound. Half the shots will exit the barrel sub-sonic, the half that don't suffer a larger drop in speed exiting the barrel thus cutting velocity deviation in half.



:cert:

Watched a couple minutes. Yes, as an engineer, I've known subsonic/transonic/supersonic makes huge differences in aerodynamic performance. Read some Navier-Stokes stuff.

Can you give me a short description of the punchline? Why is anybody interested in rimfire? I've looked at some Varmint guns that were very small caliber. SuperDuperSonic. I've looked at subsonic 300 Blackout solutions for suppression. Will this video help me at all?

I understand some of it. I am waiting for the sub sonic loads that SOF guys use. Since it will be tested way beyond any hand loader is going to do.
I know in the Mk262, Mk 318 556 rounds? ammo they are always more accurate than me.

Word. Gavin also just published a video on pushing 308 WIN to 308 WinMag velocities (well over SAAMI specs).

The guy in the video said the principle applies to all bullets, not just rimfire. This was probably beyond the point you watched but it's why I didn't qualify my original comment by mentioning a caliber. IMO the effect would be beneficial for any long range shooting done with a muzzle velocity near the speed of sound (45acp for example).

:cert:
Watched that the other day. My only 308 is semi-auto, won't be running any hot loads through that. Reliable function is the rule there.

But I did get similar results as they showed in my Ruger 243 varmint rifle (longgg 1" bull barrel) using some of techniques they utilized (I'd use case measurements for pressure indications as opposed to simple visual inspection of the case head for impressions and flattened or backed out primers). I also won't be making powder adjustments in 1 grain increments. The 243 uses 308 brass so getting ultra velocity with a 6mm bullet wasn't too much of a chore. Ruger's are built like tanks to begin with and the rifling on mine was a new thing at the time I bought it, only one side of the lands has a sharp cut which was said to add extra velocity. Didn't chrono it but I was closing in on 4100fps according to calculations before any major pressure signs became evident. That's a shit-ton of velocity! Did this just for experimentation though, not an everyday load any means.

100 yards is "a long way" with .45ACP. Some factory 230gr hardball rounds made the target with about 3 foot holdover out of my series 70 Gold Cup, some skipped in from 6 feet in front of the berm at the same holdover. Dropping bullet weight to 200 grains and increasing velocity about 100FPS allowed much less Kentucky windage and much more uniform patterns (can't quite call them groups once they exceed dinner plate size). Don't know what the BC is of either projectile but I bet it is miserable, and I suspect at least in this case means more for long range accuracy than any variation in muzzle velocity.

Spoken like a guy who hunts with 30-30 factory loads ;) I don't push the 45 beyond 75' myself but there are people who use them on metal silhouettes.

Actually my 1961 1894 with a 20 inch tube prefers old school 170 grain Winchester factory fodder while the Ranger version likes 150s at about 2100 fps.
PlusP+ 185s in the Colt print pretty close to the sights at 100.... you just have to concentrate.

4100 fps is serious business. Laser/barrel burner :seasix:
I hope there is more market adaptation of the 277 fury hybrid case to bump pressures up around 80k psi to many other cartridges. It would also be nice to see more variants of fast twist setups like the 8.6BLK with it's crazy terminal ballistics and ability to shoot both heavy grain and light grain bullets.

The 30-30 can definitely be made to shoot well. It's what started me handloading. Advertised factory MOA is 4" (I think?) and mine wouldn't even do that. Was in college at the time in a statistics class for Manufacturing Engineering. Did a final paper presentation on improving the accuracy of that gun using handloads. Don't recall my grade for the paper but considering the lib teacher acted like he needed a bomb shelter as soon as I began talking about ballistics it probably could have been better :rofl: Shrunk the group down to 1/4 the original size of the best factory load in the study :yesnod:

4MOA is still "minute of whitetail". Mine both shoot 2ish with preferred ammo... good enough for a 100+ year old design.

A guy from work had an old Marlin that did 2" inch groups with factory loads. When I told him about the improvements I got handloading he asked if I'd make him some bullets. Told him sure but he'd need give me the rifle for measurements to custom fit the loads, buy the supplies, and let me to keep any surplus components as payment. A week later he shot a half inch group and was smiling from ear to ear.

Nice. At what distance?

100 yards. It's a standard test distance around these parts. His gun might have had custom accurizing? Never saw checkering on a Ruger before, or since.