22K Hornet heavier bullets hitting higher than lighter ones

[PigButtons]

I'm trying to find the perfect combination for my SK Industries 16" custom 22K hornet barrel on a G2 Contender. I started with new Hornady brass which I neck sized. Wanting to gently fire form the casings I used 34gn Midway Dogtown bullets over 11.8 gn of Lil'Gun with Remington 6 1/2 primers. They shoot OK at 50 yards but probably just a little worse than MOA. I didn't expect much but was pleased with the uniformity of the formed brass. After fire forming I sized to length all of the brass, about half ranged up to .013 longer, and chamfered them inside and out.

I then loaded them with the same 11.8 gn of Lil'Gun, same primers, and this time Hornady soft point, Spire Point, 54.9 gn bullets. These easily shoot 1/2 MOA. But my dilemma is that at 50 yards these heavier bullets hit almost 2 inches higher than the POA, where the 34 gn went to exactly POA. My only guess is the heavier bullets cause a higher pressure in the barrel and allow the Lil'Gun to burn more effectively.

Any other thoughts?

 

[edwardware]

In pistols, heavier bullets print higher due to longer barrel dwell time increasing the elevation angle at release. If your velocity is slow enough and recoil is rotational enough, you might be seeing the same thing.

Or it could be simple combustion efficiency. Bullet weight will certainly add pressure, and if you're underpressured/inefficient with the lighter bullet, the heavier could be the necessary boost.

To find out, increase the charge and see if the POIs invert.

 

[TAJ45]

I would suggest that simple bbl harmonics is the cause.
I have seen enough YTube super slow mo pistol firings to think that the bullet is long gone before significant upward bbl motion occurs.
My opinion at this time but more than willing to listen to other ideas.... --

 

[searcher]

Any other thoughts?

The harmonic barrel vibration undulates the barrel in a circular orb - basically sending bullets off into the direction the barrel tip is undulating towards at the exact time the bullet exits the bore due to this vibration. At close range (say 100 yards, for example), say a 50 grain bullet exits at the bottom of the vibration undulation - and a 70 grain bullet exits at the top of the undulation. It can give the impression that the 70 grain bullet was going faster - but that is not always the case. Learning to control, or "tune" these vibrations is what leads us to that nice, tight group

 

[PigButtons]

Well, turns out you guys were 100% right on the harmonics. After adding a Harrel's muzzel brake /tuner the groups got absolutely tiny. The hole inside the circle is three shots from 50 yards. The two holes up and to the left of the circle are before getting the tuner adjusted. Same load, same POA

 

[TAJ45]

It was a mystery to me as well until I read about the harmonics some years back....pesky physics.

 

[TheOtherZilla]

Good luck with that Hornaday brass. I just tossed a bunch once fired Hornaday 22 hornet brass cuz the primer pockets were junk. Off center holes and brass in the primer pocket hanging out of the flash hole. A grand mess it is.. I tried to clean it up but no bueno..