Home Forums Hunting & Shooting Rimfires Supersonic POI lower than Subsonic?

was shooting a handful of 22s today, 3 10/22, 3 cz 455. Was shooting 7 different loads. Ranging from 910fps up to 1250.

On the 4th rifle(CZ 455 American, unsuppressed) I went through through the first 4 loads(CCI SV, CCI SUPPRESSED, ELEY CLUB AND ELEY TARGET) , all were within reason of how they performed in the other rifles. This rifle was zeroed with CCI SV. When I got to the first group of Supersonic ammo, it shot about 4in low. I tried 2 more supersonic loads....one 3in low, the other about 4in as well.

Distance was 50yd. How are supersonics shooting lower than the subsonic?

When you pull the trigger you have initiated a recoil impulse and wave form oscillation in the barrel. Faster bullets exit the barrel at a different phase of the oscillation/recoil impulse.

Just like shooting 300+gr. bullets in a 44Mag.

Barrel time.

I get barrel harmonics. I still can't see a 4in drop at 50 yards. I've shot a lot rifles in various calibers and have never seen this before.

Warpig602: I have seen this phenomenon numerous times in the 60+ years I have been shooting rimfire AND centerfire Rifles!
YOU have to sight in with one bullet and expect other bullets/loads/cartridges to have different points of impact - left, right, up or down different bullets/loads will often (usually?) strike in different places with the same point of aim.
Hold into the wind
VarmintGuy

I've seen different points of impact on varying loads. Truly did not make sense to me that a 1050fps round is zeroed, other rounds in the same speed range hit within an inch. Then the another laid going 200 fps faster, shoots 4in low.

Well, I guess I can't argue orhers who have experienced the same. Nice to still be surprised every now and then

To illustrate the influence of changed barrel harmonics I can do the same as you experienced with the same ammo by installing a suppressor. One of my barrels will print 6” low at 50 yds after installation.

Correct, I sometimes encounter the same when putting my cans on,hence why I zero a rilfe with it on or off and then only use it in that configuration, or make notes about correctiosn, but the change in POI affects all rounds fired. Meaning if my sub shoot high and left 3in when I put a suppressor on, subseqeunt laods will also shoot high and left. Id still expect bullets traveling faster to impact higher as thay have with the other 30 or rimfires ive owend or shot.

What would be the same is you zeroing with with the can on, and then shoot faster rounds and have it go lower.

I don't think it's a "harmonic" thing but more of a "barrel time" thing as TNrifleman said. A can adds weight to the end of a barrel and slows down how quickly it rises under recoil. I've got a rifle that does the same when I screw on a muzzle brake.

The Shadow knows.

check out varmit al's eclectic web pages . an explanation of this by a professional.

Varmint Al’s site explains much.

I had a look at Al's site but I saw a flaw in his logic comparing fixed rigid tubes with real life tubes under recoil (ignoring barrel vibration). In real life the tubes are going to be at slightly different angles when the projectile leaves the barrel for different velocities - the lower velocity leaving the barrel when it's at a higher angle due to being in the barrel longer while it's undergoing lift from recoil.

Vibration can shift in trajectory in either direction.

Dwell time in the barrel is shorter so the muzzle rise initiated by recoil impulse has less time to influence the lighter/faster projectile than it does with a slower or heavier projectile.