Zerod with Winchester bulk 22lr, Minimags hit ~ 2" lower.

[Orion8472]

I put a scope on my Henry carbine [for the heck of it] and took it to an indoor tube range. I just used crap bulk ammo fro Winchester [the 333 round box] at 50 yards. Groups not too bad, . . . about and 1.5 inch groups. Had some American Eagle and it shot a bit better. Close to the same POA. But tried some Minimags and they hit about 2 inches lower, . . . . but about a .75" group.

My question is about velocity and where a bullet will hit. Why would the Minimags hit that much lower?

 

[DPris]

Higher vel shoots flatter (lower).
Denis

 

[Orion8472]

Does anyone know of a video on this that I can use to better visualize the concept? If so, thanks!

 

[DPris]

Speed X shoots to a given point, elevation-wise.
Sights are adjusted to match, at whatever distance.

Speed Y, going faster, just shoots at a slightly lower arc in travel, or flatter. Strikes impact point lower at same distance with same sight setting & muzzle angle.

You know that no bullet travels in a straight line & ALL will arc.
Generally speaking, given same or near same bullet weights, faster bullet=flatter arc.
Denis

 

[rcmodel]

The faster ammo is getting out of the barrel sooner in the recoil cycle.
So the muzzle hasn't had time to raise as far due to recoil.

rc

 

[Orion8472]

As per the arc, . . . would it be reasonable to assume that a fast bullet and a slow bullet will have the same apex of the arc [assuming a fixed in place rifle on a bench] but the faster bullet will apex the arc further away? Which is why it would hit lower?

 

[DPris]

RC,
In a rimfire rifle, I don't think that'd apply as much as with a heavier-recoiling gun, but it is a factor.

Orion,
Not necessarily.
Denis

 

[verge]

You would need a complete course in INTERNAL ballistics and a supercomputer with a ballistics algorithm beyond what we have today. You are not only dealing with the flight of the bullet after it leaves the barrel but also the interaction between the barrel and bullet while the bullet is still in the barrel.

If you have ever watched high speed video of a rifle being fired you will see the barrel moving as the bullet is traveling down the barrel. Where the barrel is at the exact moment the bullet is exiting the muzzle does affect the Point of Impact and is not calculable with today's technology.

Although the regular external ballistics rules apply after the bullet has left the muzzle and make total sense, faster bullets fly flatter, higher BC fly flatter for longer and resist wind deflection etc. For any given load the POI could be higher or lower based on nothing more than the vibration imparted to the barrel by that particular load and whether the barrel was at the high point or low point or somewhere in between when the bullet left the muzzle.

 

[scythefwd]

http://www.rimfirecentral.com/forums/showthread.php?t=541530

lots of reading. Specifically in barrel harmonics and dampening them. Its more black magic than science right now, but only because any sufficiently advanced science will be indistinguishable from magic. AKA, we are figuring out what is happening, and how to counteract it.. but we cant begin to understand the subject at this stage...

 

[Sunray]

"...Why would the..." Different ammo. You have to try a box of as many brands as you can to find the ammo your rifle shoots best, then sight in with that ammo. You cannot just sight in.

 

[BCRider]

50 yards is not a long distance even for .22LR ammo. So neither round will be at the point where it reached the apex of its arc and is starting to fall back. Especially given the rise involved in any use of a scope.

Oddly enough Mini Mag lists the muzzle velocity as 1230fps and 333 is listed at 1280fps. But the MM's have a heavier 40gn bullet compared to the 36gn pills of the 333. However the muzzle velocity being close enough to being the same suggests that it's not the external arc that is the issue. And in any event the heavier bullet will bleed speed less than the lighter bullet when both are at the same muzzle velocity so by rights once again the MM's should be printing a little higher than the 333 instead of lower.

So that brings us back to the internal ballistics and the idea that for some reason the greater kick of the MM's is causing a different recoil dynamic in a rifle as compared to a handgun. Whatever that dynamic model is it seems to be producing a lower group from the more powerful, but similar speed MM's. And it's that situation which is producing the lower POI from the MM ammo.

In handguns the heavier or slower bullets would print higher. But with your rifle you're getting the opposite effect. Or it may be that despite the similar muzzle velocity that the MM's are spending less time in the bore due to a stronger charge accelerating them up to speed sooner so they transit the bore faster. If so then it could be that they are simply leaving the rifle sooner in the recoil cycle as RC suggested. Otherwise it's some other factor in the recoil dynamics.

 

[DPris]

Bullet weight & velocity in .22s are the two biggest factors in elevation differences, and makers' claimed velocities are not always accurate.

I got a 5-shot average of 1246 FPS at 15 feet from the muzzle through a CZ 16-inch barrel for 40-grain Mini-Mags.
Have no Win 333, but 5-shots of Win 555 36-grainers ran 1275 FPS, same distance, same gun.

Denis

 

[Davek1977]

MM's have a heavier 40gn bullet

Well, the SOLIDS do...the HP's weigh 36 grains.