Question about POI difference.

[LONGTOM]

I have a question about POI that I just don't understand.

I have a 204 Handi with the 22" barrel.
It is sighted in with factory HORNADAY 32gr VMAX ammo with a stated velocity of 4225fps.
I tried some factory HORNADAY 45gr SPs with a stated velocity of 3625fps with the same scope setting and the 45gr ammo prints a constant 1" higher.
It is still centered left to right just higher.
I don't understand how this can be.
I would think it would print lower due to the heavier bullet and reduced velocity.
I wouldn't think it was due to recoil on such a mild recoiling cartridge.
Can anyone explain this?  


LONGTOM

[securitysix]

Heavier bullet is moving slower, thus stays in the barrel longer.  Because of that, the point of impact is higher.  Pretty common thing in magnum revolvers, don't know why it wouldn't apply to rifles as well.

[LONGTOM]

I understand that in handguns because of recoil but the little 204 really has no recoil.
Beats me!
Just make no sense on this caliber.


LONGTOM

[gypsyman]

Not sure if this is it, but, maybe the bullet causes a different harmonic balance in the barrel. You can't feel the recoil, but the barrel is reacting different to the heavier bullet. (How's that for bald fat guy that doesn't have a degree in physics!!)  gypsyman

[securitysix]

I understand that in handguns because of recoil but the little 204 really has no recoil.
Beats me!
Just make no sense on this caliber.


LONGTOM

We're talking about an inch at 100 yards.  It doesn't take much of a difference to throw something off an inch at 100 yards.  That you don't perceive the recoil doesn't mean it isn't there.

Now, I might be wrong, but I'm going to stick to my guns until someone comes along with a better explanation. 

[Graybeard]

Forget everything you think you know as it just plain does not apply. With handguns it is generally safe to say slower and heavier hit higher and faster and lighter hit lower.

BUT with rifles all bets are off. Any time you change bullets, bullet weight, powder, powder charge weight or even seating depth with all else exactly the same the POI can move in any direction and often by inches. I've done enough load testing using often three bullets of same weight but different design or manufacture and with often three or four powders. I'd use same powder charge with each and go up in increments of half or full grain with each.

Many times I've seen a grain change in powder shift POI by inches and same when same powder charge is used with different bullets. Logic plays no role here the bullets will impact where they impact. Do it as much as I have and you'll just shake your head and move on.

[LONGTOM]

I pretty much have done that GB (moved on).
It just makes no sense for a heavier bullet traveling at a slower speed to hit higher from a rifle.
A handgun,yes.
Not complaining, as I use the 45s for longer shots on bigger varmints.
They do a better job on coyotes as far as knock down power at the longer ranges.

Just trying to understand the nature of the beast we call shooting.


Thanks
LONGTOM

[anweis]

Heavier bullet is moving slower, thus stays in the barrel longer.  Because of that, the point of impact is higher.  Pretty common thing in magnum revolvers, don't know why it wouldn't apply to rifles as well.

Me either, but it's the same with my muzzleloader and 6 and 7 mm rifles: heavier bullets hit 1-2 inch higher.

[jhalcott]

 Long tom, let us know when you get it figured out. Maybe we can use the info to help figure out our WIVES! I just know GB is correct on this one. No logic, just fact!

[Steve P]

Let me put it this way:  You are luckier than most in that your two groups are only an inch apart and on top of each other.  Some of us have to re-zero if we change loads. 

Don't fret the good luck!!

Steve

[fr3db3ar]

With my 223....using the same powder.

24.5 grains and a 55 vmax
25 grains and a 64 Win soft point


POI almost identical.

[Brithunter]

Hi All,

    GB has it right there is no rhyme nor reason. I am just testing and looking for the "right" laod in a Mh18 Baikal .222 rifle using IMR-4198 powder. Last sunday shot the same load just varied the seating depth lookign for the sweet spot and POI changed over 2" in some cases from 0.005" difference in seating depth  . I was shooting the Hornady V-Max 55 grain bullet and with a COL of 2.195" the rifle shot POA a groups of 5 shot with a COL of 2.190" went 1 1/2" low and 1" right the next group of 5 with a COL of 2.185" went 1" high and 1 1/2" right  .

     Seating depth in this .222 Rifle seems critical so much so I am wondering about buying a Micrometer adjustable seating die.

    Now the loads selected for further testing are the COL of 2.185" which have four shots in one hole with the other 1/2" below it and the COL of 2.195" which has three shots in one hole with the otehr two 1/2" away at 9 & 12 o'clock. In fact I am going to swop the 4x scope on it to e a 6x40 for the final testing to see if the extra magnification helps 

I had not noticed such a POI change with most other cartridges, it seems the smaller in bore you go the more this shows up. Have only worked with one .22 CF before and that was years ago when I acquired a 22-250 for a project. It came with some Federal factory ammo so I tried it and found despite a visably worn throat it still shot under MOA so I kept it as it was until the accuracy finally died.

[epanzella]

Upon ignition a shock wave travels down the barrel like the wave you see when you whip the end of a rope. As the bullet travels down the barrel the muzzle is occilating with this wave. If barrel length and bullet velocity are such that the bullet exits at either end of the stroke when the muzzle is relatively still, you have an accurate load. Bullets exiting in the middle of the whip when the speed of the muzzle is greatest are not as likely to group well. Changing the velocity of a bullet can cause it to exit the muzzle at a different point in the oscilation which can be higher, lower or to the side of the previous load. At 100 yds with a modern caliber the whip can have more affect than the trajectory. At 500 yd, gravity will not take no for an answer and the flatter shooting load will print higher. Shortening the barrel can do the same crazy thing only to a lesser extent as the barrel gets stiffer as it gets shorter.