How much does bullet weight affect POI?

[halfded]

I just put a laser grip on my revolver and it's shooting high by about 3.5". Of course, being the genius that I am, I forgot to bring the TINY allen wrench to adjust it in the field.

THen I got to thinking on the way home whether I should sight the laser to my practice ammo (158 grain) or my carry ammo (110-125 grain) which I shoot only for function testing and when I swap out for new stuff (I'm too cheap to shoot $30+ a box ammo on a regular basis).

What, if any, would be the difference in point of impact between a 110-125 grain bullet and a 158 grain bullet? Most all of my shooting (and the Tueller drill) is based at 7 yards, so I don't think there would be too much difference.

If I can keep both weights in a 4" circle at that range without having to adjust the laser, I'll be happy.

What say you, men?

 

[Shadow 7D]

look up ballistic charts for whatever it is that you shoot, way to many variables to give a pat answer, or ask in reloading, BTW what type of gun, caliber and barrel?

 

[BCRider]

On my Model 10 it makes a HUGE difference if I'm trying to hit a target bull or using it in a Speed Steel match. I shot some 125gn JHP rounds and they all hit about 3 inchs low at 12'ish yards. A few rounds of 125gn +P shot even lower at around 4 inches under the bull.

After asking here about a good load for the fixed sights Model 10 I loaded up some 158gn LRNFP's over a couple of different charges of W231. The first was a mid point load according to the tables and the other was a slightly more lively near max load. The mid load under the 158 actually shot HIGH by about in inch for the group. The near max load shot right spot on... well at least the group was spot on. About a two inch group at 12'ish yards. The best my old guy eyes and nerves can manage...

Based on what I've seen in this case and from shooting a bunch of different rounds including Magnums through my Model 19 yes, a 3 to 4 inch lower impact for the lighter bullets is about right. Especially if they are +P or Magnum compared to a softer regular .38Spl load under the 158 bullets.

The other option is to reload your own practice ammo or find practice ammo that has a bullet weight closer to your carry ammo. It doesn't need to be perfect but it would be nice to see it hitting within a couple of inches of the carry ammo like you're asking. It seems like that would make your practicing more valid. Bullet TYPE doesn't matter. 125 RN will shoot to the same POI as 125 HP.

 

[KBintheSLC]

At 7 yards, I doubt the difference will be enough to worry about. Even if it is upwards of an inch (likely less) of difference, it won't matter for defensive shooting.

 

[halfded]

Sorry, 2-inch .38 special revolver. The 110 and 125's are jacketed (remington SJHP I believe) and the 158's are lead mid-range handloads.

 

[Eagles6]

Can be a big difference in poi. I think it would be wise to sight in with the ammo that you will carry for defense.

 

[buck460XVR]

My experience has been at ranges of 25-50 yards the heavier bullet will print higher than the lighter bullet. My understanding is that the heavier bullet is harder to get started thus spends a nanosecond longer in the barrel....and this with the rising muzzle due to recoil and you get a higher POI with the heavier bullet.

 

[MICHAEL T]

At SD range the lighter will hit lower by a couple inches I wouldn't worry about it In real life they will be far from a pretty group

 

[Glasstream15]

I learned, at the range, that I practice with ammo as close as I can to what I carry. I use 95 gr jhp for range and SD in my Kel-Tec P3AT. It is a tiny gun with a sorta weak load and I like solids for SD in it. So the same load for range or SD.

9mm I have settled on 115 gr for range and SD. My G19 doesn't really care but my PF9 really prefers 115. I don't like the idea of having a lot of different ammo on hand so I stay with FMJ for range and JHP for carry. 9mm has enough power and the 115s have enough velocity that I feel confident of expansion and both 9s feed any 115 I have tried without any hic-cups, just what I want in a SD round

And .45 ACP. It was designed to shoot a 230 gr bullet and it works so sweet. Ruger KP90 is a fantastic gun and it's heavy enough to soak up recoil and second shot is just as quick, and aleast if not more, accurate than the Glock.

So I have 5 types of ammo. .380 Auto is all FMJ, 9mm is primarily FMJ with about a 1/4 of my stock being JHP for carry and shooting some at each range trip. And .45 Auto is about the same, 3/4 FMJ and 1/4 JHP, all one bullet weight and they all seem to stay at POA and POI real close. At 15 to 20 yards.

JMNSHO &, of course, YMMV

It also makes ammo storage a wnole lot easier and I am not5 giving much away if I end up with range loads while carrying. An FMJ makes a great SD round although I still like HPs in 9 and 45.

 

[Zoogster]

At close range it is velocity differences more than weight itself that changes bullet impact. Not enough distance is being traveled for the round to be heavily slowed by airflow, so it is primarily gravity.
The more time spent in the air the more it is influenced by gravity. So the round that gets to the target faster will hit higher. Generally a lighter round will be faster, so the lighter bullet weights impact higher.

This of course assumes they are being loaded to the same pressures.
If one is is loading heavy rounds to high pressure and high velocity, and light rounds to low pressures, the velocity might not be that different. A heavier round could even be loaded to higher velocities than the light rounds, resulting in it hitting higher.
Also the shape of the projectile determines what is "long range" for it. The less aerodynamic the shape the more quickly it is slowed by air resistance. This all relates to the ballistic coefficient.

At long distances heavier rounds can actually retain a better trajectory because they are slowed less by air resistance. So while a light round has been slowed significantly and as a result is dropping quickly the heavy round is bleeding velocity at a slower rate.

However even at long ranges there is a sweet spot for a given caliber. Lighter and it becomes more influenced by air resistance, slowing too rapidly. Heavier and it drops so much in initial velocity that the trajectory arcs significantly more.
Somewhere in between for a given distance there is a sweet spot for operating within certain pressure limitations of a caliber.

It is all a curve, and the curve is different for every caliber for a given operating pressure.

 

[halfded]

Went out and shot some 110 grain hydra-shocks, some +p Hornady stuff (the kind with the little ball in the end), and my 158 gr handloads. All hit within an inch or two of each other at 7 yards.

More than meets my 4" criteria.

Thanks for the info from everyone.

 

[Gadzooks Mike]

Remember that gravity being what it is, any and all bullets of any weights will drop the same distance in the same amount of time. POI depends on the speed of the bullet, not the weight. The faster a bullet gets from the gun to the target, the less it will drop. Since you can probably get a light bullet moving faster than a heavier bullet, the light bullet will drop less between gun and target, even though both will drop the same distance in a given time.

In other words, what Zoogster said.

 

[tipoc]

halfded,

Since you have the gun and the ammo then let me ask you..."What is the difference in the point of impact when you shoot your gun, with your hands, with these different types of ammo?"

Shoot at 7 yards or 10 yards, your choice, shoot with your preferred stance using the sights, and tell us, or post pics, of the results. This will also let you know the difference a whole lot better than I, or anyone else, could explain it and you get to shoot while you do your test. Where's the downside?

tipoc

 

[halfded]

Tipoc,

See post #11.

 

[tipoc]

Thanks and sorry I missed that.

On fixed sight S&Ws the sights are (or were as they may have changed them) set for about 3" above point of aim at 25 yards with a 158 gr. load. This allowed for a 6 o'clock hold on a bullseye at 25 yards.

Sights on .38s and .357s are generally regulated for 158 gr bullets on fixed sight guns traditionally. At 7 and 10 yards the difference is usually tiny at 15 and 25 it becomes more noticeable.

Experiment with different loads, over time and see what happens. But in general a lighter weight bullet will strike lower than a heavier bullet and this is irregardless of velocity. This is because the heavier bullet will recoil heavier and raise the muzzle a bit more than the lighter bullet. The heavier and slower bullet will also stay in the barrel a bit longer than the smaller faster will and the result will be the same. Generally the results don't sahow up much till 1`5-25 yards.

tipoc

 

[halfded]

Tipoc,

Please see the rest of the thread..

 

[tipoc]

I did before I posted. Note post 12.

tipoc

 

[rcmodel]

In other words, what Zoogster said.

What was said is wrong.
Gravity or bullet trajectory has nothing to do with it.

A heavier slower bullet will always shoot higher then a faster lighter bullet due to bore dwell time & recoil.

The heavy slow bullet is in the barrel longer, and gives the gun time to start recoiling up off target before the bullet gets gone.

It's especially noticable in snubbys and hard kicking magnums.

It's a proven fact.

rc

 

[tipoc]

And there is that also.

A fella named Robert Rinker has a very useful book out on this and other aspects of ballistics..."Understanding Firearm Ballistics". Not much replaces the fun of going out an experimenting on ones own though. But a good book do enhance the learning.

tipoc