effect on point of impact of bullet weight

[foszoe]

If you are dead on the bullseye with a 115 gr 9mm bullet and, keeping all other components and atmospherics equal, where would the point of impact shift on the horizontal plane (windage) of a 135 gr bullet?

I can read all about vertical movement online.

On a related note, any great books on external ballistics? Websites? Computer software? Especially interested in works that treat the problems in 3 dimensional space (without and with wind)

 

[Broom_jm]

At what distance and at what velocity? The only good answer to this question is, "it depends". Anything other than going out and shooting your ammo from your gun is pure theory.

Forgive my impertinence, but what other kind of external ballistics are there, aside from those occurring in 3-dimensional space? The true study of ballistics is pretty dry stuff. There are quite a few free software titles on the web; I prefer PointBlank. A lot of folks like JBM Ballistics.

 

[Indy_Guy_77]

All things being equal...meaning the powder charge is equal... Or that the velocity is equal? Because it can't be both...

But generally speaking, higher bullet weights will mean a slightly higher impact site. Though at most "handgun distances" the difference will be negligible.

 

[foszoe]

Distance is 25 meters. No wind. At the point the bullet exits the barrel, we are in the realm of external ballistics and ALL things are equal in external ballistics except the weight of the bullet. Powder primer etc are all irrelevant at this point because they may have differed, but they got us to the exit with equality of all external ballistic parameters, except the bullet weighs more. If the 115 gr is dead center bulls, Cana prediction be made about point of a 135 gr bullet in the left right dimensional space of the target?


As to real world, of course I tried that :-) I just wanted to keep the discussion theoretical.

The 135 gr consistently 3 inches to left of 115 gr which were in the bulls.

 

[foszoe]

Tried to clarify below. Thanks

 

[Indy_Guy_77]

Try it in a bench vice... That'll be the true measure. Everything being hand-held is all subject to....subjectivity.

-J-

 

[BehindBlueI's]

The only thing that I can think of would be "spin drift", which does affect left/right movement. Not all things are equal in external ballistics other than weight, even if we disregard wind. Bullet length, for example, affects spin drift, but I can't believe the small difference in this scenario would account for anywhere near a 3" difference at 25 yards.

 

[Bigtanker]

What bullet are you using? Cast, fmj, jhp? Are these your handloads? Once the bullet leaves the barrel all things should be equal but if the bullet diameters are different, .354 to .358 for example, the barrel could be treating the sizes differently. I have no idea but it's a guess.

Have you tried these loads in a different gun?

 

[warthog]

I tend to use the bullet that is closest to the weight of my chosen SD bullets to practice. Physics shows that that if you use the same weight bullets, no matter how hot or soft you load them, the POI will remain the same as those with your SD bullets. This was shown in a study done while I was in college some 30 years ago for a physics project. Those were my findings both mathematically and in practice within my ability to shoot them.

 

[Broom_jm]

The 135 gr consistently 3 inches to left of 115 gr which were in the bulls.

This is probably a function of your particular grip and the added recoil of the heavier bullet...and is far more important than any theoretical discussion to explain "why".

 

[scattergunner]

foszoe, I think I understand your question, and to my mind, since you excluded elevation in you question, the only things that would change POI are the rifling and shooting technique, and since we are talking theory, I will assume a ransom rest is used. Since the job of rifling is to stabilize the bullet in flight, there must be an optimal twist/bullet weight/bullet diameter/velocity sweet spot. This sweet spot would be where the standard deviation from shot to shot is the smallest, and the grouping on target is the smallest. I can't tell you where to begin to figure out what this is, but I doubt that in a 9mm at 25 yards and with either 115 gr or 135 gr bullets leaving the muzzle at the same velocity there would be a measurable difference on the POI.

 

[Sirshredalot]

I am not sure how much technical help this is, but in my 9mm Smith, 115 grain bullets have a lower impact point(maybe an inch or two) at 25 yards than do 124/125 grain bullets.

I tend to reload on the slower/conservative end of the velocity spectrum so just above starting loads for each bullet weight according to the Lyman or the Lee manuals.

I also only load lead, but I have backed up these finding with factory FMJ 115gr bullets compared to my lead loads.

God bless
-Shred

 

[rmasters744]

Shouldn't the impact be on a vertical string with a lighter bullet usually higher? Anything too far left or right would be the grip/sight alignment. In theory.

 

[wolfman]

If you are dead on the bullseye with a 115 gr 9mm bullet and, keeping all other components and atmospherics equal, where would the point of impact shift on the horizontal plane (windage) of a 135 gr bullet?

I can read all about vertical movement online.

On a related note, any great books on external ballistics? Websites? Computer software? Especially interested in works that treat the problems in 3 dimensional space (without and with wind)

Nothing will be the same. For example, even with the same powder and primer, there will be more pressure required to start the bullet moving. This in turn will increase both chamber and barrel pressure, resulting in a difference in both velocity and rotation speed. There is a lot more, but you are comparing apples to oranges here so the results can't be compared with any degree of accuracy.

 

[Broom_jm]

Shouldn't the impact be on a vertical string with a lighter bullet usually higher? Anything too far left or right would be the grip/sight alignment. In theory.

In theory, the heavier bullet takes longer to exit the barrel, pushing back on the gun and raising the muzzle more prior to exit than the lighter bullet. Some will tell you that there is no muzzle rise or recoil until the bullet leaves the gun, but this is exhibiting a lack of understanding of the science of physics. The difference in muzzle rise is very small, but experienced pistol shooters will come to realize that, all else being equal, heavier bullets have a higher POI than lighter bullets (at relatively short distances).