Effect of bullet weight on POI with same sight setup?

[jmstr]

I will try to make my question clear and concise, but I understand there are MANY variables involved.

If a Blackhawk is sighted in so that a 125gr self-defense .357Mag round impacts the target at about .7" low of POA [at 7 yards], how does changing the weight of the bullet affect POI?

Three 'basic' weight scenarios:

125Gr self-defense hallow point
158gr SP ammo [like S&B]
180gr RNFP 'bear' load [Like HSM].

I can find ways to plot the ballistic trajectory for each one, but each one of those systems asks what distance it is 'sighted in' at.


My goal is to set up the revolver to be very flat POI from 15-25 yards with 158gr strong loads [not cowboy stuff].

However, if using 125gr fast self defense, will it strike the target lower or higher, usually?

Will firing a 180 gr strike the target lower/higher than the POI for 158 grain.

Again, I am NOT talking of 158 wadcuttters or cowboy lead.

My .357mag all-purpose round of choice is the S&B 158 SP round.

Unfortunately, my LGS was bought out by another, and the range there changed its rules, to ban metallic rounds, even though the original LGS/range designed the range to handle it.

This is about consistency of rules at both indoor LGS/ranges that they own, and the only indoor ranges in town.

Thus, I am trying to use your comments to allow me to fine-tune my height of impact based on other ammo I have.

I have 500 rounds of the S&B, so I don't want to just buy new 158gr rounds, thank you very much.

[JohnKSa]

My goal is to set up the revolver to be very flat POI from 15-25 yards with 158gr strong loads [not cowboy stuff].

If you adjust the sights to be dead on at 25 yards with the load you want to shoot, then it will shoot more or less to point of aim everywhere between the muzzle and 25 yards with that load. The farthest departure from your point of aim will be at the muzzle where the bullet will impact low on the target by the amount that the muzzle is lower than the sights.

To find out how different loads shoot, you're going to have to shoot the different loads and keep notes. It's not going to be possible to do anything more than provide a rough rule of thumb: Once you have the sights set up for a particular load, heavier bullet loadings will tend to hit higher on the target, lighter bullet loadings will tend to hit lower on the target.

[g.willikers]

^^^
John is right.
Some friends and I actually did such a test, once upon a time.
We all got different results with the same loads and similar guns - all sixguns.
Gotta' shoot 'em and see where they land for you.
Probably due to personal shooting skills, recoil control, differences in the guns - (the grips and sights mostly), as well as the ammo.
Enjoy.

[RIDE-RED 350r]

+3 on the given replies...with emphasis that you may get differing degrees of change from one piece to the next..

My example: I have a S&W 629 Classic with a 6.5" bbl. Just trying different loads at a 50' indoor range I sighted in at about 1" high at 50' with 200gr XTP's loaded to near max published. After fiddling with those and being satisfied that both the revolver and I were doing good with those 200's I decided to try some 300gr XTP's loaded stout. It was a full 8" higher at POI than the 200gr bullets. I was shooting with my brother and passed it to him to send a few as a means of checking to see if it was something I was failing to do as the shooter.. He got the same results.

Now, my brother was in the booth next to me shooting his scoped S&W 29 Classic. Same bbl length, same exact gun except his Classic was blued as opposed to my stainless 629. He experienced the same phenomenon, only to a lesser degree. We assumed is was the extra weight of his revolver being scoped that played a part in this. Again, we both shot his 29 and got similar results.

So basically when you try a new ammo recipe, make sure and take it to the range and see how it shoots. Don't count on the same or even similar POI between a 125gr and a 180gr, particularly in elevation. And another benefit of trying different bullet weights is that you may find a bullet that your gun LOVES and shoots more accurately than you ever thought possible. I have a little Smith M36 that prefers lighter bullets than commonly used for 357 and 38spl. I started with 140gr XTP's when I first got it. Reason being is that it's a small little carry piece and I didn't feel the need to load it as stout as possible. I have several other Smiths, all magnums if I want more HP on the hip. So i go to the range to try out my 140gr work up rds. Overall I was getting 6-8" groups at 25' with it. The next bullet I tried was 125gr Nosler JHP. Group sizes shrunk dramatically, to about 3-4" and much closer in elevation. This piece does not have adjustable sights so you get what you get unless you are low and want to start filing the front sight. I feel pretty good about groups like that with a 2"bbl and non-adjustable sights.

I made up some 38spl using 110gr XTP but haven't range tested them yet. I look forward to trying them out, but I just haven't had the time to play at the range in awhile.

[walnut1704]

Yeah, there's a lot of variables there that make it difficult to give a definitive answer. If I had to generalize, I'd tell you that lighter bullets tend to shoot lower than heavier bullets, but the relative power level of different loads can disrupt that.

POI is affected by "barrel time", or the amount of time the bullet spends in the barrel. Since recoil begins before the bullet leaves the muzzle, the lighter bullets moving faster leave the barrel quicker and are less subject to the rise of the barrel during to recoil.

I've done a lot of reloading for fixed sight revolvers, attempting to find loads that shoot to POI. There are many other variables. Even given identical muzzle velocity, the POI can change just from switching from a fast powder to a slow powder.

You just have to work it.

[Bob Wright]

The big factor here is barrel time, not bullet weight. The faster the bullet gets out of the barrel, the lower it will hit on target. By the same token, a slower bullet will strike higher on the target. Bullet impact is dependent on where the muzzle is in the recoil arc at the time of exiting the bore.

Generally, lighter bullets are driven faster, while heavier bullets not so fast. So sighting in with a heavy (slower) load, then switching to a lighter (and faster) load, the impact will be lower on the target.

At fairly close up distances, twenty five yards or less, this makes little difference, but at extended the variation becomes greater. Also, the amount of precision desired figures in also. If you are shooting at a dime sized target, then sights must be adjusted. If shooting at a human silhouette, no change of sights is required.

I have two pet loads in the .44 Magnum, a 180 gr. JHP at 1700 f.p.s., and a 240 gr. JHP at 1400 f.p.s. At 100 yards there is significant difference. My solution was simply to buy another gun rather than adjust sights!

Bob Wright

Bob Wright

[JohnKSa]

The big factor here is barrel time, not bullet weight.

Right. But for a rough rule of thumb you can ignore barrel time (something that's not so simple to measure) and deal with bullet weight in most cases. That's because unless you're dealing with loads that are intentionally loaded light for the cartridge, a heavier bullet means lower muzzle velocity which means longer barrel time.

Things get a lot more complicated if you're comparing loads where some are not anywhere near max and others are.

[Paul105]

I know the OPs question was about the .357 Mag. Even though the below pictured target was shot with a .44 mag, similar impact differences can be expected with the .357. Also note, that in addition to elevation POI shifts, you may (most likely) also experience windage POI differences.

Target shot with S&W M69 (4.2" L-Frame .44 Mag) with rear sight bottomed out. Shot from a rest at 25 yds. Point of aim the same for each load -- dead center big diamond. Only shot two with each load to minimize target clutter and recoil induced fatigue. Each two shot group is outlined, some heavier outline to more clearly separate groups.

Point is you need to shoot each specific load to actually know where it will impact on target.




FWIW

Paul

[Bob Wright]

I just recalled an experience I had some years ago to illustrate effect of velocity on bullet impact.

I was experimenting with black powder, and loaded some .45 Colt cartridges with 35.0 gr. Fffg (3F) DuPont black powder. I shot this load at twenty five yards, using a Ruger Bisley with 7 1/2" barrel. My bullet was, I believe, a 250 gr. RNFP.

My first groups were pretty well centered in the black. However, as I continued to fire this amunition, my groups continued to climb, until I was near to being off the paper. Why?

Black powder fouling was building up in the bore and slowing down my bullets. Switching over to a JHP load, my groups began to descend back down into the black once again.

Those around me appreciated my reverting back to smokeless powder, too! It was a very still day, with the morning grass damp with dew, and smoke hung in the air and curled up from the damp grass.

Bob Wright

[RickB]

I think it would be extremely difficult to make any determinations based on shooting done at seven yards?
The location of any two bullets in a group might be farther apart than the centers of multiple groups, out to even 25 yards. That is, there would be more variation within each group, than between groups.
I wouldn't expect to see much variation in group height between 15 and 25 yards.

[James K]

A local PD issued .38 Special revolvers and ammo, and guns were either fixed sight or sighted for the 158 grain lead bullet. When they went to a +P+ load with a lighter and much faster bullet, the shorter barrel time meant that the guns shot quite a bit low, so that shots aimed at the center of mass on the old silhouette target ended up a lot lower.

The firearms instructor (who on good days actually knew which end the bullet came out) explained that the idea of the new ammunition was to damage a sensitive part of the bad guy's anatomy so he would not be killed but would be less trouble in the future.

Most of the cops believed him.

Jim

[RIDE-RED 350r]

^^^^ Are you kidding me??!!^^^^


That has to be one of the most idiotic things I have ever heard of on this topic! LOL!

[Skeets]

It seems very strange,but many Leo's IMHO,find our love and passion of our guns Very Strange too,at least till the range goes hot! Good project,best wishes Skeets