What Does This Change In Impact Point Mean?

Case in point this is my 357 magnum sp101 which is zero’d at 25 yards for a 125 grain fp at 1405 fps. It’s not much but you can clearly see the sights are pointed up. No funny business, I lined it up as fairly as I could. If the gun was not moving with the barrel in the bore it would be at least a foot or two low at 25 yards. As noted a magnum revolver really exaggerates this effect because they have a very high bore axis relative to the center of gravity and there is a lot of recoil for their moment of inertia compared to a rifle.

edit: I changed the pic because I’m trying to make this as fair if a representation as I can

Well It's time to admit defeat. I'll admit I've been under the impression that recoil really had no affect on accuracy and that recoil really wasn't noticed until the projectile left the barrel. However, I've been swayed through this and reading some of what I've been able to find in other nooks and cranny's on the internet. Including watching the slow mo vids available on YT. I guess I've never really thought of it too deeply. After dwelling on it and doing the math, it is true. Recoil DOES begin the second the primer is ignited. After that, once the projectile leaves the case, it's causing again another rearward force which MUST be accounted for regardless of whether or not that projectile is still encased in the barrel. Now, at this point all of the motion MUST be in a completely opposite direction of the direction of travel which I believe is different than what we know as "muzzle rise". I believe the muzzle rise will only measurably affect accuracy on relatively long dwell/lower velocity rounds as the rise is caused when the rearward force is stopped by the slack of the hand or rest...so it needs SOMEWHERE to go, so up it is. I don't think it has nearly as much affect on high velocity rounds as the rotation angle at departure would be much lower. SO...crow it is. Whipped cream if available. Old dogs(well...not THAT old) can learn new tricks! Old Dogmas die hard!

Take the 357 caliber and load up full house loads using H110/ww296/AA#9/2400 and load up 110gr/125gr/180gr/200gr bullets and shoot them in a 2 1/2" bbl/4"bbl/6"bbl/10"bbl firearm For some odd reason the lighter bullets will always hit lower (powder choice doesn't matter) when using the same sight picture/scope with the same settings.

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Absolutely true and has been for the past 50+ years of my handgun shooting. I first became aware of this phenomena at age 21, with a college major in Civil Engineering, while reading "Sixguns" by Keith, and later found it true in my own shooting. Take it as fact, the real world target results are clear. YMWNV, Rod (your mileage will not vary)

I will sleep much better now.

Besides the vertical shift due to recoil, (most notable with handguns). there is the horizontal shift due to torque imparted by the twist of the rifling.
I see this in changing from 185gr bullets to 230gr bullets with the M1911. The sights will need to be drifted to accommodate the difference.

I recently acquired a Taurus M856 Stainless. With my target wadcutters of 148gr with 2.8gr of Bullseye or 2.9gr of HP38, (600fps) it’s a real tack driver shooting POI/POA 7-25yds. Fixed sights are well regulated!
Use a standard velocity 158gr SWC using 3.6gr of HP38 it shoots 2” left and 3”high at 10yds. (725fps) Noticeable!
Then shift to a 105gr or even a 90gr bullet at 850-900fps and impact placement is in opposite direction and significant. With 105SWC over 3.6gr of Bullseye, impact is 4” low and 2” right at 10yds.
I watched this thread evolve as I have seen others have to come to the revelation of the difference between high velocity rifles and handguns with low velocity and relatively greater bullet mass to gun mass characteristics.
Notice how high the front sights are on the S&W .45 Revolvers of the early 1900’s. Particularly the M-25 6” target revolvers.
Even the Ransom rests pivot to take into account the flex of the human wrist during recoil.
Of course a heavy fixed receiver mounted to a heavy fixture or bench alleviates this... The original posters misconceptions. Reality is that humans fire the guns with their hands...

South Prairie Jim said:

The OP said he had a modest charge in his hand loads that when compared , did not impact the same vertical poi as a load with a different powder and bullet.
Pretty simple to understand..how bout you Dale ?

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I remember commenting on those points Jim . Seems they got lost in the conversation .

Edited to add : Someguy2800 , I applaud your patience through this , you handled it well .

Bcwitt said:

This sounds like barrel "whip". Is a vibration of barrel that shifts POI. if bullet exits when the node is down, poi moves down & viceversa. It's not drop of sight line. The trick to good accurate ammo is the bullet exits the bore @ same place in the whip cycle. That is accuracy In a nut shell. That's why benchrest guys like short heavy barrels.​

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I believe you are referring to Optimum Barrel Timing whereas until you reach that point rounds can go in any direction. Short range br has weight limits 10.5 and 13 pounds IIRC that will restrict barrel length quickly. Heavy free floating barrel can be easier to tune also less effected by heat build up over a pencil barrel. I use a 28 inch heavy varmint contour on my longe range br rifle with a weight limit of 17 pounds.

South Prairie Jim said:

I believe you are referring to Optimum Barrel Timing whereas until you reach that point rounds can go in any direction. Short range br has weight limits 10.5 and 13 pounds IIRC that will restrict barrel length quickly. Heavy free floating barrel can be easier to tune also less effected by heat build up over a pencil barrel. I use a 28 inch heavy varmint contour on my longe range br rifle with a weight limit of 17 pounds.

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South Prairie Jim said:

I believe you are referring to Optimum Barrel Timing whereas until you reach that point rounds can go in any direction. Short range br has weight limits 10.5 and 13 pounds IIRC that will restrict barrel length quickly. Heavy free floating barrel can be easier to tune also less effected by heat build up over a pencil barrel. I use a 28 inch heavy varmint contour on my longe range br rifle with a weight limit of 17 pounds.

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Yep. The point is, in a lightweight sporting rifle, you have to sight in for each load, as you do not where in the node your promo will exit. Not as big a deal in a heavy barrel.

I really think it would be rare if one load sighted in exactly the same as another built with different components and different recipe weather a heavy barrel or a sporting barrel.
I somewhat confused on the benefit of sighting a rifle for about 2 - 2.5 inches high at a 100 yards vs just sighting in exactly at the 200 line to start with.

South Prairie Jim said:

I somewhat confused on the benefit of sighting a rifle for about 2 - 2.5 inches high at a 100 yards vs just sighting in exactly at the 200 line to start with.

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200yds less walking????

CryptKeeper5 said:

200yds less walking????

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Yeah...
Don't get me started on that scenario, im tying to be polite and understand why just close/about is even an option after spending time and resources to develop a load and take a hunting trip, how would a fella calculate a firing solution on an animal for example at 475 yards if the scope adjustments are not set to a known distance ?

South Prairie Jim said:

Yeah...
Don't get me started on that scenario, im tying to be polite and understand why just close/about is even an option after spending time and resources to develop a load and take a hunting trip, how would a fella calculate a firing solution on an animal for example at 475 yards if the scope adjustments are not set to a known distance ?

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Oh I'm with you. Being a match shooter I'm just accustomed to verifying my drop at known distances. That said, I will say that here in Wisconsin, most public ranges will have a 200 and maybe a 300 yard line but not many will get you beyond that. From farms to forests...here there's just not as much open space to build ranges. The closest even 400 yard range to me is roughly 35 miles. I know it's much different out where we lived in Cheyenne. In fact, 600 yard ranges are so few and far between many matches are shot with reduced targets here. The closest NRA spec 600 yard range is 75 miles west of here. But in this state, a "long" shot is 150yds....so most hunters never need more than that.

South Prairie Jim said:

Yeah...
Don't get me started on that scenario, im tying to be polite and understand why just close/about is even an option after spending time and resources to develop a load and take a hunting trip, how would a fella calculate a firing solution on an animal for example at 475 yards if the scope adjustments are not set to a known distance ?

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Its pretty hard for a lot of people to find a shooting range or suitable place to shoot close to them that has 200+ yards in a lot of places. In the "deer stand" part of the country where shooting a deer at 200 yards is very much out of the ordinary, most people just sight in 1" to 1-1/2" high at 100 yards and call it good. I don't do it anymore but that's how I was taught to do it and a lot of people still do for better or worse.

For myself I put a target at a chosen distance then adjust my scope to exactly that bull, if I handed that rifle to my kid or a friend I can say with certainty where the round will impact. If I use a ballistic calculator it will ask me to input the range im zeroed at without a plus or minus or an approximation function.
Anyway no big deal just asking, I know my old man did the same thing before we had all this knowledge or quality of optics.

someguy2800 said:

Its pretty hard for a lot of people to find a shooting range or suitable place to shoot close to them that has 200+ yards in a lot of places. In the "deer stand" part of the country where shooting a deer at 200 yards is very much out of the ordinary, most people just sight in 1" to 1-1/2" high at 100 yards and call it good. I don't do it anymore but that's how I was taught to do it and a lot of people still do for better or worse.

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Agree!

The ballistic calculations for the 1.5" aren't that far off, at least not with a cartridge close to 3000 FPS and a spitzer bullet, what's missing is the verification, especially at the longer distances. At 200 though, it's probably "minute of deer" for most common bottle neck cartridges.

I had a young (compared to me at least) LTC out with his young son yesterday to prep for a doe hunt I'm "sponsoring" on my neighbors place next weekend. The results demonstrate what's been discussed in this thread.

He brought out his AR15 with some 55FMJ for his son to practice with. We set up his ground blind below my bench so he could rehearse using the same stool and tripod that he'll hunt with and shoot from the blind. He got to shoot on my steel pig swinger at 200 yds, much further than the shot we anticipate him having to make based on the area and blind location he'll hunt from. It really was practical practice....to include shot placement with his dad coaching.

Then we verified the zero with the 64 grain soft-points he'll hunt with The rifle was zero'd at 200 with 55FMJ. The 64 SPs impacted elevation correct, but 3 inches left at 100 with a light quartering head wind. Nowhere near a 200yd zero. We then corrected and went with the "classic" 1.5" high at 100 zero. He then proceeded to put these 2 shots on steel at 200 off the bench:



So at least in this example, different ammo had a different POI, and 1.5" at 100 is spot on for 200.

@Chuck R.
Great you get to sponsor the hunt, that sounds like fun and he s a good shot too so nicely done coach.
My old 30-30 lever gun only shoots about the size of a baseball at a hundred yards, im a lousy shot so if I would've probably missed.