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Discussion Starter · #1 ·
Can someone please explain the physics behind a strange phenomenon that I have been experiencing with my handloads for my two 45/70s. It seems counter intuitive, but with both my Guide Gun and XLR my soft loads with 405 gr bullets going around 900-1200 fps are hitting the target anywhere from 6 to 12 inches ABOVE my hotter loads at 1900-2000 fps with 300 or 350 grain jacketed bullets. This is occurring both at 50 yards and 100 yards. With both guns I am aiming at the centre of the target with Skinner sights on the GG and a scope on the XLR.

My only guess is that the slower, softer rounds are in the barrel longer and are more subject to muzzle rise caused by recoil. But I would think that gravity would play more of a roll and the POI for the slower rounds would be below the hotter ones.

Has anyone else experienced this?

Thanks.
 

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Not a clue here, I have experienced just the opposite effect.
 

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I just returned from the range where I was only shooting out to 100 yards and I was having the opposite results as well. It was frustrating because my POI was constantly 6-10 below my POA. I was shooting remington 305 gr JHP and before I was shooting 405 gr SJHP which seemed to hit high and the hornady flexitips were almost dead on. What did I learn. Keep records of what ammo impacts where and adjust your sights accordingly for the ammo you will be using on your hunt/competition.
 

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Your guess was correct. Slower loads, and particularly slower loads with heavy bullets are in the barrel longer during recoil and muzzle rise. That leaves the angle of departure higher. It's commonly seen in magnum handguns where the heaviest bullets (also slowest) impact the target higher than faster/lighter bullets.
 

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P.O. Ackley calls this barrel time. I had the high impact effect my hand loads for my 500 S&W so much that I had too call S&W for a taller front sight blade.I had lowered the rear sight as far as I could. I was using 440gr. LBT. bullets.
 

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Discussion Starter · #6 ·
looper said:
P.O. Ackley calls this barrel time. I had the high impact effect my hand loads for my 500 S&W so much that I had too call S&W for a taller front sight blade.I had lowered the rear sight as far as I could. I was using 440gr. LBT. bullets.
Yes, it must be the barrel time effect that I am experiencing. I am getting an exaggeratedly high POI with heavy bullets traveling 600-800 fps slower than my hotter loads with lighter bullets. I have experienced this often with both .357 Mag and .45 ACP (correct) in S&W handguns. But I didn't know it applied to rifles as well. I guess I should have known that the same physics would apply. What is surprising is that the big, slow, heavy bullets would still give me a higher POI at 100 yards in 45/70. It just didn't seem right.
 

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We noticed the exact same thing when we shot the same cast 405gr bullets with h4895 (middle of the road load) and trail boss powder (max load.)

22" 70's vintage 1895 w/ lyman peep sight and microgroove rifling.

Must be time in the barrel that's causing it. We were curious about it too.
 

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Hand guns are worse yet because they recoil up faster yet.
 

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Pitchy said:
Hand guns are worse yet because they recoil up faster yet.
Yes but!! The bullet is in the barrel less time with a handgun because of the shorter barrel. It is the time the bullet spends in the barrel as well as barrel rise that this what this phenomena is all about. And a whole raft of other factors too...
 

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Right, the bullet spends less time in the barrel of a handgun because the barrel is shorter.
Because the barrel on the hand gun is much shorter than the rifle barrel, it has much less mass and can flip up faster under recoil so the effect on the pistol barrel happens in much less time than it does a rifle barrel.
 

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zerbe said:
Right, the bullet spends less time in the barrel of a handgun because the barrel is shorter.
Because the barrel on the hand gun is much shorter than the rifle barrel, it has much less mass and can flip up faster under recoil so the effect on the pistol barrel happens in much less time than it does a rifle barrel.
Yes agreed. The time factor just lessens some of the effect on a hand gun barrel rise. I was thinking that very warm loads using heavy bullets, say 335gr out of a Ruger Blackhawk 45C or 44mag might be a bit confounding because on the one hand the barrel rise would be extreme, coupled by the velocity which might only be 1200fps so the bullet is spending more time in the rising barrel. Then once free the heavy bullet starts the getting the effects of gravity and velocity shedding , so maybe at 50 yds it would shoot higher, but at 100 yds and beyond might shoot lower due to the rainbow trajectory. Anyone have any experience in that regard?
 

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All this just re-inforces the fact that most any change in ammo or components there of will change the poi, making it necessary to re-zero our sights for each or any change we may make. My .44mag also shoots higher with plinking loads than with full steam hunting loads.

Cheers,
Mark.
 

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Oz said:
All this just re-inforces the fact that most any change in ammo or components there of will change the poi, making it necessary to re-zero our sights for each or any change we may make. My .44mag also shoots higher with plinking loads than with full steam hunting loads.

Cheers,
Mark.
Mark, you are absolutely correct.
 

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That theory is what I have experienced, up to 100 yards. Haven't made the comparison at longer distances but I would think that at some point down range the slower, heavier bullet would hit lower POI than the lighter, faster one.
 

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I've not been very successful in getting a heavy-bullet load and a lighter-bullet load to have anywhere near a similar POI. The best I've been able to muster was about 4" difference at 100 yards.

I've noticed, that in general, my 45-70 seems to be sensitive to component change in regards to POI shift. I've ran two different bullets (of the same weight) with all other components exactly the same, down to the lot number, and had 2" to 3" POI shift, typically horizontal, with weight making a vertical shift.

I gave up. I'll just re-zero if I need to change loads.

Or......get another 45-70. ;D
 

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How your holding your rifle makes a difference also. I hit lower while hunkered down at at bench. If I shoot off hand or in a normal sitting position with elbows on knees, I'll shoot 4" higher at 100 yds. This happens whether I'm shooting my 1895, or my 30-06.
 

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dogjaw, I have had the same experience bench shooting vs sitting upright. Now I always use my bypod when shooting from the bench because it better replicates hunting posture. Anyone know why this change in bullet impact occurs?
 

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dogjaw said:
How your holding your rifle makes a difference also. I hit lower while hunkered down at at bench. If I shoot off hand or in a normal sitting position with elbows on knees, I'll shoot 4" higher at 100 yds. This happens whether I'm shooting my 1895, or my 30-06.
findrichard said:
dogjaw, I have had the same experience bench shooting vs sitting upright. Now I always use my bypod when shooting from the bench because it better replicates hunting posture. Anyone know why this change in bullet impact occurs?
When shooting from a bench, do you notice how the recoil feels, compared to firing from "self-supported" position like kneeling, sitting, off-hand? You will feel more recoil from the bench because there is less body movement (by the shooter) to dampen it, hence less actual recoil movement. Conversely, firing from the sitting, kneeling, or off-hand positions, felt recoil doesn't hurt as bad because there is more body movement associated with the recoil, the recoil is dampened by this body movement, and with this, more firearm movement occurs in recoil - - Typically upward movement.
 

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findrichard said:
dogjaw, I have had the same experience bench shooting vs sitting upright. Now I always use my bypod when shooting from the bench because it better replicates hunting posture. Anyone know why this change in bullet impact occurs?
It's how the rifle handles during recoil. In a real life upright position, the shoulder flexes back, allowing the rifle barrel to rise more during recoil. If you watch someone shoot from a bench and then in a upright position, you can see it.
 
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