Horizontal difference between bullets

ckc123

ckc123

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I'm working on 2 loads for a 300 RUM.

the 200 grain load works good. but when I use the 150 grain, I find it shoot 4 inches low, and 2 to the right.. (at 100 yards). (but I get a nice .75' group)

should there be that much of a difference in point of impact for different bullets (200 grain nosler accu bond vs 150 remington accutip)
 
ckc123 said:
I'm working on 2 loads for a 300 RUM.

the 200 grain load works good. but when I use the 150 grain, I find it shoot 4 inches low, and 2 to the right.. (at 100 yards). (but I get a nice .75' group)

should there be that much of a difference in point of impact for different bullets (200 grain nosler accu bond vs 150 remington accutip)
Click to expand...

That seems completely reasonable to me. I have seen that much POI shift just from a couple of grains more powder while load testing.


Mark
 
I have seen that much difference in the same weight bullets with different profiles and same powder charge. sight in for the 150s just mark down how many clicks you more your scope so you can reset it when you switch back to the 200s.
 
I like the powder charge of the 150 load, so I was going to try the nosler accubond in 150's to see if they have a similiar point of impact (so I don't have to change the scope between uses)
 
ckc123 said:
I'm working on 2 loads for a 300 RUM.

the 200 grain load works good. but when I use the 150 grain, I find it shoot 4 inches low, and 2 to the right.. (at 100 yards). (but I get a nice .75' group)

should there be that much of a difference in point of impact for different bullets (200 grain nosler accu bond vs 150 remington accutip)
Click to expand...
Okay, let me get this straight... You shoot a 200gn load travelling somewhere 3000fps and the 150gn load traveling near 3500fps hits LOWER? Wouldn't the lighter, faster round have a flatter trajectory and hit higher? Always have for me in a smaller cartridge. I can understand the moving right, that's how different loads work and if you had said that the 150gn round hits HIGHER, then I could understand that.

Fellas, I am not sure how that is reasonable. Please tell me how barrel harmonics can affect trajectories in that way. I am willing to be wrong on this one and learn.

This is how I see it. 150gn round traveling at 3500fps, ZEROED at 100yds drops 34.5" by the time it gets to 500yds. A 200gn round, traveling at 3000fps, ZEROED at 100yds drops 43.5".

Or, if both are zeroed at the muzzle (shots fired at the same POA without ANY correction made) then the 150gn group should be 1/2" HIGHER than the 200s.

I have several Lee Enfields that react this way, zero for 200gn bullets. Switch to 150s and I have to LOWER the POI to properly zero. I have one No4 that shoots 125gn bullets at almost 2900fps and shoots 180s at 2400fps. With the zero at 100yds the 125 drops 77". The 180s drop 112.5". When I switched from 150gn bullets to 165gn bullets in my '06s, I had to RAISE the POI to zero them.

I need to get a scanner and scan in my collimator graphs to show you this. Left and right adjustments, cool, but having a faster round shoot lower? I just can't prove it to myself, dang, tomorrow will be spent at the bench.

Please, help me out here because MY empirical knowledge is confused by yours. You will send me back out to the bench tomorrow, just to be sure that I have it right.

Oh, and OP? I KNOW that was a typo, because a nice .75' group is actually a 9" group. But dang, that made me laugh!!! Thanks.
 
I'm surprised they are as close as they are. Some rifles are very accomadating about shooting different loads to the same place and some aren't. I've got a .300 that shoots 180 grain Accubonds and 180 grain NBTs 3 inches apart at 100 and they are supposed to be the same bullet except for the bonding. Then theres a 30-06 that will shoot anything you can close the bolt on close enough to hunt with out to 200-300. There isn't a whole lot of rhyme or reason to it.
 
rookie wildcat said:
Okay, let me get this straight... You shoot a 200gn load travelling somewhere 3000fps and the 150gn load traveling near 3500fps hits LOWER? Wouldn't the lighter, faster round have a flatter trajectory and hit higher? Always have for me in a smaller cartridge. I can understand the moving right, that's how different loads work and if you had said that the 150gn round hits HIGHER, then I could understand that.

Fellas, I am not sure how that is reasonable. Please tell me how barrel harmonics can affect trajectories in that way. I am willing to be wrong on this one and learn.

This is how I see it. 150gn round traveling at 3500fps, ZEROED at 100yds drops 34.5" by the time it gets to 500yds. A 200gn round, traveling at 3000fps, ZEROED at 100yds drops 43.5".

Or, if both are zeroed at the muzzle (shots fired at the same POA without ANY correction made) then the 150gn group should be 1/2" HIGHER than the 200s.

I have several Lee Enfields that react this way, zero for 200gn bullets. Switch to 150s and I have to LOWER the POI to properly zero. I have one No4 that shoots 125gn bullets at almost 2900fps and shoots 180s at 2400fps. With the zero at 100yds the 125 drops 77". The 180s drop 112.5". When I switched from 150gn bullets to 165gn bullets in my '06s, I had to RAISE the POI to zero them.

I need to get a scanner and scan in my collimator graphs to show you this. Left and right adjustments, cool, but having a faster round shoot lower? I just can't prove it to myself, dang, tomorrow will be spent at the bench.

Please, help me out here because MY empirical knowledge is confused by yours. You will send me back out to the bench tomorrow, just to be sure that I have it right.

Oh, and OP? I KNOW that was a typo, because a nice .75' group is actually a 9" group. But dang, that made me laugh!!! Thanks.
Click to expand...

You do not understand the concept of barrel harmonics. All your assumptions about velocity and point of impact are wrong. Changing loads changes the direction the barrel is pointed when the bullet exits because different loads change the vibration patterns of the barrel, and there is almost no way you can predict what that change will be exactly with a given rifle just from velocity of the bullet.
 
ckc123 said:
I'm working on 2 loads for a 300 RUM.

the 200 grain load works good. but when I use the 150 grain, I find it shoot 4 inches low, and 2 to the right.. (at 100 yards). (but I get a nice .75' group)

should there be that much of a difference in point of impact for different bullets (200 grain nosler accu bond vs 150 remington accutip)
Click to expand...

ckc123

In the mid 1970s I was working up loads for a 6mm Remington in a Remington 788 rifle, I switched from a 100 grain Sierra flat base bullet to a Sierra 100 grain boat tail bullet and the boat tail hit over a foot to the right at the same level. I later found a very small ding in the muzzle and had the rifle re-crowned. Barrel harmonics, the shape and weight of the bullet and your muzzle crown with effect the POI.
 
rral22 said:
You do not understand the concept of barrel harmonics. All your assumptions about velocity and point of impact are wrong. Changing loads changes the direction the barrel is pointed when the bullet exits because different loads change the vibration patterns of the barrel, and there is almost no way you can predict what that change will be exactly with a given rifle just from velocity of the bullet.
Click to expand...
Yes. Spent yesterday at the bench. I loaded and fired almost 200 .30-06 rounds. The reason I chose the '06 is because I bought a used M77 last year and it came with 5 boxes of 165gn CoreLokts. I have never worked up a round for it since it was satisfactory as it was. I loaded 20 loads each of 110, 125, 150, 165, 180, and 200gn (I only had one box of 220gn and did not want to use them). I fired the work up loads from a HyScore Precision Rifle Rest clamped to the bench.

I then went into the house, pulled the leftover bullets, and loaded 10 each of the best groupers.

I only have 50yds to work with on my place, so the groups were small as were the differences in POIs.

The 110 and 125gn printed in the same place, no measurable differences.

The 150 and 165 both printed lower, as I expected, but...

I WILL BE DAMNED, BOTH the 180 and 200gns printed almost an inch HIGHER than even the 110gn rounds!!

Barrel harmonics, in my experience, has affected left, right and up, down. But until yesterday, I have never (knowingly) had faster, lighter rounds print lower than heavier, slower ones!

And to be honest, I have never done this with the same rifle, 7 different rounds, on the same day.

Guys, Thank you! For learning me, and giving me a GREAT DAY behind the barrel!!
 
rookie wildcat said:
Yes. Spent yesterday at the bench. I loaded and fired almost 200 .30-06 rounds. The reason I chose the '06 is because I bought a used M77 last year and it came with 5 boxes of 165gn CoreLokts. I have never worked up a round for it since it was satisfactory as it was. I loaded 20 loads each of 110, 125, 150, 165, 180, and 200gn (I only had one box of 220gn and did not want to use them). I fired the work up loads from a HyScore Precision Rifle Rest clamped to the bench.

I then went into the house, pulled the leftover bullets, and loaded 10 each of the best groupers.



I only have 50yds to work with on my place, so the groups were small as were the differences in POIs.

The 110 and 125gn printed in the same place, no measurable differences.

The 150 and 165 both printed lower, as I expected, but...

I WILL BE DAMNED, BOTH the 180 and 200gns printed almost an inch HIGHER than even the 110gn rounds!!

Barrel harmonics, in my experience, has affected left, right and up, down. But until yesterday, I have never (knowingly) had faster, lighter rounds print lower than heavier, slower ones!

And to be honest, I have never done this with the same rifle, 7 different rounds, on the same day.

Guys, Thank you! For learning me, and giving me a GREAT DAY behind the barrel!!
Click to expand...

Barrel harmonics have something to do with it.

But the main reason the heavier slower bullet hits high is the "in barrel time" of the bullet. With the heavier bullet the recoil of the rifle is also greater and the barrel time is longer, so the rifle barrel is higher in recoil when the bullet leaves, causing the heavier bullet to hit higher on the target.

Also with the heavier bullet the torque produced by firing the rifle is greater and the rifle is twisted more to the left ( with a right hand twist) and a heavier bullet should hit to the left of a lighter bullet.

NormB
 
NormB said:
Barrel harmonics have something to do with it.

But the main reason the heavier slower bullet hits high is the "in barrel time" of the bullet. With the heavier bullet the recoil of the rifle is also greater and the barrel time is longer, so the rifle barrel is higher in recoil when the bullet leaves, causing the heavier bullet to hit higher on the target.

Also with the heavier bullet the torque produced by firing the rifle is greater and the rifle is twisted more to the left ( with a right hand twist) and a heavier bullet should hit to the left of a lighter bullet.

NormB
Click to expand...
Yeah, not much recoil or torque involved when the rifle is strapped and clamped into that rest. NO HUMAN FACTOR involved, I even have a remote trigger. Perhaps that's why the differences were so small.

Yes, when fired from the shoulder, I have noticed differences in torque and, as I said, I have experienced the left/right different POI.

30yrs of doing this, knowing all the theory, but never had actually proved it since I have never put it all together in one session.
 
rookie wildcat said:
Yeah, not much recoil or torque involved when the rifle is strapped and clamped into that rest. NO HUMAN FACTOR involved, I even have a remote trigger. Perhaps that's why the differences were so small.
Click to expand...


Exactly right... mimimize the effect of torque and the recoil jump ... minimize the effect. But it is still there, and is most of the reason for the difference in bullet impacts.

NormB
 
NormB said:
Exactly right... mimimize the effect of torque and the recoil jump ... minimize the effect. But it is still there, and is most of the reason for the difference in bullet impacts.

NormB
Click to expand...

Actually, torque and recoil may, in some cases, contribute a tiny bit to the change in POI, but they are never "most of the reason" for the difference. Barrels whip like a rope or a guitar string as you fire a bullet, and the changes in the actual direction the muzzle is pointing in the microsecond the bullet exits is "most of the reason."
 
In addition to harmonics, lighter bullets will generally shoot lower.
They spend slightly less time in the barrel so the gun has recoiled less and muzzle lower when they depart.
This is very noticeable in handguns.

Dan
 
rral22 said:
Actually, torque and recoil may, in some cases, contribute a tiny bit to the change in POI, but they are never "most of the reason" for the difference. Barrels whip like a rope or a guitar string as you fire a bullet, and the changes in the actual direction the muzzle is pointing in the microsecond the bullet exits is "most of the reason."
Click to expand...

Well, I beg to differ. The jump and twist caused by recoil has a much larger effect on bullet impact than the first, secondary, or 3rd order modes of vibration of barrel harmonics. The actual amount and direction of muzzle point change with harmonics would be random depending on bullet velocity and bullet exit time. The effect of recoil and torque are not random and always produce the same direction of results on target, as the shooting posters have indicated.

NormB
 
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rookie wildcat said:
I am willing to be wrong on this one and learn.
Click to expand...

Excellent news, because you are wrong. ;)

Light bullets spend less time in the barrel which means that the heavier bullet is launched at a higher angle due to the muzzle rise cause by recoil. Doesn't take a lot of increase in the angle of the muzzle to make a 5" difference at 100 yards (actually, it's .0728 degrees upward).

Now the thorny one...harmonics. Loot at barrel harmonics this way - there are no rules. A little tweak may give drastic results while something more may yield negligible ones. This cannot be scientificly quantified, it falls under the "sh*t happens" heading of ballistics. Worse still, some rifles may exhibit baffling behaviour while others, subjected to the same stimuli, will behave completely differently. There are only so many things in shooting that will follow hard and fast rules. That's part of the challenge.

I knew I'd be late to this one but I wanted to type it out anyways.

To the OP...is there a good reason that you would want to use the 150 grain bullet? You have one of the fastest 30 caliber magnums on the market, designed to make heavy bullets go fast. I would embrace that. No need to go crazy with it, but 180 or 200 grain bullets offer the high BC, sectional density and momentum that you want in a 30 caliber and you have the horsepower to make them run like lightweight bullets in a lesser cartridge. This is the reason to shoot a RUM. Plus when you jump shoot a big donkey at 35 yards you will do so with the confidence that your 200gr TTSX will hold up under the extreme force of impact that can cause lesser bullets to fail.

Embrace it.
 
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