Ok, this is weird

[RCMSTER]

I understand that, but velocity is still velocity, no matter what powder is used, correct, or not?

Ok. You lost me on the powder. B.C., aerodynamics, I understand that. But if powder A is propelling a bullet at 3111 fps across the chronograph, and powder B is propelling a bullet at 3200 fps, what does the powders have to do with bullet flight after it leaves the barrel, and is past the chronograph?

 

[bdyal1972]

I understand that, but velocity is still velocity, no matter what powder is used, correct, or not? At any rate

Ok. You lost me on the powder. B.C., aerodynamics, I understand that. But if powder A is propelling a bullet at 3111 fps across the chronograph, and powder B is propelling a bullet at 3200 fps, what does the powders have to do with bullet flight after it leaves the barrel, and is past the chronograph?

Powder burn speed in the case AND bullet travel time in barrel IMMENSELY IMPACT bullet impact! Barrel whip complicates this even more!

Try loading the SLOWEST POWDER minimum load AND the FASTEST minimum load in the same case, same bullet.

1 5 round group each.

Compare velocity vs impact location vs group size..

It will educate you even more if you throw a mid burn rate powder....

Start a ladder test on each.

Keep targets and compare the progression of the impact group location....

On extremely slow powders and 26, 28, 30 inch powders i have seen impact location go down 5 inches and BACK UP 3 inches!!!

I believe this is associated with recoil interaction with the body compared with barrel whip.... i also have seen the same phenomenon between shooting from the difference of bench, prone, prone bipod, shooting sticks and over a stump!!!

Some loads 4" vertical diffetence!!!

Some 8" vertical difference!!!!

Gotta know how position interacts with impact!

Just 2 cents from an inquisitive amature wanna be!!! With a background in physics and metrology!!!!

 

[RCMSTER]

It looks like you found a load the rifle likes. My first rifle was a 25/06 bought when I was 13. I have reloaded for it my whole life. The best I have found is H4831. 57gr with a 100 gr bullet. Smoke your bullets and seat just so no rifling marks. Of course I am partial to 4831. My brother bought a 50 pound keg for 52 dollars in 1971. Hahahaha try that now!!!!! As for your drop with 2 different bullets. Others said it first,harmonics. Who cares? Sight it in and go hunting.

Well, it's not that I really care. Just curious, that's all.

 

[Mike Matteson]

I have found over the years that difference bullets, powder, and primers all effect the POI in any rifle that I shot or develop loads for. Some not by much and some greatly. I would think that would be a no brainer. I feel that most of which as been stated is correct, but any change in makeup of reloads or change in ammo requires a trip to the range to check point of POI. A few years back going to Africa on hunting trip I brought two type of rounds for my rifle. Knowing full well there was a different POI. The change was a great mount. I finally figure out it wasn't worth the time to set up an adjust my scope for the different animal I figure taking, because you never quiet know what going show up or you come across. If I was going to go again and shot some smaller animals would bring an additional rifle for that purposes.

 

[skipglo]

I understand that, but velocity is still velocity, no matter what powder is used, correct, or not? At any rate

Ok. You lost me on the powder. B.C., aerodynamics, I understand that. But if powder A is propelling a bullet at 3111 fps across the chronograph, and powder B is propelling a bullet at 3200 fps, what does the powders have to do with bullet flight after it leaves the barrel, and is past the chronograph?

My comments are only based on my experience and just trying to help you reason thru your question in an effort to help....so this is just food for thought...if powder and burn rate wasn't a factor....then why does anyone get a SD number?

 

[RCMSTER]

My comments are only based on my experience and just trying to help you reason thru your question in an effort to help....so this is just food for thought...if powder and burn rate wasn't a factor....then why does anyone get a SD number?

Guess I never thought about that. I do believe you have a point. Thanks for pointing that out. Guess you're never too old to learn.

 

[Ga6570]

So I was out shooting my Ruger no 1, in 25-06. Trying to find an acceptable load with 100 gr swift a-frames. I have a good load with norma 100 gr soft points and 56.5 gr of accurate mag-pro. Last 3 shot groups have averaged 3/4" @ 100, and the rifle is sighted in @ 2" high at that distance. Average velocity according to labradar is 3111 fps, with an SD of 13.8.

Tonight, I load up 4 rounds with 55.5 gr of R-26. 3 of 4 shots were at slightly less than 5/8" @ 100. Average velocity by labradar was 3206 fps, with an SD of 18.7. But here's where I'm bewildered. POI of the swift a-frame was 5" south of the same grain norma bullet, while leaving the muzzle a full hundred fps faster. Anybody able to explain to me how this is? Thanks in advance for theories.

I'm pinning the velocity difference on jacket density differences. Slightly thicker jacket can create a tighter seal, and gets pushed faster.

These same differences in bullet composition can also affect the way the bullet flies as directed by the barrel. Harmonics as it has been called. It just needs to be brought into tune or "Harmony" for it to maintain the accuracy you seek. Starting to sound like a music lesson...

 

[RCMSTER]

I'm pinning the velocity difference on jacket density differences. Slightly thicker jacket can create a tighter seal, and gets pushed faster.

These same differences in bullet composition can also affect the way the bullet flies as directed by the barrel. Harmonics as it has been called. It just needs to be brought into tune or "Harmony" for it to maintain the accuracy you seek. Starting to sound like a music lesson...

You're explanation makes good sense to me. Thank you

 

[nicholasjohn]

You are correct, I shoot Silhouettes with 6.5x47 with 129gr. When I wanna shoot heavy 140gr bullets on rams, they go 3" left (on 100 yards).

There is also a lateral component to the barrel harmonics. It's part of a rotational component. Also, anything touching the barrel inside the forend channel will influence where the muzzle is pointed when the bullet exits. Sometimes it appears to be totally random, but it really isn't. It's just that it's darn near impossible to figure out what is causing the discrepancy, so it may as well be random. Things like powder burn rate affect the vibration pattern of the barrel, and the amount of time the bullet is in the barrel is a player as well. It's reasonable to expect that an extra 100 fps could make a big difference, both up & down and left/right.

Sometimes backing off the load to change velocity just a tad will make one bullet print where the other does, removing the necessity to dial the scope when you use the other load. Chasing this down would be a very frustrating process, but with all the ladder testing a lot of guys are doing, one might find a load in a slower accuracy node that happens to have a POI that coincide with where his other loads prints.

Years ago, I had what was then a heavy-bullet load for my 22-250 ( 64-grain Winchester Power Point ) and at the highest safe velocity, it shot six inches away from where my woodchuck load grouped. This necessitated dialing the scope adjustments, and back when Leupold scopes had the friction-type adjustments ( no clicks ) this was a pain in the keester. I had happened to notice when I was doing my pressure testing that a load that shot 50 fps slower hit right where the woodchuck load shot, and it shot nickel-sized groups at 100 yards - plenty well enough to shoot whitetails in the woods out to about 150 yards. So, I went out and shot a bunch of does with this meat-saver load, and didn't have to touch the scope adjustments at all after shooting woodchucks all summer long with my 55-grain load. Why the faster load with the heavier bullet behaved the way it did doesn't matter to me. That can be dealt with easily enough.

 

[RCMSTER]

There is also a lateral component to the barrel harmonics. It's part of a rotational component. Also, anything touching the barrel inside the forend channel will influence where the muzzle is pointed when the bullet exits. Sometimes it appears to be totally random, but it really isn't. It's just that it's darn near impossible to figure out what is causing the discrepancy, so it may as well be random. Things like powder burn rate affect the vibration pattern of the barrel, and the amount of time the bullet is in the barrel is a player as well. It's reasonable to expect that an extra 100 fps could make a big difference, both up & down and left/right.

Sometimes backing off the load to change velocity just a tad will make one bullet print where the other does, removing the necessity to dial the scope when you use the other load. Chasing this down would be a very frustrating process, but with all the ladder testing a lot of guys are doing, one might find a load in a slower accuracy node that happens to have a POI that coincide with where his other loads prints.

Years ago, I had what was then a heavy-bullet load for my 22-250 ( 64-grain Winchester Power Point ) and at the highest safe velocity, it shot six inches away from where my woodchuck load grouped. This necessitated dialing the scope adjustments, and back when Leupold scopes had the friction-type adjustments ( no clicks ) this was a pain in the keester. I had happened to notice when I was doing my pressure testing that a load that shot 50 fps slower hit right where the woodchuck load shot, and it shot nickel-sized groups at 100 yards - plenty well enough to shoot whitetails in the woods out to about 150 yards. So, I went out and shot a bunch of does with this meat-saver load, and didn't have to touch the scope adjustments at all after shooting woodchucks all summer long with my 55-grain load. Why the faster load with the heavier bullet behaved the way it did doesn't matter to me. That can be dealt with easily enough.

Thanks. It's been pointed out to me that I should've expected a POI difference. Well, I'm not totally ignorant, and I wasn't expecting the two to print exactly the same, I just was surprised to see 5 inches difference, that's all. That's why I asked for some opinions. I got plenty, and most all were good explanations that I understand. I got a good education with this thread, I'll say that.

 

[nicholasjohn]

Thanks. It's been pointed out to me that I should've expected a POI difference. Well, I'm not totally ignorant, and I wasn't expecting the two to print exactly the same, I just was surprised to see 5 inches difference, that's all. That's why I asked for some opinions. I got plenty, and most all were good explanations that I understand. I got a good education with this thread, I'll say that.

Me, too - thanks for bringing it up and shaking a few new ideas out of the bushes. Another thing I'd like to point out here is that there are also variables unrelated to the load that can come into play at the shooting bench. I grew up with a guy who had a marlin 30-30 that would shoot groups that you wouldn't believe. If he put the front sandbag under the forend of the rifle, it looked more like patterning a shotgun, but when he put it under the point where the forend came out of the receiver, it would consistently shoot three holes all touching each other at 100 yards. The point ? Rifles not known for accuracy can be very accurate, and the position of the rifle on the bags can be critical. The latter point was illustrated to me with my own 308, an old Browning Safari Grade with the Sako action. It shot best with the front sandbag right under the checkered part of the forend, and not only did the groups open up with other bag positions, but the POI shifted a lot. Because it was such a light rifle, recoil moved it on the bags with every shot. If I didn't re-position the rifle each time, it was a waste of time to shoot a group. Bedding in the forend channel was probably the issue here. This rifle shot extremely well when hand-held from hunting positions, and I killed a ton of animals with it. But as soon as I got the idea to try a Harris bipod on the gun, it became almost useless. This was because the bipod attaches too far forward on the forend, up there where it also didn't shoot well off the sandbags. Some rifles are fussy like this, and some are not. The ones that are not are a delight. The ones that are fussy are like having a high-maintenance girlfriend.

Lastly, I'd like to throw this on the pile - if your sling swivel catches on the front sandbag in recoil, the groups will open up and can move all over the target. It sounds pretty basic, but it's also easy to overlook. Recoil vs. barrel time with loads of different velocities can also make a big difference, even when you do pay attention to all these details.

 

[skipglo]

Guess I never thought about that. I do believe you have a point. Thanks for pointing that out. Guess you're never too old to learn.

Or to ask questions my friend. That's why we are here.....for each other man

 

[skipglo]

Thanks. It's been pointed out to me that I should've expected a POI difference. Well, I'm not totally ignorant, and I wasn't expecting the two to print exactly the same, I just was surprised to see 5 inches difference, that's all. That's why I asked for some opinions. I got plenty, and most all were good explanations that I understand. I got a good education with this thread, I'll say that.

I have been reloading for 47 years! And the only constant in this time....is something...like the pictures of the dramatic change BRASS can make...is always surprising me too. There was nothing in your question that inferred you where ignorant my friend...it was an totally honest question....and one more you might not be aware of...and just for the fun of it.....change JUST PRIMERS and load a few...you might be totally surprised by those results...I sure as He-- was and the mistake I made....I bought 1000 first go......daaaaaahhhhh