why groups move horizontally with powder change?

[calpik]

Noticed a strange thing, with some bullets/powder groups move horizontally more than vertically.

What's the reason of such behavior? (rifle is not bedded, 223rem, weatherby vanguard)

[rsrocket1]

Welcome

The speed of the bullet is only one part that influences the point of impact (POI).

For example:
A 1 grain difference in a load gives a 130 fps increase in MV. That translates to a 0.2" difference in bullet drop. You're probably seeing more movement than that with less powder change.

Your group movement is not due to the change in exterior ballistics of the bullet (purely due to change in bullet drop). It's due to the barrel whipping around and the bullet exiting the barrel while the barrel is pointing in different directions. The barrel vibrations are in 2 dimensions, left/right and up/down. The trick is to find the consistently smallest group (an accuracy node), then adjust your scope to center the crosshairs within that group.

If you're shooting a lot of bullets, the barrel is also heating up and can change its bending characteristics too. That could change the point of impact.

[AGGRO]

Once my win mag loosened the scope mount

[tonyjr]

It could be seating depth , and or crimping .
I take apart dies after about 500 to 600 reloads and run thru sonic .
The 1st magazine [ yes I keep track ] mainly for the dies to seat in , warm up barrel and get comfortable .
FYI - I use WD-40 and the W D stands for water displacement - it is a coating [ dust magnet ] not a lubricating oil

[calpik]

Welcome

The speed of the bullet is only one part that influences the point of impact (POI).

For example:
A 1 grain difference in a load gives a 130 fps increase in MV. That translates to a 0.2" difference in bullet drop. You're probably seeing more movement than that with less powder change.

Your group movement is not due to the change in exterior ballistics of the bullet (purely due to change in bullet drop). It's due to the barrel whipping around and the bullet exiting the barrel while the barrel is pointing in different directions. The barrel vibrations are in 2 dimensions, left/right and up/down. The trick is to find the consistently smallest group (an accuracy node), then adjust your scope to center the crosshairs within that group.

If you're shooting a lot of bullets, the barrel is also heating up and can change its bending characteristics too. That could change the point of impact.

That means that I have to look for a "node" (the powder charge/seating depth/other things when small change in a parameter does not change much. For example I see situation when 0.7gr powder load range does not make any difference in vertical and groups are good) for both horizontal and vertical? Like finding the spot, when small changes in powder/seating depth do not move group much both vertically and horizontally.

That's the first time I see that. Previous experiments were ok - group did not shift right/left much (usually right with increasing powder charge), mostly vertical.


Could it be something with rifle? It's not bedded, nothing is done with the rifle itself. Will "kitchen" bedding help? (howa 1500 action , standard barrel and boyds stock)

[calpik]

It could be seating depth , and or crimping .
I take apart dies after about 500 to 600 reloads and run thru sonic .
The 1st magazine [ yes I keep track ] mainly for the dies to seat in , warm up barrel and get comfortable .
FYI - I use WD-40 and the W D stands for water displacement - it is a coating [ dust magnet ] not a lubricating oil

crimping... I have a lee precision factory crimp die and every time I use everything gets worse. I do not know how to properly control it/measure it (crimping) and do not want to waste bullets anymore.
Does it realy help? rifle is bolt action...


Seating depth can change POI? Realy? Can you please explain this a little bit?

[calpik]

Once my win mag loosened the scope mount

naaah... it's 223, I have some factory ammo I use to check 0 while I experiment with reloads.
scope is ok. (at least I think so)

[ojisan]

Barrels flex in all directions when fired.
For accuracy, what you want to do is develop a load where the bullet exits the barrel timed to when the barrel is pointed straight at the target.
Usually this is done by experimenting with different bullets and powders / charges / velocities until a match-up is found.

Browning's BOSS was a threaded muzzle weight that could be adjusted to get the barrel flex to time up with whatever ammo was being used at the time.
This approach is adjusting the barrel to the ammo, rather than adjusting the ammo to the barrel.
Info on the BOSS and barrel flex:

http://www.browning.com/support/frequently-asked-questions/tune-boss.html

The BOSS did not prove to be too popular, with most precision shooters preferring to focus on adjusting the ammo.

If your gun shoots consistently, even if the POI is different with different ammo, then bedding is probably not the issue.
You just need to find a load that consistently matches up with your barrel.
Then adjust your scope to match the POI of that load.

[tonyjr]

calpik
The pressure that pushes the bullet changes from no crimp to a heavy crimp .
The more pressure , the faster the pill should turn
Different batches of cases will crimp differently .

[calpik]

Barrels flex in all directions when fired.
For accuracy, what you want to do is develop a load where the bullet exits the barrel timed to when the barrel is pointed straight at the target.
Usually this is done by experimenting with different bullets and powders / charges / velocities until a match-up is found.

....


You just need to find a load that consistently matches up with your barrel.
Then adjust your scope to match the POI of that load.

Does that mean: just find a charge with a smallest grouping (100-300 yards) and adjust your scope for that load?

[calpik]

calpik
The pressure that pushes the bullet changes from no crimp to a heavy crimp .
The more pressure , the faster the pill should turn
Different batches of cases will crimp differently .

yes, but how to control that "no crimp to heavy crimp"

[TexasJackKin]

See post 28, under the heading "Tricks to loading extruded va ball powder"

A very good explanation of the phenomenon you are experiencing.

Oh and welcome to CalGuns.....

[calpik]

See post 28, under the heading "Tricks to loading extruded va ball powder"

A very good explanation of the phenomenon you are experiencing.

Oh and welcome to CalGuns.....

thank you!

The exact weight of the powder makes a big difference in how "tolerant" it is to minor changes in charge weight and velocity.

There is no "flat spot" in velocity. More powder, whether it is at a node or not will give you more velocity. What happens is that at a node, the barrel harmonics are at a peak or valley and a slight change in velocity does not change where the barrel is "pointing". This means you get a small group of shots on the target rather than a large one.

Now, i you can get the bullet to exit the barrel at exactly the same spot every time regardless of the overall charge weight, your groups will always be small, the POI will simply move around because with one charge weight, the "whipping" barrel will be pointing in one direction and with a different charge weight, it will be pointing in another direction but with each charge, it will always point in its own direction consistently.

Of course, that's impossible because as the powder burns, it doesn't burn exactly the same every shot and there will be slight statistical variations in MV even if you could charge your cartridges to 0.001g and seat the bullet to 1 mil accuracy. So the bullets will be exiting the muzzle at different times.

If you think of the muzzle vibrating like a sine wave, the barrel tip spends more time at the top and bottom of the wave and moves the fastest in the middle. If you happen to pick a charge that makes the bullet exit the muzzle in the middle of the sine wave, you will get the worst accuracy even if you could measure out your powder to the individual stick or ball. Conversely, if you could make the bullet exit at the top or bottom of the wave, the barrel might be pointing in the same direction even if you are off by 0.1g or more (or at different temperatures, different altitudes, or slightly different bullet weights or seating depths). This is what is called an "accuracy node". Unfortunately, the barrel is whipping in 2 dimensions so it's not as simple as up/down but it's coupled with left/right too.

Each barrel length has its own accuracy nodes. That's what we are trying to find when we work up loads looking for the best groups. Barrels will have nodes at multiple velocities and some will be flatter longer than others. At a node, you can vary things a little bit and the barrel will still be pointing in the same direction. That will mean slight differences in bullet weight, velocity and barrel temperature will make almost no difference in POI.

Factory ammo is usually fairly accurate in almost any barrel length not because they have a secret sauce for finding the accuracy node of every barrel ever made, it's because they can make ammo to very close tolerances. Even Federal Value Pack or PMC .223 ammo have > 1% SD spreads in velocities. We can do better but it will likely be because we found a node rather than we were able to match their consistency in making the ammo.

For true accuracy chasing, you need at least 5 shot groups and 10 chrony readings under multiple conditions. For "minute of deer" at 50-75 yards, you probably don't even need to work up loads, just find something that feels good to shoot and have at it.

That's my free advice. Remember, you get what you pay for.

[JackEllis]

If it's a bolt rifle, forget about crimping. It's not necessary, just like it's not necessary to crimp primers for bolt guns.

My rifles are all bolt action, I hand load for the three centerfire calibers, I don't crimp bullets (or primers), and they all shoot just fine..

[stevec223]

yes, but how to control that "no crimp to heavy crimp"

Ok I will tell you how I use my FCD...
First screw die in to press unitl it just touches the shellholder... Mark the top of the FCD on the top of it at 9oclock with a sharpie...
Lower the ram with shelholder just a bit ,,, and rotate die to 3oclock position...
Lock the die loosely inplace...
Measure a loaded round at the case mouth with calipers,,, example .275...
Run the loaded round up fully into the die While you are looking down into the top of the die... Did you see the 4 slits in the top come together ???...
How close together ???
Drop ram and remeasure the the case mouth,,, as close to the bullet as possible again...
Is measurement still .275 ??.. If so tighten die (sharpie mark) to the 4oclock position and run cartridge up into die again,, and watch the 4 slits inside of the die again...
Drop ram and remeasure at casemouth again... Is measurement smaller now ?? Maybe .273 ???
Continue on this system until you get the crimp you want..
I only tapercrimp to .003 maybe,,, looking at the outside of the casemouth nearest the bullet,,, I am looking for a fine line appearing on the outside neck of my brass... This will measure .272 or so....
A heavy line is too much,,, and also while looking down into the die at the 4 slits they should barely touch... Anymore is to much and will crimp to much and damage the die and overcrimp the bullet...
It's a trial and error process,,, move slowly from the 3oclock position...
Sorry long winded but wanted to be clear...
Good shooting and ,,, Cheers....