why groups move horizontally with powder change?

[LynnJr]

The barrel on a good gun will only show vertical stringing as you vary the powder charge.
If you are getting horizontal it is either the shooter or the gun.
Bedding should be your first fix after the scope the rings and the base have been ruled out.
The Boss system works but it's a little bit too light. On a typical competition diameter barrel 6-11 ounces works best.
Gene Bukys won the biggest Benchrest match of the year three times using a tuner and they are gaining in popularity.
Accuracy is only found while the muzzle of the barrel is moving in a upward direction. If the muzzle is moving downward the gun won't group well.
When the barrel is moving upward the slower shots stay in the barrel longer so they exit the muzzle in a higher trajectory than the faster bullets. If they converge on the target that is when you will see best accuracy.

[nedro]

The barrel on a good gun will only show vertical stringing as you vary the powder charge.
If you are getting horizontal it is either the shooter or the gun.
Bedding should be your first fix after the scope the rings and the base have been ruled out.
The Boss system works but it's a little bit too light. On a typical competition diameter barrel 6-11 ounces works best.
Gene Bukys won the biggest Benchrest match of the year three times using a tuner and they are gaining in popularity.
Accuracy is only found while the muzzle of the barrel is moving in a upward direction. If the muzzle is moving downward the gun won't group well.
When the barrel is moving upward the slower shots stay in the barrel longer so they exit the muzzle in a higher trajectory than the faster bullets. If they converge on the target that is when you will see best accuracy.

Excuse my ignorance, but how does one know which direction the barrel is moving and how does one adjust it to move in the right direction?
Can you explain to a novis or point me to a book that will get me started?

[Kwikvette]

Excuse my ignorance, but how does one know which direction the barrel is moving and how does one adjust it to move in the right direction?
Can you explain to a novis or point me to a book that will get me started?

A calgunner's way of summing it up (another thread) -

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, if 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.

[Maltese Falcon]

Tag for later

[NiMiK]

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

Yes, seating depth can make a difference. I played with this idea using a mild charge. This is the jump that the bullet makes before engaging the rifling. Some bullets prefer a longer jump and some like no jump or .005" of jump.

[nedro]

A calgunner's way of summing it up (another thread) -

When I started reading what you quoted, I was thinking that, "This is not answering my question."
But it actually did a very good job of doing so.
It doesn't tell me what to do. Rather, what to look for.

When I started reloading, I was pining for a Chrono to be able to really get detailed info on my loads. So I bought a Caldwell. It is almost OK. But I have to do my calcs at a public range where the chrono has to be out where I cannot mess with it during open fire. It's always turning its self off or needing to be cycled on or off.
So its pretty much useless.
You guys are making me think real hard about getting a LabRadar.
CalGuns: Costing me money since 2014. The moment I joined up, I found out about the SSE. That cost me a cool 8 bills.
It's just been getting more and more expensive ever since.

[Kwikvette]

When I started reading what you quoted, I was thinking that, "This is not answering my question."
But it actually did a very good job of doing so.
It doesn't tell me what to do. Rather, what to look for.

When I started reloading, I was pining for a Chrono to be able to really get detailed info on my loads. So I bought a Caldwell. It is almost OK. But I have to do my calcs at a public range where the chrono has to be out where I cannot mess with it during open fire. It's always turning its self off or needing to be cycled on or off.
So its pretty much useless.
You guys are making me think real hard about getting a LabRadar.
CalGuns: Costing me money since 2014. The moment I joined up, I found out about the SSE. That cost me a cool 8 bills.
It's just been getting more and more expensive ever since.

My dad has cost me more than anyone in that, he got me into firearms

The forum (and a friend of mine) encouraged me to reload which is another hobby in itself.

In my latest load development with H1000 and .300wm, I found an accuracy node that yielded a > .5" group with no vertical spread.

I'll shoot the same loaded cartridge next week, and load a few more at different seating depths to see if my horizontal tightens up.

[calpik]

Bedding should be your first fix after the scope the rings and the base have been ruled out.

it seems that it's time to bed the rifle. I already glued the rail.

The barrel on a good gun will only show vertical stringing as you vary the powder charge.
If you are getting horizontal it is either the shooter or the gun.
Bedding should be your first fix after the scope the rings and the base have been ruled out.
Accuracy is only found while the muzzle of the barrel is moving in a upward direction. If the muzzle is moving downward the gun won't group well.
When the barrel is moving upward the slower shots stay in the barrel longer so they exit the muzzle in a higher trajectory than the faster bullets. If they converge on the target that is when you will see best accuracy.

I'm not sure if it's a right term "stringing", because groups are relatively ok, they just move right/left, instead of up/down. And that's only for bullet/powder combination, other bullets/powders behave differently.


If it's a gun (let's skip "shooter" at this moment ) , what could be a reason of such behavior? is it possible to fix at home?

[calpik]

Yes, seating depth can make a difference. I played with this idea using a mild charge. This is the jump that the bullet makes before engaging the rifling. Some bullets prefer a longer jump and some like no jump or .005" of jump.

grouping changes, but the poi is the same?


(is it possible to seat bullet to the same depth with lee dead bullet seater? or I should upgrade? NOT the runout (tools for measuring/controlling this are way too expensive for what I do right now), but the depth

[KahrMan]

Barrel flex, with more or less powder it would change poi. Question is, why to the side? Is there a muzzle break on your barrel.

Edit: on second thought it is probably just a harmonic caused by a poorly fitting stock.

[NiMiK]

grouping changes, but the poi is the same?


(is it possible to seat bullet to the same depth with lee dead bullet seater? or I should upgrade? NOT the runout (tools for measuring/controlling this are way too expensive for what I do right now), but the depth

POI was the same since I was only at 100 yards and was already zeroed with 175gr FGMM. Group 4's shift was caused by me pressing too hard on the cheekrest and seeing my heartbeat through the reticle.
Not sure what tools you currently have or if you're measuring COAL or CBTO. I measure mine based on CBTO. You can try a Hornady comparator kit as it's nowhere near the cost of competition dies.
Best tip I was given by a BR shooter was, save your fired brass and make a modified case so you can get a baseline of where your bullet starts engaging the rifling.

[LynnJr]

Nedro
When you are working up a load and your shots don't have the exact same velocity the faster bullets exit the barrel first.
If the muzzle of the barrel is climbing the slower bullets which are in the barrel longer are launched at a higher angle.
For those two bullets to group the bullet that started out higher with the lower velocity will converge or cross paths with the faster bullet at some point along its flight path.

If the muzzle of the barrel is in a downward direction the slower bullet would still stay in the barrel longer.
The faster bullet would exit sooner and the two paths would never cross at any distance.

I will post a picture that will hopefully show what I am referring too.

[LynnJr]

CalPik
Put your index finder on the forend of the stock and the barrel at the same time. Now loosen up one action screw and see if you feel any movement between the barrel and the stock. If you can the action needs to be bedded.
Repeat with each screw.

[calpik]

Barrel flex, with more or less powder it would change poi. Question is, why to the side? Is there a muzzle break on your barrel.

Edit: on second thought it is probably just a harmonic caused by a poorly fitting stock.

no , there is no muzzle brake..

ok, second voice for rifle bedding (and yes, it looks like gap in a barrel channel on a left side became smaller than it was before..)

[calpik]

POI was the same since I was only at 100 yards and was already zeroed with 175gr FGMM. Group 4's shift was caused by me pressing too hard on the cheekrest and seeing my heartbeat through the reticle.
Not sure what tools you currently have or if you're measuring COAL or CBTO. I measure mine based on CBTO. You can try a Hornady comparator kit as it's nowhere near the cost of competition dies.
Best tip I was given by a BR shooter was, save your fired brass and make a modified case so you can get a baseline of where your bullet starts engaging the rifling.

yes, that's what I do.
I have hornady comparator, calipers (electronic) and several "blanks" with special bullet seating depth.

My question was about the seating process itself. Every time I push a bullet (lee hand press and lee dead bullet seating die) I see different seating depth. I do rotate cartridges while i'm pushing bullet (they do not sit straight, I pull back a little bit, rotate cartridge and push it back and they look better).

Q1: how to seat bullets properly? OR What's the reason of different seating depth (it can differ up to 3-4 thousands of inch)
Q2: I feel different resistance while seating a bullet. What's the reason of that? - I measured case necks after sizing (lee collect sizer) , they all are around the same value, may be 1\2 of thousands of inch difference. And bullets which are seated easily usually sit deeper...