Ladder Test for finding powder charge

[mtmuley]

when my neighbors are out side I tell them. I’ve got excellent neighbors. My sons rifle has a brake so it’s like a nuclear explosion. I have a ring camera which catches some mid my stupid ideas/habits.

When I first moved into my house and 5 acres we had a ground squirrel (gopher) issue. I took care of them with a.22 LR. My neighbor was kinder. He tried the method of a rodent control outfit. Waste of money. I have a 6 foot French door in my daylight basement overlooking his property. Set up the bench, open the doors and my .222 Remington vaporized gophers out to about 300 yards. Problem solved. Interestingly he never said a word about the rugged out pests. All shots were safe before anyone asks. mtmuley

 

[Burn Pile]

I've been doing pressure ladders. Go up the ladder until you hit pressure sign or velocities you don't like. Shoot all the charge weights into a group and take notes for velocity and point of impact. IME if the barrel likes the combination of bullet, powder, and fps together the poi at 100yds will be decent and consistent until the top end charges. POI will start changing more as the peak chamber pressure increases. Then I'll pick the charge that went the fastest with no or minimal pressure sign and landed in the same area as the majority of the group. Then load up with that charge and shoot a group of 10-15 and see if it still goes well. If it does not start a new pressure ladder with a different powder. Or eventually different bullet.

 

[brockel]

I use to do ladders and once I’d find a “node” I’d load up ten and sometime find that load still wasn’t accurate. Wasted a lot of time and components. Now days I work up to pressure and then back off slightly. Load 3 up. If those 3 show promise I load 7 more and shoot the same target. If it holds true I stick with it. If it falls apart I change powder or bullets. Personally I don’t want a load thats so finicky that 0.5+- a grain of powder throws shit haywire. Ten shots 1.5” I’m happy with.

 

[ImBillT]

If you think the ladder test really works, then you would be able to repeat it several times and find the same nodes. I have not found this to be true.

I have, but it takes a pretty accurate rifle to begin with, and I’m not sure most people doing it are doing it right. My guess is that you haven’t done it with a rifle with a 20” barrel that weighs 5lbs or more, on a rifle with a 3” wide flat forend using a cartridge that barrel recoils.

I see the biggest differences at 100yds. By 300yds a lot of it is no longer visible to me on target.

You should see similar velocity increase with every charge weight increase. Too small of charge weight increase will muddy the water as bad as too big. Nodes are not about a charge weight window within which velocity doesn’t change much. That is nothing but random velocity spread. Nodes are about a velocity window that shows very little vertical on paper. The barrel is vibrating up and down. If bullets are exiting during the down swing, then a small increase in velocity will result in the bullet not only hitting the target before dropping for as long a time, but also exiting the barrel while the barrel is higher. When doing a ladder test, you should see bullet impacts rise with each increase in charge weight for a period, and then bullet impacts will settle and begin impacting the same position vertically in spite of increasing charge weight, then the impact will drop, and start climbing again. You can hit multiple nodes. Shorter, stiffer barrels have nodes closer together. Short range benchrest shooters can see 3-4 nodes during testing because they will be shooting 18-20” barrels with very little taper. 1000yd benchrest shooters may only find one because their barrels are so long, and it may not be super obvious if they’re tuning at long range, or they may even be picking up on some other effect that isn’t related to barrel vibration. I’ve shot ladders with over ten shots with a .3gr increase in powder charge in every shot that put 3-4 shots into a single small small hole followed by 4-5 shots climbing, then the ending shots all going into a single hole only slightly higher than the first 3-4 shots. The final group being .5” wide by .75-1.25” tall. I’ve also shot rifles that weren’t quite as forgiving, and hunting rifles that didn’t shoot well enough to tease anything useful out of a ladder test beyond max powder charge. But if the rifle is shooting well, it should show a node or two. Those nodes are not charge weights that yield than expected velocity increase with increasing powder charge. That is nothing but random velocity spread. Those nodes are velocity windows where the barrel vibration slightly cancels velocity spread because you’re on the up swing, thus faster bullets exit while the barrel is low, and slower bullets exit while the barrel is high. These velocity windows work with any powder and any bullet weight. Although it tends to be talked about as “finding a node”, in my experience it’s more like the opposite. I find a velocity window or two where vertical dispersion is exaggerated and outside of that, it reduces to near zero. The effect becomes a reduced percentage of your vertical spread on target as range increases, and velocity spread matters more than being on a node. Finding a load with a low velocity spread is much more valuable than finding a velocity node, but it is also much more consumptive of time, components and barrel life.

I doubt most hunting rifles are accurate enough to find nodes reliably. Not all of mine are. It may be more common with some of today’s semi custom stuff getting so good and so common.

I’m going to work my way up to pressure signs on a new barrel or with a new bullet weight anyway. Why not see where it prints and see if I can use that to my advantage? What it really tends to tell me is “this velocity window gives me more vertical dispersion than I want, so test loads above or below that”.

If a rifle consistently shoots groups that are tall and skinny, you probably need to try another powder charge. If it just kinda shoots generally not as good as you want. Then it’s not a node thing. It’s a different tuning issue, or rifle issue or operator issue. And for a hunting rifle, it’s probably still good enough. It’s also sooooo easy to get vertical dispersion just from imperfect gun handling when you’re not shooting a heavy, low recoiling rifle, with a 3” wide flat forend.

 

[ImBillT]

I use to do ladders and once I’d find a “node” I’d load up ten and sometime find that load still wasn’t accurate. Wasted a lot of time and components. Now days I work up to pressure and then back off slightly. Load 3 up. If those 3 show promise I load 7 more and shoot the same target. If it holds true I stick with it. If it falls apart I change powder or bullets. Personally I don’t want a load thats so finicky that 0.5+- a grain of powder throws shit haywire. Ten shots 1.5” I’m happy with.

Well the whole point of being on a node is that velocity spread doesn’t change poi. You should be able to go quite a bit in either direction without much vertical shift if you found a node. However, +- .5gr isn’t small. That could push you off a node on medium sized cartridges. But being off a nose would just be even worse. But the whole thing really isn’t a giant effect, and its effect becomes increasingly less important as range increases. It’s a effect that isn’t worth concerning yourself with in all scenarios, or even most hunting scenarios, but not tuning for it doesn’t mean that your rifle doesn’t have velocity windows with less vertical dispersion and more vertical dispersion. It just means you aren’t looking for them. Which as I said, isn’t a big deal.

 

[BrentD]

I have, but it takes a pretty accurate rifle to begin with, and I’m not sure most people doing it are doing it right. My guess is that you haven’t done it with a rifle with a 20” barrel that weighs 5lbs or more, on a rifle with a 3” wide flat forend using a cartridge that barrel recoils.

I see the biggest differences at 100yds. By 300yds a lot of it is no longer visible to me on target.

You should see similar velocity increase with every charge weight increase. Too small of charge weight increase will muddy the water as bad as too big. Nodes are not about a charge weight window within which velocity doesn’t change much. That is nothing but random velocity spread. Nodes are about a velocity window that shows very little vertical on paper. The barrel is vibrating up and down. If bullets are exiting during the down swing, then a small increase in velocity will result in the bullet not only hitting the target before dropping for as long a time, but also exiting the barrel while the barrel is higher. When doing a ladder test, you should see bullet impacts rise with each increase in charge weight for a period, and then bullet impacts will settle and begin impacting the same position vertically in spite of increasing charge weight, then the impact will drop, and start climbing again. You can hit multiple nodes. Shorter, stiffer barrels have nodes closer together. Short range benchrest shooters can see 3-4 nodes during testing because they will be shooting 18-20” barrels with very little taper. 1000yd benchrest shooters may only find one because their barrels are so long, and it may not be super obvious if they’re tuning at long range, or they may even be picking up on some other effect that isn’t related to barrel vibration. I’ve shot ladders with over ten shots with a .3gr increase in powder charge in every shot that put 3-4 shots into a single small small hole followed by 4-5 shots climbing, then the ending shots all going into a single hole only slightly higher than the first 3-4 shots. The final group being .5” wide by .75-1.25” tall. I’ve also shot rifles that weren’t quite as forgiving, and hunting rifles that didn’t shoot well enough to tease anything useful out of a ladder test beyond max powder charge. But if the rifle is shooting well, it should show a node or two. Those nodes are not charge weights that yield than expected velocity increase with increasing powder charge. That is nothing but random velocity spread. Those nodes are velocity windows where the barrel vibration slightly cancels velocity spread because you’re on the up swing, thus faster bullets exit while the barrel is low, and slower bullets exit while the barrel is high. These velocity windows work with any powder and any bullet weight. Although it tends to be talked about as “finding a node”, in my experience it’s more like the opposite. I find a velocity window or two where vertical dispersion is exaggerated and outside of that, it reduces to near zero. The effect becomes a reduced percentage of your vertical spread on target as range increases, and velocity spread matters more than being on a node. Finding a load with a low velocity spread is much more valuable than finding a velocity node, but it is also much more consumptive of time, components and barrel life.

I doubt most hunting rifles are accurate enough to find nodes reliably. Not all of mine are. It may be more common with some of today’s semi custom stuff getting so good and so common.

I’m going to work my way up to pressure signs on a new barrel or with a new bullet weight anyway. Why not see where it prints and see if I can use that to my advantage? What it really tends to tell me is “this velocity window gives me more vertical dispersion than I want, so test loads above or below that”.

If a rifle consistently shoots groups that are tall and skinny, you probably need to try another powder charge. If it just kinda shoots generally not as good as you want. Then it’s not a node thing. It’s a different tuning issue, or rifle issue or operator issue. And for a hunting rifle, it’s probably still good enough. It’s also sooooo easy to get vertical dispersion just from imperfect gun handling when you’re not shooting a heavy, low recoiling rifle, with a 3” wide flat forend.

You would certainly be surprised at the rifles I have used for this.