Fast and efficient ladder test.

Randy obtained a new DPMS LR-308 G-2, with 20" Barrel. He decided on 165 gr Hornady boat tail spire point, and I said let's try IMR 8208, since it worked so well in my rifle that is similar. Simmons 4-12X with a duplex reticle. I checked zero at 100 with a copy of the lowest charge, then held the point of the heavy post on steel at 300 yards, since that distance from center of the reticle was exactly equivalent to 1.0 Mil. The bullet impacted low from center, but I knew it would keep us on paper, so that was my hold, on the "+" every shot.

I do have a Razor 85mm spotting scope with a fixed 30X Mil eye piece. Randy stayed on the spotter while I shot 3 rounds through his rifle. Then I would get behind the spotter and "map" where each one landed, POI vs. POA in tenth of Mil. And write the powder charge next to the impact on the map. Photo below explains it well. We never drove to the target through 15 shots. We stayed parked in the loading room, in the shade.


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After the shooting, I drove out and retrieved the paper target. The bullets had been colored and labeled accordingly, so we knew what color bullet hole was which charge. We had a clear node at 40.0, 40.3, and 40.6 gr. Those three grouped 2".




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I told Randy usually the one in the middle of the node is the winner of the group shoot, but let's not skip a charge. Well 40.0 shot 1 1/2" tall and 4" wide at 200 yards, then I shot 40.3" gr.

200 yards.


Height is more important to me, but it was .58" wide. I just loaded the wrong photo here. That's 1/4 MOA in a plain vanilla DPMS. Will it do that every time? No way, but we did find the BEST powder charge after having shot only 22 rounds. This process took a grand total of 2 hours. Since Randy brought his press, and components prepared to load a group within the node, immediately after shooting the ladder test.

Very nice!

What distance would you do this for on a 223? 200 yards?

My personal minimum distance for a ladder test is 300 yards. And I have performed a ladder test, with a .223, at 300 yards. It worked perfectly.

I'm fact I have ladder tested the following cartridges at 300 or 500 yards, and every time it has given me the perfect powder charge. Frequently there will be a slow node (light powder charge) and a fast mode (heavy powder charge). The .308 AR, above had a clear winning powder charge, in the middle of the charge weights.

.223
.22-250
.243
6.5 Creedmoor
.260 Rem
7mm-08
.308 Win (bolt action, and AR)
7 Rem Mag
.300 Win Mag

Good to know, thanks.

Do you have a chrono available for public use? Or do you not even worry about a chrono until you find the right load?

I've got a cheap-o Shooting Chrony. It's fairly accurate, but I get real velocity by working DOPE backwards into the calculator.

Makes sense. Thanks for the helpful posts.

greatness JG !!

Very nice! I think your mapping needs improvement though...

Good work! It's always nice when things come together on the first go. I have only been loading 8208 a short while but it is rapidly becoming one of my favorite powders.

Next time I'll call you, and you can do it, then.

Actually, the next time will be Tuesday or Wednesday. Wait by the phone.

Maybe I'm understanding a ladder test wrong, but some of the results look odd to me. Were all rounds fire with the same point of aim?

Yes.

Yes.

Hard to read this one since powder charges next to bullet holes are in pencil.

In there, 3 loads grouped 2" at 300 yards. That's telling us between 40.0 gr and 40.9 gr is the node. Focus on that area and group shoot each charge.

It appears most of your 38 and 39 grain charge weights impacted higher than the 40-41 grain charges, or am I seeing something wrong? I would have expected the opposite.

I am running into the same thing on my Tikka 223. CFE223 with 25+ grains impacted well below the 23.5-25 grain charges. Really odd. My assumption is that the barrel is flexing downward for those heavier loads, but I won't pretend to say that's anything more than an uneducated guess.

The hotter loads run 2800-2900 and impact lower than the lighter loads running 2650-2750.

The three lowest impacting shots were the first shot in the mag. Weird phenomenon of an AR. The last shot in the mag i can explain. The bolt locks open, robbing gas, causing a low impact. That's why we had another round in the mag that did not get fired, so the bolt would cycle.

Lesser powder charges should impact lower than higher powder charges, and I've seen that be text book with bolt action rifles.

Some refer to it as "barrel timing". When the gun is fired a shock wave much the same as the shock wave generated from TNT, races down the barrel. When it gets to the muzzle, some of the energy rebounds and returns toward the action. Doing the same at both ends till the energy is disapated. It is the modification of this effect that that we document and take advantage of in a ladder test. Tuning our charge so the projectile leaves the muzzle during a favorable cycle of this vibration. We refer to it as an accuracy node.

I see the same thing in my AR except the first shot from the mag is ALWAYS high and slightly left. Interestingly, the last round out of the mag stays pretty tight.

I'm just gonna stick to bolt guns, single shots, and my 10/22

The lower charges impacting higher could be simply the slower moving bullets exiting the barrel later as the barrel moves upward due to recoil.
Also while I have seen changes in POI on the last round fired as the bolt remained open it hasn't been necessarily lower and the velocity has been normally the same. I would think the bullet has exited the barrel well before the bolt is even halfway back? Just a thought.

Seen last round from the mag, out of an AR-10, go low many times. I am open for another explanation as to why this happens.

If chronograph readings on that last round were constantly low then that theory would be plausible...... let us know once the research is done and data is available.

Me too.

Good reason not to use one.

Dramatically different recoil impulse could be a big part of it.

I developed this page in my data book for exactly what you're talking about, JG. Works perfectly if you have a .1 MRAD reticle.