Ladder testing

[ar10ar15man]

5 shot GROUPS is not a LADDER

Pick the brass, primer, powder, and bullet you want to shoot. To do a full test start at the lightest powder charge and go past the max maybe a grain or do. I try and start 15 tho off lands. Load them 3 tenth of a grain and up. Example my 338 Norma I started with 87 went 87.3, 87.6 87.9, 88.2 so on. Shoot all of them in 5 shot groups over a chrono and write it down. You will see the sd and es go high to low to high 3 times. Shoot off the middle lowest es and sd. You can tune from there. Example 88.5 did good with my 338 so I did 88.3-4-5-6-7-8-9 and 88.8 shot an es of 15 so I stuck with it. Then work on seat depth, start jammed, 3 off, 5,10,15,20,30,40 one of those will give you a 1 hole 5 shot group. From there that's your load and seat depth. Check it every 400 rounds or so.

 

[Chase723]

Bear with me, this post is long (you wanted specifics) but hopefully useful.

Not to confuse things but I use the Satterly load development method (You can YouTube it. 6.5 Guys did a 2 part series on it). The only thing different that I do is instead of loading 1 round at each charge weight I load 2. Essentially, it's a ladder that you shoot over a chronograph (I use a Magnetospeed). You don't have to shoot at target...the last 2 times I did it (which was actually this week) I just shot into a berm. It requires that your reloading is pretty on point, otherwise you won't see the velocity variation in a meaningful way and the data you gather will be useless. That being said, if it is on point, the data can be very meaningful and it can work extremely well.

Below are the results of doing a couple of these ladder tests for a 7mm Rem Mag using 168gr VLDs and Retumbo and 6.5 Creed using 107gr TMKs and H4350 this week, the results of which are sufficient for what I need. In the past I discovered that I couldn't get a reliable load right off the bat with a 1 round per charge weight ladder, so now I load 2 and shoot it over the Magnetospeed. I literally didn't even shoot at a target. Just into a berm. I look for velocity nodes where the muzzle velocity doesn't change much but the charge weight does (usually less than 10fps...or sometimes not at all) and actually sometimes reverses/goes down a little. I then pick the load in the middle of the node with the lowest extreme spread for the node and the lowest velocity difference (technically also an extreme spread...but since there's only 2 shots it seems silly to call it that) between the 2 shots of the same load. For my 7mm it happened to be 69gr Retumbo. For the 6.5 Creed it happened to be 44.2gr H4350.

At this point some, folks will shoot 5-10 back over the chronograph to confirm that the load has the ES and SD that they are looking for (personally I'm happy with an ES less than 30 and SD of less than 15, usually my ES is 10-20). I put that muzzle velocity into my ballistic app and load up 10-20 to test and have some fun with.

I then sight in at 100, since my POI with the Magnetospeed on is usually different than without it, and dial for 300. I shoot off a bipod and rear bag. If the wind is bad (or this is your first time doing it and don't necessarily trust what you've found) I'll shoot a 3 shot group here. If there's no/not much wind, I'll shoot 1 shot to make sure my windage setting on my zero is correct. If not, I adjust it so I'm center punching it. I then dial for 500 and shoot a 3 round group to see what I can expect. I then true my muzzle velocity based on that data.

Maybe I've just gotten lucky but it's definitely worked for me. The pics below are of the ladder data for the 6.5 (didn't take a pic of the 7RM data for some reason) and the first 3 shot groups I shot with each rifle at 500. You can see from the velocity data that between 44-44.4 the extreme spread over 6 shots was 16fps and the difference between the 2 rounds at 44.2 was 1fps. That's going to very likely be a very stable load, and it was. The other huge benefit is that you very rarely have to mess with seating depth (I've never had to) because you are identifying a load based on its current seating depth.

Doing it this way has been way more efficient for me personally and I've been very pleased with the results. It's developed some really rock solid loads. My hand is only in there for size reference later.

Sometimes you might have a couple nodes that you want to explore and I load up 6 of each of those (so I can shoot two 3 shot groups) and will have a shoot off at either 300 or 500. Best group out of those wins, though that's not always necessary.

Load development used to be a deal where I would end up shooting 60 or so rounds and have to make multiple trips to the range. The last couple times it's only been 2 trips and 22 rounds. Probably made my load development time 3-5x faster.

 

[Chase723]

Also meant to mention, just like from Alex's post, that the 1st 50-100 or so rounds down the barrel honestly seem to just get the barrel to the point where it is most consistent. You could call it a break in period, but I don't think of it as breaking it in like people used to think using some sort of prescribed cleaning regimen. I think of it as like breaking in a good pair of boots. You just have to use them a little bit and then they're perfect for a long time. Think of the bullets as the oil. Lol.

 

[JohnyRingo]

Where would you begin with ladder testing if you have a detachable box magazine and cannot start right off the lands?

 

[Chase723]

Whatever length will fit and feed from the magazine, and then I typically start 2-3gr off the max load. So say max is 69gr, I would start in 0.2gr increments at 67 and work my way up. Some people use 0.3 or 0.5gr which lets you cover a broader range faster. Works the same.

 

[JohnyRingo]

That's exactly what I did. I backed off my normal load because the bullet had to be seated deeper on my new rifle. I then went up by 0.5 grains until there wasn't a significant increase in speed. I then went with the last powder charge that yielded that last significant increase in speed. What I have read since then is that I should have split the last two powder charges in half. My groups have been okay...about 1 moa. I was hoping for closer to 1/2 moa. I am replacing the cheap factory stock that came with the XBolt Stainless Stalker with a custom, carbon McMillan Game Scout to see if that tightens the group a little.

 

[Chase723]

I would go with the load that's in the middle of the velocity flat spot with the lowest ES if you're only using a chronograph. If your following Alex's regimen (which is probably the best way, where you combine both chronograph data and are able to see your aggregate POIs) you'll see a group where charge weights (say 68, 68.5, 69) all essentially group in the same spot at 600 yards. In that instance pick 68.5 because it's a stable node (will likely have the lowest ES) and there's 0.5gr leeway on either side. You'll be amazed. Sometimes, you find a node that will group 1/2 MOA over 0.6-1gr of powder. The middle of that is going to be rock solid in pretty much every condition.

If you choose the charge weight at a point where you have an increase in velocity that's an unstable area on the pressure/velocity curve.

A stiffer stock that free floats the barrel and has pillars installed (or an aluminum bedding block or mini chassis or a full chassis) and is bedded will help, especially at 100. That's the basis for an accurate rifle and is a must for getting reliable information from what you see downrange. But beyond that the muzzle velocity variation will rear its ugly head.