Confused by results of ladder testing

D

danager

Regular
Rating - 100%
19   0   0
Location
St Albert Alberta
Hello,

I have owned my rifle for a year now, and I began to reload last month. It took a while to get all the tools and components together, providing me lots of time to read and learn. I was at the range this morning, with 8 different charge weights. I was hoping to determine the best load for my rifle, I left confused by the results.

Here are some of the details:
Remington 700 SPS Tac AAC-SD .308
Loaded once fired (in this rifle) Remington brass.
Sierra Match King 155gr HPBT
Federal large rifle primers
Hodgdon 4895 (43.5gr - 47gr)
2.92" - bullet is resting on the lands
plan to shoot 200-300 metres, only hunting paper
shooting from a bipod, supported/blocked in by sandbags

The results were not very helpful, and confusing because they grouped together. In fact, over the 8 charge weights, from 200 metres, I had just over 2" difference. I could not expect this if I tried...

In terms of checking for signs of high pressure, although I could see a slight variation from the 43.5gr to the 47gr, everything looked good. Towards the top, the bolt required a little more effort to lift, nothing concerning though.

So does this mean I can load anywhere in this range, and expect consistent results? What are your thoughts?
 
I've got a 700 in 30-06 and tried ladder testing like you did and, like you, wound up confused. What I did was load 5 rounds at each of my charge weights and shoot groups. One charge weight was much tighter shooting than the others. I suppose you could try shooting your ladder at 200 though.
 
Danager; back that sh!t up to at least 300 yards. I've been through the same thing. The way my range is set up, I have a target board at 264 yards (any further would have crested the hill used as a backstop) and the overall spread I would get through a ladder at that distance would be less than 4" - not the easiest to decipher! Several members here made suggestions that I test further out and yes, big difference and much easier to see each node. I have another board at 618 yards and when I shoot a ladder there, I need pretty much the full 4' height of the 1/2 sheet of plywood but the node clusters are so clear, it's not even funny!

Now, you don't need to go quite that far and you should have a relatively calm day but you really need to get out a bit more. As soon as you do, you'll see what I mean. Then you can load up group series and shoot them at closer range.

A lot of great help and coaching when I was trying to wrap my head around ladders in this thread:
http://www.canadiangunnutz.com/foru...tation-please?highlight=Ladder+interpretation

Good luck!
Rooster
 
Did you fire one shot of each of your eight charges, or several?

If you fired several shots of each group, how big were they?

I think you are saying that you saw no more than a 2" difference in the point of impact (centre of each group) in all eight charge weights?

If you see a difference in POI as your charge weight changes, that's a "bad" thing, though not an insurmountably bad thing - the purpose of doing a ladder test is to determine if these effects exist in your rifle/ammo combo, and if so, how to best deal with it. The ideal result is that there is little or no shift in POI as your charge weight changes - this is not a *failure* of ladder testing, rather, it is the most highly desired result!

BTW a comment on your charge weights, they range from completely modest and sensible (43.5 H4895) to what I would expect would be a much-too-hot load in my .308 rifle (47 H4895) - that doesn't mean that it's unsafe in yours, but it would be worth paying extra close attention to all the pressure signs (chrono'd velocity, primer appearance, primer pocket looseness) that you have available to you. A stick bolt lift is only one pressure sign, and while worth paying attention to, reasonably-easy-bolt-lift doesn't assure you that your pressure is reasonable.

I haven't shot the new Sierra 155 (part number 2156 on the box) very much but a commercial reloader tells me that they (#2156s) shoot well with lots of jump (meaning about .050"; he said that sometime .030" gives distinctly poorer results). Something you might try, if your touching-the-lands ammo is not grouping to your satisfaction or if you have the time and inclination to try something else.
 
I'm confused about your confusion. Rnbra asked a good question. Did you shoot one shot each of the different charge weights? That will tell you very little.

I always load at least 5 of each charge weight, and shoot each load at a different target. I am looking for group size for each load, pressure signs for each, and velocity (I shoot all tests over a chronograph). I want the most accurate load I can get with no signs of pressure at workable velocities. I don't care where each load prints on paper relative to any other load because I can sight for accuracy any time with any load.

If I could detect a difference in bolt lift effort with a "hot load" I would consider that a serious sign the load is too hot. Velocity would help verify that assumption, and I would examine the cases of that load very carefully for other signs of pressure.
 
I'm with ya on the bolt lift effort, rral22. In my experience, hard bolt lift has come on rather suddenly - well after other inital pressure signs can be observed. And yes, chronographs are helpful, as far as I'm concerned because velocity spreads tend to increase and get all "wonky" when you're out of that node pocket. Again - my experience.

Rooster
 
Thanks for the responses, I do have some work to do here.

I shot 3 round groups the first time, and all I managed to do was completely remove a 2" x 4" section of the target...
I will look at the fired rounds again, however, I can say that nothing stands out as an obvious over-pressure.
I will ask around for a chronograph, I can't justify this expense (I think I have said this before and been proven wrong).
 
danager said:
I shot 3 round groups the first time, and all I managed to do was completely remove a 2" x 4" section of the target...
Click to expand...
What you have so far: 24 rounds fired into a group 1MOA wide by 2MOA high, over a 43.5-47.0 grain charge weight interval. That's a promising start.

In my opinion: if you were interested in shooting well beyond 600 yards, it *might* be worthwhile doing an extensive ladder test. Since you're not going to be shooting beyond 300m, my take is that:
- there's no value to be had from ladder testing
- you should try a few different load combinations; if something looks good, verify it by re-testing; if it's still good, that's your load.

As to different load combinations for you to test, I'd suggest you load up ten rounds with 44.0, ten rounds with 45.0 and ten rounds with 46.0 H4895, with the same components as your first run, with your bullet seated the same way (touching the lands) - so a total of 30 rounds for you to test. If you are up for it, also load the same spread of charge weights but with the bullet .050" off the lands (so another 30 rounds to test).

Take your time testing them, shoot carefully during your testing, and be as honest as possible with yourself in interpreting your data. Take your time, let your rifle cool, let your mind relax and cool too - you need to do your best to fire every shot well, or to realize that you've made a mistake firing a shot (so you can discount it from your analysis). It doesn't matter if you do this testing at 100 or at 200, either will give you valid results; use whatever is most convenient and most conducive to you getting good shots away.

It may well be that you see no meaningful difference in group size between 44.0, 45.0 and 46.0 grains of powder. This isn't a "bug", it's a completely reasonable and plausible outcome - it doesn't mean you've done anything wrong in your testing. You might also see or not see a difference in group size with your jumped-vs-jammed bullets; again, that's OK.
 
For what it's worth, I'm fairly new to this, and started much like you (different rifles/calibers) with results that weren't bad, but that weren't telling me much.

I started loading/shooting 10-shot groups and that gave me a better idea about what was going on. I don't think that 3 shot groups was enough information to build trends with (for me).
 
I have had success with ladder tests that involve shooting 2 rounds at .3gr increments, either at one target if you can keep track of which bullets make which holes, or two targets. Shooting groups at different targets with increasing charges isn't a ladder test per say, because you want to compare the vertical drop between charges, not how they group. Do this at 300m minimum, and look for the holes that cluster together vertically. Using a chrony if you have one can also be helpful.

Once I find a range of charges that look promising, I'll shoot a series of 5 rounds groups within the range and compare the velocity spread and group size.
 
I'm confused...why are you guys shooting "ladder tests" using 3 shot groups of the same charge? That's not how ladder tests are shot. At least not how Creighton Audette devised it. The "Ladder Test" allows you to determine which "nodes" your rifle/component combination likes while at the same time reduce the number of rounds fired.
A ladder test, as I have used it, begins with 20 rounds (preferable). Each loaded to a different charge. Starting with Min and ranging to Max in .5gn increments. You fire these rounds, slowly, taking your time, using the same point of aim each time without adjustments to your equipment. Each round should be fired over a chrono and each velocity recorded. Each round should also be recorded on the target (this makes allowing the rifle barrel to cool easier since you walk out to the target each time and number the hole). When you are done, you will have 20 holes in your target. SOME of those holes will have actually "grouped" more closely than the others (normally, you will find 2 groups or nodes of 3 rounds that will be close together), these are the "sweet spots'" so many talk about. You can now extrapolate from your data, what range of charges you want to work in. I have found that the two nodes correspond generally to very near Max and about 200FPS below that. Once you have this data..i.e., two groups in the 44gn area and the 47gn area, you can break this down further by breaking those nodes of rounds with a (let's say a 2gn spread) into another ladder test.

In our imaginary case, let's say you had 6 of the 20 rounds group well. Normally, in my experience, that would be near max and then a bit lower. I would pick the one I wanted to use for whatever reason I needed. If I was trying to wring out EVERY single bit of accuracy I could, then I would then take one of those two nodes (let's say 43, 43.5, 44 and 46, 46.5, 47) and break them down further (42.5, 42.75, 43, 43.25, 43.5, 43.75, 44, 44.25, 44.5) and shoot another ladder test to see which of the 9 grouped. I have now fired less than 30 rounds and know exactly which "node" my rifle likes. I can now make up as many rounds as I have components for.

The way you guys are doing it makes no sense. You are shooting groups that are landing in the same area and are confused because you can't extrapolate your data? What data? You are shooting it away.

OP. Shoot your 8 rounds (not really enough to be conclusive, I would use weights in .3 increments giving me 13 shots, but). They will probably still land in your 2" x 4" area, but, I guarantee you, you will be able to pick out 2 nodes if you mark each shot on your target after you fire it. And you SHOULD see a difference in POI as the charge weights change, basic physics, if the round is traveling faster, it will hit higher on the target. If it is a different weight, won't agree with your barrel harmonics and will fly off. If there was no change in POI when the charge weights increases, the what would be the sense in loading more powder to get velocities and flatter trajectories beyond 2000fps?
 
Here is a ladder test I did this afternoon at 300yds.

DSC00583_zpse7d1ac01.jpg


The F/S (fouler/sighters) were 29.0gr of N140. The test weights went from 29.1 for shots 1 and 2, to 30.5gr for shots 14 and 15, in .2gr increments. My aiming point was the same for all shots. I adjusted my scope right after the F/S shots.
I also shot this over a chrony to give some idea of velocity and ES.
You can clearly see the PoI moving upwards as the charge increased, and the cluster of shots 11 thru 14. The F/S and shots 1 and 2 may also be a node I just hit the top of.
I will now shoot some 5 round groups from 28.9 to 30.2gr at 100yds and compare the group size and ES.
In less then 20 shots, I know where 1 node is, and maybe another.

I also shot another ladder with my custom .308, and it looked nothing like this. Some rifles just won't shoot a useable ladder.
 
Wildcat and Alpheus, thanks for explaining Audette's ladder. I kept reading this thread thinking someone needs to explain that the OP was trying to do Audettes and not just a ladder of successive increasind charges. Minimum distance for a scoped bolt gun is 300yds. The last 2 posts especially the picture explain the method perfectly.

Often referred to as a ladder test is 4 to 5 groups of 3-5 rounds each of incrementally higher charges with each group at a different point of aim so they can be analyzed individually. There are many variations of this. Audettes is a fairly stringent system where variation from the method will skew the results.

Willy
 
You must log in or register to reply here.
Back
Top Bottom