first successful test of hand-loads with both labradar and pressure trace

[stagpanther]

It's been a bit of a bumpy road for me coming up to speed with both systems--and I've yet to explore the full potential of what the data actually reveals. It's already very interesting to see how even minute changes in powder charges can result in dramatic changes in the read-outs.

Here are the labradar and Pressure Trace read-outs from today's test of some 6mm creedmoor hand-loads I fired through an AR10 build using 103 eldx bullets and 44.1 grs. of superformance. Except for the one flier--this was the best grouping of the different charges I did--but labradar tagged it as also having one of the highest SD's of the charge weights I did. Might be my poor shooting technique--but charge weights of even .1 gr difference seemed to have dramatically different read-outs and significantly less accuracy. It's also occurred to me that 100 yds might be a bit close for the bullet to fully spin-stabilize--not sure about that.

 

[hounddawg]

what scale are you using ?

If it is a load cell based electronic it can have an error of .1 grains. In other words a reading of 40.1 grains could be anywhere between 40.0 and 40.2. The FX 120i scale is getting to be quite popular among the precision shooting crowd. Or you can just accurarize whatever beam scale you have on the shelf for free and get kernel of powder responsiveness to where you know every load is exact

When you find the right load the you can throw a charge that is .1 off in either direction and get the same point of impact. However to do that the test loads need to as close to a single kernel as possible to test accurately

Slipped a decimal there.

thanks for the catch, fixed

 

[ligonierbill]

Slipped a decimal there.

 

[stagpanther]

I always use a balance beam scale to do my hand-loads. Jim at RSI took at look at my results--and advised me--as I sorta expected--because of the thickness of the barrel between the gage and the case mouth--I wasn't going to get much in the way of "refinable" data. As I understand it, as the thickness of the barrel goes up--the over-all range of expansion goes down, making it harder to extrapolate granular detail accurately. That's the major difficulty in using these with AR's.

 

[DaleA]

Thanks for coming back and posting. This is a very interesting thread.

 

[stagpanther]

Let me be clear--on a scale of 1 to 10 I'm at about 1.75 on understanding what I'm doing--but I'll continue to study and refine as I go. Fortunately there are others who know this stuff a lot better than I do, this sorta drifts into engineer/fizzics territory--not my strongest suit.

 

[hounddawg]

just looking at the chrono data I can tell you that you have not found the right load yet. I have no idea of what pressure trace data is supposed to tell me except my gun might blow up in my face if I load any hotter.

Your groups will come together when your ES comes down. On that target what is troublesome is the vertical distance between the farthest right hand shot and the one in the bottom center. Way too high of an ES on that load.

I feel for you, I have fair but not great results from my .223 but on the other side of that coin I am happy with all my 260 loads.

 

[stagpanther]

I do dabble in wildcats which often have scant load and pressure data available--and even that data can be questionable. That's the main reason I got PT--so I guess you could say the "not blow up factor" is a reason--but PT can do much more than just show peak pressure; but a lot of that depends on getting an optimal strain gage location, which is tough to do on an AR because that area is often going to be under the barrel nut and/or the receiver extension collar.

I do have some other loads of this same bullet/powder combo that have much less ES and SD of this same combo but which did not show good groupings (could very well be my technique)--I may take a second look at those and see if the other charge weights next to them showed "a flattening" in results that might indicate a node.

 

[hounddawg]

I don't pay much attention to groups anymore when initially developing a load. Mirage, wind or just a little too much pressure with a thumb or cheek can screw up a 3 or 5 shot group. However if the velocities are close you know that the load has potential and it was the shooter that screwed up by either missing a wind or mirage call or just cheeking or thumbing a shot.

During my initial load testing I now just use 3 shot groups which are loaded as closely as I can possibly get them to the same weight for establishing velocity trends. Then I do 10 or 15 shot groups taking extensive notes regarding wind, mirage and shooting technique errors which give me a better overall pattern for analysis