New to Chrono Testing- What does this tell me?

[Landshark9025]

Hi all, fairly new to reloading in general and casting specifically. Have done about 1,000 cast boolits in Lee 358-140 SWC. Was using the 45-45-10 Alox lube and that was ok, but was still too smokey in my revolvers. For my B-day, I got a Caldwell Crono and some Bayou Bullet coating. Once I figured out how to make the chrono work with my phone, I loaded up a bunch of boolits. I did 20 each of 3.0, 3.3, 3.6 and 3.9g Bullseye. 10 for the chrono and 10 for accuracy. What it looks like to me is the higher the charge, the more consistent and accurate, precise they became. I will say the accuracy of the 3.9g is higher than what I experienced with the 3.9g of Alox in the past- way better. But the consistency of readings on the Alox group was pretty impressive to me (even though I only had 8). Would think I would be able to get better groupings with a SD of 5. I am thinking that is due to me being more consistent with the coating? These were the first batches of Bayou I have done and they weren't all the exact same shade of gold, sorry to say. All were coated twice, then sized. Sorry, no pics of the targets.

What else can I learn from using a Chrono?

Link to spreadsheet: https://docs.google.com/spreadsheets/d/1wa83qWh378w-nXgYfqoMpBm9uK89n8z6WPsGC6JkE6A/edit?usp=sharing
115613

Thanks,

[Shiloh]

The higher powder charge with the related higher pressure gives a more complete burn. Is there less unburnt powder residue in the barrel as well??


Shiloh

[leadman]

I don't pay too much attention to the extreme spread, mostly just group size and average velocity.

It is very easy to cause a variance in the velocity of a shot by the way you grip to gun. I usually pick a load from my initial tests and load up some more of the same and shoot it again just to see if it holds up to my criteria. I may pick a load that shoots to the sights of a fixed sight gun even though it is not the top choice for accuracy.

[Landshark9025]

Thanks, Shiloh. I did not clean the gun between strings, but I can say that when I got home, a dry patch on a jag picked up nothing. It was just creased. I did inspect the barrel in between strings and nothing looked odd or different.


The higher powder charge with the related higher pressure gives a more complete burn. Is there less unburnt powder residue in the barrel as well??


Shiloh

[Scharfschuetze]

It seems counter intuitive that the most consistent load over a chronograph is sometimes less accurate than a load with a greater extreme spread or standard deviation. Still, for the most part, my best accuracy comes from loads that chronograph well, particularly in rifles and especially at ranges over 300 yards and revolvers over 70 yards or so. Each firearm is a law unto itself so testing is de rigueur and your new chronograph will certainly aid you in the endevour.

What I generally use the chrono for is to find each powder and bullet's sweet spot for the best return in velocity for the amount of powder used. I will usually find my best accuracy near that point as that is where the powder is burning most efficiently for case size, bore diameter and boolit weight. Depending on the calibre and boolit weight as well as my velocity goal for a given use (plinking, competition, hunting, etc.), I'll select the appropriate powder and the chrono confirms or refines my initial prediction or assumption. You can make a visual graph (powder weight-velocity-accuracy) easily and it will show you what your gun prefers for any given combination of components.

By the way, your results for that Model 66 using your components seem pretty much spot on. Just got 'a love S&W revolvers.

[HeavyMetal]

Group size determines load acceptance, SD is nice to have but won't tell you if the load actually shoots, only the target can do that.

Looking at your data all your SD are in line with good loads just find the one that shoots best.

I'd be more concerned with velocity, both to high and to low, as these will give you an idea of where you might be pressure wise.

I have never been one to either under load or over load a particular caliber, to many want to make a 25 auto into a 44 mag or worse make a 44 mag into a 22 rimfire, LOL!

A Chony can give you great info and you can have a lot of fun using it just don't get caught up in the tech side of it, numbers can help a lot but the bottom line is the target tells it all!

[fecmech]

The dispersion you are seeing in group size at 10 yds has nothing to do with the velocity of those loads it's pretty much all in your grip. I have seen factory target wadcutter loads with extreme spreads of 50-60 fps and 2-2.5" ten shot groups at 5 times the distance you are shooting. In general good accurate pistol loads have good even ballistics(up to 60 fps extreme spread and sd's in the teens) but until you pass 50-75 yds e/s doesn't matter much. The chronograph is nice in that it tells you your velocity but the target tells you the accuracy.

[Larry Gibson]

The data (minus the group size) tells me I would load up 30 rounds each of the 3.3, 3.6 and 3.9 gr loads (all with the same lube) and test them for accuracy shooting 3 10 shot groups each at a minimum of 25 yards, preferably 50 yards. Then with the best loa I would load 30 more of that with the same lube and then 30 more rounds of the same load but with the other lube on it and test again. At the end of that you should have a pretty concrete idea of the best load.

Larry Gibson

[shooter93]

I watch extreme spread more than anything...depending. SD takes way more rounds than a few to give a true idea I believe. If the gun is for long range shooting then extreme spread means a lot. It can drop you right out of the 10 ring in a real hurry if everything else is right. For closer ranges and most handgun or hunting rifle loads neither is super critical unless way off.

[Doc Highwall]

The thing to remember with rifles that extreme spread and standard deviation do not take into account barrel vibrations.

As was said in post #6 "Group size determines load acceptance, SD is nice to have but won't tell you if the load actually shoots, only the target can do that."

The target never lies and only tells the truth, either the load is good or it is bad. The more targets and the larger the number of shots the group contains tells you if it is a good load or not.

My initial testing is with 5 shot groups that then turn into 10 shot groups and eventually 25 shot groups. Most of the targets require 20 shots for record and 2 sighter shots so two 25 shot groups will empty the 50 round MTM boxes.

[country gent]

Another little trick is to pick up a spring piston air rifle and a large batch of the same pellets. CChrono graph this at the start of each session to see if it is producing basically the same results as the times before. Ussually a spring piston air rifle is pretty consistant so if you establish a 700fps average for 10 shots over several diffrent sessions then an 800fps average the next time set up what is diffrent, temp, barometric pressures, humidity, light, angles, or wind? WIth out a constant to prove accuracy there is a question there.

[MtGun44]

SD is not very meaningful for samples under 50 or so, and even then - does not actually
correlate to accuracy very significantly. Accurate loads OFTEN have a low extreme spread,
but not necessarily. For example Unique in .45 ACP has high velocity variation under 200
gr boolits - 100 fps extreme spread is not unheard of for 10 shots. BUT, these high variation
loads are typically quite accurate. How and why - wish I knew, I just have the raw data, not
good theory of why it is that way, let alone validation of the theory.

Larry is right - multiple 10 shot groups will tell the tale, it takes a LOT of shots to REALLY tell if
one load is more accurate than another. One or two groups can be VERY misleading. Ultimately,
we usually care little about velocity, and a lot about accuracy - and they don't necessarily go
together as it would seem logicly.

Bill

[Landshark9025]

Thanks, guys. Really appreciate it. It looks like some of you validated my previous "practice/testing", where I was putting a 7" target at 15 yards or 20 yards with the goal of getting an entire box inside the 6" ring. That was done standing, two handed, DAO. 15 yards is not bad, 20 is about my limit in terms of eyesight. I can focus on the front site, then "there's a target back there, somewhere". Not even going to pretend I can get the sights lined up on the center of a 7" target at 50 yards.

I do have a couple followup questions if you please:
Scharfschuetze: You said
"What I generally use the chrono for is to find each powder and bullet's sweet spot for the best return in velocity for the amount of powder used." What does that look like? And do you have any examples of that graph you mentioned?

HeavyMetal: Your comment
"I'd be more concerned with velocity, both to high and to low, as these will give you an idea of where you might be pressure wise." is exactly one of the things I am trying to learn here. I am pretty judicious about staying between the min and max published loads (on 223 generally about .5g below max), but how does one interpret chrono data into pressure? I would imagine it isn't exact at all, but an educated guess. The reason I am curious here is I recently loaded some 223 and they were about 300 FPS below published velocity (likely due to barrel length), and the max load exhibited no pressure signs at all. Again- I am super conservative and will likely remain that way, but when I get conflicting info from published sources, I am hoping the chrono can assist.

From 3.0 to 3.3 I picked up 43fps on my average.
From 3.3 to 3.6 I picked up 59fps- much bigger jump.
From 3.6 to 3.9 I picked up 47fps - smaller gain. Would this indicate I might be hitting the law of diminishing returns? Beginning to leave powder unburnt because of the 4" bbl? Kind of a moot point as that is max +P load for 38 SPL, but would like to know.

Thanks again, I know some of this is overthinking it for pistol- especially when there aren't that many options to play with in terms of charge weights like there is in rifle. Part of this is to cut my teeth on the chrono, how to interpret the data, what may be useful, etc. with loads that are easy and cheap to mess with. Plus, 38spl in a 357 give me margin for error.