Finally invested in a Athlon Chrono to see what my 6mm creedmoor loads was doing. The 100 and 200 yard groups are fairley good but I wanted more info before I took it out any further The ES of 60.4 and SD of 17.4 doesn't look good for long range. This was 8 shots on a clean barrel should I fire 10 fouling shots before checking the velocity? Should I fire atleast 20 rounds to have a large example to go by? Should I just shoot some groups at longer ranges and see how it does? The brass is once fired brass that has been sized and trimmed but not annealed can I anneal it after its been sized to improve neck tension consistency?
6mm creedmoor
Hornady Brass
87 grain vmax
44 grain H4350
.025 off the lands
17 fps SD, 60 fps ES is pretty much on par with commercial match ammo. You're off to a strong start. Cutting it in half is reasonably straight forward. If you're shooting under 600 yards, accuracy will be dominated by the precision of the rifle and ammo. Groups won't track 1:1 with the velocity stats, but there is a lot of overlap in the range where 5 shot ES decrease from 60 to 30 fps. Put another way, it'll be easier to find a load that is persistently accurate with 30 fps of ES than 60.
On fouling, it'll depend on the barrel and your cleaning process. Factory barrels tend to take more than match barrels. I use 3 shots for match, 5 for factory. These are the first 5 for a very soft 300prc from a factory RPR barrel somewhat past its prime but not done. Looks like 3 shots got it done.
Use more than just the stats to develop a sense of what's going on other than at the loading bench.
The problem with longer strings is more things are mixed into those stats. This is the skinny factory barrel getting tired of my 10 shot string nonsense.
You can break longer strings into shorter ones, but there will still be things influencing the stats that you can't change at the loading bench. That's either a problem or a feature depending on how you look at it.
Foulers, not good for much. Just get them done. They might still give a decent group at 100 yards.
First string at 1700 yards. Ammo case temp 52 F.
Second string. Ammo case temp 59 F.
Last 5 in the box. Ammo case temp 73 F.
I measure case temp with an infrared thermometer by laying out 5-10 of them in the top of the box.
None of this is demonstrated conclusively in 1 trip. Modern chronos let you record every shot you take. If you see it over and over again, that's a clue. I may not even have attributed the effects to the right things, but I know the first few shots out of a freshly cleaned barrel will have low velocities and by shot 9 or 10, the velocities will be less unpredictable.
Sooo, don't assume longer strings are a better representation of what works on the loading bench. Watch more than the stats, look at what happens in the strings. There is a lot of good information you'll learn to recognize.
Annealing is generally done before sizing. Over the first 3 or so firings, the neck work hardens and will spring back more. Both the neck tension and shoulder bump will be affected. Annealing removes the die adjusting overheads.
Reducing the velocity spread can be frustrating. Until you find the largest problem, steps that will give solid improvements at lower spreads won't make a noticeable difference. If there is more than one large problem, even reducing one of them may not show up in the stats until you find the others.
The way I go about it is using my current best practices for brass prep, I'll pick a primer based on case capacity then do pressure ladders with the first powder. If the powder gives good stats over a wide range of that pressure ladder, I'll use it. If it gives good stats but I run out of case capacity, I'll try the next faster powder. If the stats are less than desirable and there is still case capacity, I'll try the next slower powder.
0.025" jump is a good spot to do initial load development from. It's long enough that individual bullet differences in seating stem contact point to ogive won't change much when the round goes off. At that point, large changes in pressure have generally stopped with further increases so it'll be relatively insensitive to throat wear.
H4350 is generally a good place to start with large capacity 6s and heavy bullets. A fast QL model suggests you're demonstrating more common sense than most with pressure. With that 87 grain bullet, you might try loading a pressure ladder up with Varget to see what it does to the velocity spreads?
Your problem as a new chrono user is you'll need to define your brass prep best practices at the same time you're testing loads. If you want a couple entry points, I'd suggest switching from an expander ball to a mandrel and use real lube inside the neck. If you're using bushings, size at least 4 thou under final and use the mandrel to bring it to 2 thou under. Learn to seat a primer. Three steps should be felt. The primer moving down the pocket, anvil contact, cup contact. The seating should be fluid and continuous. Don't use a priming tool that requires a pickup tube. Find one that has enough leverage that you can seat 100 primers without fatigue but not so much you can't feel all 3 steps.
Racing 10 examples of your latest scheme against 10 examples of your current baseline is a helpful process. Maybe start with weight sorting brass. Use the 5 heaviest and 5 lightest as one set of 10, then 10 from the middle. Best case / worst case testing like that can make individual contributors pop out of the background.
That should keep you busy for a bit.
