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Help with chrono spread data - is it my reloads or the chrono?

Len5E1

Private
Minuteman
May 3, 2018
82
14
Hello everyone,

Long time reloader but never owned a chrono until I decided to start loading subsonics recently. I tried doing some research so I apologize if my questions are basic. Chrono used is the caldwell G2 that sits upside down and has LED lights.

So, I went out today and tested some 223 and 300blk handloads. I did some 10 shot strings and 5 shot strings with various weights and was very surprised at some of the random FPS spreads I saw. In general my strings would be within reason ~10-50 fps then all of a sudden I would get a shot that was 100 to even 200 fps off in a string. I'm pretty sure my loads were consistent as I took my time and hand weighed each and every round, trimmed to same size seat depth etc. After seeing this I decided to try a 10 shot string of factory 223 and saw 9 shots with reasonable spread ~3000 then right in the middle of the 10 shots I got a shot that registered 2500 fps which really makes me think its the chrono or placement of the chrono.

I had the chrono maybe 4 feet away from the muzzle but it was on rough grassy ground and might have been at a tiny bit of an angle. I'm not sure if that affects it or not. I'll post 2-3 strings below for reference but I'm looking for any advice possible as I can't properly analyze my handloads until I can rule out it being the chrono or not. If it does turn out to be the handloads then at least I know my data is correct and can work from there.

Set 1: H335 25 grains. plain jane 55 grain hornady fmj bt
2759, 2937, 2640, 2829, 2704, 2826, 2737, 2826, 2917, 2921 - This was probably the worst spread of the day at 297!! (other than the factory ammo being over 500 cause of one shot)

Set 2: H335 25.6 grains. plain jane 55 grain hornady fmj bt - This set had an average spread close to 2800 but 2 random bullets were almost 3k which I just don't understand
2804, 2999, 2953, 2823, 2813, 2764, 2767, 2832, 2804, 2818

Set 3: Varget 26.2 grains, 55 grain fmj
2883, 2909, 2888, 2882, 2865, 2932, 2878, 2827, 2859, 2868 (Spread 105 SD 28.36)

My 300blk spreads looked a LOT better so maybe it is just my 223 loads and not the chrono but I still find it strange seeing a 500 fps dip in factory ammo and the huge spread I was seeing. Let me know your thoughts.
 
I've never used that type of chrono before but I'd agree it's likely an equipment issue one way or the other.
 
I occasionally get readings that seem way off or don't even register but don't have anyway to determine what the cause is.

Since I'm using 2 different chronographs with the traditional skyscreens light conditions are a big factor.

My 2 chronographs also show different results all other things equal. One shows results about 100 fps faster. As far as I know there is no way to accurately calibrate either one of them.

One thing I've noticed over the years is the loads that have the best chrono numbers are not the loads that shoot the best.
 
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