Black Hiils 77gr TMK velocity

[ElPollo]

I’d appreciate if y’all would look at this and give me your thoughts on what would cause this.

I recently got a Tikka 223 cut to 18” and threaded for my can and took it to the range to sight in and get some chrono data. The gun shot well but I got some weird chrono data that doesn’t make sense. I shot three 10-round strings over about an hour and averaged each string. I only got 6 valid velocity estimate out of the last string (errors and forgetting to write them down). All shots were from a single 50-round box of Black Hills 5.56 77 gr TMK. The gun probably had 200-250 rounds through it prior to that and had not been cleaned. I shot all rounds over a Caldwell chrono. Temp when I started was around 55 and it was around 64 when I finished. Otherwise, no significant change in environmental conditions. The ammo was kept in the house overnight at around 68 degrees.

String 1– avg 2847 fps, SD 16.9
String 2—avg 2763, SD 49.4
String 3–avg 2672, SD 33.0
Overall—avg 2774, SD 75.6



The raw data had a pretty significant pattern of declining velocity that didn’t make sense to me. See the attached picture. The first 10 were pretty stable and about where I expected them to be, but from there on velocity started declining significantly. I was shooting at 100 off a bench. All groups were in the 1.2-1.3” range and there was no significant POI shift.

Is there anything environmental or gun-related that might cause this? Has anyone else seen high variability like this in Black Hills ammo? I intend to go run this again, but it’s spring in the SW and yesterday may have been the only calm day to sight in a rifle for the next 3 months.

Any thoughts will be appreciated.

 

[Pickettpuncher]

How’s the batteries in the Caldwell. Also, clouds, none or mixed?

 

[ElPollo]

Battery was new maybe 2-3 uses ago. No clouds.

 

[ElPollo]

Just to be clear, I am not saying Black Hills is bad stuff. This is a sample of one occasion with one box of ammo. It just followed a strange pattern that made me curious.

 

[Pickettpuncher]

I’ve never used it, but had a Caldwell at one point and the clouds, and shade would do funny things sometimes.

 

[ElPollo]

I’m starting to think you may be right about the battery in the chrono. I was struggling to get it to read for the last few shots.

 

[bigunit]

I always had trouble with my chrono chronograph on sunny days. If the sun wasn't directly over top of the chrony I would get funny numbers. Always worked fine on overcast days. The garmin xero fixed it. I would bet you're getting way more consistent velocity than what it's telling you.

 

[ElPollo]

I think my chrono battery was the issue. I shot a few more rounds out of the same box today and got consistent results with an average of 2754 fps out of an 18” barrel with an AB Raptor 8-stack. The SD was about 17 fps. This will get me about 475 yards with a MV of 1800. Note to self, just change the battery when you want to get good MV data. It’s cheaper than ammo.

 

[Matt5266]

I've noticed battery type can matter too. Only use quality batteries. As others said as clouds move over or even wind changes can alter the MV with these.

 

[lanruc]

Yeah, can’t be the Black Hills. If you need to confirm chrono issues, just shoot a string of another manufacturer ammo and you should get a similar unexpected variation in velocities.