Heat and velocity puzzle (140g absolute hammers and 180 ELDM)

[JakeC]

Do weird things happen when it gets REALLY hot? Or am I undervaluing other variables?

I shot a bullet one day at 3400 fps. 140g absolute hammer with RL 16. Two weeks later the same load in VERY similar conditions shot 3300 fps. A different load in the same rifle shot 2750 the first day and 2680-2715 the second, very different ES than prior. Chronograph was working correctly. There was a slight difference in shade intensity and some difference in the roughness of the ride on the way, but ambient temps were close. I thought. The ammo could have been a max of 10 degrees warmer the first day. Barrel conditions were basically the same. No shots fired in the interim.

First day was real hot. Windy, 100 or better, but then cooled off with oncoming rain during the testing. Chrono at thirteen feet. Second day was also hotter than forecast, conditions were pretty still and about 92-95 with little wind and increasing temperatures. Chrono at 8 feet.

Load B (eld/h4831) had been loaded for a long time, not annealed, and done when I knew less in general. so maybe there was some neck weld soaking up some pressure or something else. It was accurate at 500. Beer can accurate. But slower than before.

Load A (hammer/rl16) had been annealed, loaded, crimped, pulled, resized, reloaded, and recrimped with the same bullets and same powder. And it was 100fps or more different.

Is there a tipping point where the effect of temperature starts to snowball even on temp stable powders? Does shaking ammo because you took the wrong trail and had to jump dunes to get out have an effect? Am I missing something else? Can a cheap digital scale be THAT far off week to week but still produce SD of 5-8 fps? I thought I was going to finalize my rifle loads before I started bowhunting but if I can suddenly add an entire grain or more before pressure then I'm starting over, which is annoying.

Anyone else seen this kind of mess before? Thanks for any thoughts.

 

[WeiserBucks]

It's your chronograph.

 

[JakeC]

It's your chronograph.

Could be, but DOPE was accurate at 490 yards. And the pressure effects were different in general. Could it have been accurate either time?

Can't rule it out yet, just saying why I didn't think it was the machine.

 

[WeiserBucks]

Could be, but DOPE was accurate at 490 yards.

If you're DOPE was repeatable and accurate at 490 then nothing changed and your chronograph is giving you bogus data.

 

[JakeC]

Should have clarified, Dope was accurate when I tested it the second day, didn't test at 490 on the first day with the "faster" ammo. You're still probably right.

 

[HSmithTX]

If you are using a sky screen type of chrono you need to know a bit of chrono-fu to get consistent readings in differing light conditions. When I was using one a lot I primarily used a IPSC no-shoot (white cardboard) on top of the screens in most light conditions. If it was really bright out I would flip the target and let the screens look up at the plain brown cardboard. The only one I used that didn't need regular manipulation was an Oehler 35P, it was quite forgiving but many times more money than the typical chrono people use. Regardless I would test with a known load before chrono'ing anything for score, sometimes brown and sometimes white worked best but I think I could count the number of times I saw them work well with no cover without taking my shoes off or my zipper down and have a couple fingers to spare....

 

[Old Rooster]

I have seen IMR4350 change velocities from winter to hot summers but not like your experiencing.
Thats why I am saving my pennies for a Lab Radar for next year.I am tired of cheap chrony's I can't really depend on.
I found a spider making a home in my Chrony and webs were in the optical glass that picks up the bullet and giving me errant numbers.
I cleaned house but they could come back.
Let me know what you find

 

[JakeC]

If you are using a sky screen type of chrono you need to know a bit of chrono-fu to get consistent readings in differing light conditions. When I was using one a lot I primarily used a IPSC no-shoot (white cardboard) on top of the screens in most light conditions. If it was really bright out I would flip the target and let the screens look up at the plain brown cardboard. The only one I used that didn't need regular manipulation was an Oehler 35P, it was quite forgiving but many times more money than the typical chrono people use. Regardless I would test with a known load before chrono'ing anything for score, sometimes brown and sometimes white worked best but I think I could count the number of times I saw them work well with no cover without taking my shoes off or my zipper down and have a couple fingers to spare....

Makes sense.

 

[JakeC]

So if I'm hearing you guys correctly they can give consistent readings within one given day and then give consistent readings another day, but one or both sets of numbers is BS?

Say for example I got the same ES/sd both days but they were dozens of fps apart that would be normal shenanigans for a cheap chrono? I always assumed that it was a lot more wild and noticeable, like jumps between shots and no reads and things like that. That stinks.

 

[WeiserBucks]

They'll give different readings for 793 different reasons, sometimes huge differences, sometimes very small.

 

[HSmithTX]

Get your lighting conditions under control and most of your problems are gone. Remember, this was THE technology we had to use for a long long time and it worked for a long long time. I used to check 'calibration' on mine with a known load, this was a load that I had run across MANY different chronographs so I knew what it should be and the ES of probably 150 rounds chrono'd was stupid low. I would set up and shoot the known load and 9 out of 10 times I was cooking with gas after that one shot based on the educated guesses I made during set up and I knew I was good to go because I saw exactly what I should see. If I didn't see what I needed I would flip the cardboard and shoot another one. Depending on where the sun was etc there were some occasions where I put it away to chrono later or another day because the light was just not going to let me get good data. The other thing you need to do is set up EXACTLY the same distance away. The one I used most had a corded display and that cord was exactly how far away I shot from every time. Additionally for distance shot from, further is a better option than closer especially with rifles, you don't need gas/ash/whatever going across the screens potentially messing up readings. I sold the last one I had and bought a magnetospeed, honestly I miss it because I can't do/don't trust accuracy testing with the magneto hanging off the barrel. I didn't have that problem with the optical unit. I will buy a doppler unit sometime soon but it's a lot of money to solve a problem I didn't have a few years ago.......

 

[JakeC]

Get your lighting conditions under control and most of your problems are gone. Remember, this was THE technology we had to use for a long long time and it worked for a long long time.

I didn't have that problem with the optical unit. I will buy a doppler unit sometime soon but it's a lot of money to solve a problem I didn't have a few years ago.......

I hear ya, but I'm frustrated, lol. I bought this thing from a friend thinking how bad can it be? By this point I'm at least 50 bucks into a load I can't do anything with yet and I'm getting nothing but confusion and more wasted time/money from trying to read my established loads. Plus the money I paid for the unit. A magnetospeed would have been halfway paid for by now, ha. I think I'm just going to buy one and worry about accuracy afterward, which is cake with my gun anyway. At least I know I don't have a 150 fps ES like it told me.

I thought I had the patience to learn to use it but I got completely tricked by using it the first time and having it seem great.

 

[LRNut]

I think you are worrying too much. If that one load is beer can accurate at 500, who cares? Shoot at longer distances…any horizontal stringing?

I shot my 910 yard gong yesterday. I shoot one shot a day at that gong. Normal velocity is 2850 (285 ELD). Held a minute left for very slight wind. Velocity on LabRadar said 2080. I hit left 5" - elevation was perfect. LabRadar must have been impacted by muzzle blast from my brake. Happens every once in a while. My next shot a few hours later at the 760 yard gong was right on the money.

 

[1yotedog]

Do weird things happen when it gets REALLY hot? Or am I undervaluing other variables?

I shot a bullet one day at 3400 fps. 140g absolute hammer with RL 16. Two weeks later the same load in VERY similar conditions shot 3300 fps. A different load in the same rifle shot 2750 the first day and 2680-2715 the second, very different ES than prior. Chronograph was working correctly. There was a slight difference in shade intensity and some difference in the roughness of the ride on the way, but ambient temps were close. I thought. The ammo could have been a max of 10 degrees warmer the first day. Barrel conditions were basically the same. No shots fired in the interim.

First day was real hot. Windy, 100 or better, but then cooled off with oncoming rain during the testing. Chrono at thirteen feet. Second day was also hotter than forecast, conditions were pretty still and about 92-95 with little wind and increasing temperatures. Chrono at 8 feet.

Load B (eld/h4831) had been loaded for a long time, not annealed, and done when I knew less in general. so maybe there was some neck weld soaking up some pressure or something else. It was accurate at 500. Beer can accurate. But slower than before.

Load A (hammer/rl16) had been annealed, loaded, crimped, pulled, resized, reloaded, and recrimped with the same bullets and same powder. And it was 100fps or more different.

Is there a tipping point where the effect of temperature starts to snowball even on temp stable powders? Does shaking ammo because you took the wrong trail and had to jump dunes to get out have an effect? Am I missing something else? Can a cheap digital scale be THAT far off week to week but still produce SD of 5-8 fps? I thought I was going to finalize my rifle loads before I started bowhunting but if I can suddenly add an entire grain or more before pressure then I'm starting over, which is annoying.

Anyone else seen this kind of mess before? Thanks for any thoughts.

As others have stated, could be chrono related but don't discount your initial suspicion….. temp. This past spring I worked up a CFE/51 gr Absolute load for my sporter weight CZ 223. Getting into the warmer summer months my Labradar has confirmed that speeds jump by 100fps when temp is over 75F and groups fell apart. Come back early in the cool of morning and the load returns to normal. Now trying to find the time to get a load that works in the summer. Will that load still work when it gets cold again? Only time will tell.