Temperature vs Velocity - Gunpowder
- Thread starter todbartell
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Good idea.. maybe set it on low and fire shots a few minutes apart as it warms up. That'll show if there's any change. The internal circuit boards ( I think there's still such things??) will take longer than the outer case to warm up. It'd be hard to say just when they reach "normal temperature" for lack of a better term.
I did some reading on the topic of chronograph performance in cold weather over the last few days. One search result mentioned sensitivity to battery voltage. Not specifically the Labradar, but chronographs in general.
It'd be interesting to run two different chronographs in tandem.
I've got a velocity test to run on a new batch of H4350 in 6.5 CM loads. The chrono I use is a Competition Electronics Pro-Chrono Digital.
The numbers I've gotten from it in the past have been pretty accurate when fed into a ballistics app for drop at extended ranges out to 800m. I don't think it's as good as the Labradar, but it'll be a comparison at least.
I know what velocity I got last fall under warmer conditions with rounds loaded with the old powder. I'll run some of those first to see what shows up for velocity before trying the new powder.
I'll see if I get the same kind of results Todd did with the Labradar. It won't be that cold though.. I hope!
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So.. interesting day today. I wanted to do some velocity testing in colder weather to see if my results mirrored Todd's. Today's temperature was -6 C.
My usual 6.5 CM load is a 123 gr Match King over 42.5 gr H4350 with a CCI BR4 primer. It's been averaging 2815 fps with ambient temps between 5 and 25 C, though I haven't shot over the chronograph in a while.
I started using a new lot of powder recently and wanted to get a feel if it was the same as the old one performance-wise.
I normally clean after each shooting session with Mpro-7 gun cleaner before putting the rifle away, so each shooting session starts with at least one fouling shot.
Since I had the results of Todd's test in the back of my mind, and I was specifically looking for a velocity shift, I fired enough fouling/warming shots to be sure the barrel had stabilized. Seven of them to be exact.
The first shot was considerably slower than the rest, 100 fps slower. That seems to be the norm for this rifle. The second two shots were slightly slower than the average, then it settled in and became quite consistent.
Using rounds loaded with the old lot of H4350, the average velocity I got today was 2830 fps, 15 fps faster than I was getting in warmer weather with the same load, same batch of powder. The new lot of powder gave exactly the same results, 2830 fps average.
There are three possibilities, the first being that the barrel has gotten faster over the last six months. The rifle is relatively new, it has 312 rds through it after today's shooting. This is the most likely scenario in my mind, it stands to reason that the barrel has gotten smoother as it wears in.
Second, H4350 may actually gain velocity in colder weather. I have my doubts about that being the case. Everything I've ever read indicates the opposite, although is IS supposed to be relatively temperature insensitive.
The third possibility is that the cold affects the chronograph in some way, either the electronics or the way the optical sensors see the bullet in colder weather.
When the weather warms up again, I'll repeat the test to see if velocity drops back to 2815, stays the same, or increases.
If it drops back to 2815, I'd say it's the chronograph changing with temperature. If it stays the same at 2830 or increases, I'd say the barrel has gotten faster again, or is now fully broken in and polished.
My usual 6.5 CM load is a 123 gr Match King over 42.5 gr H4350 with a CCI BR4 primer. It's been averaging 2815 fps with ambient temps between 5 and 25 C, though I haven't shot over the chronograph in a while.
I started using a new lot of powder recently and wanted to get a feel if it was the same as the old one performance-wise.
I normally clean after each shooting session with Mpro-7 gun cleaner before putting the rifle away, so each shooting session starts with at least one fouling shot.
Since I had the results of Todd's test in the back of my mind, and I was specifically looking for a velocity shift, I fired enough fouling/warming shots to be sure the barrel had stabilized. Seven of them to be exact.
The first shot was considerably slower than the rest, 100 fps slower. That seems to be the norm for this rifle. The second two shots were slightly slower than the average, then it settled in and became quite consistent.
Using rounds loaded with the old lot of H4350, the average velocity I got today was 2830 fps, 15 fps faster than I was getting in warmer weather with the same load, same batch of powder. The new lot of powder gave exactly the same results, 2830 fps average.
There are three possibilities, the first being that the barrel has gotten faster over the last six months. The rifle is relatively new, it has 312 rds through it after today's shooting. This is the most likely scenario in my mind, it stands to reason that the barrel has gotten smoother as it wears in.
Second, H4350 may actually gain velocity in colder weather. I have my doubts about that being the case. Everything I've ever read indicates the opposite, although is IS supposed to be relatively temperature insensitive.
The third possibility is that the cold affects the chronograph in some way, either the electronics or the way the optical sensors see the bullet in colder weather.
When the weather warms up again, I'll repeat the test to see if velocity drops back to 2815, stays the same, or increases.
If it drops back to 2815, I'd say it's the chronograph changing with temperature. If it stays the same at 2830 or increases, I'd say the barrel has gotten faster again, or is now fully broken in and polished.
Interesting stuff and I'm still trying to get my head around it. Is it real or is it instrumentation?
I had tested some summer-developed loads in winter several years ago. 30-06/180grSierra/IMR4350. I can't find the data, but it was a warmish load and shooting about 50 fps slower in winter. Which was not a shock because that's what we've been told to expect.
I had tested some summer-developed loads in winter several years ago. 30-06/180grSierra/IMR4350. I can't find the data, but it was a warmish load and shooting about 50 fps slower in winter. Which was not a shock because that's what we've been told to expect.
Earlier this week I shot five different powders in four cartridges (223, 6.5cm, 7mm Rem Mag, 308Win) with both magnum and standard primers. Temp was -15c
Plan is to test same loads in +5c and again in +25c to see any trends in MV and primer consistency. I'll make a seperate thread this summer when the testing is complete
Plan is to test same loads in +5c and again in +25c to see any trends in MV and primer consistency. I'll make a seperate thread this summer when the testing is complete
From what I see in your findings and what I know from my experience...You are getting erroneous velocity readings and they are also consistently erroneous.
The larger slower bullets are for the most part following the normal velocity drop with temperature drop.
The smaller faster bullets are showing for the most part the exact opposite of what happens when temperature drops.
In any testing I have done when the temperature decreases or increases there has always been a very predictable and linear decrease or increase in velocity readings as well as sign of or lack of sign of pressure.
All things being equal you can pretty much depend on an increase or decrease of velocity of 1.8-2.0 feet per second per degree Celsius ambient temperature change with most smokeless powders.
The larger slower bullets are for the most part following the normal velocity drop with temperature drop.
The smaller faster bullets are showing for the most part the exact opposite of what happens when temperature drops.
In any testing I have done when the temperature decreases or increases there has always been a very predictable and linear decrease or increase in velocity readings as well as sign of or lack of sign of pressure.
All things being equal you can pretty much depend on an increase or decrease of velocity of 1.8-2.0 feet per second per degree Celsius ambient temperature change with most smokeless powders.
This is as interesting as any thread I've seen. If I had to guess (and I do) I would say that the colder temps resulted in slower ingnition and longer barrel time which yielded a higher velocity than one might expect. This is, of course, nothing but speculation on my part.
x2!
Thanks for these threads, tb. Really enjoyable. Great reading for days it's too cold for a range trip. (-40 with wind here this AM)
