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Ammo temp?

T

tucansam

Sergeant
Full Member
Minuteman
Jun 25, 2012
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So I've been locked away in my cave for a day watching the "Sniper 101" videos on youtube. This guy certainly seems to know a thing or two about what he is talking about, and, what makes him even more interesting, is that he obviously has some sort of engineering background, be it metallurgy or optics or a little bit of everything. His brain works a lot like mine, in that I'd rather spend three hours at the range and make calculations and only fire ten rounds total, than run up and down a steel setup slapping my AR15's trigger as fast as I can at targets six yards away.

So what I'm saying is I'm intrigued by this guy's youtube channel, and what he has to say.

I'm familiar with basic ballistics calculations, but it never even occurred to me to take into account things like ammo temp. He talks about burn rate tables (can I get those from my powder MFG's site?) and calculating additional MV based on ammo temp at the time of discharge. He also talks about a number of other environmental factors that even my Kestral 4000 doesn't compute.

I'd like to get more information on all of these crazy little variables he's talking about, particularly formulas for calculating bullet behavior based on something like ammo temp. I've done some googling, but it hasn't proven quite fruitful just yet, although I'm not exactly clear what I'm looking for.

Is this guy legit? Anyone know what ballistics software he is using to generate his tables? He seems to have a handy chart for every variable he can think of... Seems like overkill for just banging steel on a weekend, but, like I said, I'm intrigued, and I'd like to learn more.
 
tag,

I have watched the whole series myself and now find myself waiting for a new one.
 
He is quite endepth in his explanations of different variables. Almost to the point of tedium. Some things like humidity are not that big of a factor. But he is rather interesting.
 
Haven't seen the series, but most ballistic calculators will give you the option to enter temperature even if you have set up the app to use density altitude (density altitude includes temperature already). The reason for this is you can enter temperature to get a corrected muzzle velocity. Dont go off manufacturer charts, use your logbook and a chronograph. Check how much the muzzle velocity changes based on temp. Some powders, like the Varget, are pretty insensitive to temp changes, others are not. All will have some variation though. Also note that we are talking ammo temp, not ambient temperature. The external ballistics of the bullet, ie the flightpath, depends in part on the ambient temp. The muzzle velocity though will depend on the ammo temp. The two may not be the same, particularly if you leave the round cooking in a hot chamber for a couple minutes before the next shot. Usually the variation in muzzle velocity due to ammo temp is fairly small in any case, but if you account for it you have one less variable. The more variables you account for, the more you see your own shooting mechanics reflected on the target. That way you will know that your miss was poor trigger control or a bad wind call etc, rather than blaming the rifle or ballistic app.
 
Another thing about powder temp that is often overlooked is the effect on ES of the actual temp.

At a recent long range comp I attended over 4 days I found that in the early morning when the temp was quite cold I was getting a lot more vertical dispersion on my target than latter in the day when things had warmed up.

On the last day of the comp I was first up with 20 shots at 1200 yards with my .284 win loaded with H1000 and 180gn Bergers. It was quite cold with a frost that morning. I kept my ammo warm overnight and right up until the first shot it was being kept warm and out of the cold. I scored quite well on that last detail and went on to win the event, it made a difference in my opinion.
 
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Suggest you google the combined gas law, or the ideal gas law.

Within a given volume, if the temperature increases then the pressure also increases. So, leaving a round laying in the hot sunshine to increase it's temperature, or leaving it in a hot chamber for awhile before firing, may result in higher pressure when fired.

And the opposite effect if the round is cooled (pressure decreases).
 
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I too have watched his series and am glad I did. After hearing him talk about ammo temp. I decided to conduct my own test. I went shopping for one of those infrared thermometers he recommends using to get your actual ammo temperature. After buying 3 different models and returning them all because they were not precise enough (would point the gun at the wall and it would say 60-70 degrees then at an item in the frig and it would say 25-35 degrees, then at some ammo I had in the freezer for 2 hours and it would read 10-30 degrees, not very accurate) I settled on a different method that works well for me, take it or leave it.

I took some HSM factory 210 grain berger vld ammo for .300WM, put 2 rounds in the freezer for 2 hours, put 2 rounds in the frig for 2 hours, left 2 rounds in my gear bag and put 2 rounds in a glass container with a lid and left it on my dashboard cooking in the sun for 2 hours. I got my chrono out, grabbed the frozen rounds first,etc and let her rip. Frozen: 2960fps Cold: 3000fps Warm:3025 Hot: 3055 Then I input the velocity into my ballistic calculator based off of how the ammo feels to my cheek and input the ambient air temp as well. I made a dope chart based off this with my .308,.300 and .50 and found it surprisingly accurate when testing and seeing the elevation holds were dead on from 700-2100 meters. I'm not claiming it's as accurate as whatever Tiborasaurus Rex does, he knows a lot, but for all intents and purposes it works for me and I don't need to rely on any gadgets in the field as long as I am good at sensing ambient air temp based off feel. Yes Tiborasaurus Rex is legit.
 
A friend of mine told me that "they" (the mfg, presumable) did just that to test a new powder (8208xbr).

Said they put ten rounds in the freezer and ten rounds in a black ammo can attached to the roof rack of a car, let them sit for a day, took the cold ammo to the range in a cooler and shot both to determine if their powder was non-reactive to temp changes (the claim was that it was resistant). He's been trying to get his hands on said powder.

Interesting concept and I may try it.... Did you pack the cold rounds in a cooler (and if so, how did you keep the freezer rounds cooler than the fridge rounds) or do you have the ability to shoot off your patio (Colorado)? :)


ETA I also have two infrared thermometers but have not yet tested their accuracy. I need to get a mercury thermometer to keep in the ammo can with the ammo.
 
Yeah Tucansam, I was shooting off my brother's back porch in the middle of nowhere (Rangely,Co) I had the freezer rounds in a Ziploc bag and shot them right away out of a luke warm gun. RTK, I don't have my data book in front of me right now but freezing (sorry no temp, I just had them in the freezer 2 hours) was about 2960fps and so hot I couldn't touch the ammo to my lips without a burn was 3055. Now I just go off of feel, I just got frustrated with the gadgets.

I've tried this with several other calibers/rounds and have found a very similar spread.
 
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Hodgons extreme powders are supposed to be temp resistant, that's what I use in my hunting rifle and see no change from summer to winter time (h4831)...never thrown it over a chrono though in winter time.

Gunwerks has a video of them doing a test of hot vs cold ammo with hodgons extreme powder and showed very min velocity changes compared to another brand of powder that isn't temp stable.
 
They are trying to sell powder.
I gave a 8 pound jug of 8208XBR away as I didn't like it at all.
If you have a heated ice chest you can shoot all of your rounds at the same temperature.
 
Not to get to far off the subject or get to technical but I note that some are having trouble with accurate Infra Red thermometer readings.
There are several reasons for this.
1st - Some lower cost IR units are only accurate to within +/- 2% of there range. So the larger the range the greater the possible error.
Just because the unit has a resolution (digital readout) of 1/10th of a degree does not mean it has the same accuracy.
2nd - All IR units have a distance to spot size ratio. e.g. 4:1. So at 4 feet from the unit you are averaging the temp. in a 1 foot circle.
So as you get further away from the article of interest you are actually measuring it and all the surrounding items and getting an average temperature of everything within the spot size.
Simple way to fix this is remember that closer is better.
3rd - Emissivity. Don't want to get to technical with this one. Just know that with IR units if it's shinny (low emissivity) like polished brass, you are actually measuring the reflected temperature (room temp) not the actual article of interest. Dull, flat, corroded, painted surfaces have a higher emissivity and give a more accurate temperature of the article.
So for accurate brass temperature you may be better served with a "thermocouple". These are often found as an option in many electrical multimeter's.
 
All powder is temperature sensitive, even the extreme powders. It depends more on if they are ball, extruded, tubular, etc.

Velocity changes with temperature also depend on caliber, overbore, velocity, pressure, etc. For example, a 308 of going to be in general less temperature sensitive than a 7mm magnum, etc.

The only way of knowing what your powder velocity change for temperature really is to test it. Heat/Cool anmo to extreme temperatures then chrono with ELR shooting dope to confirm. That's what I do, but it is tedious.
 
Wow. I am a recovering engineer and had planned on doing this myself because I am a hoarder of data. Nice to see it done and great video; very informative. Thanks. I will be looking at picking up some of this newer powder to play with.
 
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