I zeroed my rifle when it was 50 F. I didn’t have a chronograph at the time but now I do. It’s going to be in the 90s today where I’m at. Question is if my ammo and riffle are kept in a controlled environment at around 50F and I shoot it outside within 5 minutes would that reading be indicative of a 50F temp or a 90F temp? Maybe it’s a moot point with the software like ballistic AE now? Either way just curious...
Velocities
- Thread starter Kramerica
- Start date
My experience with working up a load in cold weather, then shooting it in warm weather have been VERY educational! Some powders are temp sensitive, so I learned to work up loads in the temperature you plan on shooting.
CharlieNC
Gold $$ Contributor
The velocities will reflect 50f, the ballistics 90f @ current barometric pressure. Continue to check velocity as ammo warms, and that response can be utilized in a ballistic app to reflect that influence. If you're checking at 100yd for zero impact, you should see nothing. Characterizing the effect of ammo temp is often overlooked, I have certainly been deficient in this regard.
Dusty Stevens
Shiner
You cant keep your ammo at any temp other than ambient very reliably or consistently so let it get to ambient and then shoot it. I predict your load will be too hot.
That would be an interesting test to perform, and I would enjoy reading about the results. I hope you try it. Chrono the same load when everything aft of the muzzle is at, say, 50 F and again when at ambient temps of 90 F.
Some food for thought and of course, discussion.
My prediction would be as follows. When the firing pin hits the primer of a 50 F load in a 50 F chamber and barrel, but on a 90 F day, the quenching effect of the barrel on the propellant gases will exhibit same cooling as you would see on a 50 F day. Once the bullet emerges from the barrel, it'll fly faster and flatter compared to a 50 F day simply because the air is thinner. Muzzle velocity should be same, but as you note the ballistics will differ.
With the barrel and chamber up to ambient 90 F temps, your velocity should be higher as there is less quenching effect on the hot gases. Velocity should be higher, as would pressure.
Some say this is due to the powder being heated to a higher ambient temp, but I've yet to read a definitive test supporting this. In fact, I've read the opposite. A purposely chilled round being discharged in a hot barrel will produce a velocity and pressure almost identical to a ambient temp round in the same hot barrel, or so I've read.
Powder manufacturers go to great lengths to ensure their propellant burns at a predicable rate across the temperature ranges expected. We see those burn rates published on comparative tables, but the other side of burn rate is the volume of gas produced as the powder burns. And it is the volume being effected by the barrel quench, and therefor the resulting pressure. A slower burning powder producing more volume of gas will produce a higher velocity (if the burn front keeps up with the accelerating bullet) with less pressure than a faster burning powder producing less volume of gas.
As I wrote, food for thought.... I've never read of a test describing barrel quench effect on gas volume production yet the science of physics should predict it. In my mind it is why the mass of a heavier barrel enables long strings of shots to fly more consistent than a light weight "pencil" barrel. It's not because it bends or deforms less, it's because the barrel time of the bullets, shot to shot is likely more similar because gas volume and pressure is more similar.
Anyway, that's my pet theory.
Some food for thought and of course, discussion.
My prediction would be as follows. When the firing pin hits the primer of a 50 F load in a 50 F chamber and barrel, but on a 90 F day, the quenching effect of the barrel on the propellant gases will exhibit same cooling as you would see on a 50 F day. Once the bullet emerges from the barrel, it'll fly faster and flatter compared to a 50 F day simply because the air is thinner. Muzzle velocity should be same, but as you note the ballistics will differ.
With the barrel and chamber up to ambient 90 F temps, your velocity should be higher as there is less quenching effect on the hot gases. Velocity should be higher, as would pressure.
Some say this is due to the powder being heated to a higher ambient temp, but I've yet to read a definitive test supporting this. In fact, I've read the opposite. A purposely chilled round being discharged in a hot barrel will produce a velocity and pressure almost identical to a ambient temp round in the same hot barrel, or so I've read.
Powder manufacturers go to great lengths to ensure their propellant burns at a predicable rate across the temperature ranges expected. We see those burn rates published on comparative tables, but the other side of burn rate is the volume of gas produced as the powder burns. And it is the volume being effected by the barrel quench, and therefor the resulting pressure. A slower burning powder producing more volume of gas will produce a higher velocity (if the burn front keeps up with the accelerating bullet) with less pressure than a faster burning powder producing less volume of gas.
As I wrote, food for thought.... I've never read of a test describing barrel quench effect on gas volume production yet the science of physics should predict it. In my mind it is why the mass of a heavier barrel enables long strings of shots to fly more consistent than a light weight "pencil" barrel. It's not because it bends or deforms less, it's because the barrel time of the bullets, shot to shot is likely more similar because gas volume and pressure is more similar.
Anyway, that's my pet theory.
Ned Ludd
Silver $$ Contributor
Once the chamber/barrel steel warms up, it doesn't really matter that you've chilled the loaded rounds down. Brass is an excellent conductor of thermal energy and they will start to warm up before you're even finished closing the bolt. There is also a far greater mass of steel than brass, so the balance of heat transfer won't work in your favor. You probably can't shoot rounds fast enough to prevent some warming from the chamber/barrel. Further, a significant amount of the powder burn occurs within the first few inches of barrel, and the barrel will start to heat up as soon as you begin to fire rounds. Once the barrel has warmed up, the powder burn rate will increase regardless of whether or not you chilled the rounds down before hand. Fortunately, H4350 is one of the least temperature-sensitive powders known to man, so you may not see a huge change. You might be lucky enough that the loaded rounds behave as though the temp was lower for the first couple. However, it won't take long for things to equilibrate and the temps to rise for the reasons I stated above.
Jalen,
I'm not disagreeing with anything that's been said but as an 07FFL I do load development and ammo mfgr for rifles I build. I build rounds that travel from the Alaskan tundra to the plains of Africa where they may get left out on the hood of a Range Rover....I test my loads thru temps ranging from 0F to 160F and IMO if your ammo is at 50F it will shoot at 50F velocities. I often test frozen loads on 90* days. They respond as frozen loads, the air temp has zero effect.
I've also kept rounds in a cooler at matches for tuning reasons and have never had any trouble no matter how heat soaked the rifle gets.
First of all, heating or cooling ammunition takes hours. I cook rounds for at least an hour, most often more, and cool them in the freezer overnight. Heatsoaking or cooling the powder charge is very time intensive.
Secondly, I once spent a few mo testing the concept of rounds "cooking up" in hot chambers during a match. IMO the whole concept is flawed. Gunpowder granules are a fair insulator....In military applications where barrels get red hot a round can cook off in a sizzling chamber but that's because the outer layer of powder is subjected to nearly instantaneous heat thru the brass cartridge walls while the granules further in haven't even felt heat. But in regular rifles even when I fired 10-12-15 rds to get the chamber "smokin" (still only hot to the touch although I have had them sizzle spit.... I'm guessing 250-ish??) I have tested 6BR-ish and up to 6X47L sized rounds for 1min, 2min even 5min in a hot chamber and shown no pressure rise over the chrono.
And, in a 600yd match, I HAVE pulled rounds out and replaced them after setting and watching the weather cuz.... WHY NOT??
but I'm not convinced I've needed to.I'm happy to hear other opinions and dissension from folks who've actually TESTED this but my opinion is that your plan is sound.
People at the NRA nationals shooting 1000 yard matches have noticed 30 caliber ammo in a hot chamber for a couple minutes shoots its bullet 15 to 20 inches above call. Thats a why a rule was added stating if firing was delayed for over 2 minutes, one sighting shot would be allowed. I often came down a click every 20 to 25 seconds during a check fire to shoot to point of aim when firing resumed.
Which is why I think a shot should go in less than 15 seconds of clambering unless you want to lower the sight.
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Thanks Bart B..... I just went back and checked. I was wrong, there was no dangerous over-pressure in my testing even up to 5 minutes but there was a rise in velocities after a minute to two minutes depending on size of round.
Two different tracks operating in my brain, #1 regarding my "safety testing" which runs from 0F to 160F and #2 remembering (MIS-remembering) test results for cooking rounds in the chamber.
OP was asking about tune, not safety. My Bad
I appreciate your correction.
Two different tracks operating in my brain, #1 regarding my "safety testing" which runs from 0F to 160F and #2 remembering (MIS-remembering) test results for cooking rounds in the chamber.
OP was asking about tune, not safety. My Bad
I appreciate your correction.
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