tempeture affect on reloads?

[42769vette]

i know that my ammo will preform diffrent in cold weather than warm.

the only time i have access to my range is in winter when the corn is out and matches will be in the summer.

i plan to compete in f-class matches with my 260 and was curious if i shoot from a heated house would that better simulate summer conditions or does the temp where the bullet is traveling matter. i can shoot 800yds from the window of my reloading room.

 

[Dogtown]

Re: tempeture affect on reloads?

Environmental conditions can be adjusted for - I would mainly be worried about how temp sensitive the load is. Some powders vary more than others as the temperature changes.

 

[Lindy]

Re: tempeture affect on reloads?

Both matter.

I have measured effects of powder/chamber temperature on muzzle velocity which range from a bit less than 1 foot per second per degree F. with a good powder, to 5 feet per second per degree F. with a very hot military .300 Win Mag load.

And certainly air temperature effects density.

However, for F-class matches where you have sighters, that's less of a concern that it is for a sniper who trains in Virginia, then deploys to the mountains of Afghanistan.

 

[42769vette]

Re: tempeture affect on reloads?

i use 36.5-38 gr of n-150 and a 142 smk

 

[treebasher]

Re: tempeture affect on reloads?

I got the idea from one of Denton Bramwell's articles to get velocity readings for different cartridge temperatures.

On an 80 degree day I shot a ten shot string over the chronograph and recorded the data. Then I had ten cartridges in an ice chest full of dry ice and got velocity readings. I was quick to load the cartridge from the chest and fire it.

One thing I am unsure of is the temperature of the cartridges that were chilled in the dry ice. With the temperature probe inside of the Ziploc bag I was showing a reading of -18 but when I put the probe directly on the dry ice the electronic temperature gauge showed an error after dropping to below -30. This may have been from the sublimation of the Carbon Dioxide and lowering the surface temperature of the dry ice WAY down. So I would like to preform the experiment again with dry ice, water ice, an athletic heat pack and ambient temperature. With four sets of data I feel that a pretty accurate temperature/velocity curve can be formed. From my initial experiment I am showing approximately 2 fps increase per 1 degree F temperature rise. This also is corresponding fairly well to the outputs that the JBM Ballistic software is producing.

Here is a link to Denton Bramwell's article "Pressure Factors: How Temperature, Powder, and Primer Affect Pressure":

http://www.snipershide.com/UserFiles/Image/articles/Pressure_Factors.pdf

http://snipershide.com/Pressure

JBM Ballistics Trajectory Card:

http://www.jbmballistics.com/cgi-bin/jbmcard-5.0.cgi

Good luck.

 

[Grump]

Re: tempeture affect on reloads?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 42769vette</div><div class="ubbcode-body">i can shoot 800yds from the window of my reloading room. </div></div>
I hate you.

 

[42769vette]

Re: tempeture affect on reloads?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grump</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 42769vette</div><div class="ubbcode-body">i can shoot 800yds from the window of my reloading room. </div></div>
I hate you. </div></div>

it does make load development a little quicker

 

[ReaperDriver]

Re: tempeture affect on reloads?

I've been wondering about this question a lot but one thing I don't see discussed much is the effect of chamber temp on loads.

For instance - you develop a load that shoots well at 80F and you have good chrono numbers for it. You then shoot it and chrono it at 40F and see that it has a 50fps less MV because of the colder temps. HOWEVER.... that might be true for the 1st shot. But every shot after that is warming up in the chamber before you pull the trigger, the amount varying only by how long its sitting in there before you shoot. That is unless you are letting the barrel fully cool between each shot. But if you're shooting a 5 shot string at a reasonable pace - I'm betting the round is probably warming up enough in the 15-30 secs its in the chamber to act like something different than a 40F temp shot. And if you are rapid firing, its going to be potentially more significant - because while the round is not in the chamber as long, the chamber is probably getting considerably hotter after each round.

Has anyone ever done any kind of "Box 'O Truth" kind of look at how much does MV vary based on how long a round is chambered?

 

[42769vette]

Re: tempeture affect on reloads?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">I've been wondering about this question a lot but one thing I don't see discussed much is the effect of chamber temp on loads.

For instance - you develop a load that shoots well at 80F and you have good chrono numbers for it. You then shoot it and chrono it at 40F and see that it has a 50fps less MV because of the colder temps. HOWEVER.... that might be true for the 1st shot. But every shot after that is warming up in the chamber before you pull the trigger, the amount varying only by how long its sitting in there before you shoot. That is unless you are letting the barrel fully cool between each shot. But if you're shooting a 5 shot string at a reasonable pace - I'm betting the round is probably warming up enough in the 15-30 secs its in the chamber to act like something different than a 40F temp shot. And if you are rapid firing, its going to be potentially more significant - because while the round is not in the chamber as long, the chamber is probably getting considerably hotter after each round.

Has anyone ever done any kind of "Box 'O Truth" kind of look at how much does MV vary based on how long a round is chambered? </div></div>


kind of the reason i was asking is if me and my rifle and ammo stayed inside with the heat at 70ish would that help simulate a warmer day

 

[Greg Langelius *]

Re: tempeture affect on reloads?

Got me wondering what effect the muzzle blast would have on a window pane...; I mean, I've seen photos where folks shot their rifles from the tailgates of their P/U truck and blew their taillight lenses to smithereens...

Have a care, y'all...

 

[Unsichtbar]

Re: tempeture affect on reloads?

As TreeBasher suggested Read
"Here is a link to Denton Bramwell's article "Pressure Factors: How Temperature, Powder, and Primer Affect Pressure":

http://www.snipershide.com/UserFiles/Image/articles/Pressure_Factors.pdf

http://snipershide.com/Pressure

 

[42769vette]

Re: tempeture affect on reloads?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">Got me wondering what effect the muzzle blast would have on a window pane...; I mean, I've seen photos where folks shot their rifles from the tailgates of their P/U truck and blew their taillight lenses to smithereens...

Have a care, y'all... </div></div>

ive never watched anyone else shoot my rifle but would a 260 with a 28 in barrel have much muzzleblast. i do know a 142 smk does a number on a brang new chrono but thats another story

 

[Greg Langelius *]

Re: tempeture affect on reloads?

I don't know, but I think it's definitely worth finding out before you take a chance on opening up your home to the cold Winter air.

Greg

 

[billyburl2]

Re: tempeture affect on reloads?

Not muzzle blast, but the pressure wave of the bullet leaving the barrel at supersonic speeds might blow out the window. But as stated before, you are a lucky man to be able to shoot from your reloading room!

 

[ReaperDriver]

Re: tempeture affect on reloads?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Unsichtbar</div><div class="ubbcode-body">As TreeBasher suggested Read
"Here is a link to Denton Bramwell's article "Pressure Factors: How Temperature, Powder, and Primer Affect Pressure":

http://www.snipershide.com/UserFiles/Image/articles/Pressure_Factors.pdf

http://snipershide.com/Pressure
</div></div>

Very interesting, and kinda confirms my gut feeling about barrel temp:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">In this load, <span style="font-weight: bold">Hodgdon’s Varget is highly affected by barrel temperature</span>, with powder temperature held constant. These data were taken at an indoor range, and, as usual, the rifle was fed single-shot style. <span style="font-weight: bold">This is a very important finding. Both barrel temperature and powder temperature are important variables, and they are not the same variable.</span> If you fail to take barrel temperature into account while doing pressure testing, your test results will be very significantly affected. As nearly as I can determine, SAAMI does not rigorously control this variable, though individual testers might.

The effect of barrel temperature is around 204 PSI per degree F for the Varget load. Also, the small sample gathered with 4350, before my thermocouple meter went kerflooey, is consistent with this result. Since the 4350 sample is small, the uncertainty is high, but the best estimate is 177 PSI per degree F. <span style="font-weight: bold">If you’re not controlling barrel temperature, you about as well might not bother controlling powder temperature, either. In the cases investigated, barrel temperature is a much stronger variable than powder temperature.</span> I suspect that the mechanism for the effect of barrel temperature on pressure is from the large thermal mass of the rifle quickly bringing the primer to the same temperature as the chamber, and that what we are seeing really represents primer temperature.</div></div>

Which leads me to the theory that if all your load development has been done in fairly warm temps - you can even out the effects of th colder ambient temps in the winter by just shooting fast enough to keep the barrel warm and maybe deliberately leaving a round in the chmaber to "cook" to warm it up to your normal loads that were chrono'd in the summer. Of course that doesn't help you on your cold bore 1st shot but the follow on rounds should be closer to your expected velocities if you let the chamber warm them up.