Temp Sensitivy Question

[Cira]

This might be a really dumb question. If so I appologize. I searched and didn't see anything.

When a powder changes due to temp sensitivity, is it due to the actual temperature of the powder or the temperature of the ambient air?

In other words, can I negate the effects of temp sensitivity by just keeping my rounds warm, say in a vehicle, until they are ready to shoot?

 

[Hummer]

Re: Temp Sensitivy Question

At Aberdeen Proving Gound we tested from -65F to +140F. Ammo was conditioned in same room weapon fired in. Thus we could shoot at -65F in July and 140F in January.
When propellant testing was conducted after the other initial measurement groups were shot with M60 (now M240) at 100 yards then taken to cold room and long bursts were fired in segments for 10,000 rounds and retested for groups. If the dispersion opened up past the reject criteria the propellant was not accepted for gov't use.
Ball propellant is known to be extremely erosive if not manufactured correctly thus there was the above firing test. Since ammo gives worst case conditions at 140F that is the first test. As I left a new propellant failed and the remaining 300K were sent to burning ground for destruction.

 

[Cira]

Re: Temp Sensitivy Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hummer</div><div class="ubbcode-body">At Aberdeen Proving Gound we tested from -65F to +140F. Ammo was conditioned in same room weapon fired in. Thus we could shoot at -65F in July and 140F in January.
When propellant testing was conducted after the other initial measurement groups were shot with M60 (now M240) at 100 yards then taken to cold room and long bursts were fired in segments for 10,000 rounds and retested for groups. If the dispersion opened up past the reject criteria the propellant was not accepted for gov't use.
Ball propellant is known to be extremely erosive if not manufactured correctly thus there was the above firing test. Since ammo gives worst case conditions at 140F that is the first test. As I left a new propellant failed and the remaining 300K were sent to burning ground for destruction.</div></div>

I'm sorry I read your response three time and I don't think I understand. Are you saying that yes, the effects of temp issues can be negated by storing rounds in a standard temp and shooting in a different?

 

[AUJohn]

Re: Temp Sensitivy Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Cira</div><div class="ubbcode-body">
When a powder changes due to temp sensitivity, is it due to the actual temperature of the powder or the temperature of the ambient air?
</div></div>
Yes (both) but the powder temp makes the greatest difference. Variations due to air temp should not be noticable at shorter ranges.

 

[1SMALLJOHNSON]

Re: Temp Sensitivy Question

Bottom line answer to the top question: You're talking about two different worlds. Most folks don't recognize it, but temperatures affect on ballistics is two fold.

First, you've got internal ballistics. The temperature of the propellant bed, the temperature of the primer, and the temperature of the gun system. All those come into play when developing pressure and area under the pressure-time curve to produce energy (velocity). The boiler room is affected by temperature, and that resultant area under the curve (pressure-time curve) readily shows cause/effect with resultant velocity.

But, that's not all.....

External ballistics is a big player as well. If you've got a ballistics program, plug in identical velocities for two different samples, but temperatures at 0 degrees and 125. Now shoot them on the program and witness the difference in tragectory. It's significant, and should not be taken for granted.

Thus, temperature sensitivity is generally spoken to the "internal ballistic" sense only, as you can't affect the external ballistics. But, but, but! Bear in mind, the boolit still has to travel thru different air densities given different temperatures/humidities.

The best answer: Know your gun, know your load, shoot them under all possible conditions...and take copious notes!

 

[Hummer]

Re: Temp Sensitivy Question

There have been thousands of articles on the effects of weather on a bullet in flight but very little of what happens internally so that was not addressed.
Very few folks take into consideration what different propellants actually do to their bores that will have an effect on accuracy sometimes quickly and sometimes later. Since there is no work done on propellant erosion of bores that have been published, I thought I would explain how propellant is tested by the gov't.
Now consider this, propellant production runs are geared up to load at least a half million to perhaps three million rounds.
OK we get in say 350K for propellent acceptance testing and it flunks and we destroyed the remainder by burning, does anyone want to guess what the civilian manufacturer now does with several rail car loads of propellant that just flunked at Aberdeen?

 

[GBMaryland]

Re: Temp Sensitivy Question

I can't interject anything specific (technically), but I can tell you that with my TRG and using VV N550/N560 compared to RL-22 or H4831SC... the Vitha Vouri (sp) powers were HIGHLY temperature sensitive compared to RL-22 or H4831SC when used with a 300WM.

So this left me to develop loads based different powders and at different temps.

Obviously, once you shoot about 20 rounds, the bore and barrel are no longer anything near cold (or ambient temp), and begin heating up the cartirdge. This effect, for me, showed much more significantly with the VV powders.

However, cold shots with the high engergy VV N500 series we very consistant. [core bore at 50-75 degree F ambient]

...and N550 or N560 can push the rounds out a few hundred feet per second faster. Which was why I was playing with it... (As opposed to N150 or N160 "standard engergy powders")

 

[treebasher]

Re: Temp Sensitivy Question

The first two Denton Bramwell articles in the link below deal with pressure factors.

Link: Denton Bramwell Articles

And this is a thread discussing the same topic

Sniper's Hide search engine

 

[Cira]

Re: Temp Sensitivy Question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: treebasher</div><div class="ubbcode-body">The first two Denton Bramwell articles in the link below deal with pressure factors.

Link: Denton Bramwell Articles

And this is a thread discussing the same topic

Sniper's Hide search engine
</div></div>
Thanks for all the responses. The first article posted is really good. Here's what I got from it:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> The fundamental reason that ammunition temperature has an effect on pressure and
velocity is that heat energy absorbed by the cartridge components is energy lost to
propulsion. Warm cartridges absorb less heat than cold cartridges.
Similarly, cold receivers and barrels absorb more propulsion energy than warm ones.
Since the thermal mass of a barrel and receiver is much larger than that of a cartridge, this
effect is much stronger than the effect of cartridge temperature.</div></div>

The real basis of my question was to determine the safety and expectations on INTERNAL ballistics only and on changing the way I shoot. All of my loads are worked up with the ammo about teh same temp. My guns are usually room temp when I start and obviously heat up as I shoot. I almost never shoot really COLD bore and really COLD ammo like in a hunting scenario. However, I want to take one of my guns and loads and do some night coytote hunting soon.

So what the above tells me is that in that hunting scenario, I should be lower pressure and lower velocity. As long as it's not higher and cause a safety issue, I think I'm good.

 

[Hummer]

Re: Temp Sensitivy Question

I did witness a test where a 105MM was subjected to low temp tests with ambient ammo.
I was proof firing Air Defense Artillery tubes in a proof arena and I noticed a tractor trailer of CO2 backed up and a hose run out the back and into the arena and there were clouds of CO2 being released into the air.

While I was waiting for the gun crew to position another gun tube I sauntered over for a looksee to see what was causing the clouds. Guys were running around and I walked into the arena and this big hose from the trailer was in the breech of a 105 cooling the whole tube down. The barrel was snow white with frost and this guy was up watching thermocouple readings hooked to the tube and he called out "65 below" and the hose was removed from breech, a round was rammed home and everyone ran out of the arena and the gun fired, they ran back in and repeated this four more rounds then the hose was inserted and brought back down to -65F and same thing repeated.
The ammo was ambient which at that time was about 50 deg F. and not temp conditioned. My gun was ready and I had to leave without finding out the point of the exercise. I kept alert in case the tube let go as I had already planned on diving under our truck to escape the falling pieces but it held together.

One of the other guys in my section was testing the chain gun in the cold room (at high temp) and he was doing a cook off test. Last round cooked off and he recorded the time and shut test down for the evening. Next morning he got back and went out to check to make sure GI Johnny wasn't banging GI Mary in front of the gun port and there was no muzzle sticking out the opening. He went back in and the gun was sitting there ready to shoot. Closer investigation revealed the HE round had cooked off after being firing and it blew the muzzle off. That was his desk ornament from then on. He had a double cook off from same round.

 

[ReaperDriver]

Re: Temp Sensitivy Question

I've always assumed most talk of "temp sensitivity" dealt with pressure and velocity of a round developed either at warm or cold temps and then later shot at the other extreme. In my case, most of my initial load development occured in the NV summer in the high 90s and low 100s. I'm now shooting them in the 50s and I would expect a bit lower velocities. Conversely, I'm doing some load development now in the 40s and 50s and wonder how they will do when it gets back in the 90/100s.

Here's my question, if say a load was tested at 100F but the outside temp is 40F right now, if I let the round cook a bit in a warm chamber, am I going to see much difference than if if was shooting in the summer?