Range Report Does Temp affect more than velocity?

[Flynn]

I was shooting a new weapon (OBR 5.56) I received during last winter and was easily able to get .5 moa. During recent shooting, I'm not able to duplicate the previous results (I'm shooting about 1.5 moa now. Given the effect of heat and pressure on velocity, is this normal?

It would make sense to me as the velocity directly affects everything about the ballistics. I'm going to take a leap and say, the temp and subsequent ballistics are a direct result of the changed velocity (please someone read between the lines). Is my basic logic f#ck$d?

 

[kraigWY]

Re: Does Temp affect more than velocity?

This is just a WAG (wild ass guess)

Some guns like a given bullet at a given velocity. Or they shoot X bullet better and X velocity then they do at Y Velocity.

This is a known.

Now lets assume we are shooting at 50 degrees, X velocity works great with your bullet.

Now comes summer and its 95 degrees. We know that the extra 45 degrees will make the gun shoot about 3 min lower. Reason is higher temps make for higher pressure, hense more velocity.

OK So now X velocity (because of the temp) is X plus (whatever). Now we've reached the point where your gun no longer likes the bullet because it exceeded the velocity the gun likes for that bullet.

Wouldn't that mean your groups could go south.

 

[Flynn]

Re: Does Temp affect more than velocity?

Makes perfect sense. I was shooting at 34ish degrees this winter and shooting at 90ish degrees the other day.

 

[deersniper]

Re: Does Temp affect more than velocity?

I get rusty over the winter, just a thought

 

[Flynn]

Re: Does Temp affect more than velocity?

I was shooting better in the winter. Maybe it's all those years I spent in Alaska..

 

[UNCIVILIZED]

Re: Does Temp affect more than velocity?

The first bit's third hand info, so... I can't verify it. But I read of the experiences of a PH in Africa with loads for his .375H&H. They were such that the cases were at, or near full capacity with respect to powder volume, though not compressed. And he stated that when left loaded over the course of a hunting season, the powder charge would clump somewhat. Which he attributed to the heat, as it didn't occur with the same loads during the cooler months. So after a few months he'd pull'em apart, & reload them.

Interesting idea, though as to what, if any current powders might have a tendency for this to happen, I can't say.
But there are other members who've writen of their handloads experiencing degraded accuracy when left to sit for several months, or more. And they found it to be because the neck tension of said loads had changed due to the bullets sticking to the cases. Perhaps due to a bit of galvanic corrosion, given the dissimilar metals thing. A phenomenon which does change with temps & humidity, corrosion rates that is.
So theoretically, how much various powder grains stick together would also change with temp & humidity. Kind of like how clothes stick together due to static electricty after being in the dryer. And how anything granulated clumps more in high humidity.

Just my $0.02 worth of thoughts. Perhaps some of the more experienced reloaders here can confirm or refute said ideas.

 

[hessian]

Re: Does Temp affect more than velocity?

Increase in velocity should result in higher point of impact.

 

[Graham]

Re: Does Temp affect more than velocity?

Velocity is a function of temperature.

 

[Niles Coyote]

Re: Does Temp affect more than velocity?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 1236</div><div class="ubbcode-body">Increase in velocity should result in higher point of impact. </div></div>

Yes and no, it all depends on distance to target. If you are shooting at 100y a slower load has more bore time and is exposed to more recoil than a faster bullet causing the slower round to impact high. Further down range, time of flight will prevail.

Of course this is all subject to shooter position and the firearm support structure; if the shooter were hanging upside down it could be reversed...

 

[Sterling Shooter]

Re: Does Temp affect more than velocity?

Trajectory is primarily effected by gravity, drag, temperature, and wind. To understand the effect of temperature, you've got to observe the relationship of velocity to temperature by recording both in the data book. You need a thermometer and a chronograph. Depending, mostly, on the sensitivity of the gun powder you may or may not notice any effect on velocity. Guessing whether or not temperature is having an effect will not get you anywhere. Coming to an understanding for the effects of temperature will better assure good hits in conditions not controlled by the shooter, without trial.

 

[Fred_C_Dobbs]

Re: Does Temp affect more than velocity?

Flynn, I think you're on the right track.

When shooters speak of a barrel's "accuracy node," they're talking about a phase where the barrel's harmonics are having a minimal impact on trajectory. In other words, the vibrations all are canceling each other, which reduces how much they screw with where you'd intended for that bullet to go.

The key to pinpointing that accuracy node is in getting the bullet to exit the muzzle at the precise time that all those vibrations are canceling each other. With a given barrel, bullet and powder, that time can be identified by the muzzle velocity. So if you're using all the same bullet components, and if the temperature is different enough from when you developed that load to substantially affect your muzzle velocity, the bullet could be arriving at the muzzle either too early or too late to hit that accuracy node. That means your groups probably will blossom a bit.

Which is why many shooters favor load development methods like "optimum charge weight." It's purpose is to find you a big, wide accuracy node so small changes in temperature or the minor variations in cartridge construction will have less an impact on accuracy.

From a components standpoint, it also helps if you use one of the powders with a reputation for temperature stability, like Varget or 8208 XBR.

FWIW, I have a varmint rifle that shoots minute of gnat with loads I developed in the middle of the winter using a powder that is pretty temperature sensitive, RL-10x. On hot days, it picks up around 200 fps at the muzzle and the groups blossom substantially. I don't do enough groundhog hunting when it's 90°F+ to justify working up a reduced load so my "band-aid" solution is to carry my bullets in a cooler with a pack of blue ice. I know that sounds goofy but it shoots a hell of a lot better if the bullets are kept cool until right before they're fired.

 

[Woodlanddude]

Re: Does Temp affect more than velocity?

Another here who supports OCW for minimizing the impacts of temperature sensitivity of a powder, and also a believer in using the most stable powder you can for all the above discussed reasons.

 

[MALLARD]

Re: Does Temp affect more than velocity?

temp changes will not only change velocity but your exit times as well.

Temp sensitive powdedr or not , if your pushing 40 degree difference , your going to see some serious changes

 

[turbo54]

Re: Does Temp affect more than velocity?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MALLARD</div><div class="ubbcode-body">temp changes will not only change velocity but your exit times as well.

Temp sensitive powdedr or not , if your pushing 40 degree difference , your going to see some serious changes </div></div>

I agree somewhat, but I simply can't subscribe to the idea of groups going from 1/2 moa to 3/2 moa based on reasonable changes in ambient conditions

 

[Casey Simpson]

Re: Does Temp affect more than velocity?

Flynn, our friends our expressing that the load was not the gun's optimal load. Had it been, the load would be nutty as it is. Hence the basis for Optimal Charge Weight method of load development. Find that under Dan Newberry.

 

[kombayotch]

Re: Does Temp affect more than velocity?

If the velocity is changing, so is pressure and barrel time. If the velocity is changing, your load is getting re-tuned to some extent. Velocity change due to the temperature instability of the powder has exactly the same effect as changing the charge weight at a fixed temperature. OCW will mitigate that, but not eliminate it. You still want a temperature stable powder.

Yes, trajectory changes with atmospheric conditions, but having your velocity changing too is one more variable to worry about. And if you're load is getting tuned off of the node you were loading too, your accuracy is also going to suffer.

 

[Lowlight]

Re: Does Temp affect more than velocity?

Seeing the accuracy effects is what we did during the Robert Gradous Gunsmithing Class, we loaded up 5 different loads, changing the powder drop for the 5 and then firing them into a single 10 shot group.(2 rounds per load)

The result was a 10 shot group with varying charge that looked like this:

I have also shot the video where I used my AI AW with its 260 barrel, letting the rifle and rounds heat up in the sun, measured with a Kestrel at 100+ degrees for 1 hour. Then I took the rifle and the rounds and immediately shot 20 shots in 2 minutes on a steel target at 550 yards. <span style="font-style: italic">(Target 8.75" X 14.75" ) </span> Of which every single round hit the target. I think took a 21st round and shot it at 100 yards on a 1" Inch dot and impacted the dot. You can see this informal demonstration at YouTube Channel .

The truth is, not all rifles are created equal and even when someone believes they have a quality system, the truth can be less than flattering. With environmental conditions, you really need a bit of distance, like 300m or more before you start to see the effects beyond the .25 MOA or in big swings where you started shooting in the morning and continued into the hottest part of the afternoon, a 1/2 to 3/4 MOA, again, depending on what you are shooting and how. The bullet needs a bit of time for the effects to get worked on, if you are seeing noticeable swings inside this distance, it is more than likely a physical problem, not a temperature one, although it can help push the problem along. Very rarely do you see muzzle velocities move in one direction alone, either up or down, they usually fluctuate a bit in both directions.

In some cases, people can start to fall off, due to lack of food or fluids. Over a bit of time that can weigh on the body and mind and cause odd, or random conditions that are often confused with variations in temperature among other things.

Really the list is pretty long on what can cause variations over a long string.

 

[Casey Simpson]

Re: Does Temp affect more than velocity?

Depending on the span of charge variation, the objective observation, one might say, is the 10 shot test group is more than 300% larger, or more than three times as big, as the better shooting ammo in that gun, being, as I recall, .2 or perhaps even smaller. Do you remember the span of charge weight in this 10 shot test group?

I've experienced and seen others experience the human element deterioration alluded to above, similar to the growing argument as cold bore impact being merely a human element rather than an actual element of gun behavior. I'm beginning to agree with that as well.

 

[Sterling Shooter]

Re: Does Temp affect more than velocity?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Seeing the accuracy effects is what we did during the Robert Gradous Gunsmithing Class, we loaded up 5 different loads, changing the powder drop for the 5 and then firing them into a single 10 shot group.(2 rounds per load)

The result was a 10 shot group with varying charge that looked like this:

I have also shot the video where I used my AI AW with its 260 barrel, letting the rifle and rounds heat up in the sun, measured with a Kestrel at 100+ degrees for 1 hour. Then I took the rifle and the rounds and immediately shot 20 shots in 2 minutes on a steel target at 550 yards. <span style="font-style: italic">(Target 8.75" X 14.75" ) </span> Of which every single round hit the target. I think took a 21st round and shot it at 100 yards on a 1" Inch dot and impacted the dot. You can see this informal demonstration at YouTube Channel .

The truth is, not all rifles are created equal and even when someone believes they have a quality system, the truth can be less than flattering. With environmental conditions, you really need a bit of distance, like 300m or more before you start to see the effects beyond the .25 MOA or in big swings where you started shooting in the morning and continued into the hottest part of the afternoon, a 1/2 to 3/4 MOA, again, depending on what you are shooting and how. The bullet needs a bit of time for the effects to get worked on, if you are seeing noticeable swings inside this distance, it is more than likely a physical problem, not a temperature one, although it can help push the problem along. Very rarely do you see muzzle velocities move in one direction alone, either up or down, they usually fluctuate a bit in both directions.

In some cases, people can start to fall off, due to lack of food or fluids. Over a bit of time that can weigh on the body and mind and cause odd, or random conditions that are often confused with variations in temperature among other things.

Really the list is pretty long on what can cause variations over a long string. </div></div>

As LL is a smart guy and has more experience in this arena than most contributors here, I trust his comments on the topic. I would only add, for anyone interested in hitting where aimed, in conditions other than those controlled by the shooter, make a record of your shots in a data book, recording temp, as well as wind corrections. Also, unless you have the motor and picture memory skill to sustain aim until recoil has subsided, where the result complements the click graduations of the adjustment taken on the sight, don't think that your error is the result of just one misapplied notion. You likely have a multitude of errors, which will mask errors associated with external ballistics.

 

[Greg Langelius *]

Re: Does Temp affect more than velocity?

All I can add is that for very nearly every time I've thought I had an equipment problem, it turned out to be a "me" problem.

Greg

 

[ctressler]

Re: Does Temp affect more than velocity?

When was the last time the barrel was cleaned? A really dirty barrel or a new cleaned barrel could cause this group growth.