Do you enable Powder Temperature using Shooter?

[joeycoates]

I was out testing some loads this last weekend shooting at 700 yards (farthest I have readily available at our ranch in East Texas). I just downloaded Shooter last Friday and have been setting it up and learning how to use it. When I chrono'ed my 7RM it was 59 degree's and 41% humidity. As I was playing with Shooter and trying to learn how to use it I noticed where it said "Enable Powder Temperature" and went ahead and checked the box to enable.

I had some serious issues because when I went to shoot at 705 yards I input a temp of 63 degree's which was accurate, and since the powder temp adjustment was enabled it automatically changed my powder temp to 63. So it gave me a solution, I dialed in 13.4 MOA, and was around 8" low, or roughly 1 MOA. So I adjusted the scope 1 MOA up, and I was in business. At this point I had not played with the Shooter app powder temps so I was kind of at a loss as to why I had shot 1 MOA low. I was later playing with it and set the powder temp to 59 degree's... a change of 4 degree's in temp, and it told me to dial 14.6 MOA, right where I ended up.

Sooo, I started playing with the powder temps.


Wow, the results that came out were shocking to say the least. I entered a MV of 2800 fps to experiment with at the aforementioned 59 degree, 41% humidity and altitude of 450' above sea level. I do not have a Kestrel at this time (trying to decide whether to keep my Leica CRF1200 and buy Kestrel, or sell the Leica and buy Gunwerks LR2, kind of leaning towards LR2 as I have nowhere to shoot over 1200 yards around here) so I did not know the actual Baro Pressure. Just left it as default.

Anyway, when I put in an outside air temp of 40 degree's and let it default the powder temp to 40, it came up with an adjusted MV of 2439.57 fps...! I then tried the air/powder temp at 70 degree's and it came up with 3008.67 fps...!! So to take outside air temp out of the equation I set the air temp at 59 and just changed the powder temp between 40 and 70 degree's. Same results.

So this thing is telling me that for a 30 degree change in powder temp that I am going to get a 560fps change in MV? Now, I know that this is not accurate, but am I inputting something wrong to get these results? When I hunt I do normally have rounds in the rifle instead of taking them out of my pocket and loading when I need them so I do need to learn the differences the outside temp makes on my MV, but I know that it is nowhere near what the program is spitting out.

So am I doing something wrong or do I just leave the Powder Temp alone on Shooter? You should see the solutions it came up with at those two very different MV's!

 

[BrentM]

Are you Editing the powder temp in the Ammo field? If so, this is not what you want to do IMO. You set the zero up for the conditions of the day and leave it alone, UNLESS, you rezero in different conditions.

You adjust temp on the main page for the current conditions. Generally the differences in temp do not affect the FPS that much until you get into wide swings. For example 10 to 90 F. I have shot those conditions actually. LOL.

For me: I set the temp of the powder close to the conditions to which I shot for the zero. For example 50F. I set the atmosphere of the conditions I zero etc. This is the constant. Then I set all the parameters in which I am shooting, which is now the variable. So constant is my zero and variable is my shooting conditions. Shooter has worked extremely well for me out to 1660 yards in wide variety of terrain and conditions. Going for the mile soon. ha ha

 

[joeycoates]

No, I am not messing with the initial inputs or editing the data. This is just entering in the current data in order to come up with a firing solution. It is just giving me huge swings in MV when the powder temp is set to same as outside temp.

 

[BrentM]

OK, sorry I can't help you then. I don't have that feature on my Shooter program. It is on a iPod and I got it in February. Most be something new they added or for the iPhone.

 

[drbill]

Under the Edit Ammunition page do you have MV Variation and Powder Temp?

I put in the Muzzle Velocity and Powder Temp when I zero my rifle. Powder Temp is the temperature outside (your ammo needs to be set out so the powder becomes the same temp as outside)

Now shoot on a completely different temperature day. Have it be a significant temperature difference. I sometimes leave my ammo outside overnight and check in cooler morning temps.

Get the second shooting day Muzzle Velocity and Powder Temp. Don't put this in the Muzzle Velocity and Powder Temp, leave them alone.

Now use both days of MV and Powder Temp to calculate the difference in fps/degree change. Put this in the MV Variation.


Example...

So on day 1 3000 fps/100 degrees F
So on day 2 2970 fps/70 degrees F

You would have a 1 fps/degrees F change - put that in the MV Variation.

I believe it is the same in Applied Ballistics and Shooter.


If I am wrong someone please correct this.

 

[joeycoates]

Hey thanks drbill, that helps. I did not know what MV variation was, thought it had something to do with ES or SD. I have changed it to 1 fps for time being until I can get some hot and cold MV's.

 

[BrentM]

MV is FPS/per degree. If that is what you are doing then it likely is causing your issue. As noted by the last poster if you use 1FPS/degree a 20 degree outside temp change will give you a 20 FPS variance. That is actually quite a lot.

You will need to chono or dope this to find out the real affect. Most people input something like .25 to .5 for fps/degree. Gunwerks has a video that shows the difference in sensitive vs extreme powder variances in FPS. I think the did 32F and 90F or something like that. I use extreme powders and have virtually no variance from 10f to 90f.

 

[BrentM]

Here is the vid I was talking about. As you can see he is shooting over wide temp variance.

I guess I could be wrong about 1 fps being too much but it seems like a lot. I have not seen that much difference personally within 20 degrees of zero conditions. I like to zero my rifle close to the conditions in which I hunt though. That reduces the margin of error.

[ame=http://www.youtube.com/watch?v=aWg92Nuob3A]Using Temperature Stable Powder - YouTube[/ame]

 

[joeycoates]

Are most of the Hogdon rifle powders considered extreme? I have used some RL-22, but I prefer H1000 which I think is an extreme powder. I have some of the verious IMR powders, but I do not think that they are considered extreme although someone can correct me if I am wrong.

Thanks for the video too.

 

[BrentM]

Hogdon has both. If you look at their site they list the extremes. 4831, 4350, retumbo, h1000, etc. I shot my 6.5-284 in 10F and it was 2970. Shot it at 60f and it was 2975. ES on both was less than 15. I shoot 2940 now and ES is around 5.

IMR's are not. They are considered temp sensitive. I never worried about it until I started shooting LR and in temps with a wide range. I kind of have an issue as I am getting ready to put LR scope on my 204 and I use IMR 4064 for that rifle. I am unsure what the speed is going to be this winter for dog hunting. I have a chrono so I will test it. It is cold as heck right now so it would be good time.

 

[desertbull]

For h1000 I use only .35 fps and it seems to work well. But I live in AZ where my zero and practice shooting can be done at 100+ degrees and hunting temps will typically be in the 20-50 degree range.

If you keep your ammo in an interior coat or vest pocket when hunting, it will be warmer than than the atmospheric temps anyway so I usually just turn off the powder temp feature.

 

[MMERSS]

You should consider using same procedures same day when conducting temperature regression testing. Obviously what we are after is the change in velocity with a change in powder temperature. Depending on your chronograph and to ensure our delta V is as accurate as possible your chronograph should be set up same day throughout testing.

Here is what I do when conducting testing.

• Load 9 (3x3) rounds.
• Shoot on a cold day, cooler than your average hunting temperatures maybe by 20 degrees.
• Place three rounds on the shooting bench.
• Place six rounds in your truck and turn on the heater.
• Place three of the six rounds under your heater vent. This temperature should be around 70 to 90 deg.
• Place the remaining three of the six rounds on your rear floor or another cool spot in your vehicle. This temperature should be around 40-50 deg.

For example, outside temperatures are 20 degrees with your average hunting temperature around 40 degrees.

Place your ammo outside and in the truck as indicated above. Let your ammo set for approximately 20 minutes to stabilize the powder temperature. Use this time to set up targets (200 yards or farther if you can) and your chronograph.

Shoot your first three rounds and record muzzle velocities and outside temperature.
Let the gun cool, shouldn't take long in cold temperatures.
Place your Kestrel next to three of the rounds in your truck. After your gun cools, remove the three rounds from the truck, record temperature and shoot these rounds fairly quick. Record velocities. Let the gun cool and repeat with the remaining three rounds in the truck.

You should now have data showing an average muzzle velocity increase with an increase in powder temperature. Hopefully you have good data for approximately 20, 40 and 70 degrees. You will use this data in your program when selecting temperature regression ON.

You can also check the three round groups to see if there is any indication of significant pressure increases with powder temperature causing POI and POA and/or accuracy changes.