Powder Temperature and MV Variation Methodology

[Crews]

The quote from Joe at Geoballistics below really sparked my interest. What are the different methodologies being used to account for MV variation as a function of powder temperature? Since my first love is hunting, I am particularly interested in that first cold bore shot. I live on the gulf coast, so all the data I have is at 80-100 deg F and it works 99% of the time when I'm shooting for recreation. However, I could very easily be taking a cold bore shot from a deer stand on a freezing morning in December. I use Geoballistics and am very happy with it. Should I be building a separate profile with a different MV on a cold rifle and cold ammo?

It is my opinion that real world POI shift in an extreme environment is most likely attributed to powder temp. I realize that several apps offer a tool for tracking MV vs temp, and we still don't. This is another example of filtering noise in our solver. I'm just not a fan of making a direct correlation of ambient temp to MV. There's at least a couple more steps in that process. It will work in cases, but it's not 100%. I would rather force a user to track this type of info in a log book and identify MV stability (with not only ambient temp, but also their ammo storage and carry habits) than offer a crutch that only works half the time.

 

[howe0001]

I wonder if you kept your ammo against your body (on belt perhaps or in pocket), it would be around 80 F or so, would that make your 80-100 F data the correct data for that December morning cold, cold shot? If you place your round in the chamber just prior to taking the shot, the round would still be around 80 F at that point. IF you left the round in the chamber, and the temp outside is 20 F, then the round would be very cold. I'm just asking to make sure I understand the concept? I agree, I would like to know if that will make POI / FPS change much. OF course distance of the shot would matter too.

 

[GeoJoe]

I wonder if you kept your ammo against your body (on belt perhaps or in pocket), it would be around 80 F or so, would that make your 80-100 F data the correct data for that December morning cold, cold shot? If you place your round in the chamber just prior to taking the shot, the round would still be around 80 F at that point. IF you left the round in the chamber, and the temp outside is 20 F, then the round would be very cold. I'm just asking to make sure I understand the concept? I agree, I would like to know if that will make POI / FPS change much. OF course distance of the shot would matter too.

First, a 100fps drop will create a mathematical shift in POI of about .25in at 100 yds (175 SMK from 2700-2600). Most long range shooters are using powder that operates within that range for their typical shooting environments year round. This is a real possibility though, and even though it's a small change, it's measurable...unlike DA changes at time of zero.

Next, I also subscribe to the concept that cold shooter shift is > than cold bore shift. Cold shooter shift is POI shift due to poor fundamentals of marksmanship on the first shot, when it matters most. Rifles Only advocates dry firing to overcome this. I think it works.

As far as ammo storage on a mountain hunt, that's exactly what I try to do. Normalize ammo temp. Keep a mag stowed in a somewhat protected position for longer engagements and keep another in the rifle for the closer hasty shots if needed. It may be voodoo...

 

[howe0001]

@GeoJoe So from a GeoBallistics App standpoint, you only use one profile? one for 80-100 F , and just mentally adjust for that POI drop on cold days? or do you keep a separate profile for that temperature?

 

[GeoJoe]

@howe0001 , I don't create multiple rifle profiles based on temp vs MV changes, but that might work for you if you can absolutely attribute a POI shift to temp. This was the origin of the conversation. I'm not a fan of correlating ambient temp to MV.

The quote above is slightly out of context, and I cringed a little to see a thread started by that statement. The original quote included a previous statement on the mathematically negligible effect of tracking atmospherics at the time of zero with a 100 yard zero. Trust me, I've heard from hundreds of people over the phone claiming POI shift at 100 yards in the winter after their rifle was dead nuts in the summer. Honestly, they probably have poor fundamentals of marksmanship and need to dry fire more, but there are so many possibilities that cannot be diagnosed over the phone. The most measurable variable that we can look at likely is likely MV.

I shoot and verify data as often as possible and I suppose by default that keeps me trued with the changing seasons. I also try to normalize ammo temp and this has always worked for me.

 

[spife7980]

Im a big geoballistics fan, I just use the same profile and alter the velocity accordingly.
Make three 5-shot groups out of identical ammo, put some on ice before you head out to the range to get them into the 30s, keep some normal in the shade at ambient temp, put some in the sun to get it real hot. See what they measure when you shoot em. It might be something you need to worry about (like with my h4350 laods) or it might not be anything that matters (like wiht my rl16 loads).

You can also just reference prior data that was collected in the different seasons but if you dont have months to do so the test is easy to replicate.

 

[Crews]

The quote above is slightly out of context, and I cringed a little to see a thread started by that statement. The original quote included a previous statement on the mathematically negligible effect of tracking atmospherics at the time of zero with a 100 yard zero.

Just for the record, there isn't any negative intent here, just thought it would be a good way to kick off a conversation. I assume you know that, just wanted to make sure. I think most folks here understand the context and won't jump to any conclusions from a single quote.

 

[Crews]

First, a 100fps drop will create a mathematical shift in POI of about .25in at 100 yds (175 SMK from 2700-2600). Most long range shooters are using powder that operates within that range for their typical shooting environments year round. This is a real possibility though, and even though it's a small change, it's measurable...unlike DA changes at time of zero.


Next, I also subscribe to the concept that cold shooter shift is > than cold bore shift. Cold shooter shift is POI shift due to poor fundamentals of marksmanship on the first shot, when it matters most. Rifles Only advocates dry firing to overcome this. I think it works.

So I usually don't take any hunting shots past 600 yards. If I leave atmospheric conditions alone and simply put in a theoretical -0.25 into my zero offset, it only bumps me up 0.1mil at 600 yards. Therefore, I really get what you're saying about it really not being THAT big a deal unless you are dealing with some pretty extreme circumstances. Especially given the fact that cold shooter induced errors are a lot more likely to introduce a greater margin of error than that.

 

[GeoJoe]

Just for the record, there isn't any negative intent here, just thought it would be a good way to kick off a conversation. I assume you know that, just wanted to make sure. I think most folks here understand the context and won't jump to any conclusions from a single quote.

You’re totally good bud. ?

 

[SoCal326]

View attachment 7082082

That's some nice data. I've been looking for the same info with IMR4350. It was the only powder I could find for a while so I stuck with it. I'm about done with my keg and deciding if i want to reorder the IMR or start working with something else. Sounds like I should run the temp test myself on the IMR4350.

I always though H4350 was supposed to be pretty temp stable. Are/have people moving to RL16 for 6.5CM?

 

[spife7980]

That's some nice data. I've been looking for the same info with IMR4350. It was the only powder I could find for a while so I stuck with it. I'm about done with my keg and deciding if i want to reorder the IMR or start working with something else. Sounds like I should run the temp test myself on the IMR4350.

I always though H4350 was supposed to be pretty temp stable. Are/have people moving to RL16 for 6.5CM?

It IS pretty temp stable.

Im at .73 fps/° in my 6xc with a 105 which is a tad more than usual. Some combinations show more or less change though, maybe its just a variance between lots as well, who knows? The PRB blog got it at .21fps/° with a 6.5x47 and 140s. Other tests have shown higher and lower. Dont ever believe that it wont change at all though.

The older non-extreme and reloader powders are 1fps/° or more.

 

[Bigwheels]

In my experience trying to document MV change from temp I've noticed that the barrel has as much to do with the change as the powder does. My heavy barrel will show 1 velocity if fired after pulling everything out of the warm truck & another if I leave everything to stabilize at atmospheric temp before testing.