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Cold weather power factor calculations


cuzinvinny

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I'm thinking of switching from my 627 to my 929, for the upcoming steel challenge season. This change will require some cold weather load development. Planning on using Bayou 105 grain bullets, with WW231 powder. My goal is a 100 power factor load when the temperatures are in the 80's and 90's. What are your thoughts regarding the jump in power factor using WW231 at 30 degrees to using the same load at 80/90 degree temperatures. Will a power factor of 90 at 30 degrees, come in at a power factor of 100 at 80/90 degrees, or would you estimate it to be much higher? I prerfer to get all my loading done in the cold weather months so I can forget about it come spring and summer.

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I’d look for a clean load that’s accurate and not really worry about PF for steel. 

 

Not to sure how well a medium speed powder like 231 will do with a load that low. I’d try something faster. 

 

And I don’t think you will gain 100fps from a tempature change that small from any of the popular fast powders.  

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the only time i've noticed a big change in power factor from my loads was with elevation change. 

 

Like said before, I really wouldn't worry about power factor for steel challenge, as long as your close to 800 - 900 FPS call it a day and move on. 

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I know that my 124 grain loads with 4.0 grains of tightgroup at a 1.14 oak will be 15 fps faster when it's got versus cold. I'm talking cold as 15 degrees and hot in the upper 80s. It's so little of a difference I can't tell. The only thing I noticed was the more visible gas coming out of the comp on my 929 when it's cold. 

FYI the my 929 shoots bayou 160s the best but I like the recoil impulse of the 124s better.

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Here in the frigid northeast Ive developed and chrono'd loads in the winter and chrono'd again in the spring and checks here and there...Ive noticed variations of 1 maybe 2 pf in some extreme cases. So for steel develop a load that feels good and gives you positive target feedback and and never mind a pf or the minimal, if any change, with temp. Just remember too puny of a load wont give you hit feedback and can mislead you into unnecessary make up shots.  

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Especially for steel make sure it's accurate and clean at the PF you want.  Then it will for most powders increase in speed/pf slightly as it warms up.

 

Now if it's WST you will lose velocity as it is reverse temp sensitive.

I never liked 231 at lower pressures as it was dirtier than I liked.  You might also try Clays or ClayDot as they seem cleaner.

The lower pressure PF's can get tricky due to the unburnt granules.

For my 9mm semi-autos I use a 124 jhp & 3.0 titegroup for 113 pf, 124 coated 2.5 tite for 94 pf.  In my 627 I use 38 short colt and I've used 124 jhp & 3.1 clays 97 pf or 124 coated & 3.6 titegroup for 97 pf.  Same bullets for both and I didn't like the titegroup in the short colt as it left an occasional granule that I didn't see with 9mm's (in Semi-Auto though).  Also I'm told you can use the 38 short colt and it's moon clips in the 929.  If you have both try it and then resize with 9mm sizer and try it in the 627.  I'm curious myself.

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8 hours ago, RePete said:

 

A medium speed powder would be WW540 or Alliant Unique.

WW231 is akin to Bullseye.

231 is next to unique on the burn chart I have. Only 2 powders between them. And Bullseye is quite a ways up the list. 

 

I’m not saying 231 is slow compared to all pistol powders, I’m saying it’s slow compared to the majority of 9 minor powders that are used today. 

 

That said, I think 231 is too slow for a sub minor load, and I would start with titegroup or bullseye. Then I would look for even faster powder because you won’t get a complete burn at that light a charge at that speed. 

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the only time i've noticed a big change in power factor from my loads was with elevation change. 
 
Like said before, I really wouldn't worry about power factor for steel challenge, as long as your close to 800 - 900 FPS call it a day and move on. 
What do you see with elevation change? I live in Colorado and I seem to pick up at least 5 pf every time I leave the state.
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I live near the North East coast, 30'-40' elevation

 

I remember in Reno a couple years ago, 4500' above sea level, I was about 10-12 power factor higher than at home . 

Edited by alecmc
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I live near the North East coast, 30'-40' elevation
 
I remember in Reno a couple years ago, 4500' above sea level, I was about 10-12 power factor higher than at home . 
Interesting. I've wondered if I just have a slow chronogaph.
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On 1/19/2019 at 7:27 AM, alecmc said:

I live near the North East coast, 30'-40' elevation

 

I remember in Reno a couple years ago, 4500' above sea level, I was about 10-12 power factor higher than at home

I had the opposite end of the spectrum. I chrono'd at 60 degree's at 800' elevation 1 week before the IRC and was at 128pf. When I chrono'd at the IRC in AZ at 85-90 degrees at

around 1900' I was only a 122pf. I expected a result similar to yours so Im still suspicious about it. Unless A#2 is reverse temp sensitive to elevation/temp (cant find any indicators it is) Either my Chrono or the match one was off. 

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On 1/18/2019 at 11:34 AM, BallisticianX said:

Here in the frigid northeast Ive developed and chrono'd loads in the winter and chrono'd again in the spring and checks here and there...Ive noticed variations of 1 maybe 2 pf in some extreme cases. So for steel develop a load that feels good and gives you positive target feedback and and never mind a pf or the minimal, if any change, with temp. Just remember too puny of a load wont give you hit feedback and can mislead you into unnecessary make up shots.  

This only works if the powder isn't temp sensitive. I've been running the same load for basically a year now and I get about a 5PF swing, which is no bueno when I had my stuff dialed in at 129pf. Then again it could be elevation, or some other thing, or just because of the differences in chronographs. Finally I got sick of worrying, after a 125.4pf and bumped it up to 135 for Nats. My chrono and whatever they used for USPSA Nats and IPSC Nats are very close to each other. Area 5 was very very low. It could just also be s#!t just averaging out. I shoot 8 out of the gun and take the average and keep in mind the lower numbers just in case. I measure out 10 drops of powder so I get an average to the hundredth of a grain.
 

I'm using Bullseye, FWIW, not sure if it's temp sensitive or not. Or if things like humidity affect it (doesn't seem to, comparing Mesquite to Frostproof), etc.

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On 1/19/2019 at 7:27 AM, alecmc said:

I live near the North East coast, 30'-40' elevation

 

I remember in Reno a couple years ago, 4500' above sea level, I was about 10-12 power factor higher than at home . 

Were those your special chrono rounds? :P

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7 hours ago, swordfish said:

This only works if the powder isn't temp sensitive. I've been running the same load for basically a year now and I get about a 5PF swing, which is no bueno when I had my stuff dialed in at 129pf. Then again it could be elevation, or some other thing, or just because of the differences in chronographs. Finally I got sick of worrying, after a 125.4pf and bumped it up to 135 for Nats. My chrono and whatever they used for USPSA Nats and IPSC Nats are very close to each other. Area 5 was very very low. It could just also be s#!t just averaging out. I shoot 8 out of the gun and take the average and keep in mind the lower numbers just in case. I measure out 10 drops of powder so I get an average to the hundredth of a grain.
 

I'm using Bullseye, FWIW, not sure if it's temp sensitive or not. Or if things like humidity affect it (doesn't seem to, comparing Mesquite to Frostproof), etc.

My experience with bullseye was that it was temp sensitive. I dont recall the pf swing from cold to hot but it did change. That was one of the reasons I switched over to Titegroup, it was more forgiving with temp changes. All powders are temp sensitive. Its just how much they engineer them to limit it. Bullseye had nothing in the formula to combat it where titegroup does and my experience shows it. 

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5 hours ago, RePete said:

Bullseye is temperature sensitive, the colder it gets, the lower the velocity,  and the hotter it gets, the velocity goes up.

 

I learned this in the "80's shooting PPC.

That's what I've found on most powders and can plan for it.  The reverse where they lose velocity as it gets hot are harder for me to adjust for.

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