Accurate #7 temperature sensitivity affecting PF?

[nelson1each]

So I’m still new-ish to open. Been loading 9 major with AA#7 and Montana gold 124’s. In the heat of summer I started with 9.3 gr and it was just borderline for major PF so I bumped it up to 9.6 and it was coming in at 174 PF...bonus it made the comp work better so the dot tracked better. I shot the GA state match with that load and chrono’d there at 174 so I was like yup this load is dialed in and perfect. Mind you all that this was in the dead of summer GA heat and humidity. Fast fwd to today. I had to chrono some other stuff so I decided to spot check my current major load expecting to see similar results....nope 164...a whole 10pf lower than I was expecting. It was like 55 degrees with no humidity. Talked to an open guru and suggested to look into the AA#7 powder sensitivity. Website does say it can change 3-5% with extreme temp differences which mathematically accounts for the 50-60 FPS difference drop resulting in 10pf lower. I’ve never seen or dealt with this before so I figured I’d post and see what some of you had to say about this. Read a lot of posts on here over the years and never come across anyone talking about pf changing so drastically with a certain powder or temp. I’m certainly glad I spotted checked the chrono before showing up to the FL state match in a few weeks! 

[nelson1each]

If it matters I forgot to mention...I’m shooting a ck arms thunder open gun. Barrel has 3 holes. Bullet OAL is 1.165. Using a chrony master chronograph that I just recently had rebuilt by the manufacturer.

[36873687]

I need to check mine this winter. I’m using same set up ck with 3 1/8 holes. 172 pf an 171.8 at both majors I shot this yr. my local open guru put couple rounds in freezer an went to crono. He didn’t get 10 pf lose but it was noticeable. 

[racer-x]

Wow.

I've used quite a bit of AA7 and chrono'd in a wide range of temps. Never seen a swing like that. My guess is something else is wrong (charge, bullet weight or velocity). I suggest you verify each piece of this equation.

 

-your scale calibration.

-average weight of your powder charge. I drop 4 charges, weigh that and divide by 4 for a more precise average when setting/checking my powder charge.

-bullet weight. Sounds crazy, but I've seen some significant variations in this before.

-verify your chronograph against another chrono or with a other known loads.

 

Also, I've chrono'd that same load in my CK Thunders and it was always near 169-170PF in my guns - 9.6 AA7 -MG124JHP - 1.165 OAL. I shoot mostly 115's now(10.7@1.165) , but never had a variation like that over temperature with any of my AA7 loads.

[Jfitz427]

I’m having the same issue but with hs6. Load chronod in the 100 degree N.C. summer at around 168-169pf, and the same load was down 10-12pf a few weeks ago at around 45-50 degrees. I’m gonna probably going to have to go from 7.5 up to 8gs to get back to 168-170. I guess all powders have some degree of sensitivity. But us here in the south it really shows due to the extreme temps in the summer. 

[TRPOperator]

I run aa7 9.4 grns @ 1.165 with a pd 124 grn jhp through an akai v6 9mm. I have shot the round back in the summer at around 95° and just the other day at 38° and it was still over a 170pf. Summer was around 176 recently around 173. 

 

racer-x I do the same with powder an do a avgerage of 5 drops. 

[Stymie12000]

My loads are running 35-40fps slower in the cold. That's a 115gr. 

 

Summer (80 degrees) 1510fps, winter (40 degrees) 1475 fps.

 

That's with 10.4gr #7...

[Aircooled6racer]

Hello: An easy way to test powder sensitivity is to cool it down. What I do is put 20 rounds in a plastic baggy and then put it in the freezer. I then take them to the range packed in ice still in the baggy in a ice chest/cooler. Chrono them cold then test your other ones that have not been cooled down to see the difference. Some powders speed up when cold and some slow down. Thanks, Eric

[191138sc]

AA#7 is one of the best metering powders on the market and I have found to be temperature insensitive. You might also check for something else like OAL. If your shell plate is too loose, you will get wide OAL variation which will affect PF.

[Hi-Power Jack]

3 hours ago, Aircooled6racer said:

  put 20 rounds in the freezer.  Chrono them cold then test your other ones that have not been cooled 

 

I wonder if part of the difference is velocity is the temperature of the gun barrel ??    

 

Therefore, it would make sense to test cold ammo in a cold gun, and vice versa.

 

No scientific or personal facts, just conjecture.      

[nelson1each]

Awesome guys...thanks for all the good info. I’ve checked the OAL and it’s still a solid 1.165. Averaged out the powder drop and 9.6 was the solid average. I’m bumping up to 9.8 and gonna go get some more action on the chrono. If you could’ve only seen me at the range crunching numbers that were shockingly low...it was quite amusing. Glad to hear I’m not completely crazy

[nelson1each]

Update. Did some more chrono work today. My chrono was averaging about 1-2pf higher in the shade since it was cloudy today making the ammo about 7-8pf lower. I think it’s safe to conclude #7 is temp sensitive enough to affect PF. I don’t have access to another chrono anytime soon to rule out any possible chrono issues so I will adjust the load a bit and get to compare it to the FL state chrono soon enough. I have never shot another powder yet in 9 major but will be looking at sampling some others in hopes to find a more stable load. 

[racer-x]

On 12/17/2018 at 10:20 PM, racer-x said:

Wow.

I've used quite a bit of AA7 and chrono'd in a wide range of temps. Never seen a swing like that. My guess is something else is wrong (charge, bullet weight or velocity). I suggest you verify each piece of this equation.

 

-your scale calibration.

-average weight of your powder charge. I drop 4 charges, weigh that and divide by 4 for a more precise average when setting/checking my powder charge.

-bullet weight. Sounds crazy, but I've seen some significant variations in this before.

-verify your chronograph against another chrono or with a other known loads.

 

Also, I've chrono'd that same load in my CK Thunders and it was always near 169-170PF in my guns - 9.6 AA7 -MG124JHP - 1.165 OAL. I shoot mostly 115's now(10.7@1.165) , but never had a variation like that over temperature with any of my AA7 loads.

 

32 minutes ago, nelson1each said:

Update. Did some more chrono work today. My chrono was averaging about 1-2pf higher in the shade since it was cloudy today making the ammo about 7-8pf lower. I think it’s safe to conclude #7 is temp sensitive enough to affect PF. I don’t have access to another chrono anytime soon to rule out any possible chrono issues so I will adjust the load a bit and get to compare it to the FL state chrono soon enough. I have never shot another powder yet in 9 major but will be looking at sampling some others in hopes to find a more stable load. 

 

AA#7 is a very slow powder, so bumping your charge up a few tenths (check your primers for pressure signs) shouldn't be a problem. The CK Thunder runs great at 175PF.

Not sure I would conclude your 7-10PF reductions are due to the temp though. MG bullets have been very consistent weight for me - unlikely yours are substantially heavier. Wouldn't hurt to weigh them though.

 

Your powder scale or chrono may not be accurate. Are you able to check calibration of your scale?

Also, have you using a different batch of powder now compared to when you chronod higher PF? I've had a +8PF change in my 38S load with a new batch of powder (VV 3N38) a few years back - it happens.

 

[MikeBurgess]

On 12/17/2018 at 6:50 PM, nelson1each said:

So I’m still new-ish to open. Been loading 9 major with AA#7 and Montana gold 124’s. In the heat of summer I started with 9.3 gr and it was just borderline for major PF so I bumped it up to 9.6 and it was coming in at 174 PF...bonus it made the comp work better so the dot tracked better. I shot the GA state match with that load and chrono’d there at 174 so I was like yup this load is dialed in and perfect. Mind you all that this was in the dead of summer GA heat and humidity. Fast fwd to today. I had to chrono some other stuff so I decided to spot check my current major load expecting to see similar results....nope 164...a whole 10pf lower than I was expecting. It was like 55 degrees with no humidity. Talked to an open guru and suggested to look into the AA#7 powder sensitivity. Website does say it can change 3-5% with extreme temp differences which mathematically accounts for the 50-60 FPS difference drop resulting in 10pf lower. I’ve never seen or dealt with this before so I figured I’d post and see what some of you had to say about this. Read a lot of posts on here over the years and never come across anyone talking about pf changing so drastically with a certain powder or temp. I’m certainly glad I spotted checked the chrono before showing up to the FL state match in a few weeks! 

is the ammo your checking loaded with the same lot# as the original test?  there can be large variations in loads required for different lots of powder. A friend of mine loads aa7 and one lot change took almost a grain more for the same PF.

[TRPOperator]

I was just out today on the Chrono with 9.4 grns of AA7 @38° and it was still around 174pf out of my gun. Which is what it consistently chronoed all year. So it could be the lot# for the powder 

[MemphisMechanic]

His chrono seems like the biggest suspect variable to me.

 

I had sketchy luck with that brand of chrono in the past. My current ProChrono Digital almost doesn’t care what light you use it in. As long as it has some.

 

I’d borrow a buddies chrono and line them up so you can shoot through them both, personally.

[nelson1each]

It’s is not the same lot of powder as I’m on to a different 8lb jug of it. I certainly can’t rule out a chrono issue as I don’t have access to another anytime soon to check that but I will be able to see what the chrono at FL state says it is. As far as variables go using that chrono some other ammo/powders I have been checking have had no deviations that I can note but can’t say 100% if it’s a chrono issue until I get a chance to compare it against another. Also of note the chrono did have an issue in the past and it was recently rebuilt by the company. The different lot number though is certainly a thing. I have calibrated my powder measure and that seems to be fine. All part of the learning game I suppose. All the input is appreciated guys.

[theWacoKid]

2 hours ago, nelson1each said:

It’s is not the same lot of powder as I’m on to a different 8lb jug of it. I certainly can’t rule out a chrono issue as I don’t have access to another anytime soon to check that but I will be able to see what the chrono at FL state says it is. As far as variables go using that chrono some other ammo/powders I have been checking have had no deviations that I can note but can’t say 100% if it’s a chrono issue until I get a chance to compare it against another. Also of note the chrono did have an issue in the past and it was recently rebuilt by the company. The different lot number though is certainly a thing. I have calibrated my powder measure and that seems to be fine. All part of the learning game I suppose. All the input is appreciated guys.

 

Always test and adjust your load when going to a different lot of powder.  In fact, I do this even if going to a new jug of the same lot.  This variable creates the widest variation in pf that I've found.

[nelson1each]

7 hours ago, theWacoKid said:

 

Always test and adjust your load when going to a different lot of powder.  In fact, I do this even if going to a new jug of the same lot.  This variable creates the widest variation in pf that I've found.

Have you found this to be more frequent in AA#7? Or more of a general statement for any powder you work with?

[Sarge]

2 minutes ago, nelson1each said:

Have you found this to be more frequent in AA#7? Or more of a general statement for any powder you work with?

Any powder. I use WAC and it varies widely from jug to jug.

[theWacoKid]

1 hour ago, nelson1each said:

Have you found this to be more frequent in AA#7? Or more of a general statement for any powder you work with?

Everything, #7 included. 

[racer-x]

On 12/19/2018 at 4:50 PM, racer-x said:

...

Also, have you using a different batch of powder now compared to when you chronod higher PF? I've had a +8PF change in my 38S load with a new batch of powder (VV 3N38) a few years back - it happens.

 

I've experienced variations between lots of powders many times over the years with the powders  I use most. Enough so that I always verify my loads over the chrono when I open a new container. I haven't ever found a significant difference in the same lot of powder, but I still check & verify to be sure.

 

For the record, in the 16 containers of AA7 I've used recently, I have not found a single significant variation. AA7 has been very consistent for me.

Variations are always possible though, so its best to verify whenever starting a new container of powder.

[d_striker]

The best way to check for temp sensitivity is to do it yourself.  Put 10 rounds in a ziplock bag and put in a cooler of ice on your way to the range.  Then heat up 10 rounds.  In the summer, I simply put 10 rounds in a plastic ammo box and let sit in the sun for a bit until the brass is hot to the touch.  Chrono both and you'll see how temp sensitive that powder is.  If it's cold out, I'll heat up the ammo on the car defroster.

 

I do this before settling on any powder as temp sensitivity is too much of a variable for me to deal with at majors.  We spend thousands of dollars traveling to matches.  It's not worth it to stress about potentially going minor at a major.

 

Here was my latest test I did a few weeks ago.

 

Edited December 22, 2018 by d_striker

[bigboy69]

I've never had a problem. In the summer or winter I get 173 - 174 PF

10.3g with a 125gr blue bullet. 38 super

[muncie21]

Because of the crazy temperature swings here lately, I was able to chrono the same loads at 34*F and 52*F.  WAC, #7 and SW major were all within the SD of error when comparing loads shot on the colder day to ones from the warmer day.  Granted it was only ~15* difference.