Accuracy lost on warmer weather

[Radman]

Any thoughts from the more experiences ones? Executive summary: groups nicely in the cold and crappy in the summer heat.

2-3 years ago I developed a load for 53 grain Hornady v-max for my .223 chambered CZ 527 that has an 1:12" barrel. I developed the load in the wintertime around freezing point and was relatively happy with how it worked. I used it for raccoon dog hunting and plinking for a while, until last summer I went shooting on a very hot day (around 30 deg C or 86 deg F) and got crappy groups. Like real crappy, around 2-3 MOA at 100 meters. I just thought I had screwed up something the previous time when developing the load and hadn't tested it properly and didn't think about it that much. I had not much of those left so I shot them away and proceeded to develop a new one with different brass.

This time I again got a load that grouped nicely below freezing point. From my archive I was able to find e.g. a 8 shot group of 0,66 MOA that wasn't cherrypicked but was pretty consistent with how it grouped; also 8 shot group already proves a bit more than cherrypicked 3 shot groups. Forward 6 months; I went to range when the temperature was about 20 deg C = 68 deg F. Again really crappy grouping. My 13-shot group was 2.3 MOA and doesn't get much better by excluding a flyer or two; it was consistently crappy. The bullet holes are nonetheless nice and round.

The load is developed using a ladder test and is using Lapua Match brass and Vihtavuori N133 powder which shouldn't be too temperature sensitive.

I guess there are basically two alternatives: either the muzzle velocity or the muzzle time changes enough to somehow screw up the barrel harmonics, or then the stability is compromised as the 53gr vmax is quite a long one for a 1:12" twist. However, I'd assume the stability should be better in the summer with the thinner air and probably increased muzzle velocity.

I never shoot heavier than 50 grain ammo out of a. 22-250 with 1:12. 1:9 = 55 grain or heavier.

 

[Culpeper]

Go back to the OP. His good groups were around 32 degrees and his bad groups were around 86 degrees. That is not a large shift to blame the weather temps. I think we can eliminate that variable. Also, he has another rifle using the same powder but different caliber and shoots fine in that temperature range. The OP thinks he may have a small MV window or a bullet stability problem. The former makes more sense. It is back to double checking his load and rifle.

 

[Weatherbyshooter/Hunter]

Any thoughts from the more experiences ones? Executive summary: groups nicely in the cold and crappy in the summer heat.

2-3 years ago I developed a load for 53 grain Hornady v-max for my .223 chambered CZ 527 that has an 1:12" barrel. I developed the load in the wintertime around freezing point and was relatively happy with how it worked. I used it for raccoon dog hunting and plinking for a while, until last summer I went shooting on a very hot day (around 30 deg C or 86 deg F) and got crappy groups. Like real crappy, around 2-3 MOA at 100 meters. I just thought I had screwed up something the previous time when developing the load and hadn't tested it properly and didn't think about it that much. I had not much of those left so I shot them away and proceeded to develop a new one with different brass.

This time I again got a load that grouped nicely below freezing point. From my archive I was able to find e.g. a 8 shot group of 0,66 MOA that wasn't cherrypicked but was pretty consistent with how it grouped; also 8 shot group already proves a bit more than cherrypicked 3 shot groups. Forward 6 months; I went to range when the temperature was about 20 deg C = 68 deg F. Again really crappy grouping. My 13-shot group was 2.3 MOA and doesn't get much better by excluding a flyer or two; it was consistently crappy. The bullet holes are nonetheless nice and round.

The load is developed using a ladder test and is using Lapua Match brass and Vihtavuori N133 powder which shouldn't be too temperature sensitive.

I guess there are basically two alternatives: either the muzzle velocity or the muzzle time changes enough to somehow screw up the barrel harmonics, or then the stability is compromised as the 53gr vmax is quite a long one for a 1:12" twist. However, I'd assume the stability should be better in the summer with the thinner air and probably increased muzzle velocity.

My experience has been the same living in Arizona. "Winning in the Wind" author an F-class competitor had a segment regarding powder temperature while developing loads. What his solution was put his reloads in a cooler with the desired temperature during his load development. That worked for me during our convection oven temperatures in Phoenix.

When I develop loads, I take my best load group, velocity, ambient temperature, and energy, input the data in a spreadsheet. with the powder temperature change i.e. 1.5 FPS per degree in temperature rise and forecast what changes in velocity as it gets warmer.

Quick load will help as well, you can input the desired temperature and see the changes in velocity and chamber pressures if you have access to the software.

I'm not an expert here and certainly there are more knowledgeable shooters however I hope this helps.

 

[Kmccord]

Any thoughts from the more experiences ones? Executive summary: groups nicely in the cold and crappy in the summer heat.

2-3 years ago I developed a load for 53 grain Hornady v-max for my .223 chambered CZ 527 that has an 1:12" barrel. I developed the load in the wintertime around freezing point and was relatively happy with how it worked. I used it for raccoon dog hunting and plinking for a while, until last summer I went shooting on a very hot day (around 30 deg C or 86 deg F) and got crappy groups. Like real crappy, around 2-3 MOA at 100 meters. I just thought I had screwed up something the previous time when developing the load and hadn't tested it properly and didn't think about it that much. I had not much of those left so I shot them away and proceeded to develop a new one with different brass.

This time I again got a load that grouped nicely below freezing point. From my archive I was able to find e.g. a 8 shot group of 0,66 MOA that wasn't cherrypicked but was pretty consistent with how it grouped; also 8 shot group already proves a bit more than cherrypicked 3 shot groups. Forward 6 months; I went to range when the temperature was about 20 deg C = 68 deg F. Again really crappy grouping. My 13-shot group was 2.3 MOA and doesn't get much better by excluding a flyer or two; it was consistently crappy. The bullet holes are nonetheless nice and round.

The load is developed using a ladder test and is using Lapua Match brass and Vihtavuori N133 powder which shouldn't be too temperature sensitive.

I guess there are basically two alternatives: either the muzzle velocity or the muzzle time changes enough to somehow screw up the barrel harmonics, or then the stability is compromised as the 53gr vmax is quite a long one for a 1:12" twist. However, I'd assume the stability should be better in the summer with the thinner air and probably increased muzzle velocity.

I am reading this and you mention very hot day with 86 degrees and kind of chuckle, that is five degrees hotter than our morning low right now in TX. However, back to your problem, first thing I would say is Temp stable powder, not sure how temp stable is your powder, second would be rate of fire, not sure how fast you are firing and the contour of your barrel. Something else to consider, this has happened to me, I was shooting my 28N using H1000 for the load in a 195gr Berger, testing it before the start of deer season, it was in the mid 80's bright and sunny sitting on my bench with the ammo box open, first shot good, second shot also good, third was a little stiffer, thought that was odd, fourth was noticable more pressure. I noticed a bright shiny spot on my brass and flatten primer. I picked up the next one and that is when it hit me the cartridges are sitting in full sun heating up and causing pressure. I had to put those away for thirty minutes in the shade until they cooled down enough to stop the pressure spike. Not sure if you had the same scenario, i did not read all of the responses.

 

[ImBillT]

Ok, freeze some, and let me know how it works out. You might be right, I'm just thinking back to something that I read in the past that kinda stuck in my mind and thought it might be cautionary to pass it on, yep... I could have remembered it wrong that's life, If it's not a problem... freeze the "H" out of it. Cheers

I had a complete miss on a large elk that really bothered me, but when I shot a target the gun was dead on. I eventually wondered if the fact that it was 12 degrees outside had anything to do with being two feet high. I put the rifle, ammo included, into my deep freezer overnight, and zipped to the range in the morning while temps were in the low 20's. Gun shot dead on. No pressure signs either.

 

[Mike Matteson]

My experience has been the same living in Arizona. "Winning in the Wind" author an F-class competitor had a segment regarding powder temperature while developing loads. What his solution was put his reloads in a cooler with the desired temperature during his load development. That worked for me during our convection oven temperatures in Phoenix.

When I develop loads, I take my best load group, velocity, ambient temperature, and energy, input the data in a spreadsheet. with the powder temperature change i.e. 1.5 FPS per degree in temperature rise and forecast what changes in velocity as it gets warmer.

Quick load will help as well, you can input the desired temperature and see the changes in velocity and chamber pressures if you have access to the software.

I'm not an expert here and certainly there are more knowledgeable shooters however I hope this helps.

It's one thing to match shoot and it's another hunting in the field. The field you have to deal with what the weather is. Hot, Cold or Inbetween. I wouldn't think somebody would be carrying a cooler around with them hunting, unless road hunting. It's my understanding that the match shooting are using powders that aren't as temp sensitive. Like Varget, H4350, H4831 are some of the powder is my understanding. Your valid input is good at the range, but that's about the only place it does.
You have to know how you loads works in a types of weather. -20 to 110+.

 

[Teri Anne]

It's one thing to match shoot and it's another hunting in the field. The field you have to deal with what the weather is. Hot, Cold or Inbetween. I wouldn't think somebody would be carrying a cooler around with them hunting, unless road hunting. It's my understanding that the match shooting are using powders that aren't as temp sensitive. Like Varget, H4350, H4831 are some of the powder is my understanding. Your valid input is good at the range, but that's about the only place it does.
You have to know how you loads works in a types of weather. -20 to 110+.

It is virtually impossible to calculate the differences from -20 to +110. Too many factors to consider which include not only the differences in powder, whether it is temp sensitive or not. I doubt that there is a powder out there that is not affected by that extreme a temperature change. Powder not withstanding the effect of temperature on the rifle itself can cause all kinds of changes. Expansion and contraction of the metal as well as both wood or plastic stocks will affect how the rifle shoots. Name of the game remains, zero your rifle at the temperature you expect to encounter with the thought in mind that any drastic variation is going to cause issues.

 

[cajun]

Working up max loads close to the lands in winter and shooting that load in summer is generally not a good practice.

 

[Mike Matteson]

I haven't had a problem in shootng in -20 weather to 110+weather. It's all about knowing what and how your rifle shoots. The others is what type of powder you are using. Here a chart on Hodgdon Powders on temps sensitivity powders. Especially look at H4350, H4831, and Varget powders. Compair to other powders listed in the chart. That should open your eyes up. There only one double base powder I use in one hunting rifle, and it was tested in hot weather. that where it has been used at. the most of my shot while huntng have been one shot kills. In all types of weather and yardage from 30 to 500. I haven't work out any longer shots than that with my rifles. I do know that I can't achieve the same velocity between the single and double based powders. Generaly found that the single base powder are just a little slower, not much but some. At the same time I have a very narrow range of powders I use.
Double base powder are generally far more sensitivity to temp changes. There is some powder I won't even use for my hunting ammo.
Do some reading on double and single base powders.

 

[Weatherbyshooter/Hunter]

It's one thing to match shoot and it's another hunting in the field. The field you have to deal with what the weather is. Hot, Cold or Inbetween. I wouldn't think somebody would be carrying a cooler around with them hunting, unless road hunting. It's my understanding that the match shooting are using powders that aren't as temp sensitive. Like Varget, H4350, H4831 are some of the powder is my understanding. Your valid input is good at the range, but that's about the only place it does.
You have to know how you loads works in a types of weather. -20 to 110+

 

[Weatherbyshooter/Hunter]

Not implying taking a cooler hunting, but when developing a load for hunting at let's say 30 degrees , find that node etc. then later in the summer take that load and shoot at 85 degrees try to keep your rounds at a temperature you found that node? I developed loads at 45-50 degrees because I hunt in that temperature therefore when I practice 500 or more yards in the spring and summer preparing then I keep my rounds in a cooler to mimic the temperature I developed my loads. If it works for guys that shoot 1000 yards why not ?

 

[Mike Matteson]

Your Not Carrying the Cooler? In the past I develop loads in what ever weather it was and petty much do the same now. Being I was mostly in S. Cal it didn't make much differents. I had a load in IMR powder that was grouping under 1/2" @ 100yds. Temp was in the 40's to 50 range. Let it set until later on that year or end of June (80-90 dgrs). I fired round a shot using the same load figuring on shooting 5 rounds. It blew the primer out of the primer pocket. When home that day and took apart 49 rounds. Gave-a-way about 16 lbs of powder.
The other is once I develop a load for that rifle. It's what I stay with. First in grouping, then cold bore shots. If not on the money, I contenue working on the load until I achieve that. Weather be dam. All cold or hot weather does is increase or decrease the velocity of the bullet. Grouping should stay about the same That does change the hit location some. Again it goes back to what type of powders you are using.
What types of powders are you using? Did you open up the chart I sent out?

 

[3chester]

Probably never gonna pick 110F as a day to shoot but, if it's a Bluebird cold Winter day,with zero wind, will usually just keep the rounds in an inside coat pocket for a little heat. If have to practice in brutally hot weather,a guy can just keep cartridges in a shady spot, out of direct Sun, helps a bit on the consistency.

 

[M1A1ABRAMS]

Your Not Carrying the Cooler? In the past I develop loads in what ever weather it was and petty much do the same now. Being I was mostly in S. Cal it didn't make much differents. I had a load in IMR powder that was grouping under 1/2" @ 100yds. Temp was in the 40's to 50 range. Let it set until later on that year or end of June (80-90 dgrs). I fired round a shot using the same load figuring on shooting 5 rounds. It blew the primer out of the primer pocket. When home that day and took apart 49 rounds. Gave-a-way about 16 lbs of powder.
The other is once I develop a load for that rifle. It's what I stay with. First in grouping, then cold bore shots. If not on the money, I contenue working on the load until I achieve that. Weather be dam. All cold or hot weather does is increase or decrease the velocity of the bullet. Grouping should stay about the same That does change the hit location some. Again it goes back to what type of powders you are using.
What types of powders are you using? Did you open up the chart I sent out?

It sure got me thinking. Especially as a new reloader. I need to stay away from temp sensitive powders till I feel a bit more comfortable. And even then I may not use them, unless it's just to shoot it up for a day of fun. And a little trigger time. I believe I am going to stock up on powders that are not sensitive to temps.