Accuracy lost on warmer weather

[Rflshootr]

It's possible if the previous tune was right on the edge of the node. The same with seating depths. I've seen .005 make a group go from a .6xx to a dot on more than 1 occasion, especially in thinner barrel contours.
I'd also like to add that small capacity cases show small changes faster than a large capacity case does.
I'm not saying that this is an absolute. Mechanical things change as well with big temperature changes. Something as simple as the scope rings expanding or contracting (loosening or tightening) throughout the temperature range, especially if plastic insert rings are being used.

 

[Joe-boy]

I'm curious. How many rounds were fired between these 2 shooting times ?

Maybe 200-300 or so, not that much.

Already mentioned --Most likely just fundamentals of the rifle build to load development. Example, action screws, etc.

This is without doubt worth checking, however another load performs consistently so this seems to be related to this particular load.

 

[Greyfox]

When developing a load, particularly one that will be used in widely ranging temperature I'll attempt two things. The first will be to use a powder that is labeled temperature stable, and/or I have experienced good temperature stability with other loads.
Second, I will stay away from developing a maximum velocity load, and attempt to find an accuracy node with a charge weight that demonstrates low and/or low and predictable changes in velocity/point of impact with optimum charge weight(OCW), and ladder tests.
This approach has worked well for me with both competition and hunting loads.

 

[Culpeper]

Maybe 200-300 or so, not that much.


This is without doubt worth checking, however another load performs consistently so this seems to be related to this particular load.

Or just powder choice.

 

[shooter53]

Hi, i use vit n133 in .222 I was getting the same thing happening, I load a 100 at a time 21.5gn of vit 50 grn v-max 1/2" groups at 100 yds. But after aprox 6mths the groups opened up, It didnt matter winter to summer or summer to winter It was the same, after reading an article on here about cold weld I started to loosening and reseat the bullet it worked for me, also on this load 50 or 53 gn v-max shot virtually the same

 

[Eric H]

Very good read. There's a reason PRS shooters use these powders. https://precisionrifleblog.com/2016/06/19/powder-temp-stability-hodgdon-extreme-vs-imr-enduron/

 

[Joe-boy]

Or just powder choice.

Actually the other load was using the same powder.

Apologies for filling in the information piece by piece Didn't come to think it might be worth mentioning both were using N133 powder.

 

[Culpeper]

Actually the other load was using the same powder.

Apologies for filling in the information piece by piece Didn't come to think it might be worth mentioning both were using N133 powder.

Lol, okay I'm confused now.

 

[436]

Just a thought here, try using a small box cooler on the range to keep your ammo in on those hot days, heat and most powder don't mix well shot to shot. The ammo doesn't have to be frozen just kept at cooler temperatures where your powder choice performs better. Of course, your other option is to try changing the powder to something less heat sensitive. Good luck. Cheers

 

[Mike Matteson]

Single based powders are less sensitivity than double base powders to temp change. From what I have read, 110,120, 130,140, 150, 160, and 170 are single based powder and least problem with temp.
I changed a great many years ago to H powders. Most are temp stable to withing a few fps from low to high temp.
There is other powders out there that are double base powder being made now that are more stable. Need to do some research.

 

[Doom2]

I shoot in 30 to 100 degree temps. Much like @grayfox I usually load develop in the spring or fall and use OCW. I load in the node that is lower than the max load node. It's usually wider than the max load node so I will load on the middle of the lower node. This has worked well.

 

[Joe-boy]

Just a thought here, try using a small box cooler on the range to keep your ammo in on those hot days

Excellent and simple idea, why didn't I think this myself. Thanks, gotta try this.

 

[ImBillT]

I think something else is going on.

The 53 V-Max is near the limit for a 12" twist. A friends can shoot them well under .5MOA at 100yds, but more like 4-5MOA at 500yds. That's at 3000' elevation, and we consider 85 degrees Fahrenheit to be cool. Shooting at 100+ degrees is not uncommon. Point being, he's more stable than sea level and 68 degrees F, yet he appears to suffer significantly at long range with that bullet.

That's not necessarily the problem, but I don't believe it's a powder vs temp thing. Lots of guys shoot N-130 or N-133 here, and never complain about issues occurring when it's hot(over 100 degrees).

 

[Eric H]

Excellent and simple idea, why didn't I think this myself. Thanks, gotta try this.

Bryan Litz performed this test where they went from a cooler to a hotter climate during a match and it worked. Let us know your results.