Shooting in the heat? Groups opening up.

[Turkeytider]

I have been shooting two shots, then letting it sit upright, in the shade bolt out mattress pump singing, for 15 minutes. Then two more shots.

6 shot groups.

Im not sure it is the ammo. Garmin chronograph numbers are great. Spread of 27, SD of 7.

With those numbers, I’m assuming those are hand loads. If they’re not by chance, those would be incredible numbers for factory. With that routine for cooling, I would think that you would be fine as far as barrel heat is concerned.

I use a mattress pump, but it sounds like yours has a far superior battery. May I ask which one you use? Thanks.

 

[mxgsfmdpx]

Hello. Fellow AZ resident who shoots in the heat nearly every day.

The short answer is…

1. Stop blaming something that isn’t truly affecting your accuracy.

2. Your sample size is way too small and you are getting confirmation bias from 3-5 shot “groups”.

My ammo sits in a 140 degree vehicle, cools down to 70 degrees by the time I get to shooting spot, gets pulled out and sat in the sun or shade, none of that matters.

My guns shoot cold bore and barrel so hot you can’t shoot it anymore due to mirage in scope. None of that truly affects where the bullets land.

This is all, of course, pending something in the overall rifle system isn’t loose or causing intermittent POI shift. These can include…

Barrel touching stock, loose barrel, loose action screws, loose scope bases, loose scope rings, scopes that are known to have a “wandering zero” due to vehicle rides to and from shooting spots, the list sort of goes on from there.

Once you’ve proved that none of that is causing accuracy issues, then we start to diagnose a little further with things like ammo, barrel issues, chambering issue, etc.

To blame general accuracy from a good and known gun on sunny Arizona days is not a thing, sorry to be blunt.

 

[TheCoyote]

Hello. Fellow AZ resident who shoots in the heat nearly every day.

The short answer is…

1. Stop blaming something that isn’t truly affecting your accuracy.

2. Your sample size is way too small and you are getting confirmation bias from 3-5 shot “groups”.

My ammo sits in a 140 degree vehicle, cools down to 70 degrees by the time I get to shooting spot, gets pulled out and sat in the sun or shade, none of that matters.

My guns shoot cold bore and barrel so hot you can’t shoot it anymore due to mirage in scope. None of that truly affects where the bullets land.

This is all, of course, pending something in the overall rifle system isn’t loose or causing intermittent POI shift. These can include…

Barrel touching stock, loose barrel, loose action screws, loose scope bases, loose scope rings, scopes that are known to have a “wandering zero” due to vehicle rides to and from shooting spots, the list sort of goes on from there.

Once you’ve proved that none of that is causing accuracy issues, then we start to diagnose a little further with things like ammo, barrel issues, chambering issue, etc.

To blame general accuracy from a good and known gun on sunny Arizona days is not a thing, sorry to be blunt.

You are blunt!

Let me make sure I am understanding you correctly. You are saying that temperature of the barrel and temperature of the ammo has no effect on POI at all?

 

[mxgsfmdpx]

You are blunt!

Let me make sure I am understanding you correctly. You are saying that temperature of the barrel and temperature of the ammo has no effect on POI at all?

What I’m saying is…

Let’s say nothing in your rifle/scope setup is causing an impact shift and you are a repeatable 1 MOA shooter at 100 yards (despite what the internet will tell you, the amount of shooters and gun serious that shoot 1 MOA 10+ shot groups at 100 yards are very few and far between).

So let’s say both of the above are “proven”. Now go shot a 20-30 shot group with your gun and ammo at 100 yards and wait for the barrel and ammo to be “cool” for each shot.

Then go shoot a 20-30 shot group and don’t let the barrel cool but be sure to ensure that mirage isn’t affecting your shooting.

If you are being honest with the data, nobody will be able to tell which 20-30 shot group was shot “cold” and which one was shot “hot”.

 

[aschuler]

I agree with the above. I tend to work out new gear (including loads) in the summer and I've done it enough now to prove to myself that if it works here in the summer it's going to work anywhere, anytime.

(FWIW I do use a barrel cooler, and/or a wetted cloth if its practical)

Edited to say that the heat does affect me as the shooter, the suckage goes up from that factor for sure.

 

[TheCoyote]

With those numbers, I’m assuming those are hand loads. If they’re not by chance, those would be incredible numbers for factory. With that routine for cooling, I would think that you would be fine as far as barrel heat is concerned.

I use a mattress pump, but it sounds like yours has a far superior battery. May I ask which one you use? Thanks.

I have two of them from amazon. I am not sure who makes them. Cheap china junk. I'm actually impressed they put out a lot of air and can run probably 30 minutes on a charge. Recharge them in the truck with USB-C. One is pumpin the other is charging. I'm surprised they have lasted this long.

 

[cal30_sniper]

Hot barrels can cause stresses to arise, particularly in lower quality barrels, which will cause POI shifts. Usually that’s evidenced by a shift in the group overall, not necessarily an increase in group size. Heavier profile and higher quality barrels are generally less susceptible to this effect due to a) greater heat capacity (thicker profile), b) fewer internal stresses (higher quality), c) greater stiffness to reduce the effect of internal stresses (thicker profile).

However, I can only think of a few things that would cause groups to increase in size:
A) statistically insignificant group size (as suggested above)
B) mirage or shooter comfort issues
C) ammunition velocity changes

C) is something I’ve witnessed. Depending on temperature sensitivity of the powder used, a 30 degree temp increase can have the same effect on velocity of adding multiple tenths of grains of powder. If you were set up for a velocity node and increase MV 50fps, you may very well notice a decrease in accuracy with a particular load/rifle combo. If you’re shooting statistically significant groups, are a good enough shooter to realize the potential of your setup, and seeing repeatable accuracy decrease in a known good combo, it’s probably this. That’s a lot of ‘ifs’.

Note that if it’s a velocity node issue, you’ll likely see it regardless of how quickly or slowly you shoot (assuming you don’t slow fire while leaving rounds in the chamber to cook) as the effect is driven by ambient temp/ammo temp, not barrel temp.

 

[TaperPin]

I have a problem getting good groups recently out of a new rifle that was shooting great. Is it the heat?

Was getting 0.5 MOA. Now the groups are opening up to about 1" inch, some groups are worse like 2"... Terrible for a custom rifle. Same ammo, great rest. Whats going on here?

I can only imagine that it is heat related as I am in AZ and it is pushing 90 by the time I can shoot. I have been shooting two shots and then waiting 15 minutes with a air mattress pump pushing air down the bore before shooting again.

What is going on here? Did I damage the bore cleaning it? Do new guns start shooting great and then open up? Is the barrel just getting hot and never really cooling down?

Please tell me I didn't just buy and custom rifle that shoots 2 moa!

So what have you figured out? It sounds like your method of dealing with heat is solid. 2 MOA groups are a lot. Other than checking for loose screws, I’m quick to swap scopes, and if it doesn’t make a huge difference in half a dozen shots, switch back. If your stock is injection molded plastic, they do weird things in the heat that can be hard to pin down. Bedding issues in general can give big groups. Cereal box shims between the receiver and stock will instantly show a difference if bedding is sloppy, and no difference if bedding is good.

As always I like to clean because then it’s easy to run a bore scope into the chamber to see if anything has built up. Many custom rifles have minimum dimension chambers that carbon up quick at the end of the case neck.

Really curious to hear what ends up solving the problem.