Temperature Effects on accuracy

Lowry Wilson · Oct 9, 2014

Last March, temps in the 40's, I worked up a nice load for my .45-70 Marlin '95 (55gn H. Varget behind Remington 405gn SJSP (approx. 1700fps) and kept acceptable 6" group at 200yds, with factory iron sights. Yesterday, at 91F, exact same load, only got a 10"gp at 200yds, high and left (However, did notice that the very first round shot was in the ten ring). Did notice that the barrel got real hot after three rounds (didn't do that at 40degF) and accuracy got worse. When I let the barrel cool down for 20 min. accuracy improved (one shot at a time every 10 min). Question?-can ambient temperature really effect the accuracy that much? If so, is it the ammo temp, barrel temp, should my load be reduced, or what? Tks

Combloc · Oct 9, 2014

I know that the POI on my M1 Rifle is different in the cold of winter than it is in the heat of summer and it doesn't seem to change as the rifle warms up.

Streetgang · Oct 9, 2014

Not to throw this thread off track but Lowry Wilson is a unique handle. Would you be an ex motorcycle racer?

BradMacc82 · Oct 9, 2014

Powders can be affected by a noticeable degree in different temperatures. Hotter temperatures can increase the burn rate, IIRC.

I'm just starting to use Varget, so I can't say how temperature sensitive it is.

BigDaddy · Oct 9, 2014

According to Hogdon, in a .308 between 0 and 125 F, the velocity changes on 8 fps.
http://www.hodgdon.com/smokeless/extreme/page2.php#top
The ambient temperature definitely affects how fast the barrel heats up. At 103 degrees in west Texas, my 22-250 is too hot to touch after 2 shots.

The Marlin forum seems to have crashed on me. Mixed feelings about Varget from what I gather, but maybe that is just in cast bullets. I do not know anything about accurizing lever actions, so anything else I say would just be blowing smoke.

Twanger · Oct 9, 2014

My experience is that "it depends on the gun, the load, and the temperature of the day."

I have a 45-cal heavy-barreled muzzleloader that shoots all-lead conical bullets. The 'action' is bedded. This gun doesn't seem to care how hot the day is, or how fast it's shot. Of course, how fast can you really shoot a muzzleloader?

My 6.8 SPC with 16-in standard barrel is VERY picky about how fast it gets shot.

The Encore muzzleloader shooting sabots with maximum powder loads on hot days is also picky about rate of fire. I keep the sabots in a cooler full of ice, along with two wet towels. The towels go on the barrel to cool it down, alternating as they get hot. If the barrel gets too hot I think the sabots come apart before exiting the barrel. With a cold slug cooling the sabot and a not so hot barrel, it keeps things on the cool side of sabot blow-out land.

BradMacc82 · Oct 9, 2014

BigDaddy said:
According to Hogdon, in a .308 between 0 and 125 F, the velocity changes on 8 fps.
http://www.hodgdon.com/smokeless/extreme/page2.php#top

To be fair, you're referencing their extruded "Extreme" series of powders, which they've spent a fair amount of time on developing them to be less temperature sensitive than other powders. Which Varget is labeled as, so...

From 0 to 125 degrees, a variation of almost 200fps isn't unheard of - depending on the powder being used and the caliber.

Now in the OP's case, barrel temperature could play an effect. Also worth asking if he'd cleaned the rifle before shooting or during shooting? Was any type of copper removing solution used? Same range as previous trip? Wind conditions from first and current trip? Sight's adjusted?

BigDaddy · Oct 9, 2014

BradMacc82 said:
To be fair, you're referencing their extruded "Extreme" series of powders, which they've spent a fair amount of time on developing them to be less temperature sensitive than other powders. Which Varget is labeled as, so...

I didn't pick Varget randomly, the OP is using it, so unless there are two vesions of Varget, then velocity/pressure isn't his problem.

Aside from your other excellent points, there are some days where the problem is the jerk on the trigger, like when I worked 3rd shift (and 1st and 2nd) and after 5 cups of coffee I went to the range.

BradMacc82 · Oct 9, 2014

BigDaddy said:
I didn't pick Varget randomly, the OP is using it, so unless there are two vesions of Varget, then velocity/pressure isn't his problem.

D'oh, lapse on my end...

Aside from your other excellent points, there are some days where the problem is the jerk on the trigger, like when I worked 3rd shift (and 1st and 2nd) and after 5 cups of coffee I went to the range.

I think we all know those days very well.

Shooting a gnat's ass one day, hardly hit the side of a barn from inside the barn the next day.

I wonder if he was using the same lot # of powder as well? Hodgdon tries to make everything consistent lot to lot, but there is the possibility...

IndispensableDestiny · Oct 15, 2014

I've found that tubular magazine lever guns shoot high and to one side when they heat up. It's just the nature of barrel being strapped to the magazine tube. My Marlin 1894 does it. It makes it hard to develop a load.

My Browning BLR with a detachable box magazine doesn't do this.

Bald Fat Guy · Oct 16, 2014

Another vote for the bbl heating up, and the side effects thereof.

trickg · Oct 16, 2014

BradMacc82 said:
Powders can be affected by a noticeable degree in different temperatures. Hotter temperatures can increase the burn rate, IIRC.

I'm just starting to use Varget, so I can't say how temperature sensitive it is.

I watched a thing about the Canadian sniper team who made a record long kill with a McMillan Tac-50, .50 caliber sniper rifle. At that distance and elevation in the mountains, they had the scope doped to the max, they'd switched to American ammo, which was a bit hotter than their Canadian rounds, and they were trying to warm the rounds up in the sun to get a hotter burn rate so they could lob the shot to the target for a hit. At least that's how I remember it.

In any case, I'd say that yes, temperature affects accuracy.

Bald Fat Guy · Oct 17, 2014

Yes , tempeature *can* effect the powder burning charactics, sometimes by quite a bit. One scenatio is a North American sportsman working up a load for african hunting in cool weather at home , and having sticky extraction in 100deg weather on the hunt. Some data for some African ctgs advises dropping 5% from loads developed in cool weather.

The other way around isn't as specacular , the velocity is simply lower than anticipated, but nothing blows up or malfunctions.

BUT in this specific case , the OP stated he used Varget. Varget was the first powder introduced in Hodgons Extreme line of powders. Said powders are engeneered so as to have temperature effect so minimal as to be ignored. Their advertising touted a particular Vatget load with single digit change over wide temp range.

So yes , in his case sounds like it is the effect of heat on the bbl .

Erno86 · Oct 22, 2014

"Increasing the temperature or altitude will increase the ballistic coefficient. Increasing the barometric pressure decreases the ballistic coefficient.
Fluctuations in the humidity level will also change the air density and ballistic coefficient, but the amount is about 1 percent, but it is interesting to note that ballistic coefficient increased with the more humid air."

http://www.riflebarrels.com/bcchange.htm

E.Shell · Oct 22, 2014

Lowry Wilson said:
Last March, temps in the 40's, I worked up a nice load for my .45-70 Marlin '95 (55gn H. Varget behind Remington 405gn SJSP (approx. 1700fps) and kept acceptable 6" group at 200yds, with factory iron sights. Yesterday, at 91F, exact same load, only got a 10"gp at 200yds, high and left (However, did notice that the very first round shot was in the ten ring). Did notice that the barrel got real hot after three rounds (didn't do that at 40degF) and accuracy got worse. When I let the barrel cool down for 20 min. accuracy improved (one shot at a time every 10 min). Question?-can ambient temperature really effect the accuracy that much? If so, is it the ammo temp, barrel temp, should my load be reduced, or what? Tks

As mentioned below, it's most likely a temperature based mechanical problem, not ammo.

BradMacc82 said:
Powders can be affected by a noticeable degree in different temperatures. Hotter temperatures can increase the burn rate, IIRC.

I'm just starting to use Varget, so I can't say how temperature sensitive it is.

True that temperatures typically create exactly the effect described, but Varget is engineered to have a very low temperature reaction.

BigDaddy said:
According to Hogdon, in a .308 between 0 and 125 F, the velocity changes on 8 fps....

Yup.

The ambient temperature definitely affects how fast the barrel heats up. At 103 degrees in west Texas, my 22-250 is too hot to touch after 2 shots.

Metal can get hot to touch just in direct sun, and it gets very hard to liberate heat under these conditions.

The Marlin forum seems to have crashed on me. Mixed feelings about Varget from what I gather, but maybe that is just in cast bullets. I do not know anything about accurizing lever actions, so anything else I say would just be blowing smoke.

Varget would be likely be a little slow for cast bullets.

BradMacc82 said:
BradMacc82 said:

To be fair, you're referencing their extruded "Extreme" series of powders, which they've spent a fair amount of time on developing them to be less temperature sensitive than other powders. Which Varget is labeled as, so...

Click to expand...

BigDaddy said:

I didn't pick Varget randomly, the OP is using it, so unless there are two vesions of Varget, then velocity/pressure isn't his problem.

Click to expand...

Concur; Not a powder problem.

IndispensableDestiny said:
I've found that tubular magazine lever guns shoot high and to one side when they heat up. It's just the nature of barrel being strapped to the magazine tube. My Marlin 1894 does it. It makes it hard to develop a load....

Bald Fat Guy said:
Another vote for the bbl heating up, and the side effects thereof.

Yup.

trickg said:
I watched a thing about the Canadian sniper team who made a record long kill with a McMillan Tac-50, .50 caliber sniper rifle. At that distance and elevation in the mountains, they had the scope doped to the max, they'd switched to American ammo, which was a bit hotter than their Canadian rounds, and they were trying to warm the rounds up in the sun to get a hotter burn rate so they could lob the shot to the target for a hit. At least that's how I remember it.

In any case, I'd say that yes, temperature affects accuracy.

Docu-drama propaganda that does not stand up to rational and scientific evaluation and a whole subject unto itself.

Bald Fat Guy said:
...BUT in this specific case , the OP stated he used Varget. Varget was the first powder introduced in Hodgons Extreme line of powders. Said powders are engeneered so as to have temperature effect so minimal as to be ignored. Their advertising touted a particular Vatget load with single digit change over wide temp range.

So yes , in his case sounds like it is the effect of heat on the bbl .

Agreed.

Erno86 said:
http://www.riflebarrels.com/bcchange.htm

Everything you quote here is true, but for the average rifle, you need to get past 500 yards to be able to measure a difference under most conditions.

Erno86 · Oct 23, 2014

Everything you quote here is true said:
With 22 rimfire, it might make a difference at 100 yards, in relation to atmospheric factors --- But what really those kind of factors affect accuracy, is when I shoot my .177 caliber spring air rifle {RWS Diana Model 54} at 100 yard metallic targets.

Also...the direction of spin in the rifling, will have a causative effect on the spinning bullet, in relation to crosswind direction.

E.Shell · Oct 24, 2014

Erno86 said:
With 22 rimfire, it might make a difference at 100 yards, in relation to atmospheric factors

It will make a difference, approximately 1" per 10oF, depending on load, but this isn't 'the average rifle' as I had stated above.

--- But what really those kind of factors affect accuracy, is when I shoot my .177 caliber spring air rifle {RWS Diana Model 54} at 100 yard metallic targets.

It's all about hang time, and if you think your pellet rifle is bad, you should see my BB gun.

Also...the direction of spin in the rifling, will have a causative effect on the spinning bullet, in relation to crosswind direction.

This is called 'Magnus Effect' when referring to the vertical deflection, and there is also the 'dissimilar wind drift' phenomenon of a right wind having slightly more effect than a left when we shoot a right twist barrel.

Interesting to think about and discuss, but many many miles from the OP's actual problem....

Temperature Effects on accuracy

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