1st shot POI difference in warm versus cold barrel

[tpcollins]

I have a 450 Bushmaster I bought last year, that has a custom barrel installed on a .308 Savage action (with the Accu-Trigger) and a modified magazine. I took it out this morning and nailed the bull at 100 yards - I'm good for Thursday's firearms opener.

But it's been in the house and the barrel was probably still close to room temp when I shot. I'm not looking for difference in shooting in warm air versus cold air, but what about shooting a rifle's barrel that's still close to room temperature versus one that's cooled down from being on stand for several hours in the 20's or 30's? Thanks.

 

[Brian Pfleuger]

There’s no difference in 20, 50... 100 degrees.

Differences in barametric pressure, humidity, etc, will be more noticeable... and they won’t be noticeable either.

The *anmo* might notice... but the barrel won’t. If you’re really concerned, put your ammo in the fridge and then run outside and shoot it.

 

[gw44]

I have never had a problem !!!

 

[jmr40]

I sometimes see a very small difference between a perfectly clean barrels 1st shot and subsequent shots. But in most rifles the difference isn't enough to matter for hunting. For precision target shooting yes.

And some lighweight, pencil thin barrels will heat up enough after 3-4 shots that subsequent shots will shift POI somewhat. But once again this isn't really an issue in hunting.

I wouldn't worry about it for what you're going to do.

 

[TXAZ]

Unless you're shooting 600 yards or more, most of the 20+variables that affect POI don't significantly matter. But those that do include:

1) The shooter - hold your rifle and look at a target at 1000 yards through your zoomed-in scope. The movement is a combination of your heart beat, caffeine level, state of excitement, form and age (as in "the shakes"). (Hint, try not to touch the rifle too much when you pull the trigger for maximum precision)

2) The ammo - "the same ammo"- say 147gr ELD match from 3 vendors, will all have different POI's. (That's why higher end ammo makers have lot numbers, and a few provide specific parametric testing differences between the lots, like ELY)

3) The shooting position / mount - your crosshairs might be on the exact same POA, but a very slight tilt of the gun ("Yaw") of the barrel causes a describe-able circular pattern error as the tilt increases. Further, how you hold the gun determines how very slight changes in the rise, tilt and movement of the barrel just prior to the bullet exiting the muzzle. Again, the gun is most accurate when you're not touching it.

4) The wind - more noticable difference at longer distances, and it's a non-linear error.

Beyond that, most any other effect has no significant impact on POI at 100 yards or less.

 

[T. O'Heir]

"...The *ammo* might notice..." That'd be the powder in said ammo. Factory vs reloads might too.
A barrel is considered 'cold' if it hasn't been fired, not where it has been for an hour or more. Anyway, SE Michigan isn't going to be any different weather wise next Thursday than it was this morning. The Weather Network says 39F and partly cloudy for Detroit on Thursday. 39F isn't cold.

 

[dahermit]

Anyway, SE Michigan isn't going to be any different weather wise next Thursday than it was this morning. The Weather Network says 39F and partly cloudy for Detroit on Thursday. 39F isn't cold.

It was 27 degrees this A.M. It may be that cold or colder on opening day.

 

[Rimfire5]

I have measured a difference in POI with a cold unfouled barrel but not so much with a pre-fouled barrel. So I would worry less about the barrel if you haven't cleaned it since your sight-in.

Considering some powders will result in from 1.1 to 1.7 fps per degree F change according to Aberdeen Proving Grounds data, I would suspect that the temperature of the ammo might create a bigger difference than the same temperature change would make in a fouled barrel.

The difference in muzzle velocity between ammo kept at 70 degrees and being outside in 30 degree temperatures could be between 44 and 68 fps depending upon the powder. Even 'temperature stable powders' will see some effect of a 40 degree temperature difference. That much variation in muzzle velocity shouldn't move a bullet out of the critical zone at 100 yards but it might make a more important difference in POI at 300 yards.

 

[RC20]

Mine don't seem to care, but I do shoot at 20 degrees a lot in the winter.

Ergo, guns are out and sit for long periods. I will shoot a warmup/fowler on a couple, one it just does not seem to care.

The fouling itself moves the POI a bit but slowly and easily adjusted as you start to see it move (if I do - a good day is a couple 5 Shot x 1/4 inch groups but I have had a lot of days I was happy with under half -

 

[Mobuck]

My hunting rifle(s) and ammo stay outside for the duration of whatever time I'm hunting. If I have any question as to first shot POI, the rifle/ammo is kept outside and fires one shot per day until I'm satisfied with that POI for gun, ammo, and temp.

 

[Picher]

If you want to worry about POI change with temperature when shooting at a deer at under 300 yards, you'd better think more about whether your barrel is free-floating, whether you're using a sling and pulling the forend toward the barrel, or resting your barrel against something. Temperature alone shouldn't make any difference in your ability to hit an 8" diameter kill zone at any reasonable range with a free-floated, bolt action rifle.

 

[AK103K]

These were shot with a Remington 700V in .308 with a 10x Shepherd BDC scope at 100 yards, prone, off a bipod.

The gun was zeroed for the "cold" shot, the group above was the next four rounds

.

This was shot with a Armalite M15A4T in 5.56 with a Leupold 1.5x5 on top, again at 100, prone off a bipod.

The rifle was zeroed at a 200 yards, thats why its above the dot. Youll notice that one "low" shot again, which was the cold shot, and what the gun was zeroed for.

I clean my guns after each outing, so the bore is "clean" on the cold shot. Not sure if thats the reason for the difference or not. Ive noticed pretty much the same phenomena with most of the rifles I've had that offer that type of precision.


Ammo temperature is another factor and one you will see changes with. Cold tends to slow things down, and heat, speed them up. Vertical impacts are generally the shift you see with that.

If you shoot year round, in all kinds of weather, you will notice subtle, and some not so subtle changes. Cold shot, ammo, light, temps, etc, all add to things.

 

[Erno86]

i like to pre-shoot my rifle with at least one round before I go on a hunt; so it would hit my sighted-in P.O.I. with a slightly fouled bore.

If you bring a 70 degree room temperature bore immediately out into a freezing climate, it might change the P.O.I. first shot; because of the remaining condensation in the bore.

If one side of the barrel is heated-up significantly by the sun's rays, but the other side is not --- It will tend to change the P.O.I..

 

[Mobuck]

"I clean my guns after each outing, so the bore is "clean" on the cold shot. Not sure if thats the reason for the difference or not."

A clean bore POI is ENTIRELY different vs a " fouled, cold bore" POI. Knowing where that clean bore shot will strike is important but not the same as knowing where the first round from a fouled bore will land.
I just did a final zero check on the rifle I'm taking to New Mexico next week. One "fouling" shot with a known handload followed by one shot from the hunting ammo. Later, one patch with thin preservative down the bore. When I reach camp, I'll do the same zero check and leave the bore fouled prior to hunting. I already know this rifle will give a cold, fouled bore first shot within 1/2-3/4" of the next 2 rounds.

 

[Double Naught Spy]

Mobuck is right.

As far as I am concerned, clean bore shooting is the stuff of benchrest shooting where the competitors clean the bore vigorously between each shot to make sure they have the same amount of cleanness for each shot.

For hunting, I will occasionally clean the bore, but then will put a few rounds down range to foul it anew. I also want the same amount of cleanness for each shot and the way to do that is with a fouled barrel.

The action I clean fairly regularly.

 

[Dano4734]

My rifle is always low on the first clean shot just a tad. When the barrel gets dirty after its right on. I chalked it up to the clp cleaning and dry patch after

 

[RC20]

As far as I am concerned, clean bore shooting is the stuff of benchrest shooting where the competitors clean the bore vigorously between each shot to make sure they have the same amount of cleanness for each shot.

Actually they clean between strings.

Hunting when I was doing it was a range session to confirm being where it was supposed to be and then hunted with it like that.

After the hunt, success or not it got cleaned and put away.

That was before fouling shots etc but it wound up with 3 to 8 rounds in it depending on if there was any adjustment.

Always 3 after the last adjustment so never hunted with a clean bore.

 

[stagpanther]

Always a good idea to test that "wonder load" you found in the summer in 80 degree temps on a cold day before going out on a really cold hunt.

 

[stagpanther]

Very timely question--I'm going hunting tomorrow and decided to take a test drive of my 458 socom using 300 gr extreme penetrators driven by A1680. Last time I tried these was over the summer; just so happens it's snowing today so I thought "might as well test in the conditions I'll be hunting in."

Couple of interesting things happened--though obviously much of that can be attributed to the peculiarities of the cartridge:

1) some shots showed significant flash at the muzzle--even got my hand sprayed with some hot residue a few times.
2) POI shifted significantly between a couple of ladder charges of only a grain or so difference in a couple of cases.

I think factors such as how well your primer ignites the charge and how efficiently it burns will have a far greater influence on POI than "foul bore juju."

While the groups weren't quite as tight as they were during summer tests--I'm quite happy with the "foul weather performance" and feel it's good to go into the woods. I could also easily see the movement in the gun as the trigger broke--meaning my poor technique obviously was a contributing factor in the spread of the groups. The 458 socom--especially in warm loads--is quite the banger for the little AR15 platform.

 

[JJ45]

IMO, the change in humidity, or lack of, rather than temperature changes, can be a problem for wood stocked rifles.

Some wood stocked rifles are significantly affected and some are not...if I shoot my rifles to check zero, after the boiler in my house has been running a while, I know I am good to go hunting....I have a Savage 99 Featherweight that will change it's POI as much as 5 inches in elevation from Winter to Summer and vice versa...some of my rifles seem to be hardly affected at all.