Zero on cold gun or hot?

[1500varmint]

Posting in the stupid marksmanship section.

Do I set the zero on my scope for a cold rifle or do I set it for where the rifle shoots when the barrel warms up?

Last time I zeroed at 100 yards after I had been shooting for a while. The next time I went shooting the first few shots were low.

Do I zero cold and then compensate when the barrel starts to heat up, or do I zero hot and compensate the first XX shots until things are hot.

Thanks.

 

[_Windrider_]

Posting in the stupid marksmanship section.

Do I set the zero on my scope for a cold rifle or do I set it for where the rifle shoots when the barrel warms up?

Last time I zeroed at 100 yards after I had been shooting for a while. The next time I went shooting the first few shots were low.

Do I zero cold and then compensate when the barrel starts to heat up, or do I zero hot and compensate the first XX shots until things are hot.

Thanks.

zero at whatever the temp is when you zero. the temp is changing your MV which affects drops. if you record your zero atmosphere you can predict your hits at any temp with DOPE or a BC. at 100yds though, if you were hitting low the zero didnt change you did something. you wont see the effects of a temp change at 100 yds unless we are talking arctic to Arizona desert differences.

 

[1500varmint]

Thanks .

This is the stupid question forum so I'm going to be honest and say I don't fully understand your answer. It looks like I made some assumptions and asked the question very poorly.

I'll ask a different way.

When I go to the range I think I notice that my groups tend to move a bit after I've put some rounds through the barrel. So my firest group of 3 - 5 shots seem to group well but after another 3 - 5 shots they move a bit, so i either adjust my aim or adjust the scope (slightly) to compensate.

I've been attributing this to the barrel getting hotter and changing the way the bullets perform.

False presumption on my part??

Asked another way, should I expect the same grouping/point of aim to be consistent from my first shot of the day to my last shots (when the barrel is hot)?

Thanks!

Apologies for the poor wording.

 

[stello1001]

When I go to the range I think I notice that my groups tend to move a bit after I've put some rounds through the barrel. So my firest group of 3 - 5 shots seem to group well but after another 3 - 5 shots they move a bit, so i either adjust my aim or adjust the scope (slightly) to compensate.

what exactly do you mean by "my groups tend to move a bit"??

do they move up as in they open up, do they move as in the simply shift up or down (this is known as a POI change), do they move without any pattern, etc.

what the previous person meant was that even if your barrel is going through significant temperature changes, 100 yards would not be enough to notice a difference in POI change. It is believed that possibly you might be dropping the ball somewhere in your shooting session as it progresses. The barrel would have to go through an extreme change in temperature before we could notice a change in POI at just 100 yards. He used arctic to Arizona dessert as an example in the change of temps!

in other words, do you think that maybe as your shooting session develops, maybe a flinch also develops? Or anything wrong you think you may be doing?

 

[Deleted member 113831]

Posting in the stupid marksmanship section.

Do I set the zero on my scope for a cold rifle or do I set it for where the rifle shoots when the barrel warms up?

Last time I zeroed at 100 yards after I had been shooting for a while. The next time I went shooting the first few shots were low.

Do I zero cold and then compensate when the barrel starts to heat up, or do I zero hot and compensate the first XX shots until things are hot.

Thanks.

If it is a hunting gun, then zero cold. That is the condition your gun is likely to be in when it is used.

If a competition gun, there are two options. Either use a hot zero and record your cold bore offset and compensate for it on the first shot or two.....or, if cold zero and hot zero are less that 1 MOA apart, then zero for the average between them.

 

[1500varmint]

Thanks both.

There's probably a LOT wrong with what I'm doing, so I'll focus on that.

The last two range trips I made were at 200 yards and my groups didn't necessarily open up, but I thought my POI dropped a bit after I started to get the barrel warmed up.

I think you have both told me (very politely) that environmental factors that I'm talking about aren't really extreme, so I need to work on what I'm doing to keep my groups together.

thanks!

 

[Greg Langelius *]

Maybe. It depends on whether your barrel is responding to stresses that were (or weren't) a result of its manufacture as it heats and cools.

Some believe there is no cold vs hot barrel issue, and that the cold thing that's warming up is the shooter. I can't personally rule this out, but I am also convinced that heat changes the POI.

It may be that the barrel is altering its behavior, and/or it may be that the barrel heat is conducting through the brass case and adding the energy of heat to the latent chemical energy in the propellant (i.e the propellant mass gets heated by the chemical reaction, but if the mass starts at a higher temperature, then it ends at a higher temperature as well, creating more pressure).

And then there is the question about whether there will be only one shot intended in the engagement, or if there will be a course of fire with 10, 20, or more rounds intended.

If I can determine that the barrel has a consistent heat related change in behavior, then I take this as a fact and act accordingly. Same if it doesn't.

So:

If the only important shot is the first, then zero with a cold barrel (good luck with that, since the barrel needs to cool back to its ambient temperature, which will take some time, and will likely vary with the weather).

If the zero POI will be shared between 10, 20, etc., shots, then allow the barrel to warm up before dialing in the zero; and when shooting the Course of Fire, give the barrel a few shots before "going for score". ETA: In this instance, I do not fully chamber the following rounds, but get my sight picture before completely closing the bolt. This cuts heat conduction to the brass significantly. This will not work when shooting rapid fire with a sem; but shooting with a very consistent firing cadence might.

Greg

 

[Snuby642]

A light conture hunting barrel will move with a few shots.
A heavy target barrel does not seem to move as much.
A clean bore will start to move on some till fouled.

This is what I have found on my guns

Hunting I go cold and clean for thin barrels, expecting a one shot day.
Target I go warm and dirty and shoot till the wallet screams.

 

[Nooch13]

I’ll also offer input on this. Make sure you are paying attention to your ammo temps too. I’ve seen many guys leave a box of ammo out in the sun at the range and wonder why their Mv is higher. In addition to barrel temps, ammo temp also effects the mv.

 

[Strykervet]

You need more than one zero. I have a buddy that goes shooting occasionally, and I let him use the same M4 every time. It's identical to the one he was issued but with a better trigger. Since he doesn't keep data and conditions, each time is like starting over for him. Because it is. He's not worried about cold barrel shots, but if he zeros on a 90deg. day and then next takes it out on a 30deg. day, it's gonna be off. Add wind and forget about it.

Keep a dope book and make a habit of marking down all the range conditions, call your shots and mark your impacts. Trust me, this will make you a better shooter.

Do this, and eventually you'll have a shit ton of zeroes at all ranges in all conditions. Just look up the appropriate data and adjust your scope or irons and start from that. It should be pretty close if not spot on. Note: apply fundamentals as usual, but pay special attention to a repeatable cheek weld. What I used to do until I was comfortable with a particular rifle was to tape a dime or penny where my cheek goes and line it up that way. Not breaking a cheek weld once achieved is ideal but not always possible.

Keeping the data will also allow you to shoot the weapon within it's limits over time: if you have a 1MOA rifle and 1MOA ammo and shoot 2MOA, well, that's about perfect and you shouldn't expect better.

 

[Milo 2.5]

Zeroing for a cold bore shot is a drawn out process, every time you fire a shot you've skewed things. If a hunting gun, zero when barrel is cool, if a target gun or match type, zero according to barrel temps it will be shot at. Never zero a HOT barrel, nothing good can come from that.
I witnessed a 30 shot zero attempt one day, after 10 shots one just has to sit back and smile, saying anything is futile.

 

[308Gunner]

With everything that has been said the one thing that I do before I shoot is to get into position and dry fire 5 times, it gets my mind on the fundamentals then shoot.

 

[Nooch13]

In my post earlier, I meant to say:

In addition to ambient air temps, ammo temp also effects the mv.

 

[Nishgriff]

I realize this post is a few months old, but I have a similar question. On my AI AT 6.5CM I am getting a very consistent cold bore offset of almost exactly .5" at 3 o'clock right. After that shot the zero is pretty damn dead nuts. I don't need one round accuracy, I shoot paper and steel so it hasn't bothered me. But I was wondering if this is a normal offset? As I said, it's pretty consistent on my rifle.

Obviously it could be ME pushing the shot right. But I dry fire 5-10x before my cold bore shot, and when I let the barrel cool for 20 min or so in cold weather, I get the same offset for the next shot. The bore hasn't been cleaned yet (about 400 rounds in), and still groups average of .5 MOA with FGMM.

 

[Vodoun daVinci]

My rifle is consistently high and right when cold by about 1 MOA at 100 yards...an inch give or take. After 3 rounds it's zeroed. I just hold down and left 1 MOA on the first 3 shots and then go dead nuts center adjusting for range....1 MOA at 1000 is gonna be 10"+.

I calculate this in my DOPE. I shoot for precision and want my first round to be as close as possible. I include a first shot/cold bore in my DOPE.

Not unusual for a cold bore shot to be significantly off *if* yer zero/DOPE is for a warm/hot barrel.

VooDoo

 

[Nishgriff]

Not unusual for a cold bore shot to be significantly off *if* yer zero/DOPE is for a warm/hot barrel.

VooDoo

Thanks VooDoo, appreciate the answer!