# Hot Barrel v. Cold Barrel



## Mike Honcho (Oct 15, 2008)

Several weeks ago I took my rifle out to adjust the point of impact. I was able to make the intended adjustments, but it was a hot day and the barrel never completely cooled between groups. Last weekend I took the rifle out again. After shooting three fouling shots I cooled the barrel before shooting my first group. The first group was nine inches lower than where the rifle was shooting when the barrel was hot (I was using the same ammunition as before--same box). I adjusted the scope and cooled the barrel before shooting a second group. The second group was perfect. I then cooled the barrel and shot again. Perfect. I repeated this process two more times and each group was dead on. 

I suspect that the difference in barrel temperature is the cause of the change in the initial point of impact, but I am hoping that someone with more knowledge and experience than I posses can confirm this.


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## Loke (Sep 7, 2007)

Does your barrel contact the stock, or is it free floated? My guess is that there is a pressure point about two inches from the end of the fore end. Unless you are on a hot prairie dog town, I wouldn't worry about it as long as the point of impact doesn't shift from the ambient temps that we are now experiencing. You neglected to tell us what make and model you are shooting. Each rifle is a rule unto itself, but each model tends to have its particular tendencies.


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## Mike Honcho (Oct 15, 2008)

Winchester Model 70 Classic Sporter in .338 Winchester Magnum.


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## High Desert Elk (Aug 21, 2012)

What time of the day for each shooting session? You mentioned "several weeks ago", which should have been hotter ambient temp wise than now. Air density matters greatly. A friend of mine came up from Houston, TX for a cow elk hunt one year and his rifle was shooting low by about a foot. Granted, yes, he was coming from sea level but the rifle was sighted in with "heavier air" than here. Also, was there a cross wind that day if only a gentle breeze blowing from left to right? If so, then the bullet would have had more lift due to the magnus effect. Basically, the bullet spinning with the crosswind would cause the circuluar motion of displaced air around the bullet to travel faster at the top side giving the bullet lift (same aerodynamics that makes an airplane fly). 

Does the gun have a wood stock? If the humidity was higher that day, it could have caused a "pinch point" to happen acting like the barrel was not floated.

Just some thoughts - I may be way out on Pluto...


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## High Desert Elk (Aug 21, 2012)

Oh - forgot. At what distance were you shooting? At 300 yds I wouldn't worry a whole lot. At 100 yds, something other than a hot barrel would cause that kind of discrepency. Heated metal like that only changes by a few thousandths of an inch. Even then, it takes more heat to do that than what's generated by a few bullets running through it. Inaccuracy from a hot barrell only matters in competition shooting.


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## DallanC (Jan 13, 2009)

High Desert Elk said:


> Oh - forgot. At what distance were you shooting? At 300 yds I wouldn't worry a whole lot. At 100 yds, something other than a hot barrel would cause that kind of discrepency. Heated metal like that only changes by a few thousandths of an inch. Even then, it takes more heat to do that than what's generated by a few bullets running through it. Inaccuracy from a hot barrell only matters in competition shooting.


That TOTALLY depends on caliber, sorry no offense. You fire a "few" bullets out of my 7STW and you wont be able to touch the barrel. I don't own a .338 but I'll bet it heats them up pretty quick too.

How the barrel is made can affect how heat will warp it as well. Some barrels have cut rifling's, others are hammer forged around a mandrel. Stresses within the barrel become evident as they heat up, this is why some people do the cryo treatment, to remove those internal stresses inherent from when the barrel was made.

http://www.diversifiedcryogenics.com/gunbarrels.html

-DallanC


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## High Desert Elk (Aug 21, 2012)

DallanC-

None taken - sort of. I see your point about your caliber example. But doesn't it matter more on pressure build up of the load more than bullet diameter for heating to occur?

Also, once heated and allowed to cool slowly shouldn't the residual stresses (internal stresses) be minimal? I think it depends on if the bar stock the barrel is made from was hot rolled or cold rolled as far as anistropic and/ or isotropic properties go. If the barrel was originally hot rolled, then those residual stresses are very minimal and the barrel will expand uniform. If cold rolled and more isotropic, then the more non-uniform on the expansion.

Once again, minimal effect for the average guy. Yes, there are rifles out there that have a sucky manufacture from poor materials. I've yet to shoot a Winchester like this.

I can't touch the barrel of my .270 WSM after a few shots either but it takes a little longer on the 30-.06.


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## DallanC (Jan 13, 2009)

Heh we could take this into a fun technical discussion about metallurgical properties and such. Barrels are funny things... some string vertically, some string horizontally... sometimes the stock influences it like Loke described, sometimes its just stresses in the barrel itself /shrug

My M70 in 7STW doesn't have a problem with this... but I did have one M700 BDL that was TERRIBLE (.270). Each shot would go in a completely different direction as it heated up. Cold barrel returned to normal but once it started heating up, it started moving. As Loke stated, it was the pressure ridge in the stock. I ended up grinding out the pressure bump and allowing the barrel to float. What an amazing difference! That gun went from 3-4MOA to 1-1.5MOA with factory ammo.

I'm of the opinion that all guns should have free floated barrels if possible. The remingtons you can shim the action temporarily to simulate a floated barrel to see if it improves things or not. Its also a good idea to double check all your bolts in the action are tight.


-DallanC


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## Frisco Pete (Sep 22, 2007)

> That TOTALLY depends on caliber, sorry no offense. You fire a "few" bullets out of my 7STW and you wont be able to touch the barrel. I don't own a .338 but I'll bet it heats them up pretty quick too.


"...depends on caliber..." is a misleading statement in some ways. For example .30 caliber vs. 7mm (.28 cal.) isn't the issue. Rather the size of the powder charge in the case (related to case capacity) and the relationship of that to the size of the bore.
If you burn a lot of powder behind a small bore, like the 7mm STW mentioned you will create a lot of heat for that bore size/caliber. A .308-sized case with its much smaller powder charge and the same 7mm bore, _aka_ the 7mm-08, creates less heat because there is less fuel. So just keep in mind that this is the real factor involved here.

The other factor is the amount of metal in the barrel because this acts as a heat sink. When the heat sink/radiator that is your barrel reaches a certain level, then there is going to be the above-mentioned expansion.

With this in mind, the thickness of the barrel - which also relates to the size of the hole/bore inside makes a difference. If the same OD and contour barrel is used for both the 30-06 and 25-06, which use the same-sized case and similar powder charge, then there will be more metal, or heat sink in the .25 caliber bore for that charge to heat up.
The thinner the barrel in relation to the bore, the more susceptible the barrel will be to quick heating and expansion. If it is touching in the usual forend pressure point, the quicker the barrel will expand and "walk" the bullets - often up and right.


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## Cooky (Apr 25, 2011)

My M70 is finicky about the tension on the action and floorplate screws. Did you disassemble the gun when you cleaned it? Mine is a M70 Featherweight in .308, it has a very thin barrel and factory forend pressure, it's group moves vertically every time I take it apart. If it didn't do 1/2" groups I would bed and float it. As it is, I just leave it assembled unless I feel like sighting in again.


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## Mike Honcho (Oct 15, 2008)

There was a significant temperature difference between the two days. The first day was sunny and the temperatures were in the 90s. The second day was cloudy and the temperatures were in the low 80s. There was not much elevation difference between the two sites, maybe 300-500 feet, but there was a difference in humidity levels.

On the first day I would shoot a three-shot group and then lay the rifle in its case with the action open. After five to ten minutes I would shoot another group. The barrel was still hot to the touch when I began shooting another group. For the second day I would shoot a three-shot group and then wrap a damp towel around the barrel. I would wait until the barrel felt cool and then I would shoot another three-shot group.

I cleaned the rifle between outings, but I did not disassemble the rifle. Also, on both days I was shooting Federal Premium Vital-Shok in .338 Win. Mag. with 225 grain Barnes Triple-Shock X Bullets.

The groups on both days were tight. My concern is that my final group on the first day was 3.5" inches high at 100 yards and my first group (after some fouling shots) on the second day was 6" inches low at 100 yards. I am trying to account what would cause such a dramatic shift? I was shooting from a table with rests on both days and I did not change the way I was holding the rifle.

I am planning to spend a few hours at the Lee Kay range tomorrow or Thursday. Hopefully the POI will be where it was on Saturday.


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## DallanC (Jan 13, 2009)

I wait at least 15 minutes between shots, sometimes upwards of 20-30 minutes to make sure the barrel cools down. I also take multiple rifles to the range and rotate through them allowing them to cool.


-DallanC


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## Stickboy (Oct 28, 2010)

That is a huge change of point of impact. Sounds like you tightened the stock screws to the same spec as the day prior. Shooting the same ammo. Are you confident the scope doesn't have an issue? 

What were the groups like?


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## Loke (Sep 7, 2007)

What kind of stock do you have on your rifle? Wood or synthetic?


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## Mike Honcho (Oct 15, 2008)

The stock is wood. I am not confident that the scope is not the problem, but the groups were good. Conservatively, each group was under 1.5" at 100 yards.


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## Loke (Sep 7, 2007)

the first thing that I would look at is the fore end contacting the barrel. Vertical stringing is a classic symptom of that problem. Try to slide a dollar bill between the barrel and stock. That will let you feel where the contact is. You can try to shim the action up until the barrel no longer contacts the stock. This will give you an idea how it will perform with the barrel free floated. Then if it shoots to your satisfaction without the contact, you can sand the barrel channel until there is no longer contact. Make sure that you seal the wood where it is removed. Or you can glass bed the action and barrel channel so there is contact, but no pressure point. Some rifles will shoot well like this. On the positive side, you get to have all kinds of fun and frustration while you play with guns. Life doesn't get better than that.


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## DallanC (Jan 13, 2009)

I've had similar experience as Loke with a couple exceptions. I've seen more Horizontal stringing as a result of the forearm pressure bump contact. If there is strong contact along the side of the barrel it can give vertical stringing but usually when I get vertical strings I look at mounting issues first.


-DallanC


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## Mike Honcho (Oct 15, 2008)

I will check the contact issues later tonight. I guess I must also consider the possibility that I am the problem, but how do I diagnose operator error?


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## DallanC (Jan 13, 2009)

Support the rifle very well with sandbags to make sure it is on a rock solid base when you touch it off. 


-DallanC


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## Cooky (Apr 25, 2011)

Mike Honcho said:


> I will check the contact issues later tonight. I guess I must also consider the possibility that I am the problem, but how do I diagnose operator error?


With those kinds of groups from a .338 operator error is unlikely. If your rest is consistent (not too hard and bouncing the gun, resting on the barrel, holding the gun down by anything other than the fore grip) it may be time to try a scope you know is okay. In my experience vertical stringing that is heat related happens _within_ a group as the gun heats up and you get a tall-narrow group, that said, the same is true of broken scopes. I'll be interested in what you find.


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## Mike Honcho (Oct 15, 2008)

I checked for contact between the barrel and the stock. I was able to slide a dollar bill under the barrel without impediment. I will let y'all know what happens during my next outing.


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## DallanC (Jan 13, 2009)

Mike Honcho said:


> I checked for contact between the barrel and the stock. I was able to slide a dollar bill under the barrel without impediment. I will let y'all know what happens during my next outing.


From the barrel all the way down to the action? If so, it does seem to indicate a action mounting issue, scope mounts or defective scope.

What brand scope do you use?

-DallanC


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## Frisco Pete (Sep 22, 2007)

Make sure and do the same free-float check at the range - after shooting some.
I had a Ruger M77 .270 with a really nice wood stock, but that forend would tend to warp upwards with every little change in the weather and season. Some wood stocks are not sealed inside the barrel channel, so I used some Varathane there on this one, but it really didn't help. I ended up putting a synthetic stock on it and cured the problem.
Evidently the grain and curve of the piece of tree wood the stock was fashioned from had a natural tendency to warp in that direction.


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## Mike Honcho (Oct 15, 2008)

Yes, I checked from the barrel all the way down to the action and there was no contact. I am using a Leupold Vari-X III, 3.5-10. The rifle and scope were both bought new about fifteen years ago. However, the combination only has a few hundred rounds through it.

I will check for contact again after firing a few shots.


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## Mike Honcho (Oct 15, 2008)

I went to the range today. I was expecting that my shots would be off the mark. In fact, I was hoping that my shots would be wildly off mark, confirming that something was amiss with the scope. Unfortunately, or fortunately, my shots were not off mark.

I shot three groups today: two three shot groups and one four shot group. All groups were shot at a range of 100 yards and the rifle was allowed around fifteen to twenty minutes to cool between groups. After shooting a group, and while the barrel was still hot, I ran a dollar bill between the barrel and the stock. Like before, the dollar bill moved unimpeded. Last Saturday I was shooting approximately 3.5" high and 0.0" left and right.

The first group was three shots and approximately 4.25" high and 1.0" right. I made some slight adjustments before the second group. The second group was three shots and approximately 2.75" high and 1.0" right. After one slight adjustment I shot the third group. The third group was four shots and approximately 2.75" high and 0.0-0.5" right (This was my sloppiest group. The third shot was a flier that was 4.5" high and 0.5" left and the fourth shot was about 2.5" high and 0.75" right of the first two shots--the fourth shot is the partially connected to the second group).

After today's experience I am relieved and confused. I am relieved that my gun was still on target, but I am confused as to why there was a dramatic change between the previous outings. After seeing and reading this latest information does anyone have any thoughts about what happened between the first and second outing? Should I still be concerned? I am planning on one or two additional outings before it is game time for me, but I am still afraid that when it counts the rifle will not be true.

Not sure why the picture is aligned this way, but the left side of the picture is the top.


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## DallanC (Jan 13, 2009)

Cant say why your first group was off. Too clean of a barrel? That actually happens, in fact I never clean a rifle before going hunting if its grouping fine. 

We all love to see a cloverleaf type group out of a hunting rifle... but honestly, any normal "hunting" rifle thats within 1.5MOA or better is fine for virtually any hunter. It sounds to me you are well within the ballpark for hunting purposes. I'd take it out a time or two more, and make sure that first group out of a cold barrel stays tight, and its centered up, but from what you are describing, it sounds like something I would feel fine hunting with. 


-DallanC


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