Factory barrels stringing shots when heated?

[engineer40]

I have found that if I am willing to put in the effort, most of the time I can get fairly exceptional accuracy from factory barrels.

What I don't particularly enjoy is waiting a couple minutes between shots. Because if the barrels heat up at all, my shots start stringing all over the place.

From what I've researched this is usually caused by 2 things. 1) The factory barrels are thin so the heat affects them more. 2) The factory barrels are not manufactured with the same tolerances as a nice custom barrel so sometimes the hole is not 100% centered in the barrel. So that also causes issues when the barrels heats up.

You guys with custom barrels, how many shots can you usually fire before you see a difference in accuracy? How long do you typically wait between shots?

Thanks!

 

[Rick Richard]

Accuracy is defiantly effected by material stresses (metal), heat from firing, material thickness and machining tolerances. This is not considering other factors such as undo pressure points and the shooter.

Just like your factory barrel, accuracy does get effected by heat build up when shooting a custom barrel. However, the accuracy in most cases will not be as significant as in the factory barrel due to more consistent stresses in the metal and tighter matching tolerances.

Larger diameter barrels heat up slower (relative term) and therefore a few more rounds can be fired before accuracy is significantly affected. However, heavy adds more weight if it is a hunting rifle.

As for as shooting with factory or customs, I wait a couple of minutes before I fire the next round or until I can feel a significant change in the temp. I also only fire 3 shot groups since most of the time I am shooting for best accuracy. I believe in a hunting situation more than three shots would not be needed.

 

[engineer40]

Very concise answer Rick. You touched on everything that I was curious about. I really appreciate the response. Thanks!

 

[Deleted member 46119]

Rick answered very well.

I made a barrel "cooler" to draw air through the barrel between shots. It sped up testing time. It's a "Bug Vacuum" with a rubber donut to fit over the end of the barrel. I may "improve" it by rebuilding it to clip on like the patch catchers. Eats batteries pretty fast though.

About barrel warping under heat:
As the barrel heats the metal expands more/less in different places due to "inconsistent density" or "crystalline structure" variations.

"Custom" barrels are made with more "consistent" metal. Heat induced expansion warping is reduced.

Stress relieving "factory" and "custom" barrels helps.

There is also inconsistent heating because the flame/heat from powder ignition is not transferred to the barrel perfectly and because the underside of the barrel has less exposure to air from the stock.

On some of my BR rifles like my big barrel block 300 RUM, I have heat sensitive stickers. I have mapped how the barrel changes with temperature changes.

For a hunting rifle, I consider it a non-issue even though I still do testing to "understand" where the followup shots will go.

For a target rifle, of course it is crucial to understand where the POI will move as the barrel heats up.

 

[Deleted member 46119]

Oh, one of the supper cool things about the RPR is the open barrel shroud. Lets the air in from all sides.

 

[engineer40]

I made a barrel "cooler" to draw air through the barrel between shots. It sped up testing time. It's a "Bug Vacuum" with a rubber donut to fit over the end of the barrel. I may "improve" it by rebuilding it to clip on like the patch catchers. Eats batteries pretty fast though.

That's a good idea!

Best method I've worked out so far is to carefully plan load development on 2 rifles at the same time. So I shoot rifle 1, set it down, take the bolt out to help with cooling. Then I shoot rifle 2, set it down, take the bolt out to help with cooling. Then repeat... It usually takes long enough to switch between rifles that they have at least some time to cool.

You have to be organized though! I have shot the wrong target with the wrong rifle before. And that really ticks you off when you are doing load development! Lots to keep track of when you are doing 2 rifles at the same time.

 

[Rick Richard]

A tip is to stand the rifle up with the bolt removed for faster cooling. Heat rises and a chimney effect will be created through the barrel sucking in cooler air through the bottom of the barrel.

 

[BigMedicine]

A tip is to stand the rifle up with the bolt removed for faster cooling. Heat rises and a chimney effect will be created through the barrel sucking in cooler air through the bottom of the barrel.

Neve really gave this much thought, but it seems plausible, thanks for the tip.

 

[cholla chomper]

You dont say what brand or model you are using With the remington rifles I have found that the stocks have pressure points in the forearm that causes the barrel to move in the direction the stock pushes it as they heat up. I had a heavy barrel that would not do better than 1 1/2 groups until I replaced crappy plastic stock ( with the pressure points ) with a boyds stock, I was going to bed the stock but didnt because it now shoots 3/8 groups with the barell floated. Even grinding the barrel channel out to float the barrel would be an improvment.

 

[Dosh]

40, having two or three rifles with you to alternate shooting is a good vehicle to keep barrels cool. Here in Az there aren't many days we encounter cool enough to do this. As I mentioned on another thread we use a battery powered air mattress pump with a hose taped to an old universal bore guide. Runs on 4 D cell batteries and cools our barrels quickly and safely. There were several more elaborate barrel cooling devices mentioned. The worst I've seen at the range was a wet towel pulled from an ice chest and thrown on a hot barrel.

 

[Schnyd112]

With smaller diameter barrels heat rises chamber to muzzle pretty well. With thick barrels,open the bolt and let them sit on the bipod. There is less metal to cool above the chamber and they seem to cool faster when laid horizontally. I have a hunting gun that does not like 4-5-6 shot strings but will put 3 in .5 moa all day. My heavy barrel factory rifle will put 5 well within moa and 10 at about .80 moa. Each rifle, each barrel is different. Test it, take copious notes, and shoot as often as you can. Get comfortable with everything so if stuff goes downhill you know you can shoot each rifle with confidence.

Also remember that rapid heat change fatigues metal more than a natural heating-cooling period. I know lots try to speed up the cooling but material science tells you natural heat exchange is best. Give them time. Shoot other guns.

 

[engineer40]

You dont say what brand or model you are using With the remington rifles I have found that the stocks have pressure points in the forearm that causes the barrel to move in the direction the stock pushes it as they heat up. I had a heavy barrel that would not do better than 1 1/2 groups until I replaced crappy plastic stock ( with the pressure points ) with a boyds stock, I was going to bed the stock but didnt because it now shoots 3/8 groups with the barell floated. Even grinding the barrel channel out to float the barrel would be an improvment.

It's a Remington but it's in an aftermarket stock that has been full length bedded and the barrel is free floating as well.

But I definitely agree with you! I've shot enough military surplus rifles to know the affects of barrels touching parts of the stock with varying degrees of pressure.

 

[engineer40]

Also remember that rapid heat change fatigues metal more than a natural heating-cooling period. I know lots try to speed up the cooling but material science tells you natural heat exchange is best.

I'm not going to pretend to know very much about metallurgy, but don't people use heating up metal and then rapidly cooling it to strengthen the metal? Blacksmiths have been doing that with swords for thousands of years and many things today use the same process; high strength fastener bolts, etc...

Not picking apart what you're saying. I appreciate the input. Just thinking out load really.

 

[Schnyd112]

I'm not going to pretend to know very much about metallurgy, but don't people use heating up metal and then rapidly cooling it to strengthen the metal? Blacksmiths have been doing that with swords for thousands of years and many things today use the same process; high strength fastener bolts, etc...

Not picking apart what you're saying. I appreciate the input. Just thinking out load really.

Yes they do, they heat treat metal to harden it. If you take a knife that has been heat treated and sharpen it with a high speed rotary you can counteract the "hard" and the knife will not hold an edge as long. It can also get brittle because you changed the hardness in one part, on the edge, and not the rest of the blade. I do not know if blowing air through a barrel to cool it faster will damage it, being as bullets heat it up pretty fast already, but I have always been hesitant to cool the barrel with anything but natural airflow and time.

It's pretty well proven also, that cutting hardened steel with the wrong implement makes it less hard. Think ar500 targets that get brittle near the edges where they were cut. That's much hotter than a bullet going down the barrel,but another example of metal fatigue caused by heat