Have you ever been shooting at the range and had your groups open after you have been shooting for a while? You probably blamed it on your getting tired or fatigued. Right? You might even think your scope is malfunctioning or the mounting screws have come loose. Well there are several things that could cause this situation but the primary source of the problem is a barrel that is too hot.
A rifle barrel begins to heat up from the first shot at the range. A barrel will display it's highest level of accuracy when the barrel is allowed to cool back to the temperature close to the last shot. An excessivel hot barrel will wear faster.
How does heat affect the accuracy of a rifle barrel?
In this article we won't get too far into how barrels are manufactured but let's just say that in all manufacturing processes, stress is introduced into the metal when forming it. The barrels all go through stress relieving processes after manufacture but heat brings back the stresses, kind of like muscle memory. Some barrels have more memory than others. The hotter the barrel the more affect stress will have.
All barrels move as the bullet, under pressure, moves down the barrel. The movement consists of oscillation and vibration. If a barrel is hot then the oscillation and vibration are not the same as if the barrel were cool, or cooler. See the diagram below to get an idea of what really happens when you shoot. The diagram exaggerates what happens but you get the point.
When a round is fired there is a 5000 or so degree explosion traveling down the length of the barrel. You can easily see how a barrel would warm up pretty quickly. In really high quality barrels the effect of heat causes differences in how the barrel moves but there is much less movement than in a lower quality barrel.
The warmer the barrel gets the larger the difference in the movement during the process of discharging the shot and the more random the location of the barrel when the bullet exits the muzzle.
You might not think that a few degrees of heat would make a big difference in the movement of a barrel that is one inch or so in diameter, but it does. Remember that any movement of the barrel at the muzzle is amplified at long range. The longer the range the more effect it has. When you are trying to hit a golf ball at 200 yards it only takes a very tiny fraction of a fraction of an inch movement at the muzzle to miss.
A thin sporter barrel will heat up quicker than a bull barrel, but it will also cool quicker.
In addition, a hot barrel generates heat waves that will affect your sight picture through your scope. Now, the barrel has to be really hot to see these heat waves but it does happen especially on hot summer days.
The secret to accuracy to is have all variables be as close to the same on every shot as possible. This is why expert shooters wait for the right wind direction and speed before taking the shot. The same goes for barrel temperature.
Clearing up the cold bore misunderstanding
You hear shooters, even competition shooters refer to their first shot of the day as the "cold bore" shot. The reason they say this is because on this shot the barrel will probably be as cold as it will be all day or during their round of shooting. Because of this the shot will usually be a little outside the shots coming afterwards.
This will be especially true if the barrel has been cleaned before the first shot. It usually takes a shot or two to get the normal amount of residue in the barrel so all shots perform the same. For more information on this, read this article.
This doesn't mean that a cold bore delivers a bad shot. In essence what they are saying whether the know it or not, is that they are going to be shooting with a warm or hot barrel for the remaining shots of the session. They are not going to let the barrel cool down to ambient again.
Does this mean that they will spray shots all over the target? Not unless the shoot continuously with no time for cooling. In addition, it does mean that they will not get the accuracy the rifle is fully capable of.
Unless they fully understand whats happening, these are the guys who shoot boxes of ammo trying to make the rifle more accurate but then go home completely frustrated because the rifle won't drive tacks.
If you pay attention, you can usually get some pretty good deals on rifles and equipment from these guys....not that we would take advantage of anyone.
Do barrels wear out faster when shot hot?
Even hot weather can affect accuracy. In the southern states, on days where the temperature is over 100 degrees and humidity is over 90% I go to the range expecting to shoot groups that aren't as good as those I shoot during winter months.
All barrels wear when being shot, but all barrels will wear faster if they are shot repeatedly when very hot. Every time you pull the trigger you are sending a 5000 degree blast down the barrel. The hot steel erodes faster when in contact with the gases generated by the cartridge. So it's best to keep your barrel cooler.
Don't panic, this doesn't happen instantly. You can't shoot a 25 round mag one right behind the other and immediately ruin your barrel. But doing this repeatedly will cause you barrel to wear out faster. For more information check out this article.
Barrel manufacturers are constantly improving their products. Chrome lined and stainless steel barrels last longer than standard barrels but they all wear out eventually. It is well known that great match barrels such as a Krieger will wear less than factory barrels. This is primarily because of materials the barrel is made of, and knowledge of shooters at this level. It's the old saying, you get what you pay for.
So how long does it take to wear out a factory barrel. Most standard rifle barrels are designed to hold accuracy for 5000 rounds. With a hunting rifle most people won't shoot this much in a lifetime. I can tell you that I have rim fire rifles that have well over 5000 rounds through them and I have yet to see any noticeable loss of accuracy.
I shoot golf balls at 200 yards with a couple of these rifles with no problem. I don't mean to say that I never miss but I make contact as often as most of my buddies and some of them are shooting new barrels. I must say though that these barrels have been well taken care and have never been over shot with a hot barrel.
It is said by some authorities that the first 3 shots you fire from your barrel will have a normal affect on barrel wear - small but wear none the less. The 4th shot you fire will have the same wear affect as the first 3. The 5th shot will have double the wear affect as the 4th and continue to double with each shot thereafter.
To sum this all up, your barrel will wear faster if you shoot many rounds through it when it's really hot. The cooler the barrel when you shoot, the more accurate you will be and the longer your barrel will last. Zero and practice like you will use the rifle
If you are a squirrel hunter, every shot you take will probably be with a "cold" barrel If you are hunting prairie dogs out west, you will probably take shots often enough to have a slightly warm barrel. If you shoot in competition, your barrel might get even warmer during your round. Zero your rifle to duplicate the conditions you where you will use it.
Does this hot barrel affect cause little rimfires to be inaccurate?
The thicker the barrel the longer it takes to heat up an vice versa but little 22 ammo generates a lot of pressure and heat when being fired.
To test this put your hand on your barrel before firing the first shot to get a sense of what it feels like at ambient temperature. Then fire a 5 shot group through it and feel it again. It won't be so hot you can't touch it but it will definitely be much warmer.
You cannot expect this barrel to perform exactly as it did when the barrel was at ambient, or "cold"
If you fire another 5 shot group right away will the difference in heat make a drastic difference? Not if you are shooting at a squirrel at 25 yards, but if you are shooting at golf balls at 200 yards, it easily could cause a miss.
If you want to maximize your accuracy learn to be patient and focus on duplicating all conditions on every shot.
How to cool your barrel while shooting
Once the barrel gets really hot it can take up to 30 minutes for it to cool back down to ambient temperature. On really hot summer days, it can take longer. The best way to avoid this long wait is to not let it get this hot in the first place.
Keep it out of the sun Most barrels are a dark color which enhances their ability to absorb and store heat. A hot summer sun can greatly lengthen the time it takes to cool.
Put your rifle in a vertical rack with the bolt open and the muzzle pointing up. Believe it or not, this serves to promote a chimney effect and cool the barrel quicker. After making 5- 10 shots with a 22, I will use this method and it works great. You just have to get accustomed to not shooting every minute you are at the range.
The use of a vented stock helps minimally but does help speed up the rate of cooling.
Using a bag of ice is another option but in the summer it melts pretty quickly and too you look really goofy with a bag of ice around your barrel. On top of this it can get messy and not practical to haul an ice chest around with you.
I know bench rest shooters who actually use a small hand pump device to push water through the barrel after they complete each volley. This cools the barrel quickly and from the inside. Of course they then have to get the water out of the barrel.
They do this by running 3 clean patches with no chemicals through the barrel. Gun powder residue is water soluble and it is unbelievable how much gunk they get out of these barrels after only 5 or 10 shots.
I personally don't like putting water in my metal barrel. The two combinations cause rust and yes, I know the water isn't in there long enough to do any damage but I have spent a lifetime keeping my firearms dry and away from moisture. The last thing want to do is introduce water to them on purpose.
Another disadvantage is if you have a wooden stock, water can quickly cause wood to swell an warp putting tension on the action and barrel. This will do more to deflect your shot than even a hot barrel.
Laminate wood stocks are less susceptible to the effects of water than a normal wooden stock but it can still change point of impact enough to give you real heartburn.
Some of the pros say that one real advantage to using this technique is you can actually cool the barrel below ambient temperature. I don't see this as an advantage either as the object is keep everything the same, which means temperature. Not below the same, but I am not one to argue with the pros. .
The disadvantage to this process is it can be messy and a real pain at the range. I purchased a barrel cooling fan from Amazon. It is actually designed for doing this specific job and does it very quickly. It is powered by AA batteries so no electrical supply or outlet is required. It also fits well into the chamber. It blows ambient temperature air through the barrel from the chamber to the muzzle. No mess.
Long range accuracy is just as much about focus on duplicating conditions and process of shooting techniques and equipment As with any other endeavor, there are hundreds to thousands of variables that cause inconsistency. Champions identify the important variable and take the proper steps to control them.
In long range shooting, barrel heat is one of those very important variable that must be controlled for consistency. Take the time to make it happen using the right technique and you will be rewarded with success.