Throat erosion

[Rogue_soldier]

I'd always hear experienced shooters talk about throat erosion and barrel life like it was some distant problem I'd deal with someday....then someday showed up. I had a heavy varmint rifle that got shot a lot. And by a lot, I mean the kind of round count where you stop keeping track because the answer is always "more than I probably should have."

Most of those rounds were full-power, high-velocity loads. The rifle shot great for a long time, so I never gave much thought to what was happening inside the barrel then accuracy started slipping, not all at once and that's the tricky part. Groups opened up a little, then a little more. At first I blamed myself, then the wind, then the load, then the scope. Pretty much everything except the actual cause.

When I finally started measuring and paying attention, it became obvious what was happening. The throat, that area just ahead of the chamber where the bullet first starts its journey into the rifling had worn noticeably over time. To keep the same jump to the lands, I found myself seating bullets farther and farther out. It worked for a while but eventually there was no denying it. The barrel was simply wearing out and that was an eye-opener because barrel wear isn't something you really see day to day. It's more like watching your hair grow, nothing looks different this morning but a few years later the change is obvious.

The rifle didn't suddenly become inaccurate overnight. It slowly told me what was happening and I was slow to listen. In the end, the solution was simple...A new barrel.

The funny thing is I wasn't even upset about it. By that point, the barrel had done exactly what I'd asked it to do having had thousands of rounds, lots of range time and plenty of lessons learned. High-velocity cartridges are fantastic performers but they're not immortal. Every shot takes a tiny bite out of barrel life, eventually the bill comes due. Knowing that doesn't make it any less painful when it's time to order a replacement but at least now I understand what people were talking about all those years.

 

[Cracker57]

Just wondering what caliber your gun is? some are real barrel burners.

 

[Robin1]

I went through the same cycle with a .243 rifle, blaming myself, the scope, the ammo only to find out the barrel was worn out. It had been trying to tell me for months.

 

[Tom L]

Makes sense. Had a 12ga vented and modified barrel that lasted many years. But, combining what was likely my bad in terms of not cleaning after every hunt and always shooting 3" mag ammo, it did finally wear out. I didn't realize it until I took it to a buddy who was a gunsmith and complained I could hardly count on hitting the broad side of a barn.

 

[Morbius]

I had a .22-250 and blamed everything around me before admitting it was the gun. Good barrel while it lasted, though.

 

[Tabby]

Throat erosion is insidious. A bit of erosion happens every time you pull the trigger on any rifle, any caliber, any manufacturer and with any ammo. It doesn't matter if it's a factory barrel or a custom match grade barrel, they all erode a little bit with each and every shot. Now that this is out in the open let's talk about things that will take erosion to the point where the barrel is essentially something to add to your boat anchor for additional weight, or make a handle to place on one end or the other and use to club attacking bears to death.

Everyone knows that there are certain calibers that are known to be barrel burners. A good example of this is the 300 Rum. However were you aware that a 30-06 or any other caliber could have severe issues with barrel erosion in as little as 1000 rounds shooting target and hunting ammo at nominal velocities? It is sad but true. Ammo and high velocity are not always the culprit, the metal that the barrel is made of has more of a bearing on how long it lasts than most other issues.

As an example, back in the mid 70s, in addition to shooting high power rifle I liked to shoot metallic silhouette. I started out with one of my hunting rifles, a Remington 600 in 243 Win. Great little gun but lacked the necessary energy to knock over a ram on a consistent basis. Dead center hits and all that would happen was that the ram would rock back and forth a bit but not go over. Hearing the ding that signified a hit, similar to what you hear when shooting steel targets these days and watching the ram stare back at you essentially saying, "Nanny, Nanny, Boo Boo!" gets frustrating.
The Rem 600 got sold to a friend. A lot of competitors at the time were shooting 308s as well as a variety of other calibers. I decided I wanted the rifle for deer or other hunting, so the choice was the old reliable 30-06, could shoot anything from 130 gr to 220 gr ammo and could take anything on the North American Continent and a lot of them even in Africa. Kept my Redfield scope on it and if you hit a ram in it's hoof, it would fly off the stand when the handloaded 165 grain Sierra bullets hit it. The loads were not hot, running around 2500 FPS but enough energy to make the rams dance.

I kept track of the number of rounds fired, for all the rifles I bought new. As I started approaching the 1000 round mark I started noticing that the accuracy was going downhill relatively fast. It became difficult to hit the 200 meter chickens or the 385 meter turkeys. Took the rifle to a gunsmith, he bore scoped the barrel and the erosion was really bad. Contacted Winchester and at the time their response was that the rifle was a sporter and that 1000 rounds represented several generations of shooting by the average hunter. I had a 26 inch custom match grade stainless bull barrel. I had it chambered in 7.62 x 51 (308) and never looked back. The extra 6 inches of barrel made the 308 hit a lot harder than the standard 20 and 24 inch barrels did. It was also 0.03 moa accurate with Nosler or Sierra 165 or 168 bullets. Knocked the rams over better than the 30-06 did. When I finally sold that rifle it had over 3600 rounds through it, and was still as accurate as the day the first round went down the barrel.

Over the years I have shot the barrels out on several rifles, the latest a Tikka T3, also in 30-06. It was bought used so I had no idea how many rounds it had through it before I got it. I had put around 1500 rounds through it. When the accuracy had deteriorated from 0.4 moa to 0.9 moa again with evidence of barrel erosion I sold the rifle. No longer accurate enough for me, but still sub moa accurate so that any hunter should be more than happy with it.

Now you ask, why not rebarrel it? A new match grade barrel is going to cost between $400 and $600. It takes a skilled craftsman gunsmith to install and chamber the new barrel. By the time you get that done, it will cost more than a new rifle. I shoot for fun these days, seldom any competition and a rifle that is sub moa works for me.

In the end, barrel erosion is influenced more by the quality of the steel the barrel is made of, along with the caliber mostly influenced by high velocity and the amount of powder required to attain that velocity. A 243 loaded to 3400 fps will erode the barrel just as fast as a 300 rum. a known barrel burner.

Is your barrel going downhill? The only way to truly tell is by a deteriorating group size. Borescoping will show erosion, but only accuracy will tell if it has gotten to the point where the barrel is toast.

If anyone is interested here is a NSSF video on silhouette shooting. Things have changed over the years as far as rifles are concerned, when I was shooting the only requirement was that the gun had to weigh less than 10 pounds and the max magnification was 10X.

 

[critterpicker]

I saw a 22-250 that had a barrel wore out in under 250 rounds. It got so hot in a prairie dog town that I could smell wood smoldering. Told the guy to slow down several times ,but it was his first time out.

 

[Tabby]

When shooting in combat rifle matches we would always select new rifles or rifles that had new chrome lined barrels for team members. The reason was not to have the newest rifles, but to make sure that nobody, (I'm being nice here I really wanted to call them idiot) had shot the rifle on full automatic. The rate of fire for a M16 was between 700 and 900 rounds a minute, which was dependent on a variety of different issues with each rifle. Ammo, powder, and individual components installed on each rifle accounted for the difference. A 20 round magazine would be fired in around 1.7 seconds at 700 rounds a minute, at 900 rounds a minute the 20 round magazine is fired in around 1.3 seconds. The heat generated from 20 shots in that brief time span permanently damages the barrel and makes the rifle virtually useless for any kind of accurate shooting until the barrel is replaced. Heat is the nemesis of any rifle barrel. That is about the only reason for allowing a barrel to cool between shots. In our case during competition it was not unusual to fire 10 rounds in 60 seconds or less. Yes this was hard on a barrel, but not immediately destructive. The difference being that on full auto there is a continuous flame eating away at the barrel material. Shooting rapid fire there was a short period of time between shots which did not heat up, or erode the barrel as fast. The difference was that our match rifles, which in the case of the M16 was a new barrel shooting 40 out of 80 shots rapid fire meant that the life span of our barrels was somewhere around 2000 rounds. Slow fire, one shot per minute would extend the life of the barrel to around 3000 rounds. Shooting one magazine at full auto degraded that same barrel to between 20 and 40 rounds before it was incapable of shooting any kind of accurate group.

While there are many other factors that enter into a barrel burner designation for any given cartridge, or rifle, heat is the one thing that is common to all.

 

[Cracker57]

22-250 are known barrel burners.

 

[Tabby]

It's not the only one. There are many calibers that burn out barrels in short order. The issue here is that we are dealing with high velocity bullets. In order to achieve the velocity an excessive amount of powder is required. According to Nosler a 35 grain bullet will shoot at well over 4000 fps, some loads approaching 4500 fps. The max case length is 1.912 inches, which we pack what seems to be a benign average 38 grains of powder to achieve these velocities. What people fail to consider is that for this cartridge, case and bullet it is way overkill. Even at minimum loading shown we are still dealing with velocities over 4000 fps.

The result is that the bullet screams out of the barrel, a good 1000 fps faster than most normal high velocity bullets. The dwell time that the powder is burning may be longer than others, it will most likely be hotter and will last beyond the time it takes the bullet to traverse the length of the barrel which will leave powder burning up in the atmosphere doing nothing but causing heat within the barrel.

When one goes to the extreme with a cartridge, especially one going this fast one has to take whatever the problems associated with this level of performance and expect issues on down the line. Drop the velocity down to that of let's say a 223 and your barrel burning issues will go away. Is it really worth while?

 

[Indigo22]

I have heard of folks having fun shooting their Bi-nary 10/22's. While burning through thousands of rounds may be fun at least one guy reported that his 18" barrel's accuracy (one shot at a time) had gone from walnut sized groups to almost pie plate sized groups at 25 yards. I am not sure as to how long it took for this to happen or how many rounds it took. At the same time ammo isn't cheap nor is a Binary trigger group. The heat does a number on even a 22Lr barrel.

 

[Tabby]

There is no rifle barrel that is immune to erosion. .22 factory barrels in general, are not made of the highest quality steel that there is. This kind of works since virtually all .22 ammo is lead or guilded metal. In other words bullets that are a lot softer even than the steel the barrel is made of which results in very little wear on the rifling itself. The barrel itself cannot avoid the work of heat and hot gasses and the throat will eventually evolve until the throat, like any other barrel erodes to the point where accuracy is affected. How many rounds does it take? In the case of my Tikka T1x, which I used extensively for training as well as ammo tests and plinking has over 10,000 rounds through it. When new it would group .35, these days it's more like .45, still sub moa but there are signs of the deterioration already beginning. Since my days of instructing have pretty much come to an end the chances are that the barrel will last the rest of my lifetime and well into anyone else's before it opens the group up to over 1 moa, but it will happen. It is simply a matter of time and bullets down the barrel.