Overbore Questions

[jcisbig]

I was recently made aware of the concept of "overbore" and it was something that took me a little by surprise. I was considering buying a .30-06 and was informed that many shooters get about 3k to 5k rounds through their rifles before the rifling begins to be destroyed. Please correct me if anything I said above was incorrect.

Now for the questions! (Some are asked with assumption that the rifling is messed up after the 3k to 5k rounds)

1. Is there any way to prevent the effects of shooting overbore rounds, or would my barrel be doomed after 3k-5k rounds?

2. Is the barrel really unusable after 3k to 5k rounds?

3. What would happen to the firearm/barrel if one were to just keep shooting with it after the 3k to 5k rounds?

4. If a .30-06 barrel only lasts for 3k to 5k rounds, why would people buy rifles chambered in that caliber knowing that they will have to replace the firearm/barrel after that many rounds?

5. Does shooting damage the rifling a little bit at a time until it becomes 'unusable' at 3k-5k rounds, or does it begin at the 3k to 5k range?

Forgive my ignorance on the topic, and I appreciate your responses!

[Lycanthrope]

Every rifle can be shot out with enough rounds, but overbores have this happen more rapidly.

Generally, the lands start to erode and accuracy goes away slowly. How hot your loads are, the twist rate, barrel quality and how rapidly you fire (heat) all have an effect on how fast barrels wear.

That being said, the 30-06 is not really what I would call an overbore and is capable of hunting accuracy for a long time. My 7STW, however, started to loosen up by 1200 rounds.

Lycangetan'06thrope

[knight0334]

What was mentioned above, and in addition to:

With overbore conditions - there are depreciatable gains in velocity versus the amount of powder loaded into the cartridge. ...you gain less velocity for the bore and barrel length.

A good example is the 225 Win v 220 Swift. The 225 Win has a substantially less powder capacity, but it is within a couple hundred feet per second in velocity. Another fine example is any of the "magnum" 30 caliber cartridges(or any magnum for that matter) v the 30-06. Very little gain over a 30-06, but a heck of alot more powder being burnt.

The throat erosion is a side effect really. Not so much from overbore, but rather from higher pressures, hot gasses, and powder burning - which any 45-65K psi loading can cause easily. The higher velocities of the bullets lead to the bore being worn out from the throat to the muzzle.

You can counter some of the overbore by lengthening the barrel - getting more use of the burnt powder. If the powder isn't getting full use of - it's "overbore". But, with the longer barrel you raise bullet speed of an overbored cartridge - thus promoting bore wear.

The 30-06 really isn't overbored until the barrel is 22" or less. The 308 is overbore at 20-22" or less.

[jcisbig]

Thanks for the info.

If I was looking to buy a rifle and it didn't really matter if it was chambered in .308 or .30-06 would you recommend the .308 because the barrel will last longer?

How long (months or years) does it take you to go through enough rounds to where you start experiencing a degradation in accuracy?

[ALS]

I've seen a .308 Sniper rifle (Hart Barrel) with over 7,000 rounds through it still a tack driver. BTW the SS barrel was 26" in length.

With a .308 5000 rounds should be the minimum fired before the barrel begins to lose it's edge.

[ScaredOnce]

Unless you have very specific use in mind, the slight difference between the two may be negligable. I prefer the .30-06, but honestly the way I've used mine wouldn't matter if it was either cal.

[knight0334]

The 30-06 will allow for heavier bullets to be used. The additional powder capacity to push it, and the additional length of case to seat it deeper to stay within max COL and still have room for the needed powder.

If you shoot the same weight of bullet out of a 308 and a 30-06 at each's respected spec'd operating velocities- the 308 will outlive a 30-06. However, bear in mind - there are 30-06 rifles with perfect bore that were made in 1906.

5K-15K.. there is no set rule on how long a barrel will last. Either is a fine choice, each having their own pro's and con's - but those deferences are really minor.

[jcisbig]

It seems to me that technology improves with time relating to firearms. Since there are rifles from 1906 around that have perfect barrels does that mean that they haven't been shot much? Or were the barrels made better back then than they are now?

[Tomcat088]

Lol, Jcisbig, I didn't say the barrel would be unusable. I did say that you will start having to chase the lands with reloads, or eventually have to have the barrel set back. Alot of people who look at having a factory barrel set back would just rather buy a new factory barrel for like the same price, or consider buying a custom barrel. I assure you that the 30-06 rifles that have a perfect bore that were made in 1906 do NOT have probably 5K or 7K rounds through them, or they wouldn't have a perfect bore. As was stated by others, you will start to see a consistent degradation in accuracy. Like Lycanthrope said, it all depends on lots of factors, bullets, type of powder, charges, etc.

The reason that alot of people swear by the .30-06 and love them is because they typically use them for hunting rifles. Most guys that shoot small animals use smaller calibers like .223, .22-250, .220 swift, .243, etc. Alot of the guys that are using .30-06 for hunting don't usually put 5-7K rounds through their rifles. They sight it in once a year, then they use it to take a few deer and then put it on a shelf. If you only fire 20 rounds a year through a rifle, it'll last forever if you oil it up and clean it. Knight mentioned the .30-06 not being overbore unless you went below 22". Realize that this isn't true of all loads and will also be dependent on the burn rate/length of the powder that you're using. The .30-06 is slightly overbore, but not like the .300 winmag that I shoot. Just think about it and realize that even 5K rounds is ALOT through a bolt gun. Sure people do it all the time, but say that you shoot 20 rounds a week, that means that it would take 250 weeks or 4.8 years to burn up a barrel. That would be if you went every single week and shot that many rounds. In terms of just the cost of ammunition, say that you shot the cheap stuff like maybe Remington Core-lokt at midway, it's $17.99 per 20 and with shipping about $20 a box (the usual). So you would have to shoot 250 boxes of ammo, or spend roughly $5000 ($1 per shell) to burn through the barrel. At that point, the point is kind of mute about you spending $400 or $500 for a barrel from Krieger (after you chamber and thread it). Just some things to consider

[jcisbig]

Thanks for the info once again. I found this on the Cabela's forum:

"Barrel life is largely dependant on cartridge, barrel maintenance, and what the barrel is made of. Generally, a .30-06 is not a cartridge that is hard on barrels. So, that alone helps you dramatically.

When/If you start to experience a loss in accuracy, its more likely to be a problem with improper cleaning. Failure to keep the bore clean of copper AND powder residue will take away your accuracy faster than anything.

Today, the metalurgy of barrels is FAR greater than it was 50 years ago. That alone will increase you barrel life dramatically.

Another contributor to barrel life is whether or not you reload your own ammo. If you do reload, its possible your barrel life will be shortened due to your pushing the envelope and lack of watching your powder burn etc.

It would not surprise me if your .30-06, if properly cared for, could well exceed 10-15,000 rounds."


http://forums.cabelas.com/archive/index.php/t-691.html


In regards to cleaning, I usually use a bore snake and Hoppe's No. 9 solvent in my barrels. What do you guys use? Should I do more to preserve the life of the firearms I do already have?