Barrel Life...

[MoA]

In the Indian context this has very little meaning given the restrictions on ammunition.
However those of us lucky enough not to be limited by the laws in order to pretty much shoot as much as we want, do worry about it.

Simply put barrel life is the rough number of bullets that can be shot through a barrel before accuracy starts to deterorate.
How is it calculated?
The rule-of-thumb process, as laid out by the likes of McMillan et al is:

1. Calculate the bore area in square millimeters.

2. Use one grain of powder for each square millimeter. This is what
I call the reference, or base powder charge.

Example: .30 caliber bore = 45.6 square millimeters.
Base powder charge for .30 caliber is 45.6 grains.

A .30 cal. cartridge that burns 45.6 grains of powder should give a
barrel life of about 3000 rounds of good accuracy.

3. If a larger cartridge is used and it burns more powder, the
accuracy life in rounds for that bore size is reduced. The amount
of reduction is determined by

a. Divide the increased charge by the base charge, then square
the answer.

b. Divide that answer into 3000.

Example: .28 caliber bore has a base charge of 38.5 grains.
Cartridge burns 57.8 grains of powder.
(57.8/38.5) squared is 2.25.
3000 divided by 2.25 is 1,333 rounds.

Now what is important to keep in mind is just what one expects from an accuracy viewpoint.
For example lets say I can pretty much hold a 5 shot group at under 0.2 inches center to center consistently (I cant in reality), i.e. > 0.5 inches edge to edge. So I will swap out a barrel once my groups open up to 0.6 inches or more edge to edge which say occurs at 2000 rounds through the barrel. Now keep in mind in compititive point blank bench rest, there is often as little as 0.022 inches seperating the person finishing 1st from the one who finished 20th.
However lets consider the scenario of a hunter, who likes to shoot deer, where the accuracy window is at least 6 inches. The barrel would last a lifetime.
Also keep in mind, the average compititive shooter will go through at least one barrel a season, while a typical hunter will shoot under one box of ammunition a season.
Other factors that affect barrel life are heating. Rapid fire tends to shorten barrel life. This primarily is due to throat erosion, and fire cracking in the throat in particular. Ideally you should not exceed one shot a minute. Or in Competition, at least let the barrel cool down completely between relays.

Some calibers seem to buck the trend in barrel wear, these are generally calibers like the .30 BR, .22 LR etc, which seem to last forever. On the other end of the spectrum are calibers like the .22-250, .300 WM, .243 Win which tend to wear out very quickly.

However since in India I would hazard a guess that the average rifle is shot about two to three times a year at most, one doesnt really need to worry about it.

(I am bored and rambling now).

[nagarifle]

thanks for sharing, it s nice to know, hows the cleaning lady?

[MoA]

thanks for sharing, it s nice to know, hows the cleaning lady?

Due on Satruday as of now. She didnt drop off my laundry yesterday, so have had to buy a few shirts today...

[nagarifle]

so that means you are able to meet up with the UK ifgan on Sunday? hip hip orrray,
shell i dog and bone every one?

[MoA]

so that means you are able to meet up with the UK ifgan on Sunday? hip hip orrray,
shell i dog and bone every one?

Can confirm on Wed.

[nagarifle]

Some calibers seem to buck the trend in barrel wear, these are generally calibers like the .30 BR, .22 LR etc, which seem to last forever.

why is that?

[MoA]

Some calibers seem to buck the trend in barrel wear, these are generally calibers like the .30 BR, .22 LR etc, which seem to last forever.

why is that?

With the .22 LR accuracy at 100 meters and beyond tends to begin deteroating around 15000, this is not noticiable at 50 until about 20-30K. Hence the perception. Also given the formulae, the .22 LR tend to use less powder than the base charge.

With the .30 BR not really sure, since the velocities are fairly high 2900+ fps. More to do with the twist rate, which typically is about 1:18.

The .308 is another caliber that seems to last until about 6K. Then again the standard expectation from the .308 is about 1 MoA.

[shooter]

good post bro. very informative and worth saving/printing. surprised there were no takers.
please post one re: twist rate and accuracy.
thanks and keep them coming

[Vikram]

That is a great post,MoA.Very educative.Please keep them coming.Thanks.

Best-
Vikram

[winnie_the_pooh]

MoA,

Nice post.Barrel life would be an issue for a target shooter but not for a hunter,in my opinion.The amount of ammo that a hunter fires and the accuracy required would be considerably lower than for a target shooter.

I am sure many barrels discarded by shooters would still be perfect for hunting use.

[nagarifle]

thanks MoA, its educating

[MoA]

good post bro. very informative and worth saving/printing. surprised there were no takers.
please post one re: twist rate and accuracy.
thanks and keep them coming

Twist rate is a difficult one. Different twist rates are required to stabilise different bullet weights. Shooting heavy bullets with slow twist rates can cause bullets to yaw, and therefore loose accuracy.

For example in say a 6 MM BR you can adequately stabilise bullets with wieghts at or under 90 grains with a 1:10 twist. However in order to shoot bullets in 100+ grain category you need to get to a 1:8 twist. With the latter you can continue to shoot the lighter bullets as well, but need to keep an eye on velocities. It isnt unknown for shooters using a 68 grain bullet in a 1:8 to vaporise thier bullets before it hits the target. This is largely due to the immense strains put on the bullet jacket by the high twist rate, and high velocities.

If you google 'Don Miller's Twist Rule', you can find a spreadsheet that will claculate a guidance for twist rates for a given caliber, velocity, temperature and pressue. However it is a guidance.

There have off late been some experiments with gain twist barrels as well. That is a barrel that for argument's sake starts out as say a 1:8.5 twist, gaining to 1:8 by the time it is about 3 inches from the muzzle. While I have not tried one, I havent come across any data that seems to indicate if these are any more accurate than a constant twist barrel either.

Winnie: From the perspective of a hunter you are right. This is something I have already mentioned. However with certain calibers like the .22-250 and .243 used for varminting it is an issue. Not so much for the deer hunter though. I know a number of folks who have had their rifles for 10+ years and have barely put 20 rounds through them. Or for that matter have bothered to clean them either, and the weapons are perfectly usable.
Some of my hunting buddies will come to the range once about two weeks before the start of the hunt, shoot a couple of rounds to make sure that the rifle is still holding its zero, and then maybe shoot two more during the season and bag a deer or two or wild boar. And then the rifle is put away for the year. These are people who discard their brass as well, since they dont hand load either. All they care about is that first shot from a cold barrel, hitting within 2-3 inches of their POA.

[nagarifle]

come to the range once about two weeks before the start of the hunt, shoot a couple of rounds to make sure that the rifle is still holding its zero, and then maybe shoot two more during the season and bag a deer or two or wild boar. And then the rifle is put away for the year. These are people who discard their brass as well, since they dont hand load either. All they care about is that first shot from a cold barrel, hitting within 2-3 inches of their POA.

that is true, i just spent 10 shots zeroing my rifle and 2 shots on a deer, until next time i go out. hand loading for me, since i use a box 20 per year, is not worth the expense, so the brass gets discarded, unless you know who want 20 empty cases? i am willing to post it to them first shot is important in hunting for the obvious reason.

target shooting is noting in comparable with hunting as the demand are different from each others.

[MoA]

Depends on the caliber... I might be interested.

[nagarifle]

Depends on the caliber... I might be interested.

cal .243?