Bullet Velocity Affecting Barrel Life

Were Talking about big calibers shooting small bullets.

It is more about the ratio of bore diameter to powder capacity. It is the hot jet of gasses that kills a barrel.

Velocity is largely a function of pressure. Here is a good "rule of thumb" to use.

What follows isn't a hard and fast answer, there are exceptions at each end of the spectrum.

2400 FPS or under? Good luck shooting out the barrel in your lifetime.

2400 FPS to 2700 FPS? Barrel will have superb accuracy out through about 10,000 rounds.

2700-3000 FPS? 5000 rounds before accuracy is degraded

3000-3300 FPS? 4000 before accuracy is degraded.

3300+ FPS? 3000 rounds, if you are lucky.

None of this takes into affect things like radial or ratchet rifling, chrome or melonite bore lining, or even what alloy of barrel steel being used. Also, there is a big difference in a 55 grain projectile at 3300 fps from a 223 and a 75 gr pill at 3300 fps from a 22-250.

What happens is the hot gasses create "heat checking" in the throat and bore of the barrel. Often this is combined with nitriding and causes enough erosion to affect accuracy. More gas = more pressure = more heat, pV=nRt and all that. Heck, even unburnt powder being "sandblasted" against the throat/bore causes erosion.

So there really isn't a hard and fast answer to your question, but I hope this gets you thinking about what goes on when you pull the trigger.

Jimro

Bullet velocity

JIMRO pretty much got it right, how fast or how close together the shots are fired also has an effect on heat checking and throat errosion, thus barrel life. Al

Heard claims of nearly doubling barrel life in a 22-250 by backing off loads from 3800fps to around 3400-3500. Don't know if it's true or not since I don't shoot it. Others might chime in...

M

Shooting out barrel throat

I shoot my 22/250's at around 3400, but shoot them quick enough (fast) that the barrel gets real hot. Have shot the barrels out on both of them twice. The trick is to not let the barrel get to hot by spacing your shots. It's hard to do when them little PD's are all over the place just begging to be turned to red mist. Al

How does bullet size/diameter factor in?

From what you are saying a 7.62x39 rifle would last a long, long time.

Does the fact the the bullets have more mass and a larger diameter factor into the barrel heating and barrel life?

If so, do you have a sense of how much? Let's keep chrome lined and melonite lined barrels out of the consideration.

Shooting out a barrel

Heat and errosion in the throat area is what causes the throat to go-away, it doesn't really matter what the cal. or bullet dia. is (unless your talking rimfire) if you constantly over heat the barrel by rapid fire it is going to do damage to the throat area. Al

My experience (while limited) shows that it is linearly related to pounds of powder burned. It appears to me that "roughly" you can burn around 20 lbs of powder down a barrel before the fine accuracy is gone. The differences from 20 has to do with rate of fire and how hot you get it more than the bullet speed.

I note that bullet speed tends to relate to more powder so maybe there is more to the speed than I give it credit for.

So, run the math on your gun. If you treat it nicely figure 20 lbs. If you beat on it, figure 20 lbs and your fine accuracy will start to diminish. I know I see it already in several of my rifles at around the 20 lbs mark.

At 43,000 cup the peak flame temperature is just reaching the melting point of modern barrel steels. As the chamber pressure increases the peak flame temperature also rises and causes more bore erosion.

In simple terms the hotter the load the more bore erosion you will have corresponding to chamber pressure and peak flame temperature. (speed kills)

This may sound strange but the bigger the bullet the easer it is to push it down the barrel because of the bullet diameter and surface area to push on.

From what you are saying a 7.62x39 rifle would last a long, long time.

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Yes, a 7.62x39 would last just as long as a 30-30 lever rifle if it were shot just like a 30-30 lever rifle. I expect my older brothers CZ rifle in 7.62x39 to outlast his grandkids.

That 7.62x39 rifles/carbines are generally milsurp and shot in rapid sequence causes plenty of barrel heating which increases erosion. That most milsurp 7.62x39 rifles had chrome lined barrels mitigates erosion to an extent, but that was largely to deal with combloc corrosive primers.

Like I said, there are exceptions to the rule at each end of the spectrum, but generally it is what it is.

Jimro

Smaller bores and higher velocities wear out faster.

At least that's what 'Brassey's Essential Guide to Military Small Arms : Design Principles and Operating Methods' said.

BSW

Smaller bores and higher velocities wear out faster

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Totally agree.

The rule of thumb that a 308/30-06 barrel peaked at 3500 rounds, was worn out at 5000 rounds, is still reasonable for 600/1000 yard shooting. I have shot outstanding scores on the 300 yard Reduced target with a 308 barrel which was so worn out it gave poor results at 600 yards.

Sub caliber shooters, target shooters have migrated to 6mm and 6.5 mm bullets because excellent match bullets finally got to market, and the ballistics are excellent. However, cartridges like the 6.5-08 are real barrel burners. I have asked shooters using them, if they last 1700 rounds that is a reasonable life. The 243 Win is an outstandingly accurate round but its target lifetime is around 700-800 rounds, per guys who use them.

I met a target shooter who was using a 22-250. He told me he shot very few rounds through the thing, probably around 800 rounds a year. When he had the rifle rebarreled, he said on the old barrel, the rifling was gone for a foot in front of the chamber.

He also said, he used a lot less windage at 600 yards than the .223 shooters all around him.

The trend is towards rounds, like the 6.5 Grendel, that are slower, probably lower pressure, but certainly push less hot powder through the barrel. Tubb came up with the 6 mm X, a smaller case, keeping the excellent ballistics of a 6mm but pushing it with less powder.

At least that's what 'Brassey's Essential Guide to Military Small Arms : Design Principles and Operating Methods' said

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I don't think the younger generation reads books anymore. Good that you do.

Smaller bores and higher velocities wear out faster.

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Not exactly. Higher velocity, yes.

More gas = more pressure = more heat, pV=nRt and all that. Heck, even unburnt powder being "sandblasted" against the throat/bore causes erosion.

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Yep.

The "factor" is the volume of high temp gases relative to the bore size. Most pistol barrels last almost indefinitely because there is a relatively small amount of powder used, and most pistol rounds have little if any neck of the case. A 45acp uses maybe 6-8 grains of powder to push a .452 bullet.

Now, go to a 22-250 that uses 40ish grains of powder and squirts it thru a .224 diameter hole. Eight times more gases (and heat) pushed thru a hole that has 1/4th the area. Velocity comes at a price.

M1key said:

Heard claims of nearly doubling barrel life in a 22-250 by backing off loads from 3800fps to around 3400-3500. Don't know if it's true or not since I don't shoot it. Others might chime in...

M

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Why would anyone with 1/2 a brain do something like this? I'll never understand people owning a gun then crippling it by shooting very light loads. Before I loaded a .22-250 down to 3400 fps I'd buy a .223.

Another thing about downloading, you're giving up accuracy too because the loading density is down.

Shoot it and enjoy it. When the barrel is shot out rebarrel. I've done it and will do it again too.

It's not velocity that kills a barrel, it's the heat of the burning powder. And a barrel will only last a finite amount of powder. Load it down, you may get 200 more rounds out of it, great trade off, performance for 200 more shots.

joed,

It must really sting you that other people enjoy their firearms in a manner with which you disapprove...

As far as downloading to get more barrel life, it makes sense from an economic point of view. Less powder, longer barrel life, it is a win win. I doubt the prairie dogs will know the difference between 3300 fps and 3800 fps.

Heck, some folks load their 30-06 with 220gr lead bullets right at 2000 fps and get their deer every year. Other folks crank out 190gr VLD's from their 30-06 to shoot past 1k. Handloading sure does bring out the versatility of a round...

Jimro

Well Jimro, in all reality, that 400 to 600 fps difference WILL mean a serious loss of accuracy at distance when on P-Dog hunts. I have a couple of .22-250's. One is a custom with a Hart barrel with WELL over 5000 rounds down the tube. She will still print cloverleafs at 200 yards as long as I do my part. My load generates speeds of right close to 3900fps too! Now the other one, factory barreled, only has a few hundred down the tube (per the previous owner) and I have only put around 30 rounds through it myself. Not very accurate so when I have the time I will re-barrel it with another Hart. It more depends on the RATE OF FIRE than the load in my opinion. I always take 2 or more rifles with me on P-Dog hunts to allow for cooling time. You cook ANY barrel, I don't care if it's a small bore or a large bore, you are going to damage the throat. It's when you fire it on a cherried up throat that you smooth it out. ANY metal will become "pliable" at heatup. It's the nature of the beast.

I'm only interested in 300 yard accuracy, I figure my .308 heavy barrel Remmy 700 will be just fine right on through 10,000 rounds. 44 grains of powder down a 30 caliber bore isn't really severe. I typically load 168's at 2600 fps.

Several factors involved. More powder to a smaller bore always = faster barrel wear, but there are a few other factors as well. The angle of the shoulder and length of the neck are proven to have an effect on wear because the turbulent "rolling flowing vortex" has higher speed hence abraision and if that point is in the neck of the brass it won't be in the throat of the barrel. That might crack a neck or two but is much easier on barrels. We know this has an effect because some calibers of equal overbore nature wear faster then others. WSM cartrages are not known barrel burners despite their high capasity because of their sharp 35 degree shoulder. Barrel life for mild calibers such as the 308win run as high as 8-12,000 rounds. More overbore cartrages such as the 270win expect more in the 3-5k range, and with monster overbore mild shoulder angle cartrages such as the 264 win mag barrel life can be as short as 500 rounds!! Though proper care and cooling times double that. As you can see barrel wear is by no means a linear equation. A little extra powder can cause alot more wear. Shooting "hot" speeds up barrel wear dramaticly as hot metal is much more susceptible to the errosion of fast moving powder granules and high energy gasses.
Exact metallurgy of the barrel has alot to do with it as well but that would require me to wright a thesis level post to fully explain.

Hey Kachok, if you are going to write a thesis, PLEASE download and use Google Chrome and activate "spell check"!! Thanks!!

Freedom_fighter_in_IL said:

Hey Kachok, if you are going to write a thesis, PLEASE download and use Google Chrome and activate "spell check"!! Thanks!!

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Haha spelling never was my stong suit (not in English anyway, BTW Kachok is not an English nickname. Hint hint) No I don't plan on getting into the finer points of metallurgy that is a very long story to tell, I don't think my fingers could handle it tonight, but I will summarize by saying that harder alloys have a higher abrasion resistance, hence last longer.

joed said:

Why would anyone with 1/2 a brain do something like this? I'll never understand people owning a gun then crippling it by shooting very light loads. Before I loaded a .22-250 down to 3400 fps I'd buy a .223.

Another thing about downloading, you're giving up accuracy too because the loading density is down.

Shoot it and enjoy it. When the barrel is shot out rebarrel. I've done it and will do it again too.

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Why do people do it? Ask them. The 22-250 chambering used to be a top choice among the bench rest crowd many years ago. You didn't have to load to primer-popping pressures to punch holes in paper.

Folks have even been downloading 223 with Blue Dot and similar powders for years with excellent results. Why? Because they CAN and they WANT to. You can approximate 22LR, 22Mag, 218 Bee, 22 Hornet, 222 etc. for low noise game gathering, target shooting, teaching children to shoot...all kinds of good reasons.

M

Now why in the world would anyone load a .223 to less than 40,000 cup, stay below the 43,000 cup heat threshold, save wear and tear on his barrel and have fun doing it. (I did)