Barrel wear

M

model14

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Am I correct in saying that for a given bore size, barrel wear goes up with bullet length and velocity?

What about holding velocity and bullet length constant and changing bore size?

I suspect heat and velocity is the biggest driver of barrel wear. I don't like to think in terms of "overbore". That means nothing to the barrel and bullet after it leaves the case. In the barrel there is heat, friction, surface area, and velocity, regardless of case dimensions. I am thinking that heat generation from more powder may be the key, and that is where case size comes in. but I dunno.

I have a hard time coming to grips with a doubling in barrel life in going from a 6.5-284 to a straight .284, but that is what is being claimed. Both use the same amount of powder and have only a few hundred fps difference. Bore dimensions are very close (1/2 mm) and bullet length close also. Doubling life ??
 
Barel wear

All I can add is what I've observed with a borescope with several brand new match grade barrels. A bran new .243 A.I. barrel began to show signs of firecracking in the throat area after 80 rounds; similarly for a .22-250 A.I. barrel. A .308 barrel shows no evidence of firecracking after 400 rounds. Several 6mm BR barrels are beginning to show signs of firecracking after approx. 400 rounds.

Lou Baccino
 
I don't like to think in terms of "overbore". That means nothing to the barrel and bullet after it leaves the case.

I think you need to rethink this thought. In just about every 'case' I have had experience with, the more you neck it down, the more quickly the barrel wears. I think over bore does mean something.
 
Dennis Sorensen said:
I don't like to think in terms of "overbore". That means nothing to the barrel and bullet after it leaves the case.

I think you need to rethink this thought. In just about every 'case' I have had experience with, the more you neck it down, the more quickly the barrel wears. I think over bore does mean something.
Click to expand...

Dennis,
I agree with your statement; that's what I've observed with a borescope.

Lou Baccino
 
I think most could agree that the barrel on a 6mm-06 would wear faster than on a 35 Whelen so the ratio of bore to case wolume has something to do with it.
 
I think it has to do with a big boiler room being squished into a smaller hole. Chamber temps can flash to over 6000F in some cases.
 
Dennis's
Statement makes sense to me.
Some military studies and some peoples annicdotal evidence has suggested that some powders wear barrels faster than others so maybe not just heat but also friction from the powder is a factor?

With the the Big Case, Little Bore syndrome basically we are trying to fit a lot of hot gas through a small conduit. Creating a prolonged exposure to the hot gas.
Ted
 
Are you guys trying to say my barrel wont last long??? :eek:

12b.jpg
 
Tony,

Exactly what is the trajectory of the barrel to 200yds.....also, which gets to the target faster....bullet or barrel??? Does the case stay on the bolt face??:D

Hovis
 
Besides heat itself the molecular weight of the products of combustion and the amount of particulates and their physical properties can contribute to bore wear.
Research on double base propellants has shown that these produce more carbon dioxide than single base powders which produce carbon monoxide.
The heavier superheated molecules transfer heat energy to the bore surface more efficiently.
 
Years ago, when I worked for DuPont, I asked one of the powder chemists about this general area. The consensus among his group was that barrel wear (erosion) is mostly a chemical process rather than a mechanical one, and that temperature is the big driver (temperature is driven by the amount of powder burned), and pressure a significant factor as well.
 
I noticed that not one posting mentioned barrel steel. This has to be a consideration. We have some very talented folks posting here. Is anyone a metallurgist?

I finally got my 22-250 shooting to the point that I have simply stopped experimenting with loads.

The gun is shooting probably better than I can hold.

The gun has about 550 rounds through it according to my records.

I load mild for this caliber, and I doubt I will live long enough to shoot out this barrel. Of course, I am a senior citizen.
 
Barrel wear?

I seldom wear barrels because they are quite heavy, uncomfortable and make me look and sound like a large wind chime.
 
Military .30 caliber barrels in the 06 to .308 class using single base powders like Pyro or IMR were found to significantly improve in accuracy for the first 3,500 rounds. British .303 barrels using Cordite could begin to degrade in long range accuracy in as few as 600 rounds and usually within 1500 rounds the degradation continuing slowly and gradually from that point.

Stainless Steels in the modern sense were the result of attempts to find a barrel steel that could withstand the erosive effects of cordite. No alloys they tried were very sucessful.
 
Is there evidence that barrels wear at all?
What does firecracking have to do with wear,, or land retreat, or bore constriction?

Isn't the question really, what causes barrel potential to take a hike??
 
Mike

You make a good popint. I think "burn" might be a better term, as after you get past the initial throat area, there is no actual 'wear' at all.

I have cut barrels back as much as 1 inch, and found that the exact same deltronic pin fit as when it was new. It is amazing how little anything changes once you get past that initial area of the bore where the maximum pressure spike occurs.........jackie
 
Jackie, it's my understanding that barrels can be set back as many times as the desired tune can be reached. Also, that these barrels continue to shoot very well.
Would you say this is often true?

Further notions of mine, stretch to understand why the 'combustion area' of a barrel destroys performance.
Aside from distance to lands(which may or may not be a problem), I'm left to think it's carbon related.
Could it be groove constriction due to carbon working it's way into steel?
If so, This would swage bullets below the rest of the barrel's groove. And at this point, and with this carbon being impossible to remove, performance could only be restored by re-chambering beyond the condition.

Just a suspicion, that you might measure.
 
If any one has fired primers only with no powder, they will notice a
special kind of fowling, not found otherwise. It is very
hard to remove it. Crushed glass and powdered aluminum as well
as other materials which can be hurled into the powder , by the primers
cannot be good on steel barrels CM or stainless. That it is not
as noticeable in loaded ammo, doesn't mean its not there. The larger
bores can disapate heat better, no doubt but I think the somewhat
abrasive materials in primers do contribute
 
Mike

I have made it a habit to set competition barrels back every 300 rounds or so, mainly just to keep that initial throat area fresh. Usually, all that it takes the first two times is about .025 inch. The third time, I cut the entire thread off and start over like it is a new blank.

This has worked well for me in the past, I will continue doing it. The way I chamber barrels in the first place makes it very easy to set them back up exactly the way they came out of the lather the first time.

One of the strange things is that even though there is a new throat, and lead, the barrels require no break in. They clean just like before the set-back. You would think with that new throat, it would act like a new barrel........jackie
 
Case length may be a factor

I have a 30-284-1.650" I shoot in HBR. The first barrel Lasted through 16 lbs of 4197S and the other powders I used testing. It shot competatively for almost 3 seasons and I am guessing around 3k rounds, I don't keep track. I think just as there is great barrel life with the 30 BR, the same may be true for the the shorter, fatter case of my 30-284S. My 30-44's don't last that long.
 
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