Question about barrel wear from cleaning.

Dogleg said:
Why is it that powder burning in a barrel for about a ten thousandths of a second heats it up, but an ox-acetylene torch wouldn't do anything with a thousand or even ten thousand times the time to do it in? :confused:
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Hi dogleg, right back at you and your "character flaw"; I'll see your troll, and raise you a pedanticism or two, and throw in a genuine SWAG at no extra charge!... ;-)
  • (The powder gas is in there for typically 0.8 milliseconds; a fair bit more than a tenth of a millisecond)
  • Because of the high pressure (10,000-50,000 psi, which is roughly 1,000-3000 times as much pressure as atmospheric pressure), the density of the powder gas is a few thousand times greater than an oxyacetylene flame
  • Also, the speed of the powder gas (several hundred meters per second) is higher than the speed of a torch flame (a few meters per second). Combined with the preceding item, this makes the powder gas much more turbulent than the torch; this improves the heat transfer rate (perhaps by 2-3X?)
  • The temperature of a torch flame is actually higher than the powder gas temperature.
So if the density difference improves heat transfer by about 2000x, and the increased turbulence improves the heat transfer by 2.5x, and the lower powder gas flame temp means the heat transfer is 0.75x as much, then my SWAG is that an oxyacetylene torch will take 2000*5*0.75 = 3750 times as long to transfer the same amount of heat. Or, a torch blowing down the bore will take 3750*0.8 = 3000 milliseconds (3s) to transfer the same amount of heat to the steel as a 0.8 millisecond blast of gas from a cartridge. Now running that through my gut-feel sanity filter, I think that estimate might be somewhat high (I suspect 3s of a torch down the bore would heat the barrel somewhat more than one shot, but not too terribly much more). But I think it's in the right ballparks, and we're talking SWAGs after all, which are really only good to within a factor of 10 anyhow ;-)
​


(SWAG = Scientific Wild-Assed Guess...)

(P.S. I think I have too much time on my hands...?)
 
Granted you

Obtunded said:
The crown is the very last part of the rifle and one of the most important parts that influences the flight path of a bullet. Crown damage results in asymetrical venting of air in front of the bullet and gasses behind. It takes very very little to bugger a crown and the results can be devastating to accuracy.

I never drag anything across the crown, especially metal brushes.
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are well versed in shooting and your profession of selling barrels.

What amazes me is how many people in Canada almost NEVER look at or read what the benchrest shooters do.

When these guys and gals are shooting teen aggs dragging brushes back and forth across the crown I doubt that brass or bronze brushes whatever there composition hurts the crown that much.
 
Benchresters have long been the epitome of obsession when it comes to barrel cleanng. This changed somewhat with the adoption by some of moly coated bullets but mostly, they keep on cleaning and have proven that clean barrels shoot.
Once I started shooting "F" class, I had to shoot more shots without cleaning. What I learned was that, within the requirements in this venue anyway, so much cleaning was unnecessary. In addition, the opportunity to waste a bunch of sighters wasn't there. The sighters had to be reliable as far as POI was concerned to be of any value and there were only two of them.
I also learned that good barrels really don't foul even if you just keep shooting them. Nonetheless, when I shoot BR, I clean. Old habits die hard. I think the idea of unscrewing the brush with each pass is just silliness. Regards, Bill
 
How many rounds before most benchresters retire their 6ppc barrels?

Bill, The list of silly rituals in shooting is long and distinguished, so my obsession with bore brushes is fair game.
 
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Obtunded said:
The list of silly rituals in shooting is long and distinguished, so my obsession with bore brushes is fair game.
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Absolutely!

We sure have a lot of silly rituals to consider doing: sort bullets, clean primer pockets, weigh cases, moly or no moly, how often we clean barrels, re-do bedding, how we adjust triggers, how we choose primers, turn necks, deburr flasholes, how much bullet runout we'll accept, neck tension uniformity, neck and case wall eccentricity, etc.

I've long thought that out of 100 such things we might do in shooting, 97 of them are probably utter crap, totally worthless, and we could shoot just as well if we didn't bother with them at all. Which would sure save us a lot of time, effort and aggravation!

And yet, three of those hundred probably do matter; and it may well be most economical of our time to simply do our 100 silly rituals, rather than to try to find out which 97 rituals we can abandon!

I suppose this is yet another reason why we shooters tend to be such "colourful" characters, eh? ;-)
 
It all

Obtunded said:
How many rounds before most benchresters retire their 6ppc barrels?

Bill, The list of silly rituals in shooting is long and distinguished, so my obsession with bore brushes is fair game.
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depends how MUCH money you have at hand.

The die hard benchresters who go there to win are not concerned about barrel life or the costs of barrels. It is all part of the sport. Many of them shoot more rounds in a month than I probably shoot in a year with my PPC.

I KNOW that I do not have the cash flow that they have but I try to have a couple spare barrels every year for it. I buy them as the cash low permits.

These benchresters will be the first to tell you that there barels have not gone south due to cleaning. Bore scopes should pretty much tell the tale when checked before ever firing and watching as time goes on.

We hear it all the time that I would rather be shooting than cleaning. I can tell you I can clean my benchgun faster than it takes many of you to go out and have a smoke.

Bottom line we are all individuals and have our OWN beliefs that we may never get people to understand.

JMO
 
Ian,
Most PPC shooters will start to get nervous about a good shooting barrel at about the 1500 round mark. At this point there will be some minor erosion apparent in the throat. Seating depth will have changed and the barrel migfht be a bit more difficult to keep in "tune". One of the best barrels I ever had was still producing winning accuracy after 2700 rounds but I was getting nervous about it so I replaced it. This may have been a mistake since I went a while without winning anything.
I know that many benchresters will change barrels just hoping to get an edge when the barrel is still just fine. Many will change barrels after a bad match when the rifle was not at fault at all.
Those who use barrels utilizing a sharp edged crown may have to recrown every 4-500 shots because that crown is indeed damaged by the brush. Regards, Bill
 
Bill, what are some crowns that don't use sharp edges? (the only crowns that I know of, an 11 degree crown and a recessed crown, both have sharp edges, as far as I can imagine. Help....?)
 
Obtunded said:
How many rounds before most benchresters retire their 6ppc barrels?
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When Ebay was still allowing the sale of gun parts, there were always a stack of PPC barrels on sale with claimed barrel life in the 700 to 800rds.

My experience with match barrels also agrees that the very best accuracy of my barrels were in those first 700 to 800rds. Not saying they shot poorly after that, but the number of bughole groups certainly goes down.

If I had the budget, barrels would be where my investment would be. Some shoot, some don't - they all wear out.

Jerry
 
It was, and is among many, common practice to break the edge of the crown with a 60 degree piloted reamer. If the edge is chamfered this way, crown damage is less likely. The leading edge of the chamfer centers the brush up before it enters the bore. Without the chamfer, the tops of the exposed lands handle this chore with resultant wear to the sharp edges. I'm a believer in not leaving the lands exposed at the crown. Regards, Bill.
 
Bruce Baer is pretty adamant about removing 5/8" and re-crowning every few hundred rounds. He suggests that he can spot mild damage from cleaning and powder blast at a max of 500 rounds....No matter how careful the cleaning process.
This is on his heavy guns...maybe light guns are different?

Either way he maintains this will bring back the bugholes....I thought you guys might find this interesting....I did!
 
If I had the ability or budget, I would be setting my barrel back often too. What I have seen in the 6.5 barrels I have used up is that the throat area wears for quite a ways forward.

Most tend to focus on the throat relative to the bullet ogive (seating depth) without paying any attention to the rifling in the first 3 to 6". One barrel had the bullet still engrave on the lands at very similar OAL's as when newer but upon autopsy of the barrel showed that the rifling infront of this was very well worn.

So although the bullet did engrave, the depth of the rifling was too shallow to keep it true. Accuracy was failing fast.

Jerry
 
High intensity cartridges really do seem to mess up the entire bore.

I saw a shot out 17 Rem tube that Guntech sectioned and it was plain to see the not only was the throat gone, but almost all of the rifling was burnt out as well. I think he set that one back once?

The barrel saw serious use in the varmint fields, but it seems to me that high intensity cartridges get new barrels and not set back.

Cartridges like the 308 and 223 could probably be set back several times over their effective lives to keep up peak accuracy.

Curious to what others think here.
 
mysticplayer said:
I am in the 'don't bother with break in' and 'don't clean till the accuracy goes south' group.

Better quality barrels copper foul very little. Modern powders are very clean.

Every now and then, I will run a couple of dry patches down the bore to push out the surface carbon. I rarely chem clean anymore.

I would rather be shooting then cleaning.

Jerry
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I subscribe to this belief as well but I'm not really an experienced shooter (I've never competed).

I used to know a guy who's dad was big into shooting and he said he never used brushes, just patches.

Here's a question, do you guys pull your brushes though from the crown or push from the chamber? Do you only push in one direction (bullet direction)?

I'm quite interested since I have a new 700 on the way...
Obtunded said:
That is a greatidea Bill, I will have to try that next barrel job... great idea indeed
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Hey Ian, didn't really get a chance to chat with you last weekend. Was that your son who was showing me the rifles you had on display? What are the chances a guy could check out your shop next time he was up that way?
 
rnbra-shooter said:
Ah, OK, makes sense. How much (how deep) of a cut? Does it jump out at you when you glance at a barrel that has been crowned in this manner, or is it a pretty light and subtle cut?
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I usually cut intil the reamer reaches the groove diameter then cut another 10 thou or so. It's not real obvious but not difficult to see either. I do this regardless of the type of crown (11 degree, recessed, or whatever).Regards, Bill.
 
Wally, I just run the patch back and forth a few times, then switch until the patches turn grey. I really 'break' all the rules but it hasn't hurt my accuracy yet.

Xfan, from my 6.5 and other boomer experiences, setting back will work IF you can do it often enough. I would say 1/2 of the expected accuracy life is ideal NOT when the barrel can't hit a piece of paper 4ft from the muzzle.

So my 6.5 Mystic has an expected 1500rd accurate/competitive life. I would be set back every 600 to 750rds. That gets pricey and most of us just live with the slow decrease in accuracy.

What I know now, I wouldn't set back this barrel if I went the full 1500+rds. It would be too short for my needs - It can be salvaged if cut far enough forward.

With something like a 223 or 308, ideally, I would set back every 1500 to 2000rds and still take a nice chunk off the action end. If the barrel would allow, I would cut off the old chamber and start new instead of trying to chase the throat. Very few barrels are contoured to let this happen.

Even fewer shooters would bother looking at these barrels till they break 3000rds.

Then you would have to think, if I really want accuracy that bad that I am setting back my barrel a few times a year, why not just put on a fresh new one and get the best possible performance?

$$$$$$$ - how fast do you want to go?

Do some snooping on how Tony Boyer set up his SR BR rifles. Good thing he has barrel sponsors.

Jerry
 
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