Damage from Cleaning rod or false shoulder?

[jrm850]

I'm a little disheartened to find what appears to be slight galling at the edge of my neck and throat junction. I wish I could figure out how to take a pic with a bore scope to explain it better, but it looks like little cracks around the entire perimiter at the edge of the junction where the false shoulder would sit on fireforming rounds. I did not notice this at all before the last cleaning and have used a scope religiously during cleaning. I'm using the same Dewey rod and Sinclair adjustable bore guide that I have used for many years and have never seen this before, but my patches do leave the last ring of the brass jag exposed so I'm not ruling out cleaning rod damage. Has anyone ever heard of anything like this before?

The round count is only 176. This appeared after a 66 round match.

 

[Jay Christopherson]

It sounds like the beginning of fire-cracking to me, which would be normal wear. I could be wrong, but around 200 rounds is when I first start to notice slight cracking begin. It will become more pronounced over time. It's an indicator to keep an eye on when it comes to estimating the life of your barrel. When it becomes truly bad, I've heard (anecdotally) that it will start flaking which might show up as shiny specs in your throat where the metal has flaked off.

I could also be misunderstanding what you are describing as well... that has been known to happen...

 

[fdshuster]

jrm850: If I'm reading your posting correctly you are seeing straight line linear cracking at the mouth of the chamber, where the front edge of the case would sit before firing?

You did not say what cartridge is being used, if it's one of the "big ones", then what you are seeing is normal. I also see this type of cracking, with my borescope, in all of my barrels, beginning at around 500 or so rounds fired with my 8 twist 6BR's ( 105 to 108 gr. bullet weights) and around 1000 or slightly more with my 6BR 14 twists using the 65 to 68 gr. Bergers. 6ppc chamberings have it also at slightly over 1200 rounds fired.

There is basically two types of firecracking: the straight-line linear at the chamber mouth, the first place where cracking will show up. The second type, the "alligator skin" or "dry Arizona lakebed" forms in the leade and throat areas & will start to show after the straight-line linear.

I believe what you are seeing is completely normal & not caused by any adverse cleaning procedures. Keep watching it and you will see it gets worse as the number of rounds fired increases.

 

[jrm850]

It sounds like both of you understand what I was trying to say.
It definitely looks like the beginning of cracking, I have just never seen it happen so soon. The cartrige is a dasher. The only difference between this chamber and the way I used to do them was that I used to lightly polish right up to that junction and this one I only polished up to the shoulder. I'm wondering if leaving a sharp edge there accelerates the formation of the cracks?

 

[fdshuster]

jrm850: I can connect with what you are seeing with your 6Dasher. I saw the same with my 6BRX (same powder capacity as the Dasher) also at around 200 rounds fired. By 500 I had the beginning of the alligator skin firecracking in the leade/throat area. Nearing 1000 rounds fired the throat began to look "ugly".

I had the barrel setback & chamber re-cut and by another 200 rounds fired, it began all over again. Sooner than what I see with my 6BR chamberings. The price paid for an "improved" cartridge?

Nothing wrong with your cleaning methods & equipment used. It's the cartridge.

 

[Jay Christopherson]

It sounds like both of you understand what I was trying to say.
It definitely looks like the beginning of cracking, I have just never seen it happen so soon. The cartrige is a dasher. The only difference between this chamber and the way I used to do them was that I used to lightly polish right up to that junction and this one I only polished up to the shoulder. I'm wondering if leaving a sharp edge there accelerates the formation of the cracks?

The rifle I referred to is a Dasher as well. It seems to start the cracking process fairly quickly.

 

[fdshuster]

Donovan: Nope, sorry to disagree with you, but those are definately straight line, linear cracks. I've looked at enough barrels over the years to know the difference between cracks in the top surface of a layer of carbon, and cracks in the steel surface.

Besides that, after multiple cleanings in multiple barrels (for comparison) using JB and a bronze brush, taking every trace of any type of fouling out of the barrel, the cracks are still there. The cracks on the 6BRX barrel were so extensive that a few of them went from the front edge of the chamber mouth, up into the leade and throat areas, and when looking at the vertical edge of the chamber mouth, the extent of the depth of the cracks can be seen.

I'm also very familiar with the alligator skin cracking in the leade/throat area that can be on the surface of the carbon, (and copper layer also), and have removed them with the JB method, down to bare, clean and crack free surface. A pleasant surprise when I first thought it was surface cracking. But, there have also been times when the alligator skin cracking remained after the JB cleaning, proving (unfortunately) that the cracks are in the surface. It's just plain old erosion and its' presence cannot be denied.

ps: Never thought you were "full of crap". I have great respect for your obvious experience and knowledge.

 

[ebb]

Sounds to me like the problem was the 66 round match and all the rapid shooting involved in the match.

 

[fdshuster]

No doubt heat buildup will accelerate erosion.

 

[jrm850]

I'm pretty sure I have removed all of the carbon from the area, but I will clean again to see if there is any improvement. To clean that area I used a new 270 brush and marked my cleaning rod at a point where I could ensure the brush would not go far enough into the chamber to hit my throat ramps and twisted it in a single direction until my carbon ring was gone. I'll do the same thing again, but put the brush about halfway into my freebore to make sure I hit this spot.

One item of note is that the carbon ring was roughly .025" long because of the short brass and fairly pronounced after the 66 rounds, but there were a couple of bare spots where I could see clean steel through the carbon. I doesn't make sense that there were just some areas that didn't foul so I'm certain that the missing spots were blown down the barrel. The question is how large and how hard could those chunks be? Could they be responsible for the accelerated damage?

Regarding the 66 rounds- I averaged 11 minutes per round of 20. Certainly not good for the barrel, but not as fast as some "runners" shoot.

Anyone know a way to take a picture through a hawkeye without spending hundreds on an adapter?

 

[jrm850]

Ok, I found a camera that worked. Not the best picture but I'll either have to make an adapter or grow another arm to do better. I'll work on it.

 

[AlNyhus]

I've seen this a couple of times.

I'd get in there with some JB on a patch wrapped around a worn brush and give it 20-30 good back-and-forth strokes. A drop or two of Butches or other quality solvent on the patch, also. Clean it with 5-6 sloppy wet patches on an undersized jag, then brush it 6-8 times with the correct size bronze brush, patch it dry and see what it looks like at that point.

Good shootin'. -Al

 

[jrm850]

I'll give it a try Al. There has already been a bit of JB down the bore when this pic was taken, but only on a single patch and I wasn't really focusing on this area. I used older tan jb mixed into a softer paste with Hoppe's Benchrest for 10 strokes, then cleaned the mud out with patches of the solvent followed by dry patches, Kroil, dry patches, lubriplate.

The Hart 6br barrel that this one replaced shows none of these signs and it has a pretty high round count. I babied that one for the most part and the only time I can ever think of that it fired rounds quickly enough to replicate a 60rnd match was when I took it to SD to shoot some Prairie Dogs.

 

[fdshuster]

jrm850: Great job of taking the picture and proof that a picture is worth a thousand words. Sure looks like the beginning of surface cracking to me. I've seen identical surfaces, at the same location, on my barrels, have watched it progress as round count increases, and think of it as normal wear.

Your cracks are very short in length, clean and re-inspect every 1 to 200 rounds and you will see them grow longer. As I said earlier, one of my BRX barrels ( a Krieger 8 twist, .237" bore) developed some really long cracks that extended into the leade/ throat, one of the worst examples that made me think there was a problem with the barrel steel.

On the other hand, my 222 Remington barrels (2) had well over 1800 rounds fired, and a 30BR barrel at 952 rounds, and neither had a trace of the same firecracking. Nothing more than case powder capacity versus bore diameter = heat damage to the bore, and that sharp 90 degree angle at the chamber mouth is the first place for it to show up. Keep watching it and at around 1000 rounds or so, you will see the alligator skin firecracking develope in the leade & throat.

 

[fdshuster]

Donovan: It's very obvious to me that jrm850 cleaned the area in question down to bare metal, removing every trace of any type of fouling buildup, the same as I do. The cracking is still there, as seen with the dark lines that have depth, therefore it is cracking in the surface of the steel, and not on a layer of carbon buildup. Continue to deny, but that won't make it go away.

As for the varying rates of erosion development, (500 vs 1000), that will depend on the rate of fire. In our match's we are firing a maximum of 6 shots in 7 minutes, with a lot of cooling time 'til the next distance is fired, versus JRM's rate of 20 rounds in 11 minutes.

No I cannot predict when alligator firecracking will develop, too many variables involved, but the firecracking at the chamber is the first step, with more sure to follow. Want to stop firecracking? Stop using the barrel. Have a nice day, I'm done.

 

[jrm850]

jrm850: Great job of taking the picture and proof that a picture is worth a thousand words. Sure looks like the beginning of surface cracking to me. I've seen identical surfaces, at the same location, on my barrels, have watched it progress as round count increases, and think of it as normal wear.

Your cracks are very short in length, clean and re-inspect every 1 to 200 rounds and you will see them grow longer. As I said earlier, one of my BRX barrels ( a Krieger 8 twist, .237" bore) developed some really long cracks that extended into the leade/ throat, one of the worst examples that made me think there was a problem with the barrel steel.

On the other hand, my 222 Remington barrels (2) had well over 1800 rounds fired, and a 30BR barrel at 952 rounds, and neither had a trace of the same firecracking. Nothing more than case powder capacity versus bore diameter = heat damage to the bore, and that sharp 90 degree angle at the chamber mouth is the first place for it to show up. Keep watching it and at around 1000 rounds or so, you will see the alligator skin firecracking develope in the leade & throat.

To make this worse, I just recounted the rounds fired and I can only account for 150 total rounds. Started with 100 Lapua and have 54 twice fired and 37 once fired cases. 5 of the others were split shoulders and the other 4 were culled for one reason or another before firing.

My old 6BR barrel has at least 1500 rnds through it and looks way better. I never pushed the limits with that one though and was content to shoot mild loads because it had a factory firing pin hole and showed pressure signs easily with the 205m's I used for it. For this barrel I bushed the bolt, ground the firing pin for .0025 clearance, and ommited the ejector hole, so it's not nearly as prone to showing pressure and I've used nothing but Rem 7.5s and Magnum Wolfs which are both pretty tough cups in my book. What I'm trying to say is maybe I am shooting some loads that are way hotter than I think. The velocities are commensurate with what I read (3034 avg with 105hybrids 28" barrel) and I have had maybe 4 rounds with a lightly sticky bolt. The primers still have a nice radius at the edges.

jrm850 -

Good picture !-! .... Thanks for taking it to show the issue.

As Al wrote, its stubborn cleanup, and needs to be done more aggressively. His instructions should be fine.
I do how ever like Iosso paste better then JB paste and feel it is more effective at cutting carbon then JB.

You may want to dress it after it is 100% cleaned. I use "oiled - 400 paper" on a wood dowel, spinning in the lathe.

Keep us posted !-!
Donovan

I can see what looks like carbon remaining inside the cracks and will get it out before I polish that edge, but i don't see any elsewhere. What shoudl I be looking for? I ordered some Iosso after we talked the other day, but it hasn't arrived yet. I'm hoping I can get below those cracks with the 400 paper to eliminate the stress risers and slow this process down. I don't think it will affect accuracy much to increase that radius and it surely has to help diffuse the heat over a larger surface, kind like a sharp point on a cutting tool dulling faster than one with a slight radius.

hang on, I'm formulating another theory...
My old 6br barrel was actually a remington chamber so I had to trim all of the norma brass to even fit. I kept the case length pretty close to max so the brass was very close to this junction and that barrel looks fantastic considering its age. The brass I am using now has at least .023" of the neck exposed so there is much more metal surrounding this junction exposed to the blast and we all know the heat will focus on sharp corners and edges. Hearing the same emperical evidence from others comparing the cracking in a Dasher to the 6BR, and reading many posts about short formed Dasher cases so it kind of fits. If I had the cash to experiment, I might think about short chambering 1 dasher chamber so I could get longer case necks to emulate the conditions in the first 6BR and chambering a second just like my current barrel to compare wear rates.

In any event, I appreciate the discussion and the opportunity to hear other's opinions. There are not many locals that share my interests, so it looks like I found the right place to be.

 

[AlNyhus]

jrm850:

Quick question: Was the throating done with a seperate reamer or is the throat on the chamber reamer? Has this exact reamer been used before?

Great pic, by the way! -Al

 

[jrm850]

jrm850:

Quick question: Was the throating done with a seperate reamer or is the throat on the chamber reamer? Has this exact reamer been used before?

Great pic, by the way! -Al

It was cut with a single finish reamer that was just purchased from PTG a few weeks ago. There is a slight radius on the reamer, but the junction looks sharper through the scope than the reamer would suggest. This is the first chamber cut with this reamer.

ETA: The only camera in the house I could get to work was cell phone believe it or not. Took this with a Samsung Note II held against the eyepiece by hand. I had to get my daughter to push the button.

 

[fdshuster]

jrm850: Your picture taking method is excellent! I've tried doing the same with 2 different digital camera's and the results were disasterous. Always out of focus.

 

[jrm850]

jrm850: Your picture taking method is excellent! I've tried doing the same with 2 different digital camera's and the results were disasterous. Always out of focus.

I searched the internets forever looking for tips. I found one post where an optics guy said that there were two forms of auto focus, through the lens or external. Only through the lens versions let you use autofocus for this. He also said that it should be on max zoom or the pictures would be tiny. When I get some free time (lol) I'm going to make an adapter. It is so much easier to study the pictures blown up on a computer screen.