Help me interpret this borescope video: fire cracking, carbon ring, throat erosion

[Rick Richard]

Rick, what is your definition of a carbon ring? I'm no expert and curious what other consider. Thanks

In Wedgys illustration, the carbon ring develops at the end of the freebore and beginning of the rifling and a bit past it. This is like a ridge that is created during the machining process that creates an obstruction that can catch the carbon. Hope I explained this well enough.

 

[new2mud]

Rick and Mram10us: is this what each of you were referring to?

The green circled section I believe is not a carbon buildup but rather a low-lying area that is smoother just before the fire cracking begins.

 

[Rick Richard]

Rick and Mram10us: is this what each of you were referring to?

View attachment 192160

The green circled section I believe is not a carbon buildup but rather a low-lying area that is smoother just before the fire cracking begins.

Agree. A carbon ring would be a distinct line of build up right between the red and green lines in your illustration.

 

[LaHunter]

I would expect if you cleaned it really good with Boretech Eliminator and a bronze brush, that 'dark area' (carbon) would disappear. I gun builder/high level PRS competitor explained to me that the carbon ring forms in the location where the brass ends. I would say that dark area (green circled area) is carbon buildup.

 

[338 dude]

Hit it with some JB bore bright and go shoot

 

[Buzzsaw]

We REALLY need to see a brand NEW barrel to tell anything. But IMO, the picture above looks like carbon then cracking

 

[Beluebow]

Rick and Mram10us: is this what each of you were referring to?

View attachment 192160

The green circled section I believe is not a carbon buildup but rather a low-lying area that is smoother just before the fire cracking begins.

Carbon ring then fire cracking IMO......Using Iosso in the throat area will knock that in the head.

 

[Buzzsaw]

CLR eats carbon great, be sure to treat with alchohol and re-lube after

 

[new2mud]

We REALLY need to see a brand NEW barrel to tell anything. But IMO, the picture above looks like carbon then cracking

I realize the picture alone gives a limited... well...picture. Does the video suggest to you that it may just be smooth freebore ahead of the fire cracking?

It appears to me that section is actually low-lying and not raised with carbon. But I'm still learning here.

 

[Buzzsaw]

I have a Teslong too, really like it, but dont know what I'm looking at. Your video is great

 

[6.5-300 BEE]

Just shoot it. I once had a M70 that was rebarreled to 280 AI that I bought at a yard sale. Had 3" of nasty black, cracked throat.
Before rebarrelling I loaded some 175 Speers seated out (single loaded) and it shot MOA.

As a famous Luger was gold inlaid: "The proof is in the shooting".

 

[Greyfox]

From the OP's video, there definitely appears to be fire cracking that extends into the rifling. The carbon ring appears to be rather mild and should clean up with carbon solvent. I have found that it is quite common to see some fire cracking in the free-bore after a few hundred rounds, but generally takes much longer(1000-2000 rounds) with my 6.5x47's and 284's) for the fire cracking to extend into the rifling....unless the rifle is routinely shot "hot". I monitor fire cracking with a bore scope, actual accuracy data, and an original bullets BTO measurement for throat wear, every few hundred rounds after 500 to 1000 shots. If fire cracking into the rifling and BTO increases are present, accuracy fall-off is generally not too far behind.
Unless the OP has been running hot, it's surprising to see that level of fire cracking as early as 600 rounds. However, there have been quite a few reports of N565, a "high intensity" powder, producing premature throat erosion/short barrel life.

 

[new2mud]

From the OP's video, there definitely appears to be fire cracking that extends into the rifling. The carbon ring appears to be rather mild and should clean up with carbon solvent. I have found that it is quite common to see some fire cracking in the free-bore after a few hundred rounds, but generally takes much longer(1000-2000 rounds) with my 6.5x47's and 284's) for the fire cracking to extend into the rifling....unless the rifle is routinely shot "hot". I monitor fire cracking with a bore scope, actual accuracy data, and an original bullets BTO measurement for throat wear, every few hundred rounds after 500 to 1000 shots. If fire cracking into the rifling and BTO increases are present, accuracy fall-off is generally not too far behind.
Unless the OP has been running hot, it's surprising to see that level of fire cracking as early as 600 rounds. However, there have been quite a few reports of N565, a "high intensity" powder, producing premature throat erosion/short barrel life.

Thank you @Greyfox. N565 was great in cooler weather (45-75F), but when temps hit that magical 85+ mark I had pressure signs appear. I have switched to H1000 and it has reduced pressure signs for similar velocities, even at 85+. Plus the fact that I have heard it is a cooler-burning powder I figure I will show this barrel some love (and hope for extending its life).

Doubling the current 600 rounds puts barrel life at the lower end of what I have been told to expect from a 6.5 PRC, but if I can get it to 1500+ that would be great.

 

[6.5-300 BEE]

Next time get a 3 groove Nitrided barrel and you'll see at least 3000 rounds.

There is a reason ALL military gun bbls are nitrided.