Why is carbon (apparently) is appearing on my 30BR chamber body wall?

[Cassidy]

After cleaning my 30BR rifle chamber and bore (confirmed clean by borescope), then shooting a 35 round batch, what appears to be carbon presented on the chamber wall about .228" behind the chamber shoulder-body junction; see the 3 pics which start at the chamber mouth, then move back across the neck then to the body where the deposits are shown.

The pics show that the chamber neck is fairly clean and the usual carbon ring is present at the mouth (which I clean before shooting). I have not seen such deposits on the chamber body before and wonder if the new reamer used with tighter diameter tolerances (up to +.0002 instead of up to +.0005) including the chamber body diameter, may, upon discharge, be preventing gas flow going back between the chamber body and the case body. The gap between the case necks and chamber neck on each side is about .0015" (which is what I routinely use per Tony); the case necks show carbon sine waves (which I want per Tony) for the first 28 cases shot, then start showing wavy lines then unclear amorphous carbon deposits through shot 35 suggesting these carbon deposits on the chamber body may be accumulating and inhibiting gas flow going backward. Bullet velocity increased minimally but variably after shot #28 when I think the deposits had accumulated, and group size suffered.

Thoughts about what might be causing these deposits?

 

[chop house]

tag

 

[Bill Norris]

Kind of strange with you having so little clearance at the chamber/neck area.

 

[Cassidy]

what's tag mean

 

[Fast14riot]

Almost looks like a cleaning solution was left in the chamber and got cooked during firing.

 

[chop house]

what's tag mean

Just shorthand for interested and watching for opinions and resolution - so I can find thread again

 

[JMayo]

I always use a 40cal bore mop with a patch on it to clean the bore after cleaning the rifle.
I've found that The lug cleaner diagonal thing will leave deposits in the chamber.
I do not clean the grease from the lugs every time

 

[rwj]

Just shorthand for interested and watching for opinions and resolution - so I can find thread again

Alternatively, you can use the “Watch” button located in the upper right-hand corner at the top of the thread page…

 

[Sandstorm]

How's it shoot.?
You may need to clean more often with the tight specs your using.
My F-class chamber is nowhere near that tight and carbon will build up but I can get a few Matches between cleanings. Different powders will act differently in this regard as well.
Im no expert..just my 2c

 

[SmittyJon]

After cleaning my 30BR rifle chamber and bore (confirmed clean by borescope), then shooting a 35 round batch, what appears to be carbon presented on the chamber wall about .228" behind the chamber shoulder-body junction; see the 3 pics which start at the chamber mouth, then move back across the neck then to the body where the deposits are shown.

The pics show that the chamber neck is fairly clean and the usual carbon ring is present at the mouth (which I clean before shooting). I have not seen such deposits on the chamber body before and wonder if the new reamer used with tighter diameter tolerances (up to +.0002 instead of up to +.0005) including the chamber body diameter, may, upon discharge, be preventing gas flow going back between the chamber body and the case body. The gap between the case necks and chamber neck on each side is about .0015" (which is what I routinely use per Tony); the case necks show carbon sine waves (which I want per Tony) for the first 28 cases shot, then start showing wavy lines then unclear amorphous carbon deposits through shot 35 suggesting these carbon deposits on the chamber body may be accumulating and inhibiting gas flow going backward. Bullet velocity increased minimally but variably after shot #28 when I think the deposits had accumulated, and group size suffered.

Thoughts about what might be causing these deposits?


View attachment 1669591View attachment 1669592View attachment 1669593

It's been awhile since I read Tony's book, but I seem to remember he cleans after firing 20-25 rounds in his 6 PPC's.

Many, but not all of the folks I know in IBS Score Comp, shoot a whole yardage before cleaning their 30 BR's. That's anywhere from 50-80 rounds, sometimes more.

A few clean after every target, and the rest about 1/2 through ... maybe after 30 rounds or so.

Since that deposit is in the front of the chamber, I'd just use a bore mop wrapped with a 3" patch dampened with your favorite bore, to mope it out, followed by a dry one.

As to what causing it, I'm at a loss. It does look more like dried cleaning solution than carbon, but I could be wrong.

SJ

 

[Lucky6547]

Do you anneal? If no, perhaps the brass is hardening and not sealing as well as when it was softer…

 

[Cassidy]

I was unable to include additional info in my initial post above, had to leave, but will do to now. I think it may clarify but not resolve this matter.

The batch of 35 rounds (30BR) discussed above was fireformed 6 days ago with the intent to use this FF'd batch to tune my new barrel (chamber reamed with my new reamer). However, after FF'ing, when I saw (by borescope) the severe carbon deposit (see pics attached), I knew I could not proceed with the tune due to the apparent effect on velocity and group size changes, but instead I needed to figure out what caused the carbon deposit and eliminate it before tuning.

My thinking then was that when FF'ing, the carbon had to be coming from the case mouth the instant/nanosecond the bullet left the case mouth (the bullet was seated slightly behind the hard jam), and the detoured expelled gas/carbon had come out of the case mouth, back over the case neck, over the case shoulder, then over the case body until the case body diameter was so close to the chamber body diameter that the carbon could go no further resulting in the heavy carbon deposits (pics) behind the shoulder on the body. All this occurred, I thought, in the gap between the case and chamber.

To test my idea, I repeated (exactly) the reloading process using these same 35 FF'd cases knowing this time the only difference was that the cases were now FF'd (blown out) and now the case neck, shoulder and body should conform much more closely to the chamber wall thereby preventing the carbon deposits.

So I shot the reloaded FF'd batch a few days ago (the test shooting) and saw (borescope) the same carbon deposits on the same chamber body location (circumferentially like when FF'd). However, this time the carbon deposits were roughly by my eye about 90% less (pics attached in my original post above) than when FF'ing (pics attached). Also, the reamer body and case body increases several thousandths starting from just behind the shoulder to just ahead of the case extraction groove near the base.

This info tells me that my idea may be partly correct, that maybe these rounds using this new barrel chambered with my new reamer with tighter reamer diameter tolerances (up to .0002 instead of up to .0005) might be the cause, and maybe I need to (1) loosen the body diameter tolerance on the reamer, and/or two FF'ings may be needed instead of one so the cases better conform to the chamber (which might be the next test). That's my thinking for now. I am still thinking this over. There are some other issues I am also considering regarding the FL sizing die.

To answer your questions, I clean the chamber and bore of this 30BR rifle after every shooting session at the range and after each match, and at the end of each cleaning I borescope it to be sure the carbon ring is gone and for sure I would have noticed a carbon deposit on the chamber body wall. With another barrel which I use for matches at this time, after multiple tests, I can shoot over 60 or so rounds without it requiring a cleaning (no decrement in group size/precision). it shoots smallest groups when fouled, and I have never seen the above carbon deposits. However, this match barrel was reamed with up to .0005 reamer diameter tolerances, not the up to .0002 for the new reamer used in my new barrel. My understanding is 30BR barrels are uniquely like that; it does not often require cleaning and some 30BR shooters (including HOF) only clean after an entire match or after maybe 150 or so rounds. I do not anneal but discard cases after about 4-5 shooting or more depending on case neck thickness. Another question above is how does it shoot. Keeping in mind that this new barrel has not been tuned at all, that I used an arbitrary load, seating depth and tuner setting, the target for shooting the FF'd cases in the above described test is attached.

All thoughts and comments are welcome!

 

[ev780]

Your photos imply that deposits are not the full circumference of chamber. Is it in the same position as before? By that I mean 3 o'clock, 10 o'clock etc. Might be able to chase something down there.

 

[Cassidy]

ev - in the 3rd pic of the original post above (1st firing after FF'ing), on the chamber body wall you can see a circumferential line that the carbon is collecting mainly on and around; it is like the FF'ing pic (my last post) though the FF'ing pic shows carbon collecting in the whole interval from the chamber shoulder-body junction to that same circumferential line.

My impression is there is a circumferential groove (or ridge?) that is that line on the chamber body which corresponds to a circumferential line I can see at that same location on the case bodies (not shown) but cannot feel by running my finger nail across it on the cases. I think that groove/ridge might have been created by the reamer when reaming since there are many other ridges/groove you can see that were created by that reamer. These or this groove/ridge circumferential line in conjunction with the very small not more than +.0002 reamer body diameter tolerance leaving a very small gap between the case and chamber body there may be resulting in carbon accumulation on the chamber body wall up to that location.

However, that does not answer the question of why carbon/gas in that quantity is flowing back that far along the chamber body wall recognizing that the carbon/gas flow has to come from the case mouth instantly after the bullet leaves. I think this carbon/gas flow may have something to do with the FL sizing die since I have been unable to adjust the FL sizing die to push the neck bushing to about 1/16" from the case neck-shoulder junction (it's about slightly more than 3/32" which is more than I ever use), and I may have to use a larger diameter neck bushing to allow the case neck wall to get closer to the chamber neck wall to help narrow that gap. This is what I am thinking at the moment but will have to test this concept.

All thoughts are welcome!

 

[AlNyhus]

Couple of questions: what powder are you using and how much are you bumping the shoulders?

Also, you stated:"The gap between the case necks and chamber neck on each side is about .0015"..
So, you have .003 neck clearance with a seated bullet (when measured over the pressure ring area of the neck)?

Good shootin' -Al

 

[SmittyJon]

I was unable to include additional info in my initial post above, had to leave, but will do to now. I think it may clarify but not resolve this matter.

The batch of 35 rounds (30BR) discussed above was fireformed 6 days ago with the intent to use this FF'd batch to tune my new barrel (chamber reamed with my new reamer). However, after FF'ing, when I saw (by borescope) the severe carbon deposit (see pics attached), I knew I could not proceed with the tune due to the apparent effect on velocity and group size changes, but instead I needed to figure out what caused the carbon deposit and eliminate it before tuning.

My thinking then was that when FF'ing, the carbon had to be coming from the case mouth the instant/nanosecond the bullet left the case mouth (the bullet was seated slightly behind the hard jam), and the detoured expelled gas/carbon had come out of the case mouth, back over the case neck, over the case shoulder, then over the case body until the case body diameter was so close to the chamber body diameter that the carbon could go no further resulting in the heavy carbon deposits (pics) behind the shoulder on the body. All this occurred, I thought, in the gap between the case and chamber.

To test my idea, I repeated (exactly) the reloading process using these same 35 FF'd cases knowing this time the only difference was that the cases were now FF'd (blown out) and now the case neck, shoulder and body should conform much more closely to the chamber wall thereby preventing the carbon deposits.

So I shot the reloaded FF'd batch a few days ago (the test shooting) and saw (borescope) the same carbon deposits on the same chamber body location (circumferentially like when FF'd). However, this time the carbon deposits were roughly by my eye about 90% less (pics attached in my original post above) than when FF'ing (pics attached). Also, the reamer body and case body increases several thousandths starting from just behind the shoulder to just ahead of the case extraction groove near the base.

This info tells me that my idea may be partly correct, that maybe these rounds using this new barrel chambered with my new reamer with tighter reamer diameter tolerances (up to .0002 instead of up to .0005) might be the cause, and maybe I need to (1) loosen the body diameter tolerance on the reamer, and/or two FF'ings may be needed instead of one so the cases better conform to the chamber (which might be the next test). That's my thinking for now. I am still thinking this over. There are some other issues I am also considering regarding the FL sizing die.

To answer your questions, I clean the chamber and bore of this 30BR rifle after every shooting session at the range and after each match, and at the end of each cleaning I borescope it to be sure the carbon ring is gone and for sure I would have noticed a carbon deposit on the chamber body wall. With another barrel which I use for matches at this time, after multiple tests, I can shoot over 60 or so rounds without it requiring a cleaning (no decrement in group size/precision). it shoots smallest groups when fouled, and I have never seen the above carbon deposits. However, this match barrel was reamed with up to .0005 reamer diameter tolerances, not the up to .0002 for the new reamer used in my new barrel. My understanding is 30BR barrels are uniquely like that; it does not often require cleaning and some 30BR shooters (including HOF) only clean after an entire match or after maybe 150 or so rounds. I do not anneal but discard cases after about 4-5 shooting or more depending on case neck thickness. Another question above is how does it shoot. Keeping in mind that this new barrel has not been tuned at all, that I used an arbitrary load, seating depth and tuner setting, the target for shooting the FF'd cases in the above described test is attached.

All thoughts and comments are welcome!

View attachment 1669957View attachment 1669958View attachment 1669960View attachment 1669962View attachment 1669963

Since it always reappears in the same spot, the steel in that area may have had some inclusions, that have since burnt out. If so, that would leave pits and rough areas that allow carbon to collect.

Otherwise, I'm stumped.

SJ

 

[Cassidy]

Thanks for the feedback, SmittyJon and all! I just talked with Redding who's going to look over the FL sizing die to see why the neck bushing does not extend down the case neck farther. I'll also try larger (less constrictive) neck bushings that might allow the case necks to better seal on the chamber neck upon discharge and maybe eliminate the deposit. It will take a couple of weeks to get the FL sizing die back, so may be a while before I can test these changes and post results.

 

[358WCF]

It's too bad that the depth/thickness of things we see with bore scopes are so hard to quantify.

Curious where your bore guide stops. Does it have an O-ring?

I could be wrong, but in the 1st post the 3rd pic looks a lot like brush/fluid splatter from the back stroke to me. The circumferential line could be dirty cleaning juice stopped at the O-ring. The 4th pic in post #12 may be more of the same added? Just a thought.

 

[Cassidy]

358WCF - yes, my bore guide has a tight O-ring, so no fluid backs up into the chamber. I don't think the amount of carbon we are seeing is splatter. Am still evaluating and will try to provide more info in coming days and maybe a few weeks.