Strange whitish deposit in barrel - cause, solution"

S

Snyper

Private
Minuteman
Jan 11, 2025
7
1
Atlanta, GA
#1
I recently started to see a significant degradation in repeatability in my five-month-old CZ 457 Varmint MTR (>1 MoA @ 50 yards). I bore scoped the barrel (which has around 2500 rounds downrange, has been religiously cleaned using Boretech C4 only) and saw a whitish hard deposit, this after a deep clean (24 hour soak of chamber in C4, dry patched , then C4 wet nylon brush down the chamber multiple times, dry patched again, then C4 wetted bronze brush, dry patched again, then a light oil wet patched/dry patched). Being a relatively new shooter (this is my first rifle), thought I would turn to the very experienced rimfire enthusiasts here to see if I could get your thoughts as to what is causing this and what I should do to remove it and get the barrel back to decent shooting condition. BTW, this deposit is around the chamber area and the first 4.5" of the barrel. Borescope screen shots from video are attached.

Thanks in advance for all your guidance and help - am getting quite frustrated since I can't find much on the web and have no idea what to do to remove this deposit.

Synper.
 

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#3
I'd guess C4 in the barrel, hitting the lead & lube, is making some minor salts from either the lead or the lube contents, and you are seeing salts+ deposits. Lead remover would be my call too.
 
#4
Yeah try some Rimfire blend, let it soak for a few minutes and brush it, run a RB patch through and repeat. I am betting you will see a big difference.
 
#6
It’s leading

My B14R has some as well. Rimfire blend won’t touch it

Here’s a photo for reference I found of an airgun when I was looking into mine a while back
IMG_7634.png
 
#10
I might seem like a broken record, but ditch the nylon brush.

If you are going to brush, get Ballistol and the correct size phosphor-bronze brush. The bronze works realy well on lead and won't damage the steel, provided you do not use an abrasive cleaner; hence the Ballistol.
 
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#11
Lead out works OK but it isn’t brushless by any stretch of imagination.

I use a Lewis Lead Remover to mechanically get rid of most fouling. It’s just a bronze mesh on a jag, so you could just wrap bronze wool around a worn bore brush. That’s what I do for odd calibers like 9.3x62.

Follow up with chemical cleaner and patches.

I tried Ballistol. It is a fine general purpose cleaner. As with all general purpose things, it isn’t great at most jobs. Diesel fuel is common on our farm and it works about as well for carbon removal.
 
#12
JerkyFreak said:
I might seem like a broken record, but ditch the nylon brush.

If you are going to brush, get Ballistol and the correct size phosphor-bronze brush. The bronze works realy well on lead and won't damage the steel, provided you do not use an abrasive cleaner; hence the Ballistol.
Click to expand...
^^^^. We treat these barrels like somebody's arteries. I still use bronze brushes and Hoppes...thousands of rounds and countless cleanings I've never seen accuracy degrade on my most expensive 22lr barrels. Nylon brushes and wet patches don't remove carbon rings or leading.
 
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#13
Snyper said:
I recently started to see a significant degradation in repeatability in my five-month-old CZ 457 Varmint MTR (>1 MoA @ 50 yards). I bore scoped the barrel (which has around 2500 rounds downrange, has been religiously cleaned using Boretech C4 only) and saw a whitish hard deposit, this after a deep clean (24 hour soak of chamber in C4, dry patched , then C4 wet nylon brush down the chamber multiple times, dry patched again, then C4 wetted bronze brush, dry patched again, then a light oil wet patched/dry patched). Being a relatively new shooter (this is my first rifle), thought I would turn to the very experienced rimfire enthusiasts here to see if I could get your thoughts as to what is causing this and what I should do to remove it and get the barrel back to decent shooting condition. BTW, this deposit is around the chamber area and the first 4.5" of the barrel. Borescope screen shots from video are attached.

Thanks in advance for all your guidance and help - am getting quite frustrated since I can't find much on the web and have no idea what to do to remove this deposit.

Synper.
Click to expand...
Snyper - I'm not a rimfire guy but I have passed the attached document to some rimfire bench rest friends of mine who thought it was extremely valuable. Don't let the page count put you off...its mostly large format pictures
 

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#14
I'm wondering what influence the C4 soak had. For perspective, my cleaning regimen for both my Vudoo and my RimX over thousands of rounds is to soak the carbon ring with C4 for ~15 minutes, push that wet patch through the bore, use the back of it to wipe carbon off the crown, then a series of dry patches until they come out white.

So, most of the bore only sees one patch of C4 and is immediately wiped dry.

If I understand OP correctly, the lighter of the two colors in the borescope photos is what most of the bore looks like? It's the very dark grey discoloration that is unusual and only located near the chamber?
 
#15
KnowNothing256 said:
I'm wondering what influence the C4 soak had. For perspective, my cleaning regimen for both my Vudoo and my RimX over thousands of rounds is to soak the carbon ring with C4 for ~15 minutes, push that wet patch through the bore, use the back of it to wipe carbon off the crown, then a series of dry patches until they come out white.

So, most of the bore only sees one patch of C4 and is immediately wiped dry.

If I understand OP correctly, the lighter of the two colors in the borescope photos is what most of the bore looks like? It's the very dark grey discoloration that is unusual and only located near the chamber?
Click to expand...
The white I believe is the leading
 
#18
Baron23 said:
Snyper - I'm not a rimfire guy but I have passed the attached document to some rimfire bench rest friends of mine who thought it was extremely valuable. Don't let the page count put you off...its mostly large format pictures
Click to expand...
Interesting read, thanks Baron23. Puts a lot of the myth's to rest...hopefully.
 
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#19
John? said:
Hard tk tell from those photos. My first guess would be lead and bullet lube buildup. I would hit it with a bronze brush and the lead remover solution of your choice.
Click to expand...
Apologies for not responding earlier - had several personal things to take care of.

I have hit it with a nylon and a bronze brush (wet with C4, also separately with Rimfire Blend), bore-scoped it, and no change.
 
#22
KnowNothing256 said:
I'm wondering what influence the C4 soak had. For perspective, my cleaning regimen for both my Vudoo and my RimX over thousands of rounds is to soak the carbon ring with C4 for ~15 minutes, push that wet patch through the bore, use the back of it to wipe carbon off the crown, then a series of dry patches until they come out white.

So, most of the bore only sees one patch of C4 and is immediately wiped dry.

If I understand OP correctly, the lighter of the two colors in the borescope photos is what most of the bore looks like? It's the very dark grey discoloration that is unusual and only located near the chamber?
Click to expand...
Its the white deposit that is the issue - its very heavy in the chamber (I can't even see any dark grey in that area) as well as in the first few inches of the barrel. Rest of the barrel is completely clean given what has been done to it.
 
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#23
Firstly, my apologies to all those who responded for not replying earlier - had several things going on in parallel that precluded me logging back in and replying. Here is a full update since the original post - thoughts, feedback on what I could be doing better always welcome and appreciated!

I cleaned the barrel using Bore-tech Rimfire Blend (wet patch, then a wet bore mop for 15 minutes, then dry patches and bore-scoping, followed by another wet patch, then wet bore mop for 30 minutes followed by dry patches and bore scoping), all of which showed no change, then (in sheer frustration) by an overnight Rimfire Blend soak and dry patches which also showed no change, then by Rimfire blend soaked nylon brush / bore scoping (again no change), then the same except now using a bronze brush and bore scoping (also no change).

A friend was heading over to Whidden Gun Works in Nashville, GA for rifle ammo testing so I went along with the rifle and showed it to the gunsmith and the ammo testing guys there (what a great bunch of folks, btw!). They had never seen this issue previously either (all of them are VERY experienced, knowledgeable and helpful folks). One of the ammo test guys was intrigued (and kind) enough to clean the barrel using Kroil (and something else… a solution that I don't remember the name of) followed by more bore scoping - no effective change that either of us could detect. The next step was "Iosso paste" with a nylon brush and bore scoping - guess what…… no change! A few other very experienced barrel technicians also looked at it - general conclusion is that the barrel steel is defective - lots of tool marks as well as this white "deposit" issue - they couldn't conclude for sure whether it was (or was not) a deposit. Their general conclusion was that it was a barrel defect, and they suggested that I send it back to CZ, which process was initiated last Monday.

After bugging CZ CS every alternate day (their CS team is very busy from the conversations I had with the nice CS guys), I am now waiting for the rifle RMA paperwork to send it back to them to diagnose and advise what the issue is, and how best to fix it.

I do promise to update y'all once I hear back (it could be me who mucked it up, could be the barrel, could be Lead Oxide, could be ?????). Honestly intrigued by the root cause so I can figure out what it is and avoid/prevent it from happening again, as well as pass it on to all so we can all benefit.

Again, thank you to everybody who responded - I do highly appreciate it! Stay tuned for further updates as I find out more.
 
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