Lead buildup in chamber throat

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  • Last Post 06 September 2021
Wm Cook posted this 02 September 2021

I don't know why it's happening and I don't know how to fix it. I am very perplexed.

there's a lead buildup that looks like a ramp that formed at the end of the chambers throat in the gap between where the cartridge case's mouth would end and the reamer cut separating the chamber throat to the lede.  The rifle is a Savage 10F in .308.

The barrel has about 56 rounds through it and it's showing a buildup from about the 5 to 8 O'clock position at the end of the throat.  The buildup is longer (reaching nearer the case) in the middle and it tapers shorter as you go out to the 5 O'clock or the 8 O'clock position.  Not a shaved ring but a buildup that looks like a tiny little ramp and only on the lower half of the circumference of the chamber neck. 

I had a similar experience with a Ruger 7.62 bolt gun last year and had to replace that barrel because I damaged the bore trying to get the buildup out.  The build up on the Savage is in the same location and it looks the same.

Sitrep:

  • Normal cleaning ever 25 or so shots with 5 or 6 wet patches (Hoppy's or Butches Bore Shine) followed by 10,15 strokes with a wet bronze brush.  A few more wet patches followed by a dry patch then an oiled patch.
  • #2 Lyman
  • 311299 gas checked
  • Carnauba Blue
  • Velocity on the most recent barrel (Savage .308) was similar to the Ruger 7.62x39 bolt gun.  Sub sonic 950/1050 and trans sonic 1600 to 1800 fps. 
  • Approximately 56 rounds through the 308 barrel.  The Ruger had about 100 rounds through it before I bore scoped it. 
  • There is zero leading in the bore.
  • All hand loads had the bullet seated with the olgive into the lands just short of jam or what I call "push back" depth.
  • Turning a wet .35 cal bronze brush with Chore Boy wrapped around it has no effect on the buildup.  That little lead ramp buildup is like a weld spot, exactly like I had on the Ruger.

I use hydrogen peroxide and vinegar to clean my casting pots but that would be the last of the last options I would choose to get the build up out.  And if I get it out I need to find out what 's causing it.  I'm doing something drastically wrong to have the same problem with two different rifles in their first 100 rounds. 

Can anyone relate to this problem?  What's causing it?  How in the heck can I remove it?

I can't take a picture with my bore scope but the attached will show you where the build up is located.

If you could shed light on this I would greatly appreciate it. Bill.

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Duane Mellenbruch posted this 04 September 2021

Have you considered looking for a junk cartridge case that is as long as possible and full length sizing the case.   Then using the Lyman M die to expand the case mouth until it is a tight fit in the throat.  Chamber and eject a few times and see if that might knock loose the deposit.  It is a junk case, brass, and a tight scraper fit in the throat.  You are out very little time.

This works to remove the carbon ring in revolver cylinders.

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Brodie posted this 06 September 2021

If you want to demonstrate the lip where the bullet is being scraped you could always trim a case neck back about halfway and make another pound cast.  That should show the "lip" that is supposed to have the cast bear on it.  If you use very soft lead and do the pound cast correctly it might even show the deposited lead.

B.E.Brickey

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Ken Campbell Iowa posted this 02 September 2021

OBSERVATION ::  there are about 500 of 22 rimfire match rifles in the USA ... these all shoot 1/2 moa ( at 50 yards ) and

every one of those rifles has a little ring of lead just in front of the case.

THEORY :  maybe that ring doesn't hurt anything.  at least at the 1/2 moa level.

*****************

...oh, and after 80 years of precision metal jacket benchrest shooting, the top guys are still arguing about

" That Little Space. " ...   

hope this helps

ken

 

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Wm Cook posted this 02 September 2021

Thanks Ken. It just seems odd that I’m just noticing it. Cleaning the neck to prevent a carbon ring is SOP in jacketed benchrest competition but that brushes out easily enough with solvent. Maybe I just haven’t been as attentive enough in past years to notice. Do you think it’s common for center fire cast to show lead buildup at the end of the neck?

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Boschloper posted this 03 September 2021

Phil Sharpe talks about using mercury to dissolve lead out of a barrel. Do you have access to any?

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Wm Cook posted this 03 September 2021

I have no mercury. I read somewhere it turns lead to liquid but that you have to careful with it. Unless something turns up I might try a .25” hardwood dowel, modify one end so Chore Boy can snag on the end of it and give it a slow spin with my hand drill. Probably use a liquid of some sort, probably Hoppy’s.

Do you think that being so far into the lands with my seating depth has anything to do with causing it. Can’t figure out why it’s only built up on the lower third of the circumference.

Does anyone scope their barrels with regularity?

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Brodie posted this 03 September 2021

Wm, you could always try Amazon they seem to have access to everything.  I have been able to find dies there when they were not available anywhere else.  If that fails try chemical supply companies. 

As far as mercury metal and toxicity are concerned, do not heat the liquid mercury, the stories come from the old miners' days when they would purify their own crushed ore by mixing it with mercury metal and then boiling the mercury off leaving the gold.  It is not the metallic mercury that is dangerous, but the mercury vapor that is incredibly toxic, chronic inhalation leads to all sorts of physical problems and eventually death.  If you really worry about it wear gloves.  Gloves and masks are sort of common these days.

B.E.Brickey

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Shopdog posted this 03 September 2021

Is it possible you're scraping lead on loading,then sorta bulldozing it up in there?

One thing I do when setting up my varmint rigs(bolt guns)in the early stages is running loads up through the mags,as fast as possible... and ejecting very rapidly. This is for not only checking to see if the bullets are getting mangled,but also helps set OAL. I like a medium jam on most accuracy rigs and use this as the acid test on their length.

Another item,and am reluctant to even mention;

From my experience,each rig is going to have a certain point in the loaded round,neck OD and the clearance of that chamber where some weird blowback can occur. It has much more to it than just clearance....powder burn rates,load density with that powder,alloy,and jam. There's a cpl of my more jacked up loads,that show it and I deal with it because they're stupid accurate. It's a little bit of a nuisance,and usually get around it by changing clearance. Tough to describe,and NOT saying clearance is the major contributor.... just that it seems to be the easiest to reproduce. So,keep a very close eye on the shoulder area if you're running high velocity. Looks like little pimples on the brass. Wipes off fairly easily.

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Wm Cook posted this 03 September 2021

Thanks for that direction. Sounds like Mercury is as complicated as you make. Maybe a little drop could do it. Everything I shoot is loaded one round at a time but the push back depth for OAL might have to be double checked. The lands are showing skid marks on the 311299’s olgive so I can work backward .010 at a time till it’s just kissing. 4198 is next up so I can run 20 or so through to find the velocity and then do another scope check.

Funny that the sub sonic didn’t seem to leave a build up but the 1800 fps showed buildup.

Does anyone see such a lead ramp where the throat ends and the lede begins when they borescope? Particularly in the 5 O’clock to 8 O’clock portion of the circumference?

As a side note; shooting those subsonic’s with Bullseye is a blast. After I finish the full loads (~1700fps) accuracy check with R7, 4198, 5744 and 4227 I’ll post the velocities on line. Thanks again, Bill.

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porthos posted this 03 September 2021

i had the same problem with a wilson 45 acp. before i got a mold i bought commerical cast bullets. brand dosen't matter.  they are lubed with a hard lube. after doing some research i discovered thet the hard lube might be the problem.  cleaned out the hard lube, then re-lubed with LBT soft lube. no more leading. the lube that you are using might not be the problem, but i thought i'd mention my experience.

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Wm Cook posted this 03 September 2021

Thanks for that idea. I’v been using Carnauba Blue for a decade but to tell the truth most of that was in 22’s. Gonna try to clean the spot buildup later this morning. I’ll let you know how it goes. Bill.

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JohnForrest posted this 03 September 2021

Just thinking out loud.. you said it wasn't a shaving but a streak. Wouldn't a shaving turn into a streak once you fired the round? If you do shopdogs rapid bolt cycle test do you have shavings or small slices out of your bullets at 5 and 8 o:clock? If your bullets are a hair big that could explain why it happened on you other gun too. Just a quick idea to test.

 

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Mike H posted this 03 September 2021

In my opinion the new sharp edges of the chamber and throat is the cause of the issue,I would clean the barrel and chamber then break the barrel in with some jacketed rounds,one shot and clean,repeated for ten rounds,then try three shots and clean for three cycles,rough barrels may need more.I hope this helps.

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delmarskid posted this 04 September 2021

I’ve had my best results with copper Chore Girl by winding separated strips of it into the gaps of a bronze bore brush. I make it fit the bore nice and tight then push and pull with short strokes. I have a short rod for handguns that does the trick. Leaving a patch wet with Kroil to soak at the spot overnight has helped too.

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Wm Cook posted this 04 September 2021

What John, Mike and Delmar said is kind of what I was thinking this afternoon.  I'm kind of suspicious of solving something this difficult this fast but at least this path forward sounds good.  Then again, so did the yellow brick road.

Yesterday I shot the subsonic Bullseye with my .308 prepped 311299 bullets (sized .309) to get my velocities at 5.5, 6.0, 6.5 and 7.0 grains.  Counting the fouler, the zeroing shots and the shots for record there was a total of 27 shots fired.  After normal cleaning, the chamber neck to lede area looked good.  These were the first 27 rounds through the barrel. 

Today I remembered that after I cleaned up and switched powders to R7 I had used 5 bullets sized .311 (I run two sizes; .309 for my .308 Win and .311 for my 7.62x39) to foul the barrel and get my zero.  Once that was done I put 22 shots on record and all were with the .309 sized bullets.  If I am lucky it could be as simple as a slightly oversized bullet and a sharp new bore. 

Tonight I put a Hoppe's wet patch in the chamber where the lead build up is and I'll let it soak overnight.  If its comes out tomorrow great, if not I'll resort to 50/50 HydPer/vinegar and wet a patch, place it on the buildup and give it a few minutes before I Chore Boy the contaminated area.  If either goes well I'll load up and shoot 10 with the .309 sized bullets, clean/inspect, shoot 10 with the .311 sized bullets and again clean/inspect. 

I'm usually not lucky enough to fall into such a scripted solution to a problem so some would say that I'm probably due.  Thanks for all of the help.  Bill.

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Ken Campbell Iowa posted this 04 September 2021

just a note that a mix of vinegar ( acid ) and hydrogen peroxide is a great home recipe for rusting steel when doing a rust blue.

i think i would first try a bit of 4x steel wool wrapped on a bronze brush with a tad of any oil ... or hoppes for the smell.   3 or 5 passes might do it, and won't affect your throat at all >  the steel wool is annealed softer than your barrel steel, but harder than the lead ...

ken

 

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Wm Cook posted this 04 September 2021

Thanks Ken.  I knew about the rusting but I had forgotten it.  I had just finished trying the hyd peroxide/ vinegar solution when your message came through.  By that time I had already given up on removing the lead buildup with the hyd per/vinegar mix and thanks to your message I had plenty of time for housekeeping to prevent the rust.

The lead ramp is still wedged into the end of the case neck cut on the bottom third of the chamber.  2/3's of the circumference has a sharp 90 degree reamer cut.  The bottom third has a built up ledge that solvent, bronze brush wrapped with Chore Boy, bronze brush wrapped with 4x wool will not remove.  I even tried a 1/4" wood dowel split and wrapped with Chore Boy/4x steel wool and got absolutely nowhere.  If I ever figure it out I'll come back to this post and give an update.

Summary:

  • My best guess from feedback and from what I can see with the two new barrels I'm having trouble with is that the sharp cut made by the reamer from the case neck to lede is skimming off lead from the bullet and causing a ramp to form on the lower third of the circumstance.  If that's true, it is quite possibly that if the bullets are oversized to the bore it could make the problem worse.  And with 30,000+ PSI pounding the buildup it seems to pack the lead in tight.  These statements are speculation on my part and not a hard fact.
  • Overnight soaked in Hoppy's or patch soaking for 5 minutes with hyd peroxide/vinegar had no effect on the lead ramp from the neck of the chamber to the lede.
  • A dentist pick that I tried last year on the 7.62x39 barrel could mark the lead buildup but it's also very easy to damage the bore.  So that is not an option.
  • The only path forward I see is to buy some mercury, plug just before the buildup and dissolve the lead. 

Two last question to anyone who may be following this. 

  • Has anyone had first hand experience using mercury?
  • Has anyone started a virgin barrel with cast bullets only?

Thanks, Bill.

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Brodie posted this 04 September 2021

If you remember Onongonga or Gary, he had a barrel break-in procedure that did not even involve shooting.  Gary would saturate a pull-through bore snake with turtle wax chrome cleaner and pull it through the barrel one hundred times, he claimed it almost eliminated leading and made the barrel shoot better.  A friend of mine broke in a .357 barrel by shooting one shot and pulling a clean bore snake through, I think, ten times, then one shot and nine times and so on until he got to zero, then he shot two or three (it was several years ago) and so forth until he got to ten shots with no cleaning.  As he progressed the snake went through the bore more easily and the rifle seemed to shoot better.  He shot powder-coated cast lead bullets in the gun. 

I have used mercury to remove lead but not from a rifle bore.  I suggest that if you try it you remove all the oil or grease from the bore and chamber, plug the chamber and pour the mercury down the barrel.   It should not take much mercury to remove the lead as you will not be filling the entire bore.  Drain the mercury into a soft towel and work it back and forth which should take the lead from the mercury.  Good Luck, I hope that this has helped.

B.E.Brickey

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45 2.1 posted this 04 September 2021

The lead ramp is still wedged into the end of the case neck cut on the bottom third of the chamber.  2/3's of the circumference has a sharp 90 degree reamer cut.  The bottom third has a built up ledge that solvent, bronze brush wrapped with Chore Boy, bronze brush wrapped with 4x wool will not remove.  I even tried a 1/4" wood dowel split and wrapped with Chore Boy/4x steel wool and got absolutely nowhere.  If I ever figure it out I'll come back to this post and give an update.

You need to put the tightly wrapped bore brush on a steel cleaning rod attached to a variable speed drill and spin it at the problem point. S&W used this set up to clean heavily leaded cylinders in their repair center. It works quite well to clean the area and dull the sharp edge as many rifles have that problem.

  • Has anyone started a virgin barrel with cast bullets only? Yes, many times with a very long life span with no troubles depending on just which alloy you use.

Thanks, Bill.

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Wm Cook posted this 04 September 2021

I have to order the mercury so in the meantime I'll do as suggested and take a 35 cal brush with the copper chore boy weaved into the bristles until it is well oversized.  I already have a steel rod cut and ready for the variable speed drill.  In the morning I'll give it multiple minutes of clean, inspect, clean, inspect to see if I can wear it down. 

On new barrels starting straight off with cast bullets should I assume that you do nothing but load, shoot and inspect before working on the sharp area?

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