Lead buildup in chamber throat

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  • Last Post 27 November 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.

Patience isn’t a virtue, it’s a delay tactic.

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Crooked Creek posted this 27 November 2021

I don't want to 'derail' your thread with someone else's problems/issue, so I'll try to limit my response. I, too, am not near him and his son's rifle or loads/components, so I haven't had a personal hands on looksee. Your suggestions are good one's, much appreciated, and I will pass them on to my cousin, thanks!

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Wm Cook posted this 27 November 2021

I would try changing one thing at a time until the results change. Stuff like; clean chamber/bore and fire 20 rounds with what he always loads for and inspect, clean chamber/bore and shoot 20 rounds sized to .355 and inspect, clean chamber/bore and fire 20 jacketed bullets and inspect, clean chamber/bore and change powder charge to change velocity (go sub sonic) fire 20 rounds and inspect.

Have you reverse tamped in an unsized sized cast round and measured free bore.

Have you done a pound cast. The reverse tamp should tell you a lot but a pound cast is handy to have.

It’s frustrating not to be able to be there and help.

Patience isn’t a virtue, it’s a delay tactic.

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Crooked Creek posted this 27 November 2021

I wrote a lengthy post on The Shooters Forum regarding the 350 Legend problem, but have yet to get any solid responses. I think I have it figured out, and actually suggested to my cousin that his son take a fired case and cut some 'teeth' in the case mouth with a triangle file and drill and tap the base for a short handle. This 'tool' could then be carried in the field to keep him in business, so to speak. BTW, he did size the bullets to .356" in a Lee push through sizer. If you go to that forum you can read the entire (lengthy post). I had a similar problem years ago with a 30 Carbine Ruger Blackhawk, where after firing about two cylinders full, each chamber had enough of a 'lead ring' built up behind the headspacing 'step' that I could not seat cartridges deep enough in the chambers to clear the cylinder gate and recoil shield until I cleaned it out. It sounds like you have figured out the source of your problem, I assume you've had a talk with the guy in the mirror! 

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Wm Cook posted this 27 November 2021

I'm about 80% convinced that the buildup was self inflicted.

I've had three new barrels in the past year.  The first was a 7.62x39 Ruger Ranch bolt gun and the second was a .308 Savage 10F. bolt gun.  On the 7.62 I had about 4 or 5 molds that dropped bullets that could be used. They ranged from 129 to 200 grains.  The .308 had about 3 or 4 molds that would work. 

On each I spent an afternoon finding seating depth for each bullet.  My "habit" is to use a bushing that gives me a somewhat loose grip on the bullet.  Example; On the .308 with .014 neck thickness and the bullet sized to .310 a .336 bushing will give me a loose fit. 

With the first attempt I leave the bullet intentionally long and allow the chamber to push the bullet back into the case to what I call "jam" or more appropriately called "push back" position.  I then adjust the stem on my Wilson die so I get that COAL length and add a .020 shim.  Then I use the next size smaller bushing (.335) and chamber the round feeling the COAL effect on bolt closure and bullet sticking.  I repeat this as needed until I get to where the COAL has a slight tight bolt closure feeling and slight sticking but with zero push back. 

I have no false allusions about my skill level so for clarification I must say that I am not sure if what I'm doing is right or wrong.  But my objective is to have a firm grip on the bullet, a moderate feel to bolt closure and a slight stick that still allows a loaded round to be removed.

So with 4 or 5 efforts to find the stem length on my Wilson die to get me to the COAL I need, times the 5 different bullets, I might have chambered 100 loaded dummy rounds before I was satisfied with the bolt closure with slight sticking that still allows me to remove a loaded round without dealing with a powder spill.

As I'm trying to figure out seating depth there are certain mishaps that are guaranteed to happen.  Maybe the bushing is a bit too tight and the COAL a bit longer than I wanted and the bolt had to be forced to close (bullet had to be pushed further then it wanted to be pushed into the free bore/lands).  As this was going on with both of the first two barrels I was causing a buildup of alloy at about the 6:00 position on both barrels.  Probably even before the first bullet was fired through either barrel.  . 

The third barrel was another .308 and it only had one bullet that qualified.  Since I already had a good feel for that bullet with the first .308 so I got the third barrel figured out pretty quick.  After about 100 rounds I bore scoped it and it was clean. 

So my guess is that the alloy scrape buildup just before the free bore was caused by a tight bushing and too long of a COAL. At least that's what I think happened.  Being at the 6:00 position might have been caused by the manual feeding and the tilt of the bullet as the bolt was closing.  My worse enemy looks back at me ever day while I'm shaving. 

On your cousin's son's 350 Legend I could only take wild guesses.  Not sure what bullet he's shooting but if the bullet is sized larger than normal the driving band might be slamming into the beginning of the free bore area.  Sizing >.358, .359 might be like the driving band hitting a wall.  Like I said only wild guesses which aren't a lot of help to you.  Good luck and if you can sort it out let me know what you find.  Every thing is solvable and when you pull back the curtain it does feel so good.  Can't buy that learning experience anywhere that I know of.  On a positive note, here on the CBA forum most everyone is level headed and there aren't any "drive by" experts that throw out a two sentence reply and then walk away. Pretty good group and a lot of knowledge here. 

Thanks again, Bill.

Patience isn’t a virtue, it’s a delay tactic.

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M3 Mitch posted this 26 November 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. " ...   

 

What Ken said here - is the rifle shooting well?  Is accuracy steady or deteriorating? 

Maybe I'm just lazy, but to me one of the charms of a good cast load is you don't need to clean the bore after shooting.

Unless there is an actual problem with the way the gun shoots, and given that you have ruined one barrel trying to clean this lead ring out, you might want to consider leaving well enough alone.  Just IMHO. 

hope this helps

ken

 

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Crooked Creek posted this 26 November 2021

I had been wanting to tie this off for some time and things kept getting in the way.  I had it easy since I was needing to clean out the buildup at the end of the chamber cut just before the freebore area in my .308. I used a 30-06 case screwed (10-32nd) to a Sinclair cleaning mop handle.  If you cut a jagged edge on the expanded case mouth you can pull the bolt and feed the case into the chamber.  twisting clockwise cuts it out nicely.  I think a 30-30 will work on my 7.62x39 and a .222 case will work on my .223.   Bill.

Good to see you have a removal method. Have you figured out the 5 to 8 o'clock thing yet? I have an 'off the wall' theory that perhaps gravity is a contributor. If so, if you were to hold the rifle upside down (stock up?) and shoot it, the lead deposit should be, roughly, at 10 to 2 o'clock, and if you held it left or right, it would be at 8 to 10 o'clock or 2 to 6 o'clock, see where I'm headed? If that happens, further to my gravity theory, the cartridge is lying on the 'bottom' of the chamber, regardless of the rifle position. Are you using either new/unfired brass, or full length sized brass? If so, try fired cases (in that rifle chamber) and do a partial neck resize, leaving a portion of the neck 'fitted '(so to speak) to the chamber neck. That would center the position of the bullet to the centerline of the chamber and thus the 'step' where the lead 'ramp' occurs. One would think that 'jamming' the bullet would overcome the gravity and thus center the bullet, but it may be tilting the bullet upwards. Just some idle thoughts. My cousin's son had a similar problem on a CVA break barrel in 350 Legend, where the lead would build up on the headspacing 'lip', after just a few shots, to the point that the cartridge was held back to the extent that the action was difficult and then impossible to close.

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MP1886 posted this 26 November 2021

If you want to know a lot about powdered coated bullets message "geargnasher" .  He's a member here.

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OU812 posted this 26 November 2021

I do not know, maybe?

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ray h posted this 25 November 2021

812- when you lube powder coated bullets, is the velocity the same as a un-lubed powder coated bullet?

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OU812 posted this 25 November 2021

When you get the lead out. Try shooting lubed powder coated bullets. The soft lube will keep powder fouling soft and the powder coating will eliminate lead fouling.

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max503 posted this 25 November 2021

My 357 Contender barrel will build up a ring when I shoot 38's.  Then if I shoot a 357 the ring will hold the case so tight I have to pry or knock it out. 

I'll soak the chamber in Ed's Red then scrape the ring out from the breech end with a piece of 1/4" hardwood dowel.  Works for me.

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Wm Cook posted this 25 November 2021

I had been wanting to tie this off for some time and things kept getting in the way.  I had it easy since I was needing to clean out the buildup at the end of the chamber cut just before the freebore area in my .308. I used a 30-06 case screwed (10-32nd) to a Sinclair cleaning mop handle.  If you cut a jagged edge on the expanded case mouth you can pull the bolt and feed the case into the chamber.  twisting clockwise cuts it out nicely.  I think a 30-30 will work on my 7.62x39 and a .222 case will work on my .223.   Bill.

Patience isn’t a virtue, it’s a delay tactic.

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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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Ross Smith posted this 06 September 2021

Since the lead is building up on one side only, have you considered an alignment problem. I'm with Ken, Ignore it for a while to see if keeps growing worse or not.

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Wm Cook posted this 06 September 2021

So for those bullets that ride the bore and not the lands, the bullets would have a taper to transition into the lede instead of the .030” (or whatever that little lip measures) wall?

Either way the base would be deformed by the force of ignition but instead of a 90 degree wall it would taper into the lede by .xxx”

And with either design the bearing length would stabilize for accuracy. The difference being a softer egress into the lede/lands on one.

And a pound cast would not show the case neck cut, it would show a transition into the lede with whatever taper and whatever length deemed best?

And the pound cast would give Accurate a profile to cut a mold?

I’m stretching here. This is one of those “to be determined” advancement classes I knew I had to take for cast accuracy but didn’t expect it to come up so soon.

If any of the above comments I made are just plain stupid forgive me. I gotta lot to learn about cast accuracy. Bill.

Patience isn’t a virtue, it’s a delay tactic.

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Ken Campbell Iowa posted this 06 September 2021

Firstly, i would try to prove it is detrimental ... a good argument could be made that it is beneficial to accuracy.  think of it as a tight throat  ...

Secondly, i have seen tools made from an old cartridge case ( neck set back )  or a brass or aluminum rod ... diameter of the neck in the chamber ....

with teeth ground/filed into the front of the rod that cuts just like the cutters that coal miners use to push into the wall of coal ...  or tunnel cutters ...

if you can't make one of these, pm me, i will make you a couple ..

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

interesting that some chambers are cut with no " little space " ... the neck diameter is continued directly forward down to the bore diameter ....  i suppose the always-present compromise would be that the lead bullet would expand into that larger diameter and then be swaged down again by the throat .   but then that happens anyway.

i haven't seen any tests to see if that eliminates the lead ring ...   Ed Harris here is most likely to have some input; i believe he has mentioned this type of chamber before.

ken

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Doughty posted this 06 September 2021

If you have one available, you might try using a chambering reamer.  Insert gently and gently turn by hand.

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ray h posted this 05 September 2021

I sure hope you figure this out. As a rookie I can't wrap my head around any lead being that tough. That's what I'd expect from a steel burr.  Good luck.

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Wm Cook posted this 05 September 2021

No luck this morning. My only hope is that mercury will dissolve the buildup. That’s assuming I can figure how to plug the chamber and still allow the mercury to reach the entirety of the chamber neck. I may have to go in through the chamber.

The 30.06 case was chamfered sharp, flared, and it disfigured the buildup but didn’t remove.

A bore brush with tightly weaved copper pad material attached to a short cleaning rod chucked into a variable speed drill was spun for an extended period of time (4 times for 5 to 10 minutes each) removed a fraction of the buildup and polished the buildup to a mirror finish but it wasn’t able to reach into the 90 degree corner the reamer left at the case neck.

I’ll let you know how things go if I find some mercury. Thanks, Bill.

Patience isn’t a virtue, it’s a delay tactic.

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pisco posted this 04 September 2021

When you get the throat clean roll some cast bullets in talcum/baby powder and fire laptop it should polish things up

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