Question about lead fouling

[JakeF]

Hi guys,
I've been doing a lot of reading/searching lately about this and there's one question I had to which I have yet to find an answer. Let's assume that I have what seems to be a good diameter cast bullet for my 9mm bore & well lubricated projectile. I read in one old thread where 'EddieCoyle' said to "load them hot enough, but not too hot" to prevent leading problems.

I have what I believe to be a good starting load, and am planning to load several small batches, increasing the powder charge by 0.1 grain for each batch to try to find the sweet spot for each of my guns with an eye on any changes in accuracy from batch to batch and any issues with lead fouling as the charge increases.

My question is how many rounds would you load of each variation in order to know for sure whether or not you'll have lead fouling issues? I don't want to make the mistake of thinking that I've settled on a charge that works well, only to find that I just didn't test enough rounds for lead fouling to show up.

If the load isn't hot enough (or is too hot) for the cast projectiles I'm using, how quickly can I reasonably expect it to be evidenced by lead fouling in the bore?

 

[EddieCoyle]

I'm no cast bullet expert, but this is my understanding of the problem...

There are 3 things that can cause leading:

1. The bullet is too small
2. The bullet is too hard
3. The bullet is too soft.

If the bullet is too small, nothing you do will prevent leading. Propellant combustion gases will leak along the sides of the bullet, eroding lead off the bullet, which will be ironed into the bore as the bullet passes. In a pistol, you'll see leading all along the bore (but mostly near the breech). In a revolver, you'll see leading around the forcing cone and the first few inches of barrel. When sizing lead bullets for revolvers, it is more important to size the bullet to 0.001" larger than the cylinder throat than it is to worry about the bore diameter. You can use pin gages to measure this.

When fired, a bullet should deform slightly to fill the bore. It actually gets shorter and wider. This is called obturation. If a bullet is too hard, it will not sufficiently obturate to fill the bore, and leading will occur similar to what happens with an undersized bullet. This can be 'fixed' by using a softer bullet, or by loading hotter.

A too-soft bullet can also cause leading, but this less common in handguns than in rifles. It's usually characterized by leading nearer the muzzle.

There's a formula someplace that will allow you to calculate the proper Brinell hardness for a particular velocity.

You can get lots of good info here: http://castboolits.gunloads.com/forum.php

 

[TY43215]

I'm no cast bullet expert, but this is my understanding of the problem...

There are 3 things that can cause leading:

1. The bullet is too small
2. The bullet is too hard
3. The bullet is too soft.

If the bullet is too small, nothing you do will prevent leading. Propellant combustion gases will leak along the sides of the bullet, eroding lead off the bullet, which will be ironed into the bore as the bullet passes. In a pistol, you'll see leading all along the bore (but mostly near the breech). In a revolver, you'll see leading around the forcing cone and the first few inches of barrel. When sizing lead bullets for revolvers, it is more important to size the bullet to 0.001" larger than the cylinder throat than it is to worry about the bore diameter. You can use pin gages to measure this.

When fired, a bullet should deform slightly to fill the bore. It actually gets shorter and wider. This is called obturation. If a bullet is too hard, it will not sufficiently obturate to fill the bore, and leading will occur similar to what happens with an undersized bullet. This can be 'fixed' by using a softer bullet, or by loading hotter.

A too-soft bullet can also cause leading, but this less common in handguns than in rifles. It's usually characterized by leading nearer the muzzle.

There's a formula someplace that will allow you to calculate the proper Brinell hardness for a particular velocity.

You can get lots of good info here: http://castboolits.gunloads.com/forum.php

Add to that powder is too hot

 

[swampy]

I'm no cast bullet expert, but this is my understanding of the problem...

There are 3 things that can cause leading:

1. The bullet is too small
2. The bullet is too hard
3. The bullet is too soft.

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AKA the goldilocks solution- find the bullet that is just right.

 

[swampy]

Check out Chapter 7 http://www.lasc.us/Fryxell_Book_Contents.htm

 

[mac1911]

my experience has been.....when its not right leading shows up quickly
I had been casting for my 1911 I had no issues with leading with the lee tumble lube mold for 45 cal (memory says its .452 dia) I did not slug my bore.
I used lee tumble lube and straight wheel weight lead.....I shot over a hundred rounds before I noticed a very slight leading at the muzzle.....fast forward to needing to cast more. I used a alloy with a some tin added to help fill out in the mold a bit. Changed nothing else. after 15 rounds I was throwing shot gun patterns at 15 yards....i looked in my barrel.....yikes covered in lead. I quess I hit the to hard spectrum? I switched back to wheel weights and even added a bit of pure lead and all is well.
Cast bullets are a hit or miss try and try again.

 

[JakeF]

Check out Chapter 7 http://www.lasc.us/Fryxell_Book_Contents.htm

Great read! Thanks!!

 

[garbler]

The primary causes of bore leading as far as I know are shooting lead too fast for the lubricant or having an alloy too soft then of course bullet fit to the bore. If the bullet is improperly sized for the bore it will allow gas leakage around the base and thus strip or melt lead as the bullet starts or tries to engage the rifling. If you push a soft alloy lead bullet with too much velocity/ pressure/heat the base of the bullet will upset or obturate so radically that instead of engaging the rifling it will strip out and allow gases to leak by the base of the bullet and melt lead along the way down the barrel. Gas checks are an effective way to control this problem however these are usually fitted to cast rifle cartridges and some of the hot loaded 45 and larger pistol cartridges that are pushing a bullet in excess of 1500 fps or so. So proper bullet fit and alloy are critical to control leading then it’s all about lube. Many of the soft beeswax or similar based lubes cannot perform where high pressures and temps are generated. For these type of loads you need to use a high temp hard lube and as far as I know Rooster Red is at the top of that list. Some of the commercial blue lubes run a close second and will work for most hot loaded big bore pistol loads. Along with having the right lube and bullet sized for the barrel the bullet design is critical. The bullets must have the correct base, driving band and lube grooves for the intended velocity and application. You can have the right diameter bullets and lube but if the design does not include enough lube grooves or the correct shaped grooves then you are asking for failure which will mean leading and no doubt poor accuracy.

Bullet hardness is the next area that can create lead fouling and poor performance. For high velocity loads the lead must be hard enough to both obdurate and engage the rifling and yet not strip out under high pressure and temperatures. The topic of which alloy or bhn hardness is a subject all to it’s own but most guys I know who shoot high velocity lead bullets in revolvers or T/C’s or similar will heat treat their bullets to achieve max hardness and prevent them from softening with age. For those who buy off the shelf cast bullets it is doubtful you will find the correct alloy or heat treated bullets suitable for true high performance loads where you are pushing velocities up and past 12-1500 fps in handguns and 2000-2200 fps in rifles. To shoot lead bullets like this you pretty much need to cast your own, heat treat and finally size and lube for you guns. It is about the only way to control each of the above reasons for leading and poor performance.

One last thing that can be a headache and puzzle for some reloaders who are shooting commercial lead bullets and that is some production barrels just will not shoot lead. Marlins early Micro-groove barrels have very shallow rifling and I believe 16 grooves unlike most newer barrels with 12 or so. These barrels will not shoot lead bullets worth a damn. There are some real smart guys who have figured out how to cast special bullets for them but the average guy will not get any accuracy with lead bullets. Same with some revolvers that are really built and set up to shoot jacketed ammo. To get the max accuracy from lead bullets you most often need to re-cut the forcing cone to extend and make it a bit shallower so the jump from chamber to barrel is not so abrupt or upsetting. Honing or sizing chamber mouths also is a big help with lead bullets and on many of the earlier Ruger SA’s this was a must since some of the Vaquero’s actually had undersized chamber mouths. In essence the bullets were being swaged down as they left the cylinder and hit the forcing cone undersized. Not too good for accuracy but a whole lot of Cowboy shooters never knew the difference.

Bore leading is therefore really not much of a mystery if you understand that it is either, lead hardness, lube or bullet design and fit that can be the cause. Unfortunately if you shoot most of the commercial cast bullets that are readily available they will work for most mild or mid-level practice and range work but fail totally once you start pushing the performance envelope.

Like Mr.Coyle pointed out leading will commence immediately if things are not set up right. It is not hard to see if you can get a bore light or run a tight wire brush through the bore dry a couple of passes over a white sheet of paper — you will see lead particles coming out. In my personal experience you can almost never completely eliminate some degree of leading in some bores and with revolvers it will always be there in the forcing cone to some degree depending on how polished it is

 

[noylj]

1) what is the groove diameter of the barrel and what diameter are the bullets? Slug your barrel. 9x19 barrels can range from 0.354-0.362" and cast bullets almost always have to be AT LEAST 0.001" over groove diameter. I find that 0.357-0.358" cast bullets work great.
2) where is the leading?
A clue to what is causing the leading is where the leading first begins to appear.
If it appears near the chamber, chances are that bullet diameter or hardness are the cause. A diameter too small or an alloy too hard will allow high pressure gas to leak past the bullet, which erodes the bullet and leaves leading near the chamber.
If the leading first appears on the leading edge of the rifling, the bullet might be too soft or the velocity too high.
If the leading appears in the second (front) half of the barrel, the bullet is running out of lube.
If bullet is just barely too small, I find a quick and light tumble lube in Lee Liquid Alox eliminates the leading.
A change of 0.1gn is not enough to see any difference and a single group is not enough to judge any thing on.
Work up the load by 0.3gn increments and fire at least three 5-shot groups, on a rest and shoot at a distance of at least 25 yards, at each charge weight to actually have hope of seeing anything.
Use a dry cotton patch to brush out the barrel after a few groups and check the barrel with a bore light. There will generally be a little leading. As you continue to shoot, watch to see if the leading gets worse. If it gets worse than it was after about 20 shots, your bullet is not right and you can use the information above to help gauge what the problem is.