Handgun Bullet Obturation and Leading

[warnerwh]

I've noticed many people claim that the harder lead don't obturate enough to fill the grooves and can cause leading. However according to Laser-cast their bullets which are a 24BHN will begin obturating at 11,500 and will be fully obturated at 13,000psi. These lowish pressure numbers are less than what pressures we deal with in many handgun cartridges. I am actually thinking of magnum cartridges. These are pressures that are easily reached in any medium or full house magnum load. Even standard pressure loads reach these levels.

It is commonly recommended when someone has leading problems to try a softer alloy. The BHN of the Laser-cast bullets is quite hard and harder than any other bullet alloys from other companies I've personally seen. I get no leading with them and have read many times of others getting no leading with these unusually hard lead alloy bullets.

So as you can see I am confused. Hasn't anyone ever done a definitive scientific study? It appears there are many opinions based on experience which I agree is excellent however I'd like to see an exactly explanation of what is actually happening under the varying circumstances done in a controlled test.

If you go the Laser-Cast website and go to "Load data and Evil Roy DVD" then select "Bullet Obturation" you will see what a metallurgist wrote.

 

[StrawHat]

I am not aware of any scientific study being done, but I wouldn't be looking for one anyway. Leading has a variety of causes, bore condition bullet size, lead alloy, velocity, etc. Start casting your own and you can control several of the factors.

 

[ljnowell]

There have been many scientific studies. There has also been lots of debate on what Lasercast has to say about it. The general consensus in the reloading community is that they are not exactly correct about that.

 

[LiveLife]

I used to shoot commercial hard cast bullets from 20-24 BHN and if I did not have proper bullet-to-barrel fit (bullet diameter .001" over the groove-to-groove diameter) and drove them to high-to-max lead load data, I got leading. I don't always want to shoot max load data when I am using mixed range pick up brass with unknown reload history and prefer to use mid-to-high range load data for target loads, especially for 40S&W in Glocks (I shoot lead loads in Glocks with Lone Wolf aftermarket barrel).

Another problem is that many factory barrels are oversized. Instead of 9mm barrel having .355" groove diameter, some factory barrels can be .356", .357", and even .358"+. Instead of being sized at .451", my Taurus PT145 barrel is like .455"-.456"+. Although I could use larger sized bullets to provide proper bullet-to-barrel fit, if you have several pistols with different groove diameters, this means having different diameter lead bullets in the same caliber and keeping track of which reloads are which.

Missouri Bullet Company offers bullets in 10, 12, 15, 18 BHN depending on the caliber/application and explains the reason behind the different BHN offerings on their Technical page. I use 18 BHN in 9mm and 40S&W and my barrels are sized at .355"-.356" for 9mm and .400"-.401" for 40S&W. When using mid-to-max range lead load data, I do not get leading in my barrels. I use 12/18 BHN in 45ACP and my barrels are .451"-.456"+. 18 BHN bullets do not lead in my M&P45 and Sig 1911 using mid range load data (200 gr SWC with 5.0 gr of W231/HP-38) but will lead in PT145 and accuracy was poor/erratic. When I switched to 12 BHN bullet, leading stopped in PT145 and accuracy returned using the same load and even lighter target load (200 gr SWC with 4.0 gr of Promo/Red Dot).

Mastercast Bullets lists 14 BHN for their "softer" cast bullets and Z Cast Bulletz indicates 14-16 BHN. I have ordered an assortment of Z Cast bullets in 9/40/45 to try and will post my impression/range report in a new thread.

Z Cast uses a Lead Alloy Mixture containing Lead, Antimony and Tin and has a BHN hardness of 14-16,

Here's more information on bullet alloy hardness and obturation by Glen Fryxell - http://www.lasc.us/FryxellCBAlloyObturation.htm

Glen's free ebook chapter 7 covers definition, location, cause, prevention and removal of leading - http://www.lasc.us/Fryxell_Book_Chapter_7_Leading.htm

 

[918v]

I've noticed many people claim that the harder lead allows don't obturate enough to fill the grooves and can cause leading. However according to Laser-cast their bullets which are a 24BHN will begin obturating at 11,500 and will be fully obturated at 13,000psi. These lowish pressure numbers are less than what pressures we deal with in many handgun cartridges. I am actually thinking of magnum cartridges. These are pressures that are easily reached in any medium or full house magnum load. Even standard pressure loads reach these levels.

Obturate what exactly?

Are the bullets increasing in diameter by .0001"? .001"? .01?

What kind of gun were they using? Cuz I can guarantee that a LaserCast .453" 200gr LSWC will not obturate a S&W 25-2 cylinder throat at any sane pressure.

 

[dragon813gt]

It depends on where the leading is, in the barrel. There are many causes and they show up at different points. People are obsessed with shooting high BHN these days. It's not necessary in most instances. The standard wheel weight alloy is harder then the old "hardball" ammo that was used during the early part of the 20th century. Focus on the cause of the leading. Most if the time the hardness of the alloy is not the problem.

I can't blame a company for playing up the hardness angle. People fall into the same traps time and time again. The Internet helps push this along as well with it's wealth of misinformation.


Brought to you by TapaTalk.

 

[LiveLife]

Before my local bullet caster retired, I spent some time at his shop help produce like 10 year supply for me to shoot.

While he was casting, we discussed many things like accuracy and leading, but when it came to hardness, he said many commercial casters use 20-24 BHN because it will withstand the rough handling of trucking and handling by UPS/FedEx staff who often toss/drop shipping boxes.

He casted his bullets around 20 BHN but advised me to push them hard to obturate and not lead in the barrel. He supplied Cowboy Actions match shooters in three counties and casted those bullets softer along with offering them in 20 BHN.

When I was shooting the last of the bullets he casted, I found out about Missouri Bullet on THR several years ago and Brad has been my cast bullet supplier since. Now that I have shot 12/18 BHN bullets, I would not shoot lead bullets harder than 18 BHN ever again. As to condition of the bullets that are shipped to me, even softer 12 BHN bullets arrive at my house in California after cross-country journey in pretty good shape and I hardly see lube knocked off the bullets.

How MBC bullets (even softer 12 BHN bullets) look when they arrive in California after a long rough truck trip from Missouri.

Picture of bullets pulled from boxes with light coating of lube on the surface (more than likely from transport in long rough truck ride)

Picture of bullets with surface wiped showing condition of lube

 

[918v]

BHN does not matter if everything is perfect. But with factory guns, nothing ever is.

I do wanna say this about LaserCast: they make the most consistent, highest quality, commercial bullets on the market today. The stuff I have in my possession weighs in at +\- one grain. Every bullet's lube ring is full of lube. Every bullet is perfect, with no dings. Every bullet looks like it was turned on a lathe, with perfectly crisp edges. They are pure joy to look at.

But, they lead in my revolvers. No, not because they are not a match for the cylinder or the bore. They lead the forcing cone, the frame, and the cylinder crane. I have to use them in my pistols only.

I use 12 BHN Missouri bullets in my revolvers. No issues. Wonder why?

 

[ljnowell]

standard wheel weight alloy is harder then the old "hardball" ammo that was used during the early part of the 20th century

Hardball is jacketed ammo, usually with a super soft swaged core.

 

[popper]

Lead work softens. Take, as an example, a 20 BHN slug. Hit the base with a pressure greater than the strength of the material. Only the base softens and squishes to fill the bbl, lets assume it drops to 10 BHN (fictional number). I haven't found any data to indicate it gets softer. With enough pressure applied for a long enough time, the entire CB would work soften, squish and be 10 BHN. Same thing happens at the rifling grooves. Too much pressure and the CB will shear (break off) and it will strip in the rifling. It NEVER goes back to 20 BHN! Now for CB friction, softer rubs off easier. Gas cutting, more for softer lead. So you all know this already. We get to balance all this. So for HV (high pressure for a longer time), we use 20 BHN and a GC. Holds to the rifling and reduces cutting at the base. LV we use 10 BHN, let the CB squish and hope for no gas cutting. In both cases we use oversized CB to force squishing in the rifling. High BHN and the CB will size the case and give good neck tension. Low BHN and the case will size the CB, perhaps smaller than bore size, with lousy neck tension. Remember, that book pressure number? It only exists for maybe an inch of bbl. Simple, right? It's your sandbox, go play in it. Just my 2 cents.

 

[mdi]

Lotta good replies so far. But the key to shooting clean/leading-free, accurate lead bullets is bullet to gun fit. If the bullet starts out at the correct size for your gun, obtruation isn't of concern or necessary. If a bullet is too small, it can be 30 BHN and still lead the bore. It's the dynamics of gas "leaking" around the bullet base, melting bullet sides and depositing the molten lead on the bore surface. Properly fitted bullets will seal the bore against hot gasses and prevent leading (this is why a gas check works). I've used this simple "theory" for nearly 15 years to prevent leading in all my guns shooting lead up to Magnum velocities (wheel weight alloy to mebbe 1400 fps.).

I agree with the reason commercial casters use hard alloys is for shipping purposes, also playing on a new caster's thoughts of "harder is better". A lot of commercial casters' bullet lube is also formulated for sticking on the bullet during shipping/handling.

 

[rcmodel]

Whether the bullet fits a revolver bore or not isn't as critical as whether it fits the chamber throats or not.

If it doesn't fit the throats, and is too hard to obturate, gas cutting has already happened before the bullet gets out of the cylinder and you will have leading.

rc

 

[ranger335v]

No lead alloy is as hard as the softest jackets so saying a lead bullet alloy is 'too hard' is nonsense.

Obturation means an undersize bullet, lead or jacketed, gets kicked in the base so hard it drives forward faster than the forepart can move and that swells the diameter to fully match the bore. If we start with a bullet that is as large as the throat and rifling no swelling can occur nor is it needed. And, once the throat and grooves are sealed there is absolutely no value to size lead bullets any larger - a thou or so larger may do no harm but it certainly can't do any good.

Low power loads don't prodice enough acceleration to produce much obturation so it's critical to have the proper diameter bullet. Hard bullets that are undersize to start with will surely gas cut and lead no matter how hard the alloy is or what lube is used. Light (for caliber) bullets don't have a lot of resistance to acelleration so it's important for them to be proper diameter even in hot loads. A hot magnum revolver load will accellerate even very hard and undersized bullets to not only obturate but will easily set the nose of a SWC back to make recovered bullets look almost like wad cutters.

Antimony makes lead feel and test hard but that's deceptive. As molten wheel weights cool, the antimony solidifies as hard crystals before the lead does, the end result is like a bunch of rock pebbles in a wad of cheese; it will feel hard but the hard stuff is only held together in a soft lead matrix and the lead tends to rub off on the bore just like cheese. We need to add a couple percent of tin to wheel weights to keep the antimony in alloy as it hardens.

Low to moderate speeds don't put a lot of stress on the bullet lube so most anything will work okay. Magnum speeds (starting about 1,100 fps maybe?) greatly benefit from a high grade lube. The old NRA Alox/beeswax formula is hard to equal and nothing is better.

Get the hardest bullets you can find, make sure they are no smaller than your pistol needs, use a high quality lube and load in the upper to high range of speeds. Your accuracy will probably be excellant and leading, if any, will be light whether the bullets are gas checked or not.

 

[popper]

Like ranger335 says, so we add Sn, to lock up the Sn or a grain refiner, S or As. Unless the CB is oversized, swelling only occurs at the base.

no swelling can occur

not exactly correct. Pressure on the base forces the base to push on the lead in front ( and so on) and the lead in front pushes on an air column. As I stated earlier, when the BHN goes down, the pressure to swell the lead decreases. Slow powder give a longer pressure curve and 'swells' the base all the way down the bbl. Fast powder kicks the base, maybe for 1/10" and that is all. I think muzzle leading is caused by ow pressure where the CB stops swelling and all the junk behind it blows by. I suspect chamber side leading is due to the same effect, CB hasn't swollen yet, junk gets deposited when it does, but not scraped away by the CB.

 

[Walkalong]

I can guarantee that a LaserCast .453" 200gr LSWC will not obturate a S&W 25-2 cylinder throat at any sane pressure.

I agree with this.

A bullet in a cylinder throat has little to no resistance on it. It has to bump up and bump up fast while freewheeling through the throat. A bullet that is too hard is not going to do so, and leading is the result.

Bevel base bullets do not help.

Whether the bullet fits a revolver bore or not isn't as critical as whether it fits the chamber throats or not.

If it doesn't fit the throats, and is too hard to obturate, gas cutting has already happened before the bullet gets out of the cylinder and you will have leading.

Plain and simple.

 

[kelbro]

I would like to see photographic proof of obturation of a lead bullet. Soft or hard. Cast one at .428 and shoot it through .432 throats and a .431 bore and measure it.

 

[243winxb]

use pure lead

SAAMI - OBTURATION The momentary expansion of a cartridge case against chamber walls which minimizes the rearward flow of gases between the case and the chamber wall when the cartridge is fired. BULLET UPSET In Interior Ballistics: The change of bullet form due to chamber pressure. In Exterior Ballistics: The expansion of a bullet upon impact with target.

 

[rcmodel]

Some good obturation info here:

http://www.beartoothbullets.com/faq/index.htm

rc

 

[Striker Fired]

Fit, Fit, Fit, Fit, and fit = no leading
most other things are minor
Harder does help in shallow rifling, but????

 

[ljnowell]

I would like to see photographic proof of obturation of a lead bullet. Soft or hard. Cast one at .428 and shoot it through .432 throats and a .431 bore and measure it.

Why, it will only come out at the diameter of the barrel it went down? Not sure what your point is in that statement? Do you need to see proof that water is wet and ice is cold?

 

[LiveLife]

Fit, Fit, Fit, Fit, and fit = no leading

I absolutely agree that fit is king with lead bullets. But a lot of us don't cast and we must buy what commercial bullet casters offer in sizing.

For my .455"-.456"+ groove diameter PT145 barrel, where can I find bullets sized at .456"-.457"?

Not to mention the cases will bulge quite a bit when I seat the oversized bullets.

Besides, since I have two other pistols that shoot .452" sized bullets fine (Sig 1911/M&P45), having two different sized bullets is out of the question, nor having to adjust the seating/taper crimp dies whenever I switch to different sized bullets.

For me, using a softer 12 BHN bullet was the logical and economically feasible solution that did not require any change to my die settings.

 

[StrawHat]

I would like to see photographic proof of obturation of a lead bullet. Soft or hard. Cast one at .428 and shoot it through .432 throats and a .431 bore and measure it.

The American Rifleman printed photos of bullets fired from a S&W M17 with the barrel removed. The bases had swollen to about 31 caliber. From a 22 LR cartridge with a heel based bullet.

Frequently, shooters of the Springfield Single Shot Rifle use undersized bullets and they slug up to fit the .461 or larger bores.

 

[mdi]

No lead alloy is as hard as the softest jackets so saying a lead bullet alloy is 'too hard' is nonsense.

Obturation means an undersize bullet, lead or jacketed, gets kicked in the base so hard it drives forward faster than the forepart can move and that swells the diameter to fully match the bore. If we start with a bullet that is as large as the throat and rifling no swelling can occur nor is it needed. And, once the throat and grooves are sealed there is absolutely no value to size lead bullets any larger - a thou or so larger may do no harm but it certainly can't do any good.

Low power loads don't prodice enough acceleration to produce much obturation so it's critical to have the proper diameter bullet. Hard bullets that are undersize to start with will surely gas cut and lead no matter how hard the alloy is or what lube is used. Light (for caliber) bullets don't have a lot of resistance to acelleration so it's important for them to be proper diameter even in hot loads. A hot magnum revolver load will accellerate even very hard and undersized bullets to not only obturate but will easily set the nose of a SWC back to make recovered bullets look almost like wad cutters.

Antimony makes lead feel and test hard but that's deceptive. As molten wheel weights cool, the antimony solidifies as hard crystals before the lead does, the end result is like a bunch of rock pebbles in a wad of cheese; it will feel hard but the hard stuff is only held together in a soft lead matrix and the lead tends to rub off on the bore just like cheese. We need to add a couple percent of tin to wheel weights to keep the antimony in alloy as it hardens.

Low to moderate speeds don't put a lot of stress on the bullet lube so most anything will work okay. Magnum speeds (starting about 1,100 fps maybe?) greatly benefit from a high grade lube. The old NRA Alox/beeswax formula is hard to equal and nothing is better.

Get the hardest bullets you can find, make sure they are no smaller than your pistol needs, use a high quality lube and load in the upper to high range of speeds. Your accuracy will probably be excellant and leading, if any, will be light whether the bullets are gas checked or not.

"Too hard" for a lead alloy bullet has nothing to do with jacket hardness. Like comparing apples to bananas. A jacketed bullet does not melt and deposit jacket material on the bore the same as lead when gas leaks around the base. A lead bullet that is too hard to seal the cylinder throat/bore will deposit lead in the bore. Simple...

 

[Walkalong]

Frequently, shooters of the Springfield Single Shot Rifle use undersized bullets and they slug up to fit the .461 or larger bores.

With soft alloys.

 

[243winxb]

Plastic deformation