Handgun Bullet Obturation and Leading

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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?
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No, even though water is wet and ice is cold, bullets will not always come out that way. I have been casting for many years and have recovered a lot of bullets from the berm and test media.

I have fired the example that I outlined in an old Colt 44 Special and have seen that they did not bump up to the barrel diameter with 12 BHN and 18 BHN alloys. I did not have any really soft bullets to try at the time and wanted to see if that was the differentiator. And yes, they leaded like the dickens.

I shoot soft to medium (8 BHN-12 BHN) in most of my revolvers now and have almost no leading. I believe fit is the key factor to reduced leading and increased accuracy.
 
I have fired the example that I outlined in an old Colt 44 Special and have seen that they did not bump up to the barrel diameter with 12 BHN and 18 BHN alloys. I did not have any really soft bullets to try at the time and wanted to see if that was the differentiator. And yes, they leaded like the dickens.
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Those bullets proved the point then. I have had loads in 45 acp that leaded horribly because they did not "bump up" and seal properly. I loaded the EXACT same bullet hotter, so it was going faster with more pressure and leading would go away or get minimal.

I guess the point of my statement is, these are all things that back up the concept of obturation. If you do not have perfect fit and do not obturate, it will lead. If you do have perfect fit, it doesnt matter.
 
I have fired the example that I outlined in an old Colt 44 Special and have seen that they did not bump up to the barrel diameter with 12 BHN and 18 BHN alloys. I did not have any really soft bullets to try at the time and wanted to see if that was the differentiator. And yes, they leaded like the dickens.
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Bullet diameter increase is directly proportional to pressure. At 44 Special pressures, 12BHN bullets won't increase in diameter much, if at all.

I read something somewhere that pure lead will increase in diameter as little as .002" at handgun pressures. Linotype will swell by something like .0002". I do not believe the .22LR swelling to .31 Caliber story. That is physically impossible.

Obturation is not bullet swelling. It is the sealing of the bore by a swelling bullet. The bore stops the swelling and contains the bullet.

Therefore, one must match the bullet to the largest diameter it may encounter, and that is the cylinder throat in most cases.
 
"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

I think it's fully correct. Pressure on the base increases as pressure increases, that's a given, but combustion (chamber) pressure is not BHN dependant. The issue I was addressing is how much any bullet can swell; if a bullet can possibly get larger than groove diameter (without blowing the gun up) I need more education! And it isn't the resistance of the air column in a bore that sets bullets back, it's the inertia of the bullet's own mass resisting accelleration. That's why heavy bullets obturate better than light bullets. ??

My point of lead/hardcast vs. jacketed wasn't leading, it's that no cast bullet can possibly be as hard as a jacketed bullet and even undersize jacketed stuff obturates if the charge is hot enough. The normal "hot" charges for .44 Spec and .45 LC are quite modest; obtruation isn't likely to change hard cast bullet diameter much so they had better start out the right size.
 
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if any bullet can possibly get larger than groove diameter without blowing the gun up I need more education. ??
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If a revolver has cylinder throats larger then bore dia, which many do, then the bullets should be soft enough to obturate to throat diameter.

Then the forcing cone sizes it back down to bore dia.

rc
 
ranger -
combustion (chamber) pressure is not BHN dependant
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correct. weight of CB (inertia = 0) and getting squeezed to bore size create resistance to allow base pressure to build. Lube grooves will swell and CB may get longer. lead has to go somewhere. This does bring up another point, that hard lube must get squeezed some by the groove swelling to get lube on the bore. If the CB is hard enough and pressure low enough, you run out of lube, cause none gets pushed against the bore.
 
“the obturation thing” obturate:OBTURATE.

Gas beats the bullet out the barrel every time, there is no such thing as sealing the barrel with the bullet. there is a lag between a seal and leakage. Some claim the ol’ cleaning rod is the cause of throat and muzzle erosion.

F. Guffey
 
Yes there is, otherwise lead bullets would lead the barrel no matter what.
 
Sure would. Gas cutting leads throats and especially forcing cones. If you keep shooting it will continue down the bore until it is coated. Skidding bullets is about the only thing that will lead as badly as gas cutting. The lube helps make that seal. You can shoot a hard undersized bullet that leads a bore severely, then use wax gas checks with the same bullet/load, and it will not only stop leading cold, it clean the bore of lead from the non gas checked rounds. Been there done that. No guesswork.
 
lead bullets will always leave a little of itself behind in the barrel. how much is the important part.

murf
 
I have shot hundreds of rounds of .45 ACP with zero leading. Absolutely no sign at all.
 
This is getting funny. Post #30, ammo and hard backer board (terminal ballistics caused it). Lead is not elastic! That CB doesn't get larger in dia. when it leaves the bore of ANYTHING. Yes, some alloys will have ~.001 'springback', like when you push it through a sizer. OK, let's continue the 'elastic' theory. You fire, the CB expands due to pressure, expands more when leaving the bbl. Elastic - it should then shrink, the pressure is greatly reduced. Elasticity is defined as the ability to RETAIN shape when pressure is CHANGED. Concrete is highly elastic, till it breaks. lead is malleable - it deforms from pressure and stays deformed.
 
"lead is malleable - it deforms from pressure and stays deformed."

Yep. Any lead alloy "elasticity" for bullets is so small as to be irrelivant.

I don't agree that lead bullets must leave anything in the bore. Most of mine leave the bore bright and shiney, in fact cleaner than jacketed.
 
"..if any bullet can possibly get larger than groove diameter without blowing the gun up I need more education. ?? ---- If a revolver has cylinder throats larger then bore dia, which many do, then the bullets should be soft enough to obturate to throat diameter."

Okay, you're right, I wrote imprecisely. I was speaking in general terms for pistols without making a detailed allowance for revolver cylinders. My point was that the size of what the bullet passes through is what determines it's max diameter, not chamber pressure or BNH.
 
“the obturation thing” obturate:OBTURATE.

I was visiting a bench rest forum when the subject of gas being faster than the bullet, there was something about flow, fluid and sudden starts, and of course there was that thing about ‘time as a factor’, I casually mentioned a photographer taking pictures at about the same time the trigger was pulled. He did not have a clue what the picture was about. His picture was recognized as being worthy of being included in a book of award winning photographs.

The photograph included a cloud of visible moisture created by compression, a smoke ring, the projectile and escaping gas behind the projectile that ran 90 degree to the bore, with definition, meaning the lands of the barrel could be counted in the gas pattern. Point? Before the photograph everyone thought there was a blast, most of what the photograph recorded was and is not visible. The photo changed the understanding of the events that take place when the trigger is pulled, and time is a factor.

Then there were the curious, the ones that are able to say “I DO NOT KNOW! BUT! I have resources”, sure enough, in a short time it was decided pressure at 10.000 psi +++ has no problem getting ahead of the bullet.

I am the fan of the running start, I want my bullets to have a jump start, I am not worried about hot high pressure, metal cutting gas cutting bullets or barrels, I have more barrels, chambers and bullets than I can ware out,

Then there is the muzzle taper caused by cleaning rods, I tape the joints on old heavy duty cleaning rods, I do not push a cleaning rod, I pull and I make my own bore snakes, it is impossible to jam one up in the bore.

F. Guffey

The photograph was taken +/- a few years of 1912.
 
I agree that in many cases gas overtakes the bullet. Gas travels at 7000 FPS afterall. But that only occurrs when there is an initial mismatch between the bullet and the bore.

In many cases, especially with 9mm pistols and .30 caliber military rifles, there is a .002"+ bore to bullet mismatch that allows gas to blow past the bullet.

But with properly fitted lead bullets, there is no gas blowby. I have shot upwards of 500 rounds through my 1911 without a hint of leading. If there was blowby, the barrel would have leaded up within 100 rounds.
 
While not the article I mentioned, F. W. Mann in "The Bullets Flight From Powder to Target", mentions an experiment using a very short barrelled rifle and lead bullets. He seems to have gotten quite a bit of "slugging up".


http://castpics.net/subsite2/ClassicWorks/The_bullet_s_flight_from_powder_to_targe.pdf

The article starts on page 60 with a photo on page 64. It is an interesting book, for those who would care to read it.
 
I don't post much here, mostly just read, but wanted to share some recent results with lead bullets. Got significant leading just forward of the forcing cone in my GP100 with Missouri Bullet 158 gr SWC (BHN 18) and 5.5 grain Unique. Also got bad leading in the same place with 5.7 and 6.0 grains. (As a side note, the Lewis Lead Remover is a great tool). I thought that maybe I was not achieving enough pressure on these Brinell 18 bullets, so I bumped the charge up to 6.5 grains. No leading whatsoever after 50 rounds - and accurate! By the way, these bullets are a snug fit in my cylinder bore.
 
Have MB cast some out their 12BHN alloy for you and use the lower powder charge if you wish.
 
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