Obturation , PRB and rifling

[Vaino]

Hi Paul....I don't doubt that a tight fitting over powder wad would obturate the bore and thereby improve the efficiency of the load. But...it's just something else to keep track of while hunting, so I wouldn't use it.

The "paler" whatever preceding the RB could be some gas escaping via the grooves but not in any great quantity....it would be diluted. Some gas would escape through the patch mat'l in the grooves just before the RB starts to move or slightly later and leakage would diminish as the RB proceded up the bbl.

My .54 cal. elk load uses a .535 RB w/ a .022 thick patch which more than fills the grooves, but I have some doubts whether it resists the gas pressure. Cloth isn't that hard and it stands to reason that 12,000 - 15,000 psi would force some gas past the patch mat'l in the grooves. This patch/ball combo does imprint the patch weave onto the ball, but isn't difficult to load.

I agree w/ Dan on the reason a RB doesn't compress... the inertia and friction aren't great enough.

Interesting discussion, but I do think that many MLers are shot using a "loose" patch/ball combo and are still fairly accurate....Fred

 

[zimmerstutzen]

BTW. Neatsfoot oil is obtained by boiling the shin bones of calves

 

[LaBonte]

BTW. Neatsfoot oil is obtained by boiling the shin bones of calves

Used to be, but since the 1930's most (if not all) is in fact made from hog lard - that info is per the manufacturers such as Lexol....

and mink oil is in fact from ranch raised mink - it's not a different form of neats foot oil and is in fact a different type of oil altogether than neats, etc.

 

[Dphar]

BTW. Neatsfoot oil is obtained by boiling the shin bones of calves

Used to be, but since the 1930's most (if not all) is in fact made from hog lard - that info is per the manufacturers such as Lexol....

and mink oil is in fact from ranch raised mink - it's not a different form of neats foot oil and is in fact a different type of oil altogether than neats, etc.

I know Neatfoots, in general, is no longer neatsfoot as would have been found in the past. I have read that is encompasses almost any animal fat oil. I am sure lard oil tops the list though given quantity available.
But Mink oil, if its rendered from mink fat is still an animal fat oil. But honestly I have not put any thought or research into it other than to know that the reduction in fur prices has surely reduced the number of mink being raised. If Mink oil has any large volume specialty use its likely is shorter supply than it was in 1955 or 1965. When there were mink farms all over the northern states. Wild mink are hardly worth catching right now based on prices listed for last year. But I have not looked at the current forecast. The various pastel etc mink colors found in farmed mink are likely higher than the 6-12 bucks I see in a quick search for wild mink.

Sperm Whale Oil is not a plant or animal fat and DOES have different properties as a patch lube. Its less slick than most Neatsfoot for example.
But its also unavailable unless one has ties to the Japanese whaling boats.

Dan

 

[LaBonte]

Almost all mink oil comes from China or teh former USSR, where they are heavily farmed and not the USA or Canada. It is also "different" than other animal fats being a palmitoleic (sp?) meaning it resists rancidity better than most other fats whether animal or plant based.

and yes Sperm whale oil is technically an unsaturated liquid wax not an oil, but it is still derived from the tallow and other fats of the whale and consists of a mix of fatty acids and fatty alcohols (Ballistol is in fact an early attempt to make an analog of whale oil). While whale oil is no longer legally available one can get jojoba oil which is almost identical in chemical composition to sperm whale oil. I've compared both (still have a VERY small amount of old pre-illegal whale oil which I keep for oiling my many times great grand daddy's 1872 pocket watch) and can't tell the difference in side by side comparisons as a patch lube. Any one wanting to try Jojoba oil, it is available commercially and Lexol Leather Conditioner is another readily available source that includes jojoba.

 

[cynthialee]

Now you guys got me wondering how well seal oil would work. I have an Inuit friend in Alaska who tried to get me to eat seal oil and whale blubber for years. :barf:

 

[Ordnancebob]

If one watches high speed video of modern cartridge guns one will typically see some gas escape the muzzle well in advance of the bullet.
This is because the bullet does not instantly obturate in the bore.
As well as a puff is initially seen at the breach as the cartridge case takes time to obturate in the chamber.
With our muzzleloaders again I expect in high speed video we would see a puff of gas well before the projectile as it would take time for the projectile to obturate in the bore. With a loose or incomplete forward obturation the amount and lenght of time of this initial puff of gas would very.

Sua Tela Tonanti
Ordnancebob

 

[LRB]

Is it gas or water vapor from the humidity and air compression that is seen? Modern bullets are typically larger than the bore. How would gas get around the bullet, as the bullet enters the rifling before the gas does? I seriously do not believe a copper jacketed bullet is going to expand to any measurable degree when fired, and certainly not after it is engraved during the initial entry into the rifling with it being over sized to start with. Assuming the bullet is the correct match for said bore, which will be .001, to occassionally .002 larger than the groove to groove size, in a jacketed bullet, or even lead. If there is any blow by, it would occur at the throat, and not on down the bore.

 

[Dphar]

If one watches high speed video of modern cartridge guns one will typically see some gas escape the muzzle well in advance of the bullet.
This is because the bullet does not instantly obturate in the bore.
As well as a puff is initially seen at the breach as the cartridge case takes time to obturate in the chamber.
With our muzzleloaders again I expect in high speed video we would see a puff of gas well before the projectile as it would take time for the projectile to obturate in the bore. With a loose or incomplete forward obturation the amount and lenght of time of this initial puff of gas would very.

Sua Tela Tonanti
Ordnancebob

If I remember correctly Sam Fadala's photos show FLAME before the patched ball. Unless a wad was used over the powder that would improve the seal.

Dan

 

[Dphar]

I guess Denmark or one of the other Scandinavian countries is heavy into mink ranching as well.
I did not bother to look at its properties.

Jojoba is also a liquid wax from what reading I have done and this should make it similar to Sperm Oil.
I still have almost a quart of Sperm oil apparently from an old Singer Sewing machine company 55 gal drum someone obtained years ago.
Dan

 

[Joel/Calgary]

and yes Sperm whale oil is technically an unsaturated liquid wax not an oil, but it is still derived from the tallow and other fats of the whale and consists of a mix of fatty acids and fatty alcohols (Ballistol is in fact an early attempt to make an analog of whale oil).

With respect, my understanding that the "sperm whale oil" used for precision lubrication was the lighter fraction of the liquid bailed from the "case" in the head of the whale, not that rendered from the blubber. The heavier fraction of this liquid was precipitated at low temperatures (it's all liquid at whale body temperature) and used for the best candles. It was quite different from the oil rendered from the body fat, which was much like that rendered from other whales' blubber and similar to other tallow oils, and was mostly used for lamp oil, again, as I understand it.

Regards,
Joel

 

[CoyoteJoe]

I believe you are correct in that LaBonte, true "sperm oil" comes only from the head of a sperm whale, "whale oil" is rendered from the blubber of any whale. True sperm oil is a much higher grade oil and much more expensive than whale oil as was used in lamps. That is what made the sperm whale the most highly prized.
There is no doubt that breechloaders employing bullets of full groove diameter or even larger do obturate the bore but there is likely still some initial blow by since the bullet must be somewhat smaller than the chamber and the bore is not filled until the bullet has moved from chamber into bore. The very best accuracy obtained by Dr. Mann in his early 20th century breechloading rifles still came from bullets of bore diameter which upset to fill the grooves just like their muzzleloading predecessors. Those were loaded either from breech or muzzle but were placed in the bore ahead of the chamber and easily beat any bullet seated in the cartridge case which had to first move from the chamber into the bore.
I too doubt a "perfect seal" is obtained by even a very tightly patched ball and I doubt a round ball upsets when fired, unless perhaps when loaded over a wad. Thus I don't doubt there is some escape of powder gas ahead of the ball, probably more so with a loose patch & ball combo, and of course the air in the bore will be compressed and expelled ahead of the ball.

 

[zimmerstutzen]

Dr, Mann's buddy, Harry Pope did him better by loading the cartridge full of powder after he muzzle loaded the bullet through a false muzzle. ie, no chamber throat or free bore to permit blow by.

My best accuracy in my trapdoor is obtained by seating the lead bullet out so far that closing the breech forces the bullet into the rifling.

You know if I I swing a bat at a 50 caliber lead ball and send it off at 70 ft per second, it still "obturates" from the blow. When a fired 50 cal lead ball hits the soft tissue of the game, it "obturates". I find it difficult to believe that a pure lead ball would not have it's shape altered in any respect by the multiple "G-forces" put upon it during firing. Just sayin.

 

[LRB]

When firing a ball, the ball is being pushed and not struck suddenly as in with a bat. The powder does not explode, but rather burns.

 

[zimmerstutzen]

The ball is pushed by the bat as well. Considering the nearly instantaneous additional G-forces when a rifle is fired, which provides more smack? I think perhaps the powder "pushing" the ball.

I remember jumping off the low diving board and landing on my belly. That soft cool water sure knocked the snot out of me, and I was barely moving compared to a rifle ball.

 

[LRB]

The bat striking the ball is instantaneous applied force, but the powder burn when you fire a ball is not instantaneous. If you strike a ball with a bat, it hits the ball as a high speed, high force collision. When you fire the ball from a gun barrel, the ball starts moving slowly as soon as the powder begins forming enough gas pressure to move it, with a gradual increase in velocity relative to the speed and amount of gas formation. It is being push started rather than being the stationary object in a hi speed collision with a force already in full motion, which is basicly what happens when a barrel bursts due to a short seated ball or obstruction.

 

[Joel/Calgary]

You know if I I swing a bat at a 50 caliber lead ball and send it off at 70 ft per second, it still "obturates" from the blow. When a fired 50 cal lead ball hits the soft tissue of the game, it "obturates". I find it difficult to believe that a pure lead ball would not have it's shape altered in any respect by the multiple "G-forces" put upon it during firing. Just sayin.

Sorry, but I just have to jump in here. "Obturate" is a technical term used in many areas of science and technology, it means to seal or stop-up something, and it is a transitive verb - something obturates something else. Those balls you're (hypothetically) hitting may indeed deform, flatten, bump-up, or whatever, but there is nothing for them to seal, so they cannot obturate anything.

This pedant really needs to get to bed.

Regards,
Joel

 

[Dean2]

Hate to say it to another Calgarian, but you are wrong. Obturate is correctly used in this case. It is the expansion of the lead ball and patch, to fill the lands and grooves and stop up the barrel so the gas does not exit before the ball. I am not convinced this happens with a patch and ball, but it does with hollow base/skirted lead bullets and conicals. With patch and ball it is the tight fit that stops up the gas behind it in the barrel, the ball does not expand when initially fired.

Detailed Explanation for those who are into that sort of thing.


Oturation in firearms ammunition. With reference to firearms and air guns, obturation is the result of a bullet or pellet expanding or upsetting to fit the bore, or, in the case of a firearm, of a brass case expanding to seal against the chamber at the moment of firing. In the first case, this both seals the bullet in the bore, and causes the bullet to engage the barrel's rifling. In the second case, it seals the case in the chamber and prevents backward travel of gases against the bolt. The thin brass case easily seals the chamber, even in low pressure rounds like the .22 CB, but expanding or upsetting the bullet sufficiently for effective obturation requires sufficient pressure to deform the bullet material. The formula used to calculate the pressure required for solid base bullets is:

Bullet's BHN x 9.80665 N/kgf×106 mm²/m² = [N/m²] = pressure in pascals
Bullet's BHN x 1422 = pressure in pounds per square inch[2]
The constant 1422 is a mathematically derived number. The number comes from converting the pressure in kgf/mm² (which are the units used to measure BHN) to lbf/in² (which are the units used to measure cartridge pressure). That is:

Conversion factor = 25.4 (mm/in) x 25.4 (mm/in) x 2.2046 (lbf/kgf) = 1,422.
Note that this number should only be used with cast lead plain-base bullets. It does not apply to jacketed or gas-check cast bullets. Below is a chart containing various bullet alloys, the BHN, and the PSI required to expand a bullet to the bore:




Material BHN Pressure (psi) (MPa)

Pure lead----- -5-----7,110---------49
1:20 tin/lead---10-----14,200-------98
1:10 tin/lead 11.5 16,400 113
Pure copper 40 56,900 392

Pure lead is very soft, and can be expanded or upset by most firearm cartridges, but the pressures required are higher than those encountered in most airguns. To allow obturation in airguns, pellets use soft alloys in conjunction with a thin, concave base designed to expand more easily. Some firearms ammunition, such as Foster slugs and hollow base wadcutter bullets, also use a hollow base to allow the bullet to expand and conform to a barrel's irregularities, even as the chamber pressure drops as the bullet travels down the barrel (see internal ballistics). For example, it is not uncommon for revolver barrels to have a slight constriction at the breech end where they thread into the revolver's frame; a hollow base bullet will expand to fill the larger diameter of the barrel after passing through the constriction.

To prevent excessive deformation in high pressure rifle and magnum pistol cartridges, lead bullets are often covered in copper or another harder alloy. These bullets are generally designed to swage to fit upon firing.

 

[Joel/Calgary]

With respect, I beg to differ. I forget which major cast-bullet site that is quoted from, but it still doesn't make this misuse of the term correct. It is just accepting the common but incorrect informal misuse of the term in internal ballistics (only) conflating one possible mechanism with a specific result. Various things can obturate the bore - tight wadding, tight patch & ball, projectile engraving at the breech or muzzle, or even deformation of the projectile on firing. For that matter, if the bullet is partially upset but this does nor seal the powder gasses, then the deformation of the bullet has NOT obturated the bore. Every internal-ballistics discussion I have seen in technical publications (admittedly not a large number) uses "obturate" just as in other technical and scientific areas - some object or mechanism obturates some other object or a system, which then may or may not directly include the original object (the obturator could be external to the obturated deformable vessel). The bump-up of a bullet may PRODUCE the obturation of the bore, but this deformation of the bullet is not the obturation itself, but is instead the mechanism producing it.

It is possible that I may be fighting a rear-guard action in the evolution of the English language, but in all other technical realms where obturate/obturation is used, it is used consistently.

Regards,
Joel

 

[Vaino]

I'm w/ you on this one.....Fred