From whence the myth of the dangerous air gap?

[DocRock]

From the 1880s through the first world war, schuetzen competitors frequently breech seated bullets, either loading from the muzzle end, or using devices to do so from the breech end. Breech seating means that the bullet is not just loaded into the lands, but is sufficiently far into the barrel to fully engrave and thereby seal the bore. There are accounts in old timey gun rags of chaps thus seating bullets as much as 3/8" ahead of a case mouth full of black powder, albeit often with a few grains of pistol powder to duplex the load and promote cleaner burning. Roberts, De Haas, Sharpe and others all discuss the process and none of them, nor contemporary gun rags, discuss the terrors of the dreaded air gap.

Why?

In virtually every post in which a newbie is asking about loading black powder, the warning about the catastrophic effects of an air gap, from ringing the barrel to mayhem and death, are passed on. And, yet, for some 140 years, it has been common practice among an admittedly small and esoteric, if not hermetically sealed, community of single shot rifle fans and schuetzenvolk. Indeed, I have been getting to know my recently acquired tesching built on a mini-1871 Mauser receiver in 9.5x47R and have been breech seating with a plugged case and using propellant cases with 45-50 grs black powder and an air gap of about an eight of an inch to 250 grs greasers and paper patch, to no ill effect whatsoever and some growing signs of accuracy. I experimented with breech seating with my 45-70 RB replica, 73 grs of 1.5 Fg behind 500 grs paper patched slicks and 1/8" - 1/6" of gap and, while I abandoned the effort having found the Postel bullet shot much better conventionally loaded, again, there were no ill effects.

So, where does the myth of the dangerous genius air gap come from, or, given that where there is smoke, there is fire, what are the circumstances that gave rise to this concern and warning?

While speculation is welcome, if anyone has access to early source material documenting the concern and warning, it would be greatly appreciated.

 

[arcticap]

I don't really have an opinion either way, but "the myth" against leaving air space is only a caution as something to avoid.
It seems controversial enough that even the modern experts disagree.
Perhaps things were learned since the advent of smokeless powder that serve as a basis for the warning.
Or better steel has negated many of the reasons why it's recommended to avoid air spaces.
Maybe the concern involves the combination of both hard fouling accumulating in the barrel along with the many variables of individual load construction.
Even if the myth only promotes better accuracy and consistent shooting results, that alone may be a valid enough reason for the myth to be perpetuated.

In one thread there are a some posts that mention that barrels do or can get ringed.
One was by Jim Watson in Post #16 in the thread link below.

And in the BPCR.net reloading guide, the author mentions that it's a matter of caution since:

"Recently there has be quite a few reports in the USA concerning modern BPCR which have suffered "rings" or "bulges" in their barrel or chamber region.

All these have been cause when smokeless powder loads were being fired.

Such damage can of course be caused by black powder as well but NEVER when a BP charge is made which has zero air space inside and when there is NO obstruction inside the barrel." --->>> SEE POST #25 https://www.thehighroad.org/index.php?threads/bp-load-compression.648625/

 

[Dave T]

It's what I've always been told, and I admit I've passed it on many times. I don't have any answers but wanted to thank DocRock for raising the question. arcticap's post is interesting and I look forward to hearing from others.

Dave

 

[wmgeorge]

MuzzleBlasts magazine ran an article a few months ago that pretty much debunked the ringed barrel with BP. Your going to need to read the article and testing and draw your own conclusions.

 

[.38 Special]

MuzzleBlasts magazine ran an article a few months ago that pretty much debunked the ringed barrel with BP. Your going to need to read the article and testing and draw your own conclusions.

Just what I was going to say. For those who don't have access, the authors essentially did everything they could think of to damage a barrel with a short-started or inadequately seated ball and didn't even come close. It was only when they loaded normally and then short started another ball that they were able to get satisfactory explosions.

<edit> It seems to me that Sam Fadala undertook a similar exercise a few decades ago. I will dig through some books when I get home to see if I can find it.

 

[J-Bar]

"Myth" may not be the best term. There are enough examples of ruptured or ringed barrels caused by trying to shoot out a short-started ball or squib to justify some concern about space or "air gap" between powder and projectile. I spent some time today scanning through Ned. H. Roberts book, "The Muzzleloading Cap Lock Rifle" trying to find any discussion about air gaps, and was unsuccessful. Mr. Roberts, his uncle Alvaro, and all the blackpowder gunsmiths he quotes in his book simply assume the ball is going to be seated all the way down onto the powder. There is a lot of discussion about how much compression is needed for accuracy, which makes for interesting reading, but does not answer Doc Rock's question. The rule about eliminating air gaps must be a very old one.

The explanation that makes the most intuitive sense to me goes like this: A bullet or ball, whether in a muzzle loading gun or in a brass cartridge, that is quite close to the powder charge can begin to move before the powder is completely burned. The bullet's inertia is overcome by a lower pressure wave as the powder begins to burn, so that the bullet can accelerate down the barrel as the pressure behind it increases. (Look at any loading data for any cartridge caliber: as bullet weight goes up, maximum powder charge goes DOWN. It takes a while for the bullet to start to move. Heavier bullets have more inertia, so pressure rises to the maximum with less powder.) If the bullet or ball (or mud or snow in the barrel) is a significant distance from the powder, then the powder can burn more completely before the pressure wave hits the bullet, which has now become essentially an immovable obstruction. The obstruction cannot move out of the way of the expanding gasses fast enough, and the barrel may fail...getting ringed or blowing out.

So the problem of air gaps must be a matter of degree. A little gap is OK, a big gap might be a problem. How much gap is too much? When does an air gap become "significant" enough to be dangerous? I think there are too many variables to make a rule. Variations in caliber, projectile weight, barrel thickness, powder charge granulation and volume, lubrication, etc. etc. would all come into play. How to make sure there is never a problem? Just don't allow any air gap in the first place.

Eliminating air gaps is not a myth. It is simply a good rule of thumb that errs on the safe side because there are so many other variables coming into play if an air gap is allowed.

 

[.38 Special]

I suppose I regard it about the same as the "detonation" phenomenon sometimes ascribed to small charges of fast burning smokeless powder. We know that something is going on, but we don't know exactly what, and it doesn't appear that anyone has ever been able to make it happen on purpose.

 

[DocRock]

"Myth" may not be the best term. There are enough examples of ruptured or ringed barrels caused by trying to shoot out a short-started ball or squib to justify some concern about space or "air gap" between powder and projectile. I spent some time today scanning through Ned. H. Roberts book, "The Muzzleloading Cap Lock Rifle" trying to find any discussion about air gaps, and was unsuccessful. Mr. Roberts, his uncle Alvaro, and all the blackpowder gunsmiths he quotes in his book simply assume the ball is going to be seated all the way down onto the powder. There is a lot of discussion about how much compression is needed for accuracy, which makes for interesting reading, but does not answer Doc Rock's question. The rule about eliminating air gaps must be a very old one.

The explanation that makes the most intuitive sense to me goes like this: A bullet or ball, whether in a muzzle loading gun or in a brass cartridge, that is quite close to the powder charge can begin to move before the powder is completely burned. The bullet's inertia is overcome by a lower pressure wave as the powder begins to burn, so that the bullet can accelerate down the barrel as the pressure behind it increases. (Look at any loading data for any cartridge caliber: as bullet weight goes up, maximum powder charge goes DOWN. It takes a while for the bullet to start to move. Heavier bullets have more inertia, so pressure rises to the maximum with less powder.) If the bullet or ball (or mud or snow in the barrel) is a significant distance from the powder, then the powder can burn more completely before the pressure wave hits the bullet, which has now become essentially an immovable obstruction. The obstruction cannot move out of the way of the expanding gasses fast enough, and the barrel may fail...getting ringed or blowing out.

So the problem of air gaps must be a matter of degree. A little gap is OK, a big gap might be a problem. How much gap is too much? When does an air gap become "significant" enough to be dangerous? I think there are too many variables to make a rule. Variations in caliber, projectile weight, barrel thickness, powder charge granulation and volume, lubrication, etc. etc. would all come into play. How to make sure there is never a problem? Just don't allow any air gap in the first place.

Eliminating air gaps is not a myth. It is simply a good rule of thumb that errs on the safe side because there are so many other variables coming into play if an air gap is allowed.

This sounds very plausible and would explain why breech seating not only does not cause ringing but is deemed a mechanism to enhance accuracy, while larger air gaps could be catastrophic.

 

[OrangePwrx9]

Probably a question of degree; a small airspace being harmless while a large one is destructive.

I have ringed a barrel on a TC Black Mtn Magnum. Short started a conical. It was only about 4" from the muzzle when the deed was done. Charge was reasonable, my shoulder doesn't like more than 90 gr of Pyrodex. Didn't know I did it at the time, just knew that a barrel that had shot excellent groups with conicals suddenly became very inaccurate after an odd/weak sounding discharge. Became aware of what I'd done when I went to clean the barrel.

After sending the barrel back, TC agreed with my assessment but replaced the barrel free of charge anyway. Felt terrible about it partly because the gun shot conicals like a champ.

 

[Navy Six 2]

Several years ago The Black Powder Cartridge News periodical had an informative article about this subject. I wish I could remember the details, but as we are now up to issue # 109, it will take me some time to locate that particular one.

 

[whisler]

The article in Muzzle Blasts stated that they short started the ball only the length of the short starter so a very large air gap. They used charges up to 150 grains of 3F with no detriment. They even used an old Damascus barrel and could not ring it. Fully loading the gun and then short starting another ball did damage things. In fact it blew the Damascus barrel apart.

 

[skeeterfogger]

IMO a gap ahead of the powder of negligible distance is very different than a starter distance from the muzzle. Add in the amount of charge too. As far as right off the charge I consider the comparison of head space in modern. Ive shot rounds that when closing the bolt it feels like the projectile is being either pressed into the riflings or pushed back in the case. In other words a snug bolt. I've read about rifles that actually shot better with a jump to the riflings. So I think one has to consider how much air gap is considered questionable and the charge.

 

[Armored farmer]

You cant compress water, or oil, or metal, or many other substances. You can , however, compress air. It doesnt take much powder to cause a pressure spike large enough to banana peel a barrel.

I offered to volunteer at s Christian event focusing on getting kids involved in outdoor hobbies like hunting and fishing. I was assigned to oversee a blackpowder rifle shooting booth as one of many stations where the kids could get 'hands on' experience.
Kids were standing in line to shoot a t/c inline .50 muzzleloader. A couple of younger 20something guys were running the booth, one of them owned the rifle. After several shots the rifle started getting difficult to load. I was talking to the kids and keeping an eye on the loading procedures. Soon the guys were trying to hammer another slug/plastic wad combination down the bore....but it hung up about a foot down.
"I'll shoot it out" was the solution of the gun owner as he proceeded to cap it with a 209 primer. The kids were beginning to get backed up at our location because they had been struggling with the gun. There was probably more than a dozen kids standing nearby. I finally had to become assertive that nobody was going to fire that gun until the barrel was cleared.
That day, the kids learned how to remove a breech plug and clear an obstruction. A couple of wet-behind-the-ears young men learned how not to blow up a gun with two 50gr pyrodex pellets.

 

[skeeterfogger]

You cant compress water, or oil, or metal, or many other substances. You can , however, compress air. It doesnt take much powder to cause a pressure spike large enough to banana peel a barrel.

I offered to volunteer at s Christian event focusing on getting kids involved in outdoor hobbies like hunting and fishing. I was assigned to oversee a blackpowder rifle shooting booth as one of many stations where the kids could get 'hands on' experience.
Kids were standing in line to shoot a t/c inline .50 muzzleloader. A couple of younger 20something guys were running the booth, one of them owned the rifle. After several shots the rifle started getting difficult to load. I was talking to the kids and keeping an eye on the loading procedures. Soon the guys were trying to hammer another slug/plastic wad combination down the bore....but it hung up about a foot down.
"I'll shoot it out" was the solution of the gun owner as he proceeded to cap it with a 209 primer. The kids were beginning to get backed up at our location because they had been struggling with the gun. There was probably more than a dozen kids standing nearby. I finally had to become assertive that nobody was going to fire that gun until the barrel was cleared.
That day, the kids learned how to remove a breech plug and clear an obstruction. A couple of wet-behind-the-ears young men learned how not to blow up a gun with two 50gr pyrodex pellets.

Please tell me you made it home with the weapon no longer in their possession. That is insane.

 

[Armored farmer]

Please tell me you made it home with the weapon no longer in their possession. That is insane.

No, it belonged to one of the guys (son of a friend). I did however leave him with a new understanding of compressed air in a gun barrel.
He wasn't too happy that I made him backpedal in front of those kids.

 

[Dave T]

A bullet/projectile any distance from the charge (several inches to somewhere down the barrel) becomes nothing more than a barrel obstruction. I think J-Bar has struck the nail upon the flat part.

Dave

 

[TheRodDoc]

This guy tested the air space thing in his own hand made muzzle loader. He didn't say what this barrel was made from, but other barrels he has made were made from of the shelf DOM tubing.



Here is his overload video with the same barrel. No stock on it though.

 

[whughett]

The mystery to me is how the column of air trapped between the projectile and powder charge gets compressed to where it’s creating more pressure than the powder charge. In the millisecond of combustion would not it’s oxygen be consumed by the burning of the black powder charge and the space be filled by expanding gases. I can vaguely comprehend that if the column is long enough It’s pressure might increase, but greater than the force needed to make that increase, sure above my education level.

 

[DocRock]

Thanks for lots of good input. The emerging consensus seems to be that there is no “myth” rather a question of degree. That large gaps seem to be dangerous, perhaps because they allow creation of two forces, a compressed air wave followed by the expanding propellant gasses from black powder. This is particularly true in muzzle loaders. Small gaps, such as in breech seating bullets do not seem to allow for this effect and while there are examples of gaps up to 3/8” and more without calamity, the rule of thumb guidance of 1/16” to 1/8” would suggest an awareness that keeping the gap small is important. This all seems to suggest that the warnings about the dangerous air gap are valid and that erring on the side of caution is the side to err on.

 

[Catman42]

i ringed a new good quality stainless steel barrel because of a air gap. did it with pyrodex which is not supposed to ring a barrel. its not a myth, it can happen. that is why the oregon rifle barrel co. uses a tiny amount of lead in the muzzleloading barrel so they dont burst if their is a air gap. they bulge. then you have to get a new barrel. dont get a air gap. you will ruin what you have. it is proven science. not B.S. ask me i did it. had to make a carbine out of a long rifle because of my neglect. also my dad old 1920/s 22 long rifle. had a ringed barrel because of a obstruction in the bore. it is retired and only to look at now. you can ring a chamber in any gun if you are not careful. air gaps are bad. and they cost a truck load of money to do over. im not afraid to admit i did it, maybe it will save someone here for doing the same.

 

[arcticap]

There was a long thread about the reason for these platinum plugs with a vent hole being placed in some original high end muzzle loaders.
It was not without controversy since Dixie recommended that folks drill similar holes in their drums as a way to improve percussion cap flash into the powder charge.
However most references seem to claim that it was a blow out hole, a safety feature to relieve back pressure in the Damascus barrels. --->>> http://www.blackpowder411.com/builder/tips-tools-with-fred-stutzenberger-part-20/



The caption for the Figure 1 photo above states:
" Fig. 1
In the early percussion days, it was feared that a completely sealed breech would be under too much pressure for safety.
A platinum vent was inserted in the breech under the nipple to relieve pressure.
Observe the shape of the vent hole that was designed to be removed with a turnscrew. "

Within the text of the article is states:
"...For the caplock shooters, I should mention that James Purdey, one of the most famous of the British gunmakers, also put platinum vents into his percussion breeches (Fig. 1) to relieve back pressure...."

 

[Catman42]

articap, mi cannot thank you enough for bringing up the science and the picture and the reply. years ago when i saw with my own eyes such a thing then read about it i put it on every one of the 15 sidelocks i built for customers. it cause a more sure ignition as it relieves the back pressure created by air trapped behind the patched ball. i also found for what reason i dont know that the breech ares of the back of the barrel was cleaner after each shot. i think it provided faster ignition also. im sold on the idea. i had a customer i sold a gun to in upper new york who has eleven side locks beside the one i sold him. he said he could never get them to fire consistently. i could not tell you if he did every thing perfect or not in loading and reloading but when he drilled a tiny hole at the point showed on your picture he never ever had a miss fire again. i never bring up what you just did as ive experienced dozens of naysayers who want to hang me for doing so. everything from your just plain dumb to you just ruined a good gun. i'll back you, ive used it and i like it. i cant thank you enough for that reply.its old science that works and should be revived again.

 

[dave951]

A Sharps has a BIG air pocket by design and filling the space with filler kills accuracy. The air gap "myth" isn't exactly what I'd call a myth but in most muzzleloaders, the projectile should be seated on the powder as most black powder guns perform best with a degree of powder compression.

 

[woodnbow]

Probably a question of degree; a small airspace being harmless while a large one is destructive.

I have ringed a barrel on a TC Black Mtn Magnum. Short started a conical. It was only about 4" from the muzzle when the deed was done. Charge was reasonable, my shoulder doesn't like more than 90 gr of Pyrodex. Didn't know I did it at the time, just knew that a barrel that had shot excellent groups with conicals suddenly became very inaccurate after an odd/weak sounding discharge. Became aware of what I'd done when I went to clean the barrel.

After sending the barrel back, TC agreed with my assessment but replaced the barrel free of charge anyway. Felt terrible about it partly because the gun shot conicals like a champ.

I felt the same way after Chrony replaced the screen on my F1 shooting Chrony. I’d damaged it by hitting it with a .54 caliber felt wad fired behind a roundball. They actually had a warning about protecting the screen when shooting black powder, which I ignored and the results were predictable but they wouldn’t cash my check... great company. As was TC...

 

[Catman42]

i like to hear that im not the only one who has done something we only like to read about. thanks for those replys.