Blow out hole on percussion guns

[Col. Batguano]

Maybe this is a question for the originals' section, but about a year ago I picked up a beautiful English 1858 vintage SxS double percussion rifle. Forward of the breech, where a vent hole would be for a flont gun, is a small threaded plug, which is bored through. It's very small. I didn't measure the diameter, but it looks about the size of a # 65 wire drill bit. The gun is not a conversion from being a prior flint gun. Obviously, upon ignition, gas vents out this hole. What is the purpose of it? To keep peak pressures down? It is a damascus twist set of barrels.

Sorry, no pics. I'll try to post some tomorrow

 

[BlackHillsBob]

boy did you open up a can of worms but thanks for it. its their for faster more positive ignition. when the primer fire goes in their is no back pressure building up and the fire advances faster and doesnt get blown back to the nipple. ive seen it on high end side locks from the 1840. their are nays sayers here that just cant believe that. well thats their problem. all the percussion side locks ive built ive done that to them. no complaints yet.

 

[Zonie]

You don't suppose the builder thought that venting the breech would help the flame from the percussion cap get into the chamber better do you?

Dixie gunworks tells people to drill a small hole in the drum on their percussion guns to do this. Black hills bob posted about drilling a small vent hole in the breech to do this.

Do you have any idea about when your rifle was made?

 

[arcticap]

I found a reference indicating that in caplocks, the vent hole was intended to relieve the back pressure of a sealed breech for safety reasons:--->>> http://www.blackpowder411.com/builder/tips-tools-with-fred-stutzenberger-part-20/

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...."

The caption for the Figure 1 photo below 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. "

 

[Col. Batguano]

As per your article, and coincidentally, the gun IS a James D. Purdey (made in 1858). And it looks almost exactly like that (different engraving though).

 

[arcticap]

That's an interesting coincidence.

 

[BlackHillsBob]

the one i saw was a 50 cal very very high end silver mounted 1/2 stock cap lock from the 1840/s.it has a tiny hole in back of the cumbustion chamber. i think it may have been platinum lined. ive done it to about 20 of guns ive built and a friend did it to his 11. he never ever has a missfire any more. now all the nay sayers will say if he cleaned and loaded right he wouldnt have the problem. so i will send his name and address to those who say that about him and they can work it out with him. he is a 6 ft 6 logger and loves that sort of thing, verbal or otherwise. you can work it out will him.as usual zonie has the most common sense reply of them all. thanks.

 

[52Bore]

I have 2 early originals that still leak thru the PT vent holes.

 

[fleener]

I would not shoot those old guns with leaks in them. I think you need to give them to me, and I will take care of them for you.

Fleener

 

[kansas_volunteer]

The pressure inside the barrel is equalen in every direction. So, the pressure of the gas exiting the hole will always be the same pressure as that inside the barrel. What that might have to do with back pressure i don't know.

Anecdotal claims the little vent Improves ignition does not prove the hole reduces misfires or does anything of value. Maybe by firing a hundred rounds from multiple rifes of identical construction, some vented some not, truly valid results could be obtained.

 

[smoothshooter]

I would not shoot those old guns with leaks in them. I think you need to give them to me, and I will take care of them for you.

Fleener

You guys are obviously in need of a third-party intermediary to receive the leaky guns in question from 52 Bore, thoroughly examine and extensively test fire them in the hunting fields and on the sporting clays ranges to ensure the guns in question are safe enough for Mr. Fleener to use.

 

[bang]

I found a reference indicating that in caplocks, the vent hole was intended to relieve the back pressure of a sealed breech for safety reasons:--->>> http://www.blackpowder411.com/builder/tips-tools-with-fred-stutzenberger-part-20/

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...."

The caption for the Figure 1 photo below 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. "

View attachment 9408

Ok. I somewhat understand. But what back pressure due they mean? Is it pressure build up from primer ignition hampering thermal travel or the back pressure from charge ignition? My initial take on it is to ease the expansion of the main charge to lower stress because it indicates the early days of percussion. Metal quality and such.

 

[arcticap]

I suppose that there could be multiple reasons for having the platinum vents on the early percussion guns since many have been speculated about as being valid possibilities.
There could be a primary reason and less important secondary reasons.
A search for photos of Purdey percussion guns shows many examples of guns built having them, and even some flintlock conversions can be found to have them.
Many of them appear to have a damascus barrel.
I don't know if there are any historical records left by Purdey or other original gun makers that list their reasons for installing them.
But at some point they stopped being routinely installed even on the Purdey guns.
Since the British guns were proofed, they must have been subject to some heavy loads during proof testing.
The reference that I mentioned above could have some expert historical knowledge or documentation but simply choose to not divulge any additional reasons for the vent being present.
I think that it's notable that for whatever reasons, current makers don't usually ever include such vent liners in their percussion builds even though they seem to have been more common during earlier times.
Perhaps advances in percussion caps, nipple design and metallurgy have rendered the the vent liners to become obsolete.
At least one person posted about how dangerous the hot gases are that exit from the vent which he witnessed to cause very serious injury to flesh.
And concern about moisture coming into contact with powder was mentioned as another reason for not installing one.

 

[bang]

I suppose that there could be multiple reasons for having the platinum vents on the early percussion guns since many have been speculated about as being valid possibilities.
There could be a primary reason and less important secondary reasons.
A search for photos of Purdey percussion guns shows many examples of guns built having them, and even some flintlock conversions can be found to have them.
Many of them appear to have a damascus barrel.
I don't know if there are any historical records left by Purdey or other original gun makers that list their reasons for installing them.
But at some point they stopped being routinely installed even on the Purdey guns.
Since the British guns were proofed, they must have been subject to some heavy loads during proof testing.
The reference that I mentioned above could have some expert historical knowledge or documentation but simply choose to not divulge any additional reasons for the vent being present.
I think that it's notable that for whatever reasons, current makers don't usually ever include such vent liners in their percussion builds even though they seem to have been more common during earlier times.
Perhaps advances in percussion caps, nipple design and metallurgy have rendered the the vent liners to become obsolete.
At least one person posted about how dangerous the hot gases are that exit from the vent which he witnessed to cause very serious injury to flesh.
And concern about moisture coming into contact with powder was mentioned as another reason for not installing one.

For sure would not want any body part near it. Being on lock side of flinter when it goes off can be bad enough.
Moisture too. Would have to be extremely small opening to still keep moisure out. So small that the relief privided would be essentially useless.
Considering barrels back then were flat plate rolled around rod and forge welded or damascus forge welded I'm going with metal quality and virtually primitive processes. The best NDT was ring test and proof load.

 

[Feltwad]

The vent hole on most percussion guns and rifles was never meant has a safety blow out device , the main reason for these were to act has air vent for faster ignition with the ignition of the cap ,on the later guns they were nearly all platinum but the early ones were screwed in iron ones The most early ones were patent by Samuel Nock enclosed are images of Nocks patent .
Feltwad
Nock Patent

 

[arcticap]

The vent hole on most percussion guns and rifles was never meant has a safety blow out device , the main reason for these were to act has air vent for faster ignition with the ignition of the cap ,on the later guns they were nearly all platinum but the early ones were screwed in iron ones The most early ones were patent by Samuel Nock enclosed are images of Nocks patent .
Feltwad
Nock Patent

I'm don't understand the connection between Nock's Patent Breech and the percussion vent hole.
Nock died in 1804 and his patent breech was dated 1787 which I thought was before the percussion era.
Did he design the percussion vent hole in the photos?

Do you think that the early percussion caps may have been much weaker than today's that led them to need an ignition boost?

 

[Rifleman1776]

Dixie gunworks tells people to drill a small hole in the drum on their percussion guns to do this

In the early days of this game, the DGW catalog was the 'bible' of muzzleloading and just about the only reference source available to most of us who were learning. However, as I gained experience it became apparent the things printed in the DGW catalog were often wildly incorrect and some potentially dangerous. Today, it is, IMHO, a source to be avoided and not trusted.
As for the vent/blow out plug, I find this thread very interesting even if the theories postulated and, to this day, unproven and highly debatable. I had always thought those platinum plugs were safety valves. e.g. "blow out" plugs. To me, seeing that 99.99% of all ml rifles and shotties, both originals and current builds do not have them, it seems that proves they are not worthwhile.

 

[Feltwad]

I'm don't understand the connection between Nock's Patent Breech and the percussion vent hole.
Nock died in 1804 and his patent breech was dated 1787 which I thought was before the percussion era.
Did he design the percussion vent hole in the photos?

Do you think that the early percussion caps may have been much weaker than today's that led them to need an ignition boost?

The patent breech was by Henry Nock the vent hole was patented by Samuel Nock who was Henry Nock nephew he died in 1851the screw in vent holes in the photos were guns built by Samuel Nock, I do not think that the early percussion caps were weaker .The first percussion caps were made of iron like a top hat shape with a fultimate compound and invented by Joshua Shaw, the first gunmaker to build a percussion cap gun was James Rowntree of Barnard Castle Co Durham England this he built for Joshua Shaw before 1817 when Shaw emigrated to America
Feltwad
Samuel Nock Percussion Guns

 

[arcticap]

Thank you for the information about Samuel Nock.
Oherwise I wouldn't have known that he patented it.

One reason for asking about the strength of original percussion caps is because I'm not aware of any of these percussion vents
being installed on military guns or muskets which used a stronger musket cap.

 

[Pete G]

I read somewhere that the plug was for safety in case of detonation. I believe that 200 years of experience have invalidated this concern.