Author Topic: Breech design question. (Read 4365 times)

Victor3 · « **on:** April 14, 2009, 02:20:26 AM »

I'm pondering a simple, removable breech design. Not necessarily for loading, but for cleaning if need be. Could be useful for rifled barrels if they get leaded near the breech.

All other considerations (sealing, ease of removal, etc) aside, would there be any problem with simply bolting a breech on?

For example, let's say a 1" bore with a 3" diameter 4130 steel breech. A 1" thick steel disk at the rear, attached with 4 x 3/8-16 cap screws (each having >100K psi yield strength), in an equally spaced bolt circle. Length of engagement into the breech, 1".

Would this present any problem if using screws that are designed for the type of stresses that would be encountered?

I know that the above is a little unconventional and doesn't 'sound right.' Aside from that, are there any engineering considerations that would make such a design unsafe?

Double D · « **Reply #1 on:** April 14, 2009, 03:36:32 AM »

Victor.

How do you achieve a seal?

Way back in the olden days when I was trying to make a living as a gunsmith and supplement my income by making cannons. Most of the cannons I made back then had a removable breech plugs. I made the breech plug like a big muzzleloader breech plug. Some had V threads later ones had acme threads. The back of the cannon from the rear reinforce back was the breech plug. The Breech plug was removed with a spanner wrench. The Parrots were just the cascable back. Some had a socket he set screw in the bottom of the barrel, most did not. I made 10 or 12 of these back in the late 80's. Several of these got some heavy firing while I was still in the area and no complaints other than the the set screws got lost. I did put anti seize grease on the threads.

Last time I heard about one was 8 or 8 years ago shortly before my friend in California died. I had built one for his friend. Ben told me his friend still fired the gun regularly and he had no problems.

GGaskill · « **Reply #2 on:** April 14, 2009, 11:27:26 AM »

In my experience, using a good grease like wheel bearing grease or something of similar consistency will prevent any leakage from the breech. One could also use something like the leather pad used in large bore bag artillery; put a metal disk at the rear of the chamber with a soft leather pad behind. The pressure will force the disk against the pad which will be forced outwards and seal the breech.

Cat Whisperer · « **Reply #3 on:** April 14, 2009, 01:43:55 PM »

WOW. Good question. Suggest this be a place to post alternative designs.

Suggest finer threads for maximizing strength, also better grades of bolts.

How about a sketch to start out with?

I'll do some work in AutoCAD. I think we could easily come up with a dozen designs, half or a quarter of which could be good designs.

There are ways of using the pressure within to effect the seal easily - by design. We NEED to explore these and apply the newer disigns to the older applications (blackpowder fueled cannons).

GGaskill · « **Reply #4 on:** April 14, 2009, 02:23:12 PM »

Actually even a rubber pad would likely work. Either rubber or leather would eventually need replacement I would think but not on a shot by shot basis. You could even design the breech such that the metal cap was captured between a shoulder at the back of the chamber and the front of the breech bolt.

And the use of an aluminum foil powder bag would pretty much complete the seal. It would probably be an effective seal even without the metal disk and leather/rubber disk.

Artilleryman · « **Reply #5 on:** April 14, 2009, 02:54:05 PM »

If I were to build a cannon with a removable breech, I think I would just go ahead with a breechloading design.

Blaster · « **Reply #6 on:** April 14, 2009, 03:18:11 PM »

Quote from: Double D on April 14, 2009, 03:36:32 AM

I did put anti seize grease on the threads.

I sure agree with DD on the anti-seize for the threads. Here's what I applied to the threads of the breech nut. Works well but can be kinda messy. I believe almost any auto parts store will carry this stuff.

GGaskill · « **Reply #7 on:** April 14, 2009, 04:43:21 PM »

I think I would just go ahead with a breechloading design.

The problem with most small breechloading designs is that they assume the use of a cartridge which brings big brother into the picture even if a cartridge can be found/constructed.

Victor3 · « **Reply #8 on:** April 14, 2009, 10:46:46 PM »

Well, my main point was about the bolted construction. I suppose it will be okay(?) I would use A286 screws, a common fastener material used to join jet engine sections together. Tough stuff that should be appropriate for this application.

On the sealing, I was thinking of an o-ring groove in either the end of the bbl, or in the rear bolted on plate. That way, the only extra piece required would be the o-ring, and it's easily replaced.

Along the lines of GGaskill's idea, I was also considering a 1/4" thick silicone 'washer' in the center of the rear plate, retained with a steel washer and bolt. This would put it all in one unit. The steel washer would squish the silicone seal into the chamber. Silicone washers should last a long time, and are easy to punch out of sheet stock. The diameter could be adusted with the bolt for a perfect fit in the chamber.

I think the simplest idea is GG's use of the foil cartrige base as the seal. If a form for the powder bag were made to make it close to chamber diameter, all that would need to be done (I think) is to add ~1/4" length of crumpled/flattened foil in the back end of the cartrige. This should seal it up nicely upon firing, and there would be no need of any extra parts.

In reality, if the breech face and rear plate were faced perfectly flat and assembled tight, I don't believe there would be much in the way of leakage or need for a secondary sealing element; not enough for there to be any danger of erosion by gas-cutting anyway. Yet another tip from GG - grease - should take care of that completely. Some of that sticky open gear lube goop should do it.

Victor3 · « **Reply #9 on:** April 14, 2009, 11:10:01 PM »

Quote from: Double D on April 14, 2009, 03:36:32 AM

Most of the cannons I made back then had a removable breech plugs. I made the breech plug like a big muzzleloader breech plug.

DD,

That would be my 1st choice, and the one I'm more prepared for.

The bolted construction is just random thought, but I wanted to bounce it off of you guys to see if it might be viable. It might help others who don't have access to equipment or tools to make big threads.

Double D · « **Reply #10 on:** April 15, 2009, 02:55:32 AM »

Something I have not seen for years is my book on those guns I made back in the olden days. The plugs were all single point cut-internal and external. I do not recall the thread size I used. All the cannons I made were 1 inch bore in 4 inch stock so I would guess breech plugs would have been 1 1/2-6 tpi or 1 3/4-5 tpi in the V threads. The Acme threads were a similar pitch. I didn't do alot of acmes as I was just learning them. A fellow named Doug Titus taught me how to do them. He showed me the set up, ground me a tool and gave me an acme thread guage---where did they go?

Doug was a millwright and not a Machinist, he fixed machines in the saw mills of northern California. I learned a lot from the man and only knew him a couple of months before I moved away and got a real job---or at least one that paid enough for me to eat regular.

cannonmn · « **Reply #11 on:** April 15, 2009, 09:38:31 AM »

I can't find the pictures I posted a few mos. ago of our removable-breech 40MM blackpowder cannon, but we just never worried about doing anything other than closing the breech with a screw plug. We shoot it and there doesn't seem to be a problem,. despite having no special gas seals.

gary michie · « **Reply #12 on:** April 15, 2009, 11:02:33 AM »

Hi:

If I was going to install a breech plug, I think I'd put a copper washer at the rear of the powder chamber, backed up with the plug. The plug would have buttress threads single point cut ;like Whitworth invented for just such use. Buttress threads are VERY strong and as you back them off free up, the first form of anti seize.

Victor3 · « **Reply #13 on:** April 16, 2009, 10:59:39 PM »

Quote from: Cat Whisperer on April 14, 2009, 01:43:55 PM

I'll do some work in AutoCAD. I think we could easily come up with a dozen designs, half or a quarter of which could be good designs.

CW,

I'm glad you mentioned AutoCAD. I haven't been able to open my LT for about a year for some reason. Now that I've installed a bunch of Windows updates (to get TurboTax to load), I tried it and it's working again.

Now get off that thundermug and make some pictures.

Cat Whisperer · « **Reply #14 on:** April 17, 2009, 12:05:37 AM »

I have a .50 bore cannon with a breech plug. The copper disk (washer) is on the end of the plug. It tightens against a shoulder, sealing the breech. In theory it should work. It practice it leaked some (evidence of blowby). Seal depends on how tightly the plug is torqued vs how much pressure trying to push it open.

I like the concept use in our 155/Self-propelled howitzers. The pressure pushes against a stainless 'bowl' which is filled with a neoprene. The backward pressure squeezes the neoprene out to the sides effecting the seal. More pressure, more sealing effect.

I think that concept could be used to push an o-ring into place.

moose53 · « **Reply #15 on:** April 17, 2009, 03:50:57 AM »

A very effective design with 100% seal ( no blow by ) . Easy to make with a lathe , or drill press if you want to work at it a bit more. Rear disk doesn't have to be copper. The rubber plug was finished shaped a with a air sander.

http://www.gboreloaded.com/forums/index.php/topic,93883.0.html Reply #6

Double D · « **Reply #16 on:** April 17, 2009, 04:14:54 AM »

Are we talking apples and oranges here?

Victor, is the breech design you opened the discussion with a breech loader or a muzzle loader?

I can see the need for seal in the breech block of a breech loader, I don't see the need for a copper or rubber seal in a properly made breech plug in a muzzleloading cannon.

Cat Whisperer · « **Reply #17 on:** April 17, 2009, 04:59:41 AM »

The seal (should) keep the corrosive elements from combustion out of the threads.

Double D · « **Reply #18 on:** April 17, 2009, 05:17:38 AM »

A properly made breech plug face will seat in the bottom of the breech plug recess. The seating/sealing takes place on the face of the breech plug at the rear of the chamber on the breech plug seat and not at a shoulder of the plug the rear of the barrel. There may even be a slight gap at the shoulder ala Mauser barrel fit.

This eliminates gas flow back up threads.

gary michie · « **Reply #19 on:** April 17, 2009, 01:24:51 PM »

Hi:

The reason I said copper washer is that Whitworth and armstrong both used them in there rifles, the whitworth when not breech loading and I think the armstrong just used one.

Frank46 · « **Reply #20 on:** April 17, 2009, 04:46:27 PM »

I have some copper flashing I got at the local junk yard. i use it when I don't want any marks on the machined surfaces. Don't know how thick it is as I wrap the item a few times to prevent the chuck jaws from digging into the finished surface.
When I worked for a living at the generating station I would come upon a much thicker copper that was used as gaskets. About 4-5" wide and about 3-4' in diameter. Still have a few pieces laying around. Make up your bolt then cut your copper gasket just slightly oversized, then drill and tap for something like 8x32 and use copper nails from the local boatyard or boat supply house. Thread the nails and then rivit the heads. This way your gasket won't be going anywhere soon. On steam lines we use a "flexitallic" gasket which was circular and in between the circular windings was a insulation material. Once these gaskets had been compressed they had to be replaced as they would no longer provide a good seal. Many's the time I had to tru up a damages gasket surface on a flange that had been cut by steam. Hours of figure 8 motions with an oil soaked stone to lap out the channels cut by the escaping steam. A flexitallic gasket would probably work and be easier to replace when it no longer sealed. Frank

Victor3 · « **Reply #21 on:** April 17, 2009, 10:12:02 PM »

"Victor, is the breech design you opened the discussion with a breech loader or a muzzle loader?

I can see the need for seal in the breech block of a breech loader, I don't see the need for a copper or rubber seal in a properly made breech plug in a muzzleloading cannon."

Could be for either really. Just exploring removable breech designs that might be safer and more convenient than a fixed one. A secondary sealing element might not be required for some designs, but it couldn't hurt, right?

Some may be asking "why a removeable breech in a muzzle-loader?"

I think an easily removable breech could be handy for cleaning between shots, even in a muzzle-loader. It would be easier (and I believe safer) to have the bore clear to swab it through. No need for worming, and you're guaranteed to extinguish any remaining embers before the following shot.

You could of course leave the breech attached while shooting and remove it at the end of the day for a final cleaning.

Also, for bore/chamber inspection on a deep, small diameter bore with a fixed breech, it can be hard to see what's going on down there. Depending upon the construction of the chamber bottom, it can be hard to clean. I'm sure that some chambers with a flat bottom (as in a plugged sleeve design) are not cleaned completely by their owners as it would require a special scraper to get gunk out of the corner. This could eventually lead to combustable residue building up (especially if using loose powder), and a higher possibility of corrosion that can't be easily detected nor removed.

Another reason for a removable breech might be ease of manufacture for some folks. Not everyone has the equipment and/or skill required to fabricate a safe heat-shrunk & welded breech. However, a guy with a lathe can usually cut ID/OD threads, or at least bore & tap a hole for a plug made from a bolt.

Victor3 · « **Reply #22 on:** April 17, 2009, 10:59:24 PM »

Quote from: Double D on April 17, 2009, 05:17:38 AM

A properly made breech plug face will seat in the bottom of the breech plug recess. The seating/sealing takes place on the face of the breech plug at the rear of the chamber on the breech plug seat and not at a shoulder of the plug the rear of the barrel. There may even be a slight gap at the shoulder ala Mauser barrel fit.

This eliminates gas flow back up threads.

There's a lot of geometry (thread form/fit, parallelism of faces, etc) going on that determines if the seal will be perfect or not.

Using a replaceable seal between the seating surfaces makes up for any error in machining and/or wear that's sure to happen over time.

Double D · « **Reply #23 on:** April 18, 2009, 04:25:24 AM »

Flush sealed tight fit is achievable in Muzzle loader rifles and pistols... Then Gary Michie says Whitworth and Armstrong used breech plugs with copper seals with there RML's... that tells me there are different issues at play in the larger cannon.

In breech plugs that were constantly removed for loading and field cleaning, it is obvious the amount of force needed to seat them could not be to great or personel in the field would not be able to remove them. The greater surface area of the larger breech plug would also make it difficult to get an adequate seal the greater pressures without some sort of gasket material.

Maybe I should rethink my breechplugs.

Cat Whisperer · « **Reply #24 on:** April 18, 2009, 07:06:35 AM »

From the .50 cal cannon that has a threaded plug pushing against a shoulder squeezing the copper disk washer, I think the presure from firng either or both stretches the action or compresses the bolt such that there is some leakage. Square thread would be better.

As with the pictures posted earlier, there are designs that use the pressure to increase the seal as the pressure is increased. That to me is smart.

cannonmn · « **Reply #25 on:** April 18, 2009, 01:35:28 PM »

Here's one way to help seal the breech. Make the cannon with a seating surface at the rear of the chamber as you can see in this cannon, made from a 40MM Army cannon barrel. If you want to do more to prevent any gas leakage, the simple addition of an O-ring or whatever your favorite kind of gasket is, should work fine.

We've fired this one many times and havent' had any noticeable gas leakage past the threads, so we haven't bothered to put any other kinds of sealing in place. We haven't had any powder fouling of the threads either, so maybe the system "as built" is good enough.

The carriage is home-made out of oak and hardware store stuff. It is pretty much an exact copy of a USLSS "Lyle" gun carriage, except for the elevating screw.

My friend Ed (the "star" of "cannonmn" videos on you-tube,) who built this gun, shoots various projectiles in it. One type is the rear half of a Navy 40MM projectile with copper rotating band removed, and replaced by a lead band he epoxies on in the knurled groove left when the original band is removed. He buys lead sheet or strip that fits the groove somewhere, and wraps it around a couple of times until the rotating band it forms is the correct diameter. Cast lead projectiles work well too. He has used a short, separate section of the rifled 40mm barrel to cast lead projectiles, so of course they come out of that mold already rifled. The adjustable rear sight is from a US Krag rifle ca. 1898. The front blade sight is also some kind of rifle sight, I've forgotten exactly which weapon it came from...

Since my company is now a sponsor I guess we can say that we sell 40" lengths of this type cannon barrel for $399. plus shipping, or one 20" length for $249. plus shipping. The bores are new, unfired, and usually still have cosmoline in them.

Victor3 · « **Reply #26 on:** April 18, 2009, 10:39:14 PM »

Quote from: Double D on April 18, 2009, 04:25:24 AM

Flush sealed tight fit is achievable in Muzzle loader rifles and pistols... Then Gary Michie says Whitworth and Armstrong used breech plugs with copper seals with there RML's... that tells me there are different issues at play in the larger cannon.

It's "achieveable", but I wonder how often it's accomplished.

A metal to metal seal in a ML rifle breech plug has to be made along with a close fit between the exposed area (ahead of the tang) and the end of the barrel. Otherwise it looks crummy with a gap. It takes careful fitting to get a compression seal, no external gap, and also have the tang line up where it's supposed to be.

As evidenced by a few plugs I've seen from Italian ML rifles, they go for a nice cosmetic fit outside, and let some kind of goop make the seal in the threads, not a tight fit at the front end of the plug.

I've read that similar was done on some original military rifles; pine tar or asphalt on the threads was relied upon for the seal. It's not like they were going to need to be removed very often. Unlike cannons, rifles were sometimes viewed as disposable items (if replacements were plentiful).

Double D · « **Reply #27 on:** April 19, 2009, 05:17:43 AM »

Quote from: Victor3 on April 18, 2009, 10:39:14 PM

It's "achieveable", but I wonder how often it's accomplished.

Often!

Quote

A metal to metal seal in a ML rifle breech plug has to be made along with a close fit between the exposed area (ahead of the tang) and the end of the barrel. Otherwise it looks crummy with a gap. It takes careful fitting to get a compression seal, no external gap, and also have the tang line up where it's supposed to be.

At the Gunsmithing school-College attended in the scratch built black powder rifle construction classes were were taught breech plug construction and all plugs were designed to seat solid on an inner seating ring at the back of the chamber. The plug seat and the face of the breech plug were machine cut. The hole was slightly deep. The back of the barrel was then spotted and filed until the face of the plug contacted the seat and there was slight contact at the rear of the barrel. The breech plug was then set with a breech plug wrench. The barrel if octagon was then used as a mandrel and put in the milling machine and the profile, reliefs and tang were machined. Later the tang was shaped and and bent.

The fitting process is very similiar to how a Mauser barrel is fit. The face of the barrel contacts the barrel seat at the bottom of the threads inthe action. The shoulder of the barrel does not contact front of the action, there being about .001 gap.

Quote

I've read that similar was done on some original military rifles; pine tar or asphalt on the threads was relied upon for the seal. It's not like they were going to need to be removed very often. Unlike cannons, rifles were sometimes viewed as disposable items (if replacements were plentiful).

We were told pine tar and asphalt were early anti sieze and the application of heat would melt them for plug removal.

That's small arms. The key to fitting the breech plug was setting it with a wrench. It was also supposed to take out the slack in the threads. If the pressure was on the tang and back of the barrel there could be slack in the threads and firing could cause excessive set back and leakage. It is the technique I used with the cannon breech plugs I built. Early in their life none of the breech plugs showed signs of leakage. The only problem was the socket head set screw I used on some kept falling out.

I have never been able to wrap my head around the my mind around that slack bit...it seems to me that the pressure isthe same for both seating points.

After Gary Michie's comments I got to thinking about the physics. The tremendous amout of torque that would be need to seat the plugs plus the greater surface area and the increased effect pressure has on this larger surface area puts in place a whole other set of dynamics.

I think this clearly demonstrated by the various efforts made to seal the breech plug using gaskets and obdurating ring in large bore guns.

Victor3 · « **Reply #28 on:** April 19, 2009, 08:27:08 PM »

Thanks for the explanation DD...

"The plug seat and the face of the breech plug were machine cut. The hole was slightly deep. The back of the barrel was then spotted and filed until the face of the plug contacted the seat and there was slight contact at the rear of the barrel. The breech plug was then set with a breech plug wrench. The barrel if octagon was then used as a mandrel and put in the milling machine and the profile, reliefs and tang were machined. Later the tang was shaped and and bent."

From your experience doing it correctly, it can be seen how labor intensive it is, and why it's not always done that way in high volume settings. I know for a fact that some modern copies are not done the way you describe. I've seen them. (99% of the time, nobody will ever know the difference since the plugs are rarely removed).

You have the knowledge and experience. However, for a guy building from his 1st kit and fitting a pre-machined plug in his garage, I figure it may get done right......... Once in a while..... Maybe.

gary michie · « **Reply #29 on:** April 20, 2009, 02:47:31 PM »

Hi:

I feel that the seal was a big problem for the first breech loaders. If you look at all the drop-ins, screw on, or ins, wedge its, and like the Whitworth a rotateing hammer,There must have been a leak problem. On smaller cannons you may get along fine with what would not work on a larger scale.