12 gauge chamber inserts...

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TripleF said:
I would think CanAm has a good perspective into what sells, caliber wise. So any caliber that is popular would be a good start. Plus, I have not seen anyone in Canada that sells these (lately or at all) or I am not looking hard enough. And I much rather spend my cash in Canada than south of the border.
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Yes.
 
smellofspentcasings said:
I want two 45/70's inserts to make a poor mans double gun.
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I think a lot of the larger and/or more powerful calibers would produce too much pressure on the action. a .73 bore shotgun at has a .42in^2 surface area, at 11500PSI that produces 4800 pounds of force on the action. That's the SAAMI limit.

a .44 magnum has 0,144in^2 of surface area, at 36000PSI that produces 5200 pounds of force. Already over spec for the shotgun. These are available - a bit odd since they could in theory produce excess pressures.

.45-70 has 0,165in^2 of surface area, at trapdoor levels of 28000PSI you'd get 4600 pounds which is OK, at lever action levels we'd have 6590lbs. Well over the limit.

30-30 has a case diameter of about .40, at 42000PSI we have over 5200lbs of force on the breech.

.308 can produce over 9000 pounds of force on the breech face.

I feel that for safety's sake thing should be limited to the lower pressure pistol rounds. Even 7.62x39 and .223 would exceed SAAMI rated breech forces in a shotgun barrel :(
 
gyppo said:
I think a lot of the larger and/or more powerful calibers would produce too much pressure on the action. a .73 bore shotgun at has a .42in^2 surface area, at 11500PSI that produces 4800 pounds of force on the action. That's the SAAMI limit.

a .44 magnum has 0,144in^2 of surface area, at 36000PSI that produces 5200 pounds of force. Already over spec for the shotgun. These are available - a bit odd since they could in theory produce excess pressures.

.45-70 has 0,165in^2 of surface area, at trapdoor levels of 28000PSI you'd get 4600 pounds which is OK, at lever action levels we'd have 6590lbs. Well over the limit.

30-30 has a case diameter of about .40, at 42000PSI we have over 5200lbs of force on the breech.

.308 can produce over 9000 pounds of force on the breech face.

I feel that for safety's sake thing should be limited to the lower pressure pistol rounds. Even 7.62x39 and .223 would exceed SAAMI rated breech forces in a shotgun barrel :(
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I could be missing something, however, is the physical insert/adapter not taking most of the pressures you outlined, instead of the shotgun's chamber, where by eliminating the pressure concerns? In other words, the main pressure vessel (the actual barrel) is the adapter while the shotgun barrel is more of an exhaust port.

That is not saying that I am completely eliminating the shogun barrel out of the pressure equation, but it plays a lesser role.
 
TripleF said:
I could be missing something, however, is the physical insert/adapter not taking most of the pressures you outlined, instead of the shotgun's chamber, where by eliminating the pressure concerns? In other words, the main pressure vessel (the actual barrel) is the adapter while the shotgun barrel is more of an exhaust port.

That is not saying that I am completely eliminating the shogun barrel out of the pressure equation, but it plays a lesser role.
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Its a bolt thrust problem. The rearward force against the bolt face is simply not that high for a shotgun. Can't say the same for rifles.
 
Very good info. As always, the devil is in the details - thank goodness someone thinks of these things!

The lower pressure rounds then. Maybe 7.62x25 because it is small and cheap and 45/70 ... well because it's awesome. Perhaps 45acp and 9mm would work as well.
 
Suther said:
Its a bolt thrust problem. The rearward force against the bolt face is simply not that high for a shotgun. Can't say the same for rifles.
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That's the reason H&R uses two "different" (different heat treatment) receivers in their handi-rifles and shotguns. They will only install shotgun, muzzleloader, .357 and .44 barrels on the weaker SB1 receiver. The SB2 receives a different heat treatment and can take .500S&W, .308, .444, .45-70, 30-30 barrels etc. That gives us a sense of which calibers are suited to shotgun receivers and which ones aren't.
 
Pistol calibers are fine AFAIC, heck make one in 7.62x25 and I'd likely buy a case of ammo (and perhaps a companion Tok to go with).

They make 3" that can be used in pumps I have no interest that personally. Although 20g or perhaps 16 or 410 might interest me. 10-12" rifled in pistol calibers would be great.
 
gyppo said:
That's the reason H&R uses two "different" (different heat treatment) receivers in their handi-rifles and shotguns. They will only install shotgun, muzzleloader, .357 and .44 barrels on the weaker SB1 receiver. The SB2 receives a different heat treatment and can take .500S&W, .308, .444, .45-70, 30-30 barrels etc. That gives us a sense of which calibers are suited to shotgun receivers and which ones aren't.
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I see.
 
A friend of mine had several of these, the 12 - 18" versions, for the HR rifle I believe. Had a lot of fun testing the accuracy of pistol cartridges, pleasantly surprised at 100 yards. Great for bench shooting, but generally for slow plinking. Personally I can't see the use for a 3" insert that would not deliver reasonable accuracy.
 
Darkw said:
Make them rifled and at least 6" long. Just do the russian 7.62x25x39x54 surplus cartridges as a package. No-one else does this to my knowledge. You have a guaranteed winner here with all the short shotties that are selling like hot-cakes!

Cheers
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Yes PLEASE! Russian adapter package, no one does it and it would be AWESOME! :D

(providing its safe of course... a x54R might be too much, but a x39 would be incredible)
 
TripleF said:
I could be missing something, however, is the physical insert/adapter not taking most of the pressures you outlined, instead of the shotgun's chamber, where by eliminating the pressure concerns? In other words, the main pressure vessel (the actual barrel) is the adapter while the shotgun barrel is more of an exhaust port.

That is not saying that I am completely eliminating the shogun barrel out of the pressure equation, but it plays a lesser role.
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CGN educated me on this several years ago :p Take what I'm saying with a big dose of salt because this is as I understand it - please correct me if I'm wrong.

Thrust is a function of cartridge base surface area. I'm no expert but it's my understanding that it's both pressure created by the cartridge and how that pressure is distributed across the cartridge base surface area.

The other side of the issue is that most shotgun receivers don't have sufficient strength to handle that thrust - shot shells are relatively low pressure and high cartridge base surface area - meaning they can have soft thin bolt faces and large firing pin openings. The result is collapsing bolt faces, damaged or failing locking mechanisms and collapsed/ruptured primers lack of support with the oversized/shotgun sized firing pin hole.

This is why there are SB1 and SB2 models of the same break action shotgun. One is only capable of handling low pressure cartridges and the other is built with rifles in mind.


ALSSSSo there's been some mention of the fact that thrust is also affected by cartridge adherence to chamber walls - hence why it can be dangerous to have heavily lubricated cartridges or chambers in some weaker actions. When fired the brass temporarily adheres to the chamber walls and basically holds itself from sliding backwards. If the cartridge is lubed, or say, housed in an insert, the bolt face pressure can actually increase because the brass is adhered to the adaptor and not the barrel, so can still slide backwards and increase the thrust on the bolt face.
 
H Wally said:
CGN educated me on this several years ago :p Take what I'm saying with a big dose of salt because this is as I understand it - please correct me if I'm wrong.

Thrust is a function of cartridge base surface area. I'm no expert but it's my understanding that it's both pressure created by the cartridge and how that pressure is distributed across the cartridge base surface area.

The other side of the issue is that most shotgun receivers don't have sufficient strength to handle that thrust - shot shells are relatively low pressure and high cartridge base surface area - meaning they can have soft thin bolt faces and large firing pin openings. The result is collapsing bolt faces, damaged or failing locking mechanisms and collapsed/ruptured primers lack of support with the oversized/shotgun sized firing pin hole.

This is why there are SB1 and SB2 models of the same break action shotgun. One is only capable of handling low pressure cartridges and the other is built with rifles in mind.


ALSSSSo there's been some mention of the fact that thrust is also affected by cartridge adherence to chamber walls - hence why it can be dangerous to have heavily lubricated cartridges or chambers in some weaker actions. When fired the brass temporarily adheres to the chamber walls and basically holds itself from sliding backwards. If the cartridge is lubed, or say, housed in an insert, the bolt face pressure can actually increase because the brass is adhered to the adaptor and not the barrel, so can still slide backwards and increase the thrust on the bolt face.
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Awesome, thank you for the enlightening info, hence CanAm's early post about the bolt thrust concern in 54R, where the surface area of the shell's brass is greater compared to a cartridge casing's smaller contact area with greater bolt thrust per surface area, as others have also pointed out. Now I understand, thank you all.

With all that in mind, as I said previously, 9mm Luger rifled adapter at 8" in length or more would be ideal. However, if 3" adapters would be where CanAm would start, then I'll be in for that too.
 
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H Wally said:
ALSSSSo there's been some mention of the fact that thrust is also affected by cartridge adherence to chamber walls - hence why it can be dangerous to have heavily lubricated cartridges or chambers in some weaker actions. When fired the brass temporarily adheres to the chamber walls and basically holds itself from sliding backwards.
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I think this would also happen in the adapter, as the pressure would force the case walls against the adapter. Even at its thickest point just at the case web a .308 case can only withstand about 4000 pounds of pressure before the case head fails and wants to blow out of of the insert, leaving the shotgun action with the job of holding back the remaining 5200lbs. If the action can handle 5200lbs things are golden, but if it isn't strong enough to take that 5200lb force and it fails, the full 9200lb of force from the gasses will be unleashed on the bolt face :(

here's a simple but very good image showing how the forces act on the chamber (It isn't mine) showing what happens. You can see that if the action isn't strong enough (or if there's too much head space) the case head will separate even though there is a huge friction force on the rest of the brass.
http://s2.photobucket.com/user/briansmithwins/media/excessheadspace.jpg.html
 
The adaptor could be two part. Unscrew the base, insert cartridge and screw it back on. That provides the support. The base contains spring loaded firing pin.
 
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