.50 BMG Chamber

[NavyVet1959]

Will a 12-gauge shell physically chamber in a .50 BMG rifled barrel? I stumbled across a relatively cheap .50 BMG chambered barrel blank online and it got me to thinking about a possible project for a breech loading bottleneck 12-gauge.

[Pipefitter]

I remember seeing some fool on facebook that somehow fired a 50BMG cartridge in a single shot break action 12ga. IIRC he had to wrap electrical tape around a portion of the 50BMG case to get it to hold in the 12ga chamber, (and the trigger was pulled by a very long string so no Darwin awards there).

[NavyVet1959]

I remember seeing some fool on facebook that somehow fired a 50BMG cartridge in a single shot break action 12ga. IIRC he had to wrap electrical tape around a portion of the 50BMG case to get it to hold in the 12ga chamber, (and the trigger was pulled by a very long string so no Darwin awards there).

Yeah, I saw that also. I'm curious whether the other way would fit though -- a 12-gauge shell in a .50 BMG chamber. No, I'm not going to be firing a shotshell in a .50 BMG barrel (although it would be interesting to see what that sort of "choke" ended up doing). I'm curious if a 12-gauge shell with just powder in it could act as the powder charge for a .50 bullet that was inserted into the barrel from the breech by hand. I seem to remember someone postulating something similar (although I don't think it was with a .50 BMG barrel) on one of the forums that I frequent awhile back, but I don't remember where or whether they ever attempted it. Anyway, I was just curious if it would *physically* fit an the rim would catch on the edge of the barrel. It's one thing to look at the SAAMI specs on the cartridge and think that it *might* work, it's another to actually have a barrel to test it on. I was hoping that perhaps someone in this subforum had a .50 BMG rifle and a 12-gauge shell that they could give it a quick try.

[Faret]

12 won't fit 20 ga does but will not fit in the shell holder. Now if you had some brass 16 ga and turned the rim for the extractor grove you could be on to something.

[rockrat]

I think the 12 Ga. FH, they take 50 bmg brass and swage a rim on, and use it in a 12ga 3.5" chamber. They fireform the case to be able to load 12ga slugs in the rifled barrel. I think they use bolt action shotguns, that have acutal lugs on the bolt. Maybe kind of like the gun that just sold on S&S. A 12ga slug gun and 12,000 fpe.

[NavyVet1959]

12 won't fit 20 ga does but will not fit in the shell holder. Now if you had some brass 16 ga and turned the rim for the extractor grove you could be on to something.

Looking at the specs on the actual cartridges, I see the following:

.50 BMG:
http://www.dave-cushman.net/shot/50bmg.html
base diameter: 0.804"
shoulder diameter: 0.714"
distance from base to shoulder: 3.006"

12-gauge 3" shell:
http://www.saami.org/pubresources/cc...-gauge%203.pdf
rim diameter: 0.886"
base diameter: 0.809"
neck diameter: 0.797"

16-gauge 2-3/4" shell:
http://www.saami.org/PubResources/CC...ge%202_3-4.pdf
rim diameter: 0.819"
base diameter: 0.744"
neck diameter: 0.731"

20-gauge 2-3/4" shell:
http://www.saami.org/PubResources/CC...ge%202_3-4.pdf
rim diameter: 0.766"
base diameter: 0.697"
neck diameter: 0.684"


Now, these are maximum cartridge dimensions and one would assume that *minimum* chamber dimensions are slightly higher, but from what I've seen on the shotshell dimensions, that's only 0.001" difference.

Just looking at these numbers, what it tells me is:

• the 12-gauge rim will not fall through the .50 BMG chamber
• the 12-gauge brass base is slightly larger than the .50 BMG cartridge in that same area, but it is small enough that variances in .50 BMG chamber size or 12-gauge shells *might* allow it to partially fit in the chamber
• the 12-gauge neck diameter appears to be too large for the .50 BMG chamber.
• the 20-gauge rim diameter is smaller than the base of the .50 BMG chamber, so it would fall through the chamber until it hit the neck of the .50 BMG chamber
• the .50 BMG chamber would have a diameter of about 0.7215" at the 2-3/4" mark
• the 16-gauge shell would have a loose fit at the base and a tight fit at the neck in the .50 BMG chamber

Unless anyone has any empirical evidence to the contrary, I'm thinking that it would be best to just to take a 12-gauge chamber reamer to the .50 BMG barrel to get it to fit correctly. The barrel is 33" long and 1.65" in diameter (unprofiled), so I don't think taking a few thous off the chamber is going to make much of a difference since the bullet would be manually seated up to the rifling anyway.

[Faret]

Should have said the 12 ga does not go in all the way. It will start about 1/4".

[rockrat]

If you are going to shoot slugs, remember you will be swaging a slug of about .670" down to .512" and the associated wadding too.

[NavyVet1959]

If you are going to shoot slugs, remember you will be swaging a slug of about .670" down to .512" and the associated wadding too.

Nawh, I'm thinking of just loading the 12-gauge shell with powder and manually seating an appropriate diameter bullet to the rifling. Kind of like when the old 16" guns on the battleships loaded the projectile, rammed it home, and then loaded the bags of powder. Well, except that the powder would be all contained in a 12-gauge shell (that had no projectile loaded in it). I had seen one of the threads about the 12-gauge FH awhile back and it got me to thinking when I stumbled across the .50 BMG barrel the other day.

Yeah, I know -- totally impractical as a "sporting arm" and a waste of money... But it wouldn't be the only thing in my safe that would fall under that category and some of them were a lot more expensive than what this would cost of make.

[NavyVet1959]

Should have said the 12 ga does not go in all the way. It will start about 1/4".

OK... Thanks for giving it a try for me... That means that I will need to have the barrel reamed for a 12-gauge chamber.

[Faret]

Still not sure of what you want to do. If you want the 12 ga to go all the way in it will have to be reamed do to the taper of the 50 BMG chamber.

[NavyVet1959]

Still not sure of what you want to do. If you want the 12 ga to go all the way in it will have to be reamed do to the taper of the 50 BMG chamber.

Yeah, that's what I had pretty much expected from the dimensions that I quoted previously.

End result of this would be a single-shot 0.512-ish projectile that did not require arsenal primers or .50 BMG brass and would still be classified as a "12-gauge shotgun".

[Tackleberry41]

Couldn't you just cut off part of the chamber end of the barrel, then use a 12ga reamer, or maybe even a 20ga?

[NavyVet1959]

Couldn't you just cut off part of the chamber end of the barrel, then use a 12ga reamer, or maybe even a 20ga?

Yeah, but that would shorten the barrel. Since the .50 BMG chamber is just slightly smaller than a 12-gague shell when it it fully inserted, it would seem easier to just ream the .50 BMG chamber instead of cutting the barrel and then having to ream more. Besides, I want that .50 BMG bottleneck in the chamber.

Went to order the barrel the other night and it was out of stock. I hate those sites that have something listed with a "purchase" button and then you don't know it is out of stock until you actually try to buy it.

[Faret]

I hate those sites that have something listed with a "purchase" button and then you don't know it is out of stock until you actually try to buy it.

And they do not let you know how many they have in stock!

[NavyVet1959]

And they do not let you know how many they have in stock!

Yeah, you go and search for the best price and after you are sure that you have found it, you press the "purchase" button, only to find out that they don't have it in stock. I suspect that their website is not tied into their inventory system.

[Tackleberry41]

I ran into this issue buying a tool recently. Someplace like Midway you know if they have it or not. PTG tools theres no way to know, got an email same day 'order #..' had USPS shipping on it, no tracking, but small enough to go in some sort of envelope. 4 days later another email thanks for your order, but its back ordered 4-6 weeks. Fine Ill just cancel the order, no problem, for a 20% cancellation fee because 'it was already in the shop'. Which means an order slip in a pile with a bunch of others. Hope they dont expect any future business.

[NavyVet1959]

Well, I found a seller on eBay that had the same barrel for $175 + $15 shipping. 30" barrel, 1-15" twist rate, 1.625" OD, and already chambered for .50 BMG.

It should arrive next week, so I'll have yet another unfinished project to add to my gun safe.

[Deadpool]

I wonder how much powder would fit in that 12ga hull. Scary if the pressure spec is lower after reaming the chamber to fit the 12ga.

It would be sweet to use an 870 or 500 receiver with that.. And use a 2nd 12ga shell as your projectile loading ram. That is, a shell you chamber that seats a boolit, and cycle it out but leaves the boolit in the throat. Fill the mag tube for double pump, or fill only with charge shells since the projectile shell would be longer.

[Geppetto]

Just remember with that project that you probably don't want to big a gap between the 12ga shell and the projectile. I would think that you would need to use an "over powder" card or wad, and then if you have any airspace to the projectile, you could potentially ring your chamber. or if the gap was too large, it might act as a barrel obstruction?