Lets talk reamers, again

[merlin101]

I'm in the process of building a "stub" gun. I bought a unchamber but rifled .357 barrel and turned it down to fit into a cut down 12GA barrel. It's all installed and was a semi press fit and then epoxied in place, I never realized how much space epoxy takes up!
I made the mistake of making it fit to tight and with the 'step' of the chamber to barrel it must've trapped epoxy in there making it extremely difficult for final fitting. Any way that's all behind me and chamber reaming is the next step, I'm planning on using a .357MAX from 4D any feed back there? If I do go with the MAX I know I can still use .357 Mag but can I go all the way down to .38Sp.? Do I need to rent all the extras they have like the GO-NOGO gauges? Can you tell this is new territory for me? Any advice would be appreciated.
Oh yeah, the REAL next step is the extractor but I'm thinking ahead.

[Texas by God]

If you glued it in flush you'll cut the rim recess with the reamer. The rim is the same for all three cartridges. I agree about the epoxy and I had to yank one back out and get rid of the compression at the step- what a mess.

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[Wolfer]

It’s been awhile since I’ve used 4D but have always had a good experience with them.
I personally don’t get the gauges when doing rimmed cartridges. A piece of scotch tape on the back of a case works pretty good.
In the case of my rolling block I wanted the headspace pretty minimal. Once I got pretty close I started trying different cases. Wow! They are certainly not the same but are very close. Once I found a thick one I used it as a go gauge. Haven’t had any issues with it.

[DougGuy]

I agree with using dummies for a gauge. Use what the gun will actually chamber and fire.

[John Taylor]

A 357 Max on a 12 gauge may be a problem. First the bolt thrust is about 1,000 pounds more. Second , the firing pin may be too big and the primers may blow. The 357 mag may also have firing pin problems but the pressure should not be a problem for the action.

[Jedman]

Take John Taylor's advice and bush your firing pin and reduce the tip diameter to .075 max.
If you haven't already read the similar posts in the barrel works sub forum above this one.
You haven't mentioned what brand or model of 12 ga. You are converting. The H&R is one of the easier brands to work with as they make small firing pin shotgun frames and you can buy ejectors for rifle calibers as small as 22 hornet and you can get one for the 357 mag or 22 jet that has the same rim.
Making or modifying a 12 ga. ejector can be done many ways depending on what your shotgun has already. Some are simple enough you can make a replacement without a milling machine by using hand tools. It sounds like you have a lathe to use so you can turn a steel " washer " with the 12 ga. rim on the OD and bore or drill the center hole to .375 + so the reamer can cut the rim recess and make the washer as thick as the upright part of your ejector.
Then you can silver solder it to your 12 ga. ejector and cut the width to fit.

Remember we all like to see pictures of your project, Good Luck !

Jedman

[skeettx]

Yes, you can shoot 38 Specials in a Max chamber
Mike

[merlin101]

Thank you all for the info. I will take John Taylor's advice and stick with .357MAG I rarely load hot but no sense in taking chances. I hadn't decided what or how on the ejector but then while driving thought of using a washer! DING the light bulb came on.
The donor gun is an older Savage that while seeing little use it also saw little care. I hope I don't have to bush the firing pin but one step at a time.
I saw an old Iver Johnson with a unique lever at a LGS in real rough shape and may do an other in a similar caliber.
When I got the 357 barrel I also got a .22Hornet Bbl and am looking for a smaller/lighter 20 or .410 frame for that one.
This is fun!

[uscra112]

Lemme get this straight......you're just gluing the barrel into the stub? No thread? No cross pins?

[Cap'n Morgan]

Lemme get this straight......you're just gluing the barrel into the stub? No thread? No cross pins?

A strong bond between stub and barrel is not necessary. There is hardly any "lengthwise" pressure on the barrel - only the force of the bullet against the rifling will seek to pull/push the barrel forward. That is why a "slam shotgun" will function with a floating barrel: https://www.youtube.com/watch?v=gm-aqkAnhNE

[uscra112]

Not for long. The radial expansion of the chamber at every shot, and the torque from the rifling, are going to break that bond, unless the gun is limited to something no more powerful than .22 Long Rifle. Speaking as a (retired) dirty-fingernail make-a-nickel penguineer of 40 years experience. Let's look at the example of the old Hopkins & Allen rifles, which had a tapered cross pin to retain the slip-fit barrel; no thread. A cheap way of doing a takedown. I've collected a few, and can tell you that the system was/is notorious for loosening up with age, even though they were built for blackpowder loads, and usually in pistol cartridges at that. The "medium frame" H&A was made in .32-40 and even .38-55, but not for long. It was dropped even before smokeless powder had become the default for loading those cartridges.

I wouldn't do what the O.P. seems to be doing on a bet, given the cartridge he's proposing. And just BTW the strong forms of Loctite will be more resilient than Acraglas resin.

And when I needed a .357 Max reamer, I found that I could buy one outright from Dave Manson with a proper throat, which SAAMI reamers do not have, for a price that made renting look less than attractive. Held short, it made a very accurate .357 Magnum barrel for my Contender. I came to regret lengthening it to Max dimension in the end.

[Texas by God]

I'm testing my 44-40in12ga. Topper carbine every chance I get with low + P Unique/200 loads. The GM barrel is turned to a easy slip fit at chamber and bore and is glued in with around 30 square/round inches of JBweld. If it lets go I'll report it here first. I've seen that glue do some pretty amazing things so I'm not worried.

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[Willbird]

A strong bond between stub and barrel is not necessary. There is hardly any "lengthwise" pressure on the barrel - only the force of the bullet against the rifling will seek to pull/push the barrel forward. That is why a "slam shotgun" will function with a floating barrel: https://www.youtube.com/watch?v=gm-aqkAnhNE

The cartridge case in the chamber is a piston that is trying to push the barrel out of the stub. Some simple math can tell us how much force is generated.

Easy math is just the OD of the case, "proper math" would be the ID of the case.

.358 for round numbers.

Pi * R ^2 will give us the square inches of area. so 3.14 * .179 ^2 = .100 square inches.

.100 square inches times 35,000 PSI gives us 3500 lbs of force trying to fire the barrel out of the stub at peak pressure, prudent design would be to build to withstand 7,000 lbs of force.

Just gluing it in for a short distance of stub is probably very unsafe. I would not want to be anywhere around when something like that was being fired. The barrel should be threaded into the stub.

Gluing in a full length liner like they do for 22lr involves a lot more square inches of bonded area.

Bill

[Cap'n Morgan]

.100 square inches times 35,000 PSI gives us 3500 lbs of force trying to fire the barrel out of the stub at peak pressure, prudent design would be to build to withstand 7,000 lbs of force.

Sorry, but it's not as simple as that. What you have is a force pushing against the receiver (and the chamber wall) and the base of the bullet. As long as we're dealing with straight-wall cartridges, almost all the "forward" pressure will work on the base of the bullet, not the barrel itself.

[Jedman]

I have built over 2 dozen stub and lined barrels , some in relatively hi pressure chamberings with nothing but epoxy. I have never had a single time where any of them have loosened, moved without any cross pins or other reinforcements.
One of the best examples I can give you of the strength of a proper epoxy joint is myself and another member here on this forum have built several smokeless muzzleloaders from 45-70 barrels on H&R handi rifles. All we did was epoxy in a breech plug that was lathe turned to resemble a 45-70 case with a primer pocket made for a 209 size primer with a O ring around the flash hole. The rifle my friend has the breech plug has negative headspace when the rifle was closed to fire so the breechplug was not supported by the reciever standing breech at all.
He has fired the gun with smokeless powder well over 50 grs. Hundreds of times and the breech plug only having several square inches of bond area has never let go.

Jedman

[Texas by God]

So- chamber inserts that can be loaded into a shotgun to shoot say-9mm Luger- will blow up your gun? Please explain why not? I'm referring to the removable sub caliber adapters that are on the market.

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[skeettx]

OK, let us clarify.

the insert is not a straight pipe, but has some major and minor external dimensions.

The major diameter (bigger than the original firearm bore size,
will keep the insert from squirting out the muzzle of the firearm.

The breech will keep the insert from moving to the rear.

The "glue" is there to anchor the insert in the firearm.

Correct???

Mike

[Texas by God]

Yes, the barrel blank is turned with a shoulder to correspond with the end of the shotgun chamber. The remainder is slightly under bore size. It wouldn't squirt out even without glue. I've read of cutting the barrel off and leaving a monobloc to thread the new barrel into; which is great if you have the talent and machinery to do so. I've gone the easier route, as Jedman mentioned. The original shotgun lockup is still intact to protect me if something goes awry. Even if the glue failed.

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[Willbird]

Sorry, but it's not as simple as that. What you have is a force pushing against the receiver (and the chamber wall) and the base of the bullet. As long as we're dealing with straight-wall cartridges, almost all the "forward" pressure will work on the base of the bullet, not the barrel itself.

It is indeed "as simple as that". It is a simple pressure vessel. Intelligent design is to build for 200% of worst case loading..at least 200%.

Worst case if we only fired SAAMI ctg is an oiled case/chamber...and the end result is the numbers I worked, up the action is the only thing holding the case in the chamber....with an oiled case/chamber no doubt the glued in barrel stubs will fail and the barrel will go downrange.

If you think that is untrue then prove it. The brits used a "copper crusher" system that worked exactly like that, it used oiled cases and measured rearward thrust which crushed a tubular "crusher", they did the math and derived chamber pressure the same way the American copper crusher system worked.

Different folks have cleaned chambers with alcohol and fired 30-30 Ackley improved ctg with no breech at all....the cases stayed in the chamber, if the case had been fired several times the PRIMER left at 2,000 fps, and easily penetrated 3/8" plywood. Firing regular 30-30 or oiling the chamber caused the cartridge case to leave the chamber at 2,000 fps measured by crono.....45/70 had enough taper to leave the chamber as well.

Less than smart ideas work right up until they do not....I do not even want to be in the same county with folks firing rifles that have the barrels glued into the stubs.

The OP did not use glue in shear to hold his barrel in, it should be fine the way he did it. he also has a LOT of square inches of glue in shear anyway, much longer than the typical "barrel stub" job.

Bill

[ulav8r]

The cartridge case seals the chamber, so there is no gas behind the end of the barrel to push it out of the shotgun barrel. Slip in adapters work quite well with just a couple of o-rings to keep them in place, epoxy will hold them much better.