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Double Rifles, Single Shots & Combinations >> Building Double Rifles & Gunsmithing

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boxlockexcelsior
.224 member


Reged: 20/01/22
Posts: 3
Loc: United States
shotgun double rifle conversion + donor gun
      #360956 - 23/01/22 07:57 PM

[color:blue] [/color] [image]https://imgur.com/a/XEmHhYj[/image]

An absolute dream of mine is to convert my grandfather's Stevens 5100 SXS to a double rifle. All it is, is a safe queen sitting around collecting dust anyway. I never use it & it's in great condition. The lockup on the doll's head is still very strong & crisp. The only problem I have been able to discern in it's design is that there is no double underlug. There is only one lug & the doll's head. It seems very strong though, maybe 550 grain 45-70 strong? The single underlug worries me. It feels very strong, but doesn't look like there's much material to the single underlug.

I've got a mockup for ya!...It starts with a Stevens 5100 & two unturned 28" barrel blanks @ $225 a piece from preferred barrel blanks. Take the already bored blanks (to your preferred caliber) to your local machinist (everyone knows one). There's a circular 90 degree shelf at the end of the 2&3/4 inch chamber that the machinist can turn the blanks down to via lathe; using the chamber-to-barrel union as a horizontal circular shelf & ensuring the bullet doesn't try to twist the sleeve out of the barrel. The measurements have to be precise by calipers so the inserts will fit snugly. As a caveat, I am not a fan of the monobloc design, even though my design is heavy but minimalistic, without embellishment & heavy new sight wedges. Maybe just buy chrome-moly barrels instead of stainless? I think if you're going to chop up a gun, you just lost the dual functionality of it. This wouldn't be a tack welded insert, just so snug that one would have to tap the inserts out with a mallet from the muzzle to remove them. After the chamber side & meat of the barrels are turned down that part is done.

Next is bushing the firing pins so you don't crater primers, by just drilling the firing pin holes out until you're about 1/8 inch away from the overall diameter you've decided on for the bushings. Then, tap the bushing holes with a tap & dye. Afterward comes the hard part...finding commercially available firing pin bushings & not having to go all the way to Westley Richards to find them in the proper size. My thought on a field expedient bushing would be a cut down grade 8 threaded bolt, with something like a .065 hole drilled through the middle. Screw in the completed bushings, & don't forget to drill spanner wrench divots in the outer edge of the top of the bolt shank, so you can get the bushings back out!

One of the other minor last steps would be to construct a new ejector that takes advantage of the vertical strength of the breech face, i.e. the ejector extends all the way up to the 2nd lockup on the top. The barrels breech side & the ejector would have to be milled on a vertical milling machine, so the ejector indexes with the breech/barrel face & the barrels line up circularly with the ejector. Also, there would need to be set screws on the breech/barrel face that keep the barrels in their proper orientation. Possibly that position could be under the new ejector, seated flush with that face.

Finally, thread the outer inch of an exposed 28 inch barrel, after cutting off one inch for muzzle rings/retainer nut use. The 5100 has a 26 inch barrel, so one extra inch out the front of the muzzle for male threads & one inch left over to make female threads from the remaining stock. Now, the rib on the 5100 is kinda' small so the exterior of the nut has to be tight tolerances. Also, the retainer nut has to be over bored so the bullet doesn't try to re-engage rifling.

Also, the inserts would have to be bored out for cartridge length and headspace...I don't think they do that from the factory. But, I would like a double rifle that I could re-convert to "Papa's ole' shotgun" & still have functionality, albeit changing out ejectors. Which leads me to another question: The shotgun should still fire shotgun shells with smaller firing pins, right? Without having to change out bushings?

If the inserts are quality made to tight tolerances, it should pattern just like a ole' scattergun...i.e. just point and shoot out to 50-75 yards. Almost everyone in America has an old shotgun of this sort. If there were kits to do this commercially available for some models, money could be made...

I have read that bushing the firing pins are a must for the higher pressure loads, i.e. 40-44,000 psi and above. I'm sure it would help in a shotgun to bush em' at 20-30,000 psi...Do you guys think that with the bushed firing pins, this thing would hold up to those higher pressures with only one underlug?

If I go ahead with the project I will be buying, "Building Double Rifles On Shotgun Actions by W. Ellis Brown", heck I might just buy it anyways.

What'd ya say...order some .375 H&H blanks...She might be able to handle it with the bushed firing pins!


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260rem
.375 member


Reged: 16/04/06
Posts: 757
Loc: NSW Australia
Re: shotgun double rifle conversion + donor gun [Re: boxlockexcelsior]
      #360958 - 23/01/22 09:18 PM

I suppose it could work, for me out to 75 yards there's nothing wrong with a SxS ball gun.
I know it seems a bit half arsed but if done right it's a, deadly combination.

I've been hunting with a ball gun for a while now although factory made and it's the most versatile gun I have. You can take RB or slug loads for deer ect and chuck some shot on the belt for bunnies ect if the days going slow.


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crshelton
.333 member


Reged: 10/11/15
Posts: 379
Loc: Republic of Texas
Re: shotgun double rifle conversion + donor gun [Re: 260rem]
      #360967 - 24/01/22 03:09 AM

Tip-- Buy The book BEFORE making any decisions on your safe queen!
You will find it an interesting and educational read and it will answer most, if not all of your questions.

Ellis is a hunter with rifle and shotgun and a good shot with a DR on running feral boars.
He teaches classes at gunsmithing schools and I was invited to sit in a Friday class where he taught not far from my home. The next day, we hunted boars at the Boars Nest in OK. I was standing behind Ellis when the chase dogs drove a boar down a creek bottom and than out to Ellis. Boar dodged to the right as Ellis fired first barrel but the second barrel dumped the boar as it raced by. Quite a show!

--------------------
CRS,NRA Benefactor Member, TSRA, DRSS, DWWC, Whittington Center
Android Ballistics App at http://www.xplat.net/


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DarylS
.700 member


Reged: 10/08/05
Posts: 26414
Loc: Beautiful British Columbia, Ca...
Re: shotgun double rifle conversion + donor gun [Re: crshelton]
      #360970 - 24/01/22 04:40 AM

Buy the book. I think your expectations of having a DR capable of handling 40,000psi or over, are not realistic. Perhaps it is listed in the book as being a viable prospect.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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crshelton
.333 member


Reged: 10/11/15
Posts: 379
Loc: Republic of Texas
Re: shotgun double rifle conversion + donor gun [Re: DarylS]
      #360972 - 24/01/22 06:13 AM

Daryl,
Not being a gunsmith or gun maker, I do not consider myself qualified to tell the OP go/no go on his project plan, BUT the more that he knows about the process and its advantages and limitations, the better decisions he can make. That way I bear no guilt or credit for the result.
Have the book and have read it multiple times, but am not an authority on the subject matter.

--------------------
CRS,NRA Benefactor Member, TSRA, DRSS, DWWC, Whittington Center
Android Ballistics App at http://www.xplat.net/


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3DogMike
.400 member


Reged: 29/01/15
Posts: 1404
Loc: Western Slope, Colorado USA
Re: shotgun double rifle conversion + donor gun [Re: crshelton]
      #361021 - 25/01/22 09:00 AM

Mr. boxlock could just get the quick & dirty answer as to suitability of grandpa's Stevens by contacting Aaron Little thru his FaceBook. https://www.facebook.com/amlittlebespokegunmaker/

My personal take? Bushed firing pins would be the lipstick on a pig, the action is not suitable for containing "Nitro" (.375 H&H belted) pressures. That "antique" (excuse me, vintage) action is not quite equipped with double underlugs, 3rd bite, and steel intended for the pressure.
Shotgun ~8,000-10,000 psi modern rifle ~ 40,000-55,000 psi

- Mike

--------------------
"Here's to killing people you don't like with people you do"

"Will Rogers never met a fighter pilot"
- Anon

“Always carry a flask of whiskey in case of snakebite, and furthermore always carry a small snake."
-- W. C. Fields


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DarylS
.700 member


Reged: 10/08/05
Posts: 26414
Loc: Beautiful British Columbia, Ca...
Re: shotgun double rifle conversion + donor gun [Re: 3DogMike]
      #361030 - 25/01/22 02:49 PM

By all means, contact Aaron. Yes - good idea.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V


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NitroXAdministrator
.700 member


Reged: 25/12/02
Posts: 39066
Loc: Barossa Valley, South Australi...
Re: shotgun double rifle conversion + donor gun [Re: boxlockexcelsior]
      #361051 - 25/01/22 05:38 PM

https://imgur.com/a/XEmHhYj

Trying to get the image to work? And now the link does.

--------------------
John aka NitroX

...
Govt get out of our lives NOW!
"I love the smell of cordite in the morning."
"A Sharp spear needs no polish"


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boxlockexcelsior
.224 member


Reged: 20/01/22
Posts: 3
Loc: United States
Re: shotgun double rifle conversion + donor gun [Re: NitroX]
      #361120 - 26/01/22 06:39 PM

The book is on the way...Also emailed preferred barrel blanks. They said that they can turn custom barrel blanks to fit the inner diameter of my specific barrels for ~ USD $295 a piece. They can also thread the muzzles, crown the barrels and create muzzle caps for an additional $80 a piece. I don't think this is too bad, considering the man hours usually required to turn something like a barrel down on a lathe & threading. Also, I wanted to be involved in the conversion, but cutting the man hours this way seems pragmatic. The only thing is, they need a schematic of the inner diameter of the barrels. I was thinking of doing a plaster or plastic mold of the i.d. then, measuring the mold/s. I wish there was an old blueprint online, like at Numrich's that would tell me the exact taper. Because, the bore goes from about the extreme of 15/16 at the breech to 13/16 at the muzzle. I probably should contact Mr. little bespoke gunmaker also, as he has assuredly already ran into these problems. I also, have an old Boito that has relatively the same dimensions I could test chamber pressures on, after headspace reaming, and I don't mind it blowing up before the final proofing on the Stevens.

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260rem
.375 member


Reged: 16/04/06
Posts: 757
Loc: NSW Australia
Re: shotgun double rifle conversion + donor gun [Re: boxlockexcelsior]
      #361121 - 26/01/22 06:46 PM

I would have thought the you would thread the inside of the barrels, then screw the new barrels in.

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Wayne59
.400 member


Reged: 20/06/15
Posts: 1219
Loc: Lagrange Ga. USA
Re: shotgun double rifle conversion + donor gun [Re: 260rem]
      #361156 - 27/01/22 11:48 AM

Put grandpas gun back in the safe. Your children or grandchildren might appreciate it. Go to Simpson ltd and purchase a doner gun. The sight is full of them.

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boxlockexcelsior
.224 member


Reged: 20/01/22
Posts: 3
Loc: United States
Re: shotgun double rifle conversion + donor gun [Re: Wayne59]
      #361508 - 04/02/22 07:40 PM

Well, I crunched the chamber pressure numbers & they are as follows:

Baseline donor gun 12 ga. 2&3/4 chamber: .8100/2=.405 head/base radius
3.14*(.405*.405)=.5150385 square inches of area
.5150385*11,500psi SAAMI spec= 5,922.9 lbs. applied to breech

45-70 calc.: .505/2=.2525
3.14*(.2525*.2525)=.200194625
.200194625*28,700 SAAMI mean value=5,745.5 lbs. applied to breech

.35 Remington: .458/2=.229
3.14*(.229*.229)=.16466474
.16466474*35,600psi max SAAMI spec= 5,862.0 lbs. applied to breech

The .35 Rem. gets honorable mention, because the 45-70 values I referenced aren't even the highest- test loads available for the 45-70, those going over the baseline value of 5,922.9 lbs.

I think the relationship here between head/base diameter and pounds of force applied to the breech relates to surface area. A 12 bore spreads the force out over a larger area vs. centerfire rifle cartridges that are very intense, in a smaller package/with a smaller footprint.

This kinda' bums me out...I was hoping for a larger caliber. But something like the .416 Rigby I calculated at 14,161.3 lbs. applied to the breech...way over.
Are there flaws in the calculation?...Well, if you sub in even 17,000 psi in the donor gun calculation for the SAAMI spec, it produces only a mere 8,755.6 lbs. of force applied to the breech...
It's because the force is spread out over a larger area in square inches of surface area of the cartridge head/base diameter.
That's my thoughts. Thanks for listening.


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