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Double Rifles, Single Shots & Combinations >> Paradox and Bore Guns
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Longknife
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Reged: 17/04/08
Posts: 263
Loc: Illinois
Building a Bore Rifle....
      #354669 - 27/06/21 02:12 AM

I have been wanting to build a 20 ga. bore rifle for some time. This rifle will be used mainly for deer and maybe a few pigs at shorter ranges, so no magnum shoulder breaking loads will be needed. I plan on loading in 20 ga shotshells and shooting a one ounce (437 grains +or-) slug over 70 grns (+ or -) of BLACK POWDER. I dont use smokeless and never will. If you were planning such a beast what would be your rifling specs? Twist and groove depth? And what slug design would you prefer with your suggested twist rate? Thanks, Ed

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Longknife

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LRF
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Reged: 28/03/11
Posts: 350
Loc: minnesota ,usa
Re: Building a Bore Rifle.... [Re: Longknife]
      #354676 - 27/06/21 10:56 AM

What would length of a 20 ga diameter projectile, that weighed 437 grains, be? What are you predicting as a muzzle velocity be for this vision of yours?

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LRF
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Reged: 28/03/11
Posts: 350
Loc: minnesota ,usa
Re: Building a Bore Rifle.... [Re: Longknife]
      #354677 - 27/06/21 11:13 AM

Typically you use the greenhill formula to get an estimate. Fortunately there are calculators on the web.
Here is a link to one of them:
Grennhill calculator

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Marrakai
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Reged: 09/01/03
Posts: 3591
Loc: Darwin, Top End of Australia
Re: Building a Bore Rifle.... [Re: LRF]
      #354679 - 27/06/21 11:52 AM

The problem with using a modern-made rifled 20ga barrel blank(s) may be that most are rifled with twist rates for sabot use, and have enfield-style lands and grooves.

Slow-twist rifling for round-ball or stubby slug would be my preference, along with wide grooves and steep narrow lands in keeping with period profiles for BP and lead-bullet bore rifles of ~120 years past.

For some reason the latter is hard to find off the shelf, impossible to find on this side of the pond unfortunately.
I am on quest for a 16-bore barrel blank myself!
Did somebody say howdah pistol....?

The other option may be to make a button for an oval-bore barrel. Less BP fouling, potentially....

--------------------
Marrakai
When the bull drops, the bullshit stops!
--------------------------------
www.marrakai-adventure.com.au

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LRF
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Reged: 28/03/11
Posts: 350
Loc: minnesota ,usa
Re: Building a Bore Rifle.... [Re: Marrakai]
      #354685 - 27/06/21 09:25 PM

For example a 20 ga (.614 diameter) projectile in the form of a straight cylinder .614 long would weigh ~520 grains and would require a twist of around 92 inches. And stability would be very questionable. If your not going to use a sabot, as mentioned above, then I suggest you look into a basic design like the regular rifled slugs or miniball, in other words hollow base with a rounded nose so that you can get some length to the bullet and in turn increase the required rate of twist. In addition this would move the center of gravity forward in the bullet and the center of pressure closer to the rear of the bullet, which is natural stability for a projectile in flight.
As to the style of rifling, there are a hundred different schools of thought on that subject. And frankly it weighs much on personnel choice. Personally I would look for one most easily cleaned. Then of course you need to find a finished barrel blank or find a barrel smith who would make it or make it yourself. A daunting project without experience or tooling for such.
Good luck

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260rem
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Reged: 16/04/06
Posts: 757
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Re: Building a Bore Rifle.... [Re: LRF]
      #354693 - 28/06/21 11:01 AM

My question is why bother with rifling at all?

I can shoot 75 yards easily with my smoothbore 12ga so getting the same or better accuracy from a regulated 20ga is very possible.
It's also a more flexible gun like that, maybe look at putting a 1/4 rib with open sights on a 20ga and regulating it with screw in rifled chokes.

Loading brass cases with a load of the dirty black stuff behind a Svarog paradox slug or Lyman style slug will be about perfect for what it seems your after.

But the other side of the coin is there's, no better reason for buying a gun other then because it's what you want.

But from my own experiences I prefer my 12ga ball and shot gun over my double rifle as it's just such a flexible hunting gun that I can use on anything I'm ever going to hunt if I can do my part.

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One shot is all you need.

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Tom_H
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Posts: 336
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Re: Building a Bore Rifle.... [Re: 260rem]
      #354694 - 28/06/21 09:57 PM

I am sure that Daryl will be chiming in on this.

I am curious about what action you want to use.
It is easy enough (albeit time consuming) to monoblock a single shot.

That being said, when I was working on my 20ga I went with a 66 twist. It was meant for Lightfield and Brenneke slugs which it did very will with 100yd groups around 2" or less. With the velocity you are looking at, that twist will give you some flexibility. A bit fast for round balls but capable of stabilizing slugs.
Personally, I don't think that you need any more than a round ball (around 350gr). My 58 has shot through every deer and pig that I have ever taken, so I would think that would be the case for the 62 as well.

As far as dimensions, I matched my barrel to the cases I planned on loading with. I measured the inside of a Brenneke hull (I am thinking .625) and went with .005 rifling. I am not sure about the forcing cone.
You will need a piloted reamer because of the rifling although you could probably chamber it with a forcing cone reamer and finish the rim recess with a regular reamer.

You may want to reach out to Bob Hoyt in Pennsylvania.

2379 Mt Hope Rd, Farfield PA
717-642-6696

He rifled a few barrels for me and has a good reputation.

Good shooting.

Tom

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Carbonation without fermentation is tyranny

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EDELWEISS
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Reged: 22/11/05
Posts: 608
Loc: Gettysburg
Re: Building a Bore Rifle.... [Re: Tom_H]
      #354695 - 29/06/21 12:27 AM

I wanted a "real" Paradox Bore Rifle Gauge Gun since the time I first read about them. It seems like every time I saw one, I didnt have the money and when I had the money, I couldnt find what I wanted. Then I toyed about having one made but couldnt find a builder that I trusted or could afford. I promised myself it would be the "only" gun Id use so whatever I spent would be worth it...

Then I found a SxS smoothbore that shot factory slugs in nice groups. No its not a "real" but it shoots like a real one maybe better. I had a gunsmith install simple sights for a little easier aiming past 50 yards (OK and because a real one would have sights). My ideal gun would have used brass cases, and maybe I could try loading brass slugs but I dont see the advantage, beyond vanity.

It truly has become my "one gun" for Hogs. It hits pretty much everything I point it at and drops Hogs like the Hammer of Thor. I say all this as an encouragement for you to pursue your goal

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If it's not custom, it's just borrowed

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Huvius
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Reged: 04/11/07
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Re: Building a Bore Rifle.... [Re: EDELWEISS]
      #354696 - 29/06/21 12:44 AM

Mossberg slug barrels are easy to find and as far as I can determine, the 20ga fully rifled barrels have a 1 in 36” twist.
Properly modified one should work for a monoblock or shoe lump barrel.
I’ve entertained this very idea using a single barrel trap gun I have.
It seems like the most straightforward conversion for an amateur gunsmith. Of course, I could just shorten the barrel and see how she does as a 12 smoothbore. Maybe some day…

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He who lives in the past is doomed to enjoy it.

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Tom_H
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Re: Building a Bore Rifle.... [Re: Huvius]
      #354706 - 29/06/21 01:39 PM

Hello Huvius.

I originally looked into the fast twist thing and using the formula, the slug worked out to 900gr.
I cut a mold for a 450 and was never able to get it to stabilize properly in my rifled NEF. Could have also been operator error but it was also the reason I went to the 66.

Tom

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Carbonation without fermentation is tyranny

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Longknife
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Reged: 17/04/08
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Loc: Illinois
Re: Building a Bore Rifle.... [Re: Tom_H]
      #354716 - 30/06/21 12:34 AM

Thanks guys for all the advice. I am planning to have a barrel made so I will not be useing a ready made barrel. Tom, I have had B Hoyt rebore and make me barrels and he does do excellent work. I like your idea of a 66 twist and i dont think that is too fast for a ball or a slug. TLRF below is the slug I have been looking at it weighs 425 grains in WW lead. Keep in mind that these molds are custom made and can be modified to any configuration I desire. I can even design my own mold. I have used the green hill formula many times and it always come out in the 90's twist range which would take a too much powder to stabilize a basically "square" slug. I do want to keep this in the managable 70 grain powder range. I am only wanting 1200 give or take velocity at shorter ranges much like the old paradox guns, what twist did they use? Not a whole lot of info on them.,,,Ed

http://accuratemolds.com/bullet_detail.php?bullet=62-425S

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260rem
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Reged: 16/04/06
Posts: 757
Loc: NSW Australia
Re: Building a Bore Rifle.... [Re: Longknife]
      #354717 - 30/06/21 12:55 AM

If your looking for a good ball mold I've been using the Russian Svarog molds, cast a great ball, I've found the .678 mold to be the best accuracy wise and it cast a 1oz ball.
Sit that on a 20ga felt cushion and it's easy to load and shoots great.
Their match slug is pretty good too, kill great as well. But the paradox mold that cast a slug very similar to the one you posted the link to will do a brilliant job.
Last I checked they had a good selection of those in 20ga options.
I'm thinking about adding one to my collection.

--------------------
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Tom_H
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Reged: 13/04/05
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Re: Building a Bore Rifle.... [Re: Longknife]
      #354719 - 30/06/21 01:00 AM

That is a great looking mold Ed. I don't know if the .620 diameter is the best option though as I would rather be able to size a slug down than hope that it bumps up to diameter.
Looks like a topic for another thread.
Huvius mentioned a single barrel trap gun. I believe that the perfect hammerless stalking rifle type gun can be built on Savage 219 or 220 (old model)
If you look inside it isn't much different than the small frame snap action German tell rifles.
They were chambered to cartridges as large as 30-40 Krag so strength is no issue.
Barrels can usually be refitted from Savage 94 single shots if you are monoblocking. It also gives an opportunity to have a gun with multiple barrels including rifles.

Cheers.

Tom

Edited by Tom_H (30/06/21 01:02 AM)

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Longknife
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Reged: 17/04/08
Posts: 263
Loc: Illinois
Re: Building a Bore Rifle.... [Re: Tom_H]
      #354736 - 01/07/21 01:25 AM

Tom. Accurate mold will make any size I desire but I need to get a barrel made and slug it first to determine what dia slug will work best. I am thinking .001 under groove depth?...Ed

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Longknife

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Marrakai
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Reged: 09/01/03
Posts: 3591
Loc: Darwin, Top End of Australia
Re: Building a Bore Rifle.... [Re: Longknife]
      #354754 - 01/07/21 06:57 PM

I would think 1 thou OVER groove diameter

... but my lead-bullet/black powder experience is far inferior to many here.

--------------------
Marrakai
When the bull drops, the bullshit stops!
--------------------------------
www.marrakai-adventure.com.au

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Longknife
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Reged: 17/04/08
Posts: 263
Loc: Illinois
Re: Building a Bore Rifle.... [Re: Marrakai]
      #354802 - 03/07/21 01:07 AM

Marraki, You may be right! Many BPCR bullets are sized .001 over GD and sometimes .002 over GD. There is not too much info out there on shooting these large "shotgun" slugs,,,Ed

Edited by Longknife (03/07/21 01:08 AM)

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