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Joined: May 2023
Posts: 23 Likes: 1
Boxlock
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OP
Boxlock
Joined: May 2023
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In theory if you bore the monobloc for the barrels so the barrels touch at the muzzles and the center of the bores are level you will be really close. You want to explain that to me? They would be tapered inwards in relation to each other by a couple degrees just due to the outer profiles of the barrels. If each barrel is angled towards center just 1 degree (2 degrees included angle) the center line of the theoretical perfect pattern will be offset to the other side about 2 feet at 40 yards. The patterns might overlap at 40 yards, but the center of the patterns would be four feet apart. I would say, "if I did the math right," but I used a triangle calculator on my cell phone. If the ap did the math right. My plan was to basically bore the block and make spacers such that the center line of the chamber was almost exactly the same distance apart as the center line of the muzzle. P.S. I've been playing with the idea of using a clamshell design as opposed to a one piece mono block. It would simplify some of the setup issues for machining. I'll probably cut a mono block anyway, but I've got to setup and figure out the basic geometry and do some basic plans before I decide the best approach for me. The center line of the chambers is restricted by the firing pin locations on the frame.
Last edited by Bob La Londe; 06/03/23 08:18 PM.
-- Bob La Londe - CNC Molds N Stuff Proffessional Hack, Hobbyist, Wannabe, Shade Tree, Button Pushing, Not a real machinist!
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Joined: Jul 2012
Posts: 4,556 Likes: 232
Sidelock
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Sidelock
Joined: Jul 2012
Posts: 4,556 Likes: 232 |
Bob, I am given to understand that it is more than a math problem, the effect of the shooters body and "hold" affects the point of impact and is very difficult calculate. Granted, this is likely easier to see with a double rifle than a shotgun, but it is still there. Milling the rear part of the top rib is often done as you described. One thing I recall and didn't mention is when drilling the holes for the barrels in the monoblock, they would leave one of them smaller than the other. This is to give them the ability to move it slightly, if final measurements show movement is necessary. Mike
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Joined: Dec 2011
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Sidelock
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Sidelock
Joined: Dec 2011
Posts: 910 Likes: 45 |
There is also the effect of recoil that moves the movement laterally and slightly down. If you have access to other barrel sets you can measure the center of the breach and the center of the muzzles and find the basic angles. When relaying ribs I use a jig that has level surfaces to lay the barrels on so the center of the bores are parallel at the muzzle. That leaves the patterns vertically, and the angles of convergence will overlap the patterns horizontally. The rub comes in the fact if you just bore sight the barrels you may not get where you want. They may appear to crossfire sooner than you want .
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Joined: May 2023
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Boxlock
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Boxlock
Joined: May 2023
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There is also the effect of recoil that moves the movement laterally and slightly down. If you have access to other barrel sets you can measure the center of the breach and the center of the muzzles and find the basic angles. When relaying ribs I use a jig that has level surfaces to lay the barrels on so the center of the bores are parallel at the muzzle. That leaves the patterns vertically, and the angles of convergence will overlap the patterns horizontally. The rub comes in the fact if you just bore sight the barrels you may not get where you want. They may appear to crossfire sooner than you want . I only have two other doubles. One is an OU and the first barrel tends to shoot a little low. The second shoots dead on. Both are centered. The other is a .410 side by side. One barrel shoots a little low left. Second barrel shoots dead on. This is based on fixed patterning with a sheet of butcher paper stretched between two posts. If I adjust I can hit with them in the field.
-- Bob La Londe - CNC Molds N Stuff Proffessional Hack, Hobbyist, Wannabe, Shade Tree, Button Pushing, Not a real machinist!
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Joined: May 2023
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Boxlock
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Boxlock
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Haven't done a darn thing with this in two months. I've just been sort of thinking my way through it. More and more I like the idea of a mono block, but fitting the barrel lump seems like it could be its own issue. Would it be strong enough to make a mono block for the barrels and the barrel lump that engages the frame separately and bolt and solder them together? I think if it is made with just the right tolerance the recoil force will all be on the faces of the frame, not on the barrel lump.
-- Bob La Londe - CNC Molds N Stuff Proffessional Hack, Hobbyist, Wannabe, Shade Tree, Button Pushing, Not a real machinist!
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Joined: Mar 2002
Posts: 2,857 Likes: 384
Sidelock
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Sidelock
Joined: Mar 2002
Posts: 2,857 Likes: 384 |
The circle on the lump is fitted to distribute recoil and help keep it on face.look up joining a sxs on the internet also the book guncraft has a good explanation.
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Joined: May 2023
Posts: 23 Likes: 1
Boxlock
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Boxlock
Joined: May 2023
Posts: 23 Likes: 1 |
One of my projects is this double 16 ga "MAC SXS Shotgun - manufacture nat. d'armes de chat" (C&R) action I bought a while ago. Stock and action is complete. No barrels, block, or forend. I found a good deal on a couple unfinished generic barrels a while back and put them in the safe next to the action. I don't plan to be a shotgun builder so I didn't want to buy an expensive reamer for it. Besides 16 ga isn't that common anymore. I also didn't want to start building the mono block (still debating clamshell or mono block) and foot or designing the spacers for the rib until I had the barrels reamed to size. It's just sat there all lonely in the safe for all this time. A sad pile of parts.
Brownell's had a long forcing cone reamer as out of stock ever since. Its been a while now. I could buy one elsewhere for 3 times the price. That would be great if I was going to do more than two barrels, but I'm not. I even consider looking up SAMMI specs and just making a d-bit reamer, but the value wasn't worth the time. Especially since I'd probably mess up the first one and have to make it twice.
I just got a notice that Brownell's had theirs in stock again for the same great price. I logged on to see if my C&R license discount applied, and not only did it apply there was a discount code automatically applied too. The total including tax, shipping, and insurance was less than the original price. I got a friction burn on my fingers getting my credit card out of my wallet. In a few days I'll be the proud owner of a second shotgun barrel reamer (I already have a 20 from a different project).
Last edited by Bob La Londe; 06/03/24 08:13 PM.
-- Bob La Londe - CNC Molds N Stuff Proffessional Hack, Hobbyist, Wannabe, Shade Tree, Button Pushing, Not a real machinist!
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Joined: May 2023
Posts: 23 Likes: 1
Boxlock
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Boxlock
Joined: May 2023
Posts: 23 Likes: 1 |
I still kinda want to choke these barrels, but that might be beyond me... or beyond my budget anyway.
-- Bob La Londe - CNC Molds N Stuff Proffessional Hack, Hobbyist, Wannabe, Shade Tree, Button Pushing, Not a real machinist!
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Joined: May 2023
Posts: 23 Likes: 1
Boxlock
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Boxlock
Joined: May 2023
Posts: 23 Likes: 1 |
I have this crazy idea of making a clamping fixture to compress the barrel tips, and then bore the barrels to modified.
-- Bob La Londe - CNC Molds N Stuff Proffessional Hack, Hobbyist, Wannabe, Shade Tree, Button Pushing, Not a real machinist!
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Joined: Jan 2004
Posts: 6,983 Likes: 490
Sidelock
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Sidelock
Joined: Jan 2004
Posts: 6,983 Likes: 490 |
I have this crazy idea of making a clamping fixture to compress the barrel tips, and then bore the barrels to modified. Clamp the left to right or top to bottom?
_________ BrentD, (Professor - just for Stan) =>/
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