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Double Rifles, Single Shots & Combinations >> Double Rifles
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BB308
.224 member


Reged: 09/03/06
Posts: 4
Bore Spacing; Breech and Muzzle Ends
      #54057 - 04/04/06 07:51 AM

I'm curious as to how much double rifle barrels are angled inward so they regulate properly down range. If some folks could post the distance between chamber and muzzle centers on their double rifles, I'd sure grin a lot. It may be easiest ot mesasure the distance between the left sides of both; that's the same as between centers. Thanks in advance. Bart

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Marrakai
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Reged: 09/01/03
Posts: 3595
Loc: Darwin, Top End of Australia
Re: Bore Spacing; Breech and Muzzle Ends [Re: BB308]
      #54073 - 04/04/06 01:18 PM

We've been here before just recently, but I can't find the link. Maybe someone else has it to help BB308 out?

The reason this is a fairly pointless exercise is that the barrels on a SxS double rifle are not straight. They start out parallel, and perpendicular to the breech-face at the chambers, and are curved inwards somewhere towards the muzzles to achieve regulation. The spacing and amount can vary substantially between manufacturers and indeed among their individual offerings.

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

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DUGABOY1
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Reged: 02/02/03
Posts: 1340
Loc: TEXAS USA
Re: Bore Spacing; Breech and Muzzle Ends [Re: BB308]
      #54132 - 05/04/06 10:31 AM

What Marrakai said! The fact is, the measurement you are asking for will only give you a starting point for regulating a double rifle with the same weight, barrel conture, and ballance, of the one measured. It still will not regulate the other rifle even when useing the same exact load!
Regulation is not an exact science, but starts with an educated guess,( the measurements you asked for) and must be completed by trial, & error, the way it has been done for 250 yrs. There are known reasons for this being the case, and I suggest you do a search on regulating a double rifle, on this forum, to get those reasons. They have been posted here many times!
It's old news to most of us, but if you can't find the strings pertaining to this subject, there are those here who can explain it again. Marakai is one who knows. I can explain it, but I don' t have the gift of makeing the most of the written word, like most here!


--------------------
..........Mac >>>===(x)===>
DUGABOY1, and MacD37 founding member of DRSS www.doublerifleshooterssociety.com
"If I die today, I have had a life well spent, for I've been to see the Elephant, and smelled the smoke of Africa!"

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4seventy
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Reged: 07/05/03
Posts: 2210
Loc: Queensland Australia
Re: Bore Spacing; Breech and Muzzle Ends [Re: BB308]
      #54136 - 05/04/06 11:50 AM

Bart,
Not sure why you are needing a bore spacing measurement, are you building a double?
If so there are many here who would like to know more about your project I'm sure.
Regarding the bore spacing on say a double built from scratch, I use the "old four thou to the inch" as a rough starting point.
This equates to approx 100 thou pull in at the muzzels.
All this does is provide SOME convergence at the front and then the rifle is shot to see what happens.
Chances are the two barrels could shoot miles apart or miles crossed and each will usually be at different heights.
Make a decision on how much to alter the spacing after seeing where the gun shoots at 25 yards or less using 100 thou pull in.
Regulating from scratch means you have to start somewhere regarding convergence and I use 100 thou as my starting point.
First shots fired need to be at very close target range to ensure both barrels are on the paper.
Increase target distance as you improve the regulation.
Hope this helps.

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BB308
.224 member


Reged: 09/03/06
Posts: 4
Re: Bore Spacing; Breech and Muzzle Ends [Re: 4seventy]
      #54139 - 05/04/06 12:18 PM

No, I'm not building a double rifle. Just curious about how much they're toed in at the muzzle. This stems from a discussion with some folks some of which claim there is no rifle movement from recoil until the bullet leaves the muzzle. I know from years of competitive highpower shooting that there is some and a double rifle has quite a bit else both barrels could be aligned straight at a 50 yard target and that's where they would shoot except for elevation correction needed.

I'm curious as to where the muzzle axes actually cross for regulating at 50 yards. My guess is it's somewhere around 30 to 40 yards. That's why I wondered what the bore center spacing was at the breech and muzzle so I could approximate the angle the muzzles were crossed in at. It was explained to me by Marakai that the barrels actually curve inward from their parallel alignment for the first several inches of bullet travel. From that, I could approximate the muzzle axes angles. If one starts at 100 thousandths convergence for 24 inch barrels, that's 14 minutes of angle assuming both barrels are straight; they're each crossing enough to point about 3.5 inches to the opposite side at 50 yards.

Thanks for your help.

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unspellable
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Reged: 06/03/04
Posts: 187
Loc: Iowa
Re: Bore Spacing; Breech and Muzzle Ends [Re: BB308]
      #54226 - 06/04/06 04:19 AM

That part of the recoil movement that takes place between ignition and the bullet exiting the muzzle is termed "jump".

The most straightforward illustration of this in fire arm design is the fact that the front sight on a heavy caliber revolver is noticably higher than the rear sight so the axis of the barrel is pointed downward when the sights are on target.

It's been my experience that those who claim there is no such thing as jump will not be convinced no matter how much evidence for it you come up with.

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tinker
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Reged: 12/03/05
Posts: 4835
Loc: Nevada
Re: Bore Spacing; Breech and Muzzle Ends [Re: BB308]
      #54230 - 06/04/06 04:53 AM

In Greener's book, he notes that in preparation for regulation the barrels are typically set up to bore sight the same spot sixty feet from the gun.
There might be something in that piece of information for you.


--Tinker

--------------------
--Self-Appointed Colonel, DRSS--



"It IS a dangerous game, and so named for a reason, and you can't play from the keyboard. " --Some Old Texan...

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