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Convergence. Now there's a subject that potentially opens a whole new can o' worms.

If we were, for the sake of example, to decide that we wanted our double rifle to be zeroed for 75 mards, ought we to worry too much about true convergence ? If we assume that the bores are parallel, and separated by a calibre, then it ought to be the case (all other things being equal) that we could obtain a group at 75 mards that is simply three calibres measured edge to edge. Regulating the barrels to shoot to the same point at that distance would give a theoretical single calibre hole which, we grant you, is better than three calibres. However, at ranges other than the regulated range, the group size would increase. Hence for practical purposes, might we not be better accepting that a three calibre group size is passable for our needs in the knowledge that it will be a three calibre hole at any distance?

It would be an interesting test...

That assumes that the barrels will be sleeved parallel.

Whatever convergence/grouping you decide on it will still need to be regulated for that unless you just take pot luck grouping/scattering convergence/divergence after sleeving and chambering.

Hmmm, maybe someone can recommend a sleever who is up to the job... :)

That is assuming the barrels have been sufficiently well aligned on the donor shotgun, what alignment is sufficient for a shotgun cartridge at out to 30 yards might not be sufficient for a rifle at 100 yards?

An excellent point, Cassandra, and well made.

All you oomanses out there in possession of a small bore, say 28 gauge or 410, shotgun, and a laser cartridge / alignment gizmo thingy can help with this one. How accurately are the barrels aligned?

That will only tell you about that particular gun and the accuracy will depend on the quality and fit to the gun of the laser cartridge / alignment gizmo thingy.

They are usually close enough for pit work but that is about all, the MK1 eyeball does just as good.

Oh WOWSY ! oomans, just look what we've discovered on 'tinterweb!



http://www.hoferwaffen.com/hofer_52s.php?id=14&lang=en

meles meles wrote:How accurately are the barrels aligned?

They're not very accurately aligned. They don't need to be. This is also why true double rifles are very expensive, even in plainest of finishes. The amount man hours and skill regulating barrels is huge. Likewise, the regulation of such is finalised within a very tight set of parameters.

Hmmm, it needn't be that difficult nowadays. With modern CNC controlled machinery and ED deep hole drilling it ought to be a doddle to make two properly aligned barrels. Longthorne Hesketh take that approach to their shotguns...