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Nitro:

.470 didn't clarify the point of his post and perhaps my assumption was incorrect, but I sure thought I got his meaning. In my experience, yes, if the barrels cross-fire say 2" at 50 yards, they will usually cross-fire 4" at 100.

Rant: on

The point is, a double rifle that does that consistently with correct ammunition NEEDS REPAIR. THEY'RE NOT SUPPOSED TO DO THAT. That is the purpose of "regulation". If we were to accept that all double rifles cross-fire and nothing could be done about it, then the barrels could simply be welded together perfectly parallel and we would accept that they would be uselessly inaccurate beyond 50 yards. No need for expensive regulation and double rifles would be cheap.

A perfectly regulated side by side rifle should print like this at 50yards, 100 yards, etc.: oo. A perfectly regulated O/U should print like this: 8. All double rifles, not just big bores, have to be built to allow for movement of the axis of the bores away from POA during barrel time. With a side by side rifle, fired from the right shoulder, the right barrel recoils in a sine arc up and out to the right. The left barrel wants to go up and left, but there is a natural resistance to this for a right handed shooter, with the result that the left recoils in an azimuth closer to the vertical. Recoil movement begins while the bullet is still in the tube and the period of this movement before the bullet leaves the barrel is called barrel time. Adjusting the convergence and divergence of the barrels so that they print to a common POI despite the barrels being headed in different directions at the moment the bullets exit is called regulation.

Because the barrels recoil away from each other during barrel time, and in different arcs, if the barrels were perfectly parallel, they would print wide, with the left well to the left of the right and higher (because the left recoils closer to the vertical during barrel time than does the right). As a result the barrels cannot be perfectly parallel in either plane. As a rough rule of thumb for nitro calibers of .400 up, the barrels are given .003" of convergence per inch of barrel length in the horizontal plane when they are brazed together. Thus, a .400 with 26" barrels will start with about .078" convergence. Likewise, they are given a similar amount of divergence in the vertical plane (this divergence is too small to see on nitros, but pay attention to the muzzles of the larger caliber BPEs - it is sometimes actually visible). When the rifle is complete, in the white, regulation is performed with the ammunition intended for it. If the barrels cross-fire, the solder between the barrels is softened with heat and the muzzle wedge is pushed in to spread the barrels apart. The opposite is done if they are shooting wide. Vertical dispersion is corrected by moving the left barrel up or down in a special jig with set screws. Ideally (and this is where the good stuff gets separated from the scrap iron), this process isn't complete until the rifle puts the rights on right and lefts on left an inch or so apart at 50 yards. Set this way, the barrels will not cross-fire at any hunting range that is sane for a double rifle. I have two that shoot like that - neither cross-fires even well out beyond 100 yards.

The addition of a scope and mounts after regulation will often mess it up. The extra weight on top of the barrels dampens movement during barrel time with the usual result (but not always - some doubles tolerate it with no change in regulation at all) of the barrels cross-firing. Thus, if the rifle is to be scoped, it should be ordered that way or re-regulated when the scope is added, if necessary.

This guy is a Krieghoff dealer and the quote appears to be in reference to rifles of that make. He seems to state that these rifles are regulated to cross at 60 meters. I've fired the Krieghoff side by side in .500/.416, .375 Flanged Magnum and 7X65R extensively. I didn't fire the .500/.416 beyond 100 yards, but it didn't cross-fire at that range. I fired the .375 and the 7X65, both of which were scoped, out to 200 yards and neither cross-fired. All three are very accurate.

The only explanation I can come up with for that quote is that he was referring to rifles that had not been reregulated after adding the scope with the expectation that they would then cross-fire, which is unacceptable (am I missing something or are we not talking about a NEW RIFLE here?). Either that, or he doesn't know much about his product, which isn't especially rare among double rifle dealers. I once bought a .450/.400 3" rifle from a dealer who has sold many hundreds, if not thousands of double rifles over the years. He promised that he would send 100 rounds of factory Kynoch along with it. He sent .450/.400 3 1/4" ammo, insisting that they were the same and it would work just fine! I know another Krieghoff dealer personally and what he doesn't know about double rifles would fill a small library.

So, just zero the scope with the most accurate barrel and use your double rifle like a single shot. Oh, PULEEEEZ.

Rant: off
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"Serious rifles have two barrels, everything else just burns gunpowder."