Berthier Carbine sights are offset

[rayg]

Sorry but I just couldn't let go of this, had to prove it one way or another. It was hard to determine if the carbine sight was offset with the early model blade sights because it was hard to measure that. imore did a good job on measuring. I looked at the M16 carbine I just got and you can really see it on that sight. The sight on the M16 carbine was changed from instead of offsetting the sight on the barrel, they centered the sight and offset ground the sight about .090. It's as I said in my previous posts earlier, the bore points right of the sight center on carbines. And I also think I am correct when I said the reason why the bore needs to point more to the right of the sight on the carbine is because the carbines have much thinner barrels and the initial flex upon firing full power loads would be to the left because of the left hand rifling twist. This would cause the bullet to move left to the same as the sight. The low velocity cast bullets just didn't have enough power to cause that flex so they shot where the bore was pointed which confused the issue.
The carbine barrel is .510 dia and the Lebel and Berthier barrels are .585 dia. So the carbine barrel is .075 thiner which would cause the barrel to flex a lot.
Here's my earlier post on Gunboards questioning the sight vs bore zero. And the thread here. Ray.
http://forums.gunboards.com/showthre...rthier-Carbine
Why is does my French Berthier 8mm carbine have flyers always to the right


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[vintage hunter]

rayg, like I said before the only way to prove your theory is to buy, beg or load some full power rounds and find out. Carbine barrels are normally lighter than rifle barrels but at the same time they are just as, if not more, rigid due to the shorter length. When fixed in a machine rest a revolver will more often than not out shoot a rifle due to this fact.

[jmoore]

Easy enough to get full powered ammo, it's made new!:

[rayg]

Ok, why else would they offset the sight. Has anyone fired their Berthier carbine with full loads and if so, did it shoot center?

VH, "When fixed in a machine rest a revolver will more often than not out shoot a rifle due to this fact. "
Maybe so, but that is a real short barrel and most have pretty thick/stiff barrels and I can't imagine there would be much flex in such a short stiff barrel. A 17.8 super thin .310 dia barrel would be a lot less rigid especially with loads much more powerful then a handgun load you think, Ray

[vintage hunter]

Ray, when I said revolver I meant the hand cannon variety used for hunting big game with barrels from 7 1/2 to 10 inches long, not the concealed carry pop guns with 2'' bbls.

[rayg]

All barrels flex to some extent when fired. Some more then others depending on thickness, length, caliber and ammo. I remember seeing a slow motion video of a rifle barrel flexing upon firing one time. Ray

[Patrick Chadwick]

the initial flex upon firing full power loads would be to the left because of the left hand rifling twist.

Could you please explain that?

I have not yet worked out why that should be, unless the action has an asymmetrical lug arrangement. That would be nothing to do with the rifling. The enormous pressure acting on the front edge of the grooves, as a result of the bullet being pushed from behind, will produce torsion in the barrel, tending to "unwind" the rifling. This will presumably act to twist the rifle about the barrel axis. This would be in a clockwise direction for a left-hand rifling, but because the mass is distributed unevenly around the barrel axis, and more mass is below the center line, I would expect the barrel to move to the right, not left.

I am not saying that you are wrong, just that I have not yet been able to work it out.

Patrick

[vintage hunter]

Ray, have you taken into consideration that your barrel could be bored off center?

[jmoore]

Ray, have you taken into consideration that your barrel could be bored off center?

Have you seen his previous thread? Why a new thread, I haven't a clue, but no, there's not that much meat in the barrel to be that much off. That and my carbine is identical (with photos and measurements and everthing!). They're supposed to be that way. He just wants to shoot a load for which it's not regulated.

Humph. Time for bed.

[rayg]

Could you please explain that?

I have not yet worked out why that should be, unless the action has an asymmetrical lug arrangement. That would be nothing to do with the rifling. The enormous pressure acting on the front edge of the grooves, as a result of the bullet being pushed from behind, will produce torsion in the barrel, tending to "unwind" the rifling. This will presumably act to twist the rifle about the barrel axis. This would be in a clockwise direction for a left-hand rifling, but because the mass is distributed unevenly around the barrel axis, and more mass is below the center line, I would expect the barrel to move to the right, not left.

I am not saying that you are wrong, just that I have not yet been able to work it out.

Patrick

Patrick, The front sights of Berthier carbines apparenty are offset about .090 and because of that, they bore sight to the left of the sight. Not just mine but other samples. There must be a reason that they are designed that way. Others posters that have shot them say they shoot center target using full power loads.
Maybe the rifling has nothing to do with it, but whatever takes place when the carbine is fired with full loads, it moves the bullet to the left in line with the sight. The only explaination I can think of, is the barrel must flex to the left when the bullet leaves the muzzle upon firing. Why else would it shoot center and not to the right. Ray