Why is does my French Berthier 8mm carbine have flyers always to the right

[jmoore]

Could it be like the Mauser 71s?

[Patrick Chadwick]

My M71 shoots to the same POI at 100 meters as at 50 meters (horizontally, of course. Vertically, there is a noticeable drop).

This offset Berthier POI is one of the most awkward forum questions I have met. Apart from checking that the barrel is not bent and that the muzzle crown is clean and square to the bore - the usual things that you would check on any rifle before purchase - I am stuck for suggestions in this case.

Patrick

[rayg]

I guess I'll just might have to buy some 8mm jacketed bullets in the 200 gr, weight and see what happens with a full load. I only like to fire cast bullets as they are much easier on the weapons and of course on me!
Maybe I can find a few bullets for sale instead of a whole box. I'm sure all I'll be able to find will be the .323 ones and not the proper .327 size but I understand the .323 ones do bump up and shoot ok.
I have some military 8mm ones I bought for my ZF41 Mauser that I haven't shot yet, Always shot cast in that rifle also. I could pull the bullets and use them but I don't think the bullets would be heavy enough to equal the original bullet weight. Ray

[rayg]

Well I went back and looked again and now I'm not so sure if the sight is offset. It's really hard to get a good set-up where you can really tell as I don't have a couple of squares. I keep getting a different reading each time. Ray

[rayg]

Apparently the carbines sights were not offset according to these photos posted on the gunboards site, Ray
Moving rear sight on Berthier Carbine?

[Patrick Chadwick]

rayg - have you checked the muzzle crown really carefully?

Whatever the sight setting, that carbine ought to produce groups nearly as good as the long rifle at 50 yards. A bit looser because of your PWF (Personal Wobble Factor) on the much shorter sight radius.

A tip: holding the barrel up to the light and looking down the muzzle end is not good enough. People like to show off with this, but if you are not a professional barrel maker it is just show. You are blinded by the light coming down the barrel, and cannot evaluate the crown. Try it like this:

Make a tight roll of white paper and push it into the muzzle so that it sits about 1/4" below the crown. Then stand the rifle upright in a support aranged so that you can rotate it. Do this in daylight, or, if you are working in a cellar, position a lamp to shine straight down onto the crown.

Then take a watchmaker's eyeglass and look diagonally at the crown, not straight down the barrel (which will not work anyway, because your head would shut out the light). The paper roll (I use white felt cleaning plugs, but they do not seem to be available outside Mauserland) will reflect the light so that the crown is well illuminated. It will also show up any rust close to the muzzle Now slowly rotate the rifle to inspect the entire circumference. You will soon see if the crown is damaged or worn assymetrically (pullthroughs!). This is probably the most common fault with old service rifles, and just about every one of mine has been recrowned. And it has improved every one so treated.

If you have not done this yet, please do it as your next action with this rifle. Recrowning is a dramatic-sounding word, but it is only necessary to remove just enough metal to get a clean and symmetrical edge to the muzzle so that the bullet does not receive an off-axis shove as it emerges from the muzzle. A gunsmith should do it in a few minutes for less than the cost of wasting a couple of clips of original Lebel ammo on futile tests!

Patrick

[jmoore]

Hokay, the sight is offset on mine about 0.090" (!) Not adjustable either- it's built in. I thought as much, but had to confirm.

Photos in about 12-18hrs or so, when I have access to another computer.

[rayg]

Just to make sure, I went and bore sighted again and it is as I said the first time, the bore points right of the sight. I sighted at a vertical window frame about 50 yrs away.
I don't think a damaged crown would change the bore sighting being off.

Patrick, if you can, go to the Gunboards site and view the photos of the sights vs bores.

Is it me or does the #3 photo that is more of a straight on shot of the bore according to the bore shadow, look like the sight is slightly canted to the left, (photo right). And on #4 where the bore shadow shows the bore is more pointed to the left, (photo right), but the sight is straight. Or am I reading more into it? Ray



PS, Patrick I would like to compliment you on your knowledge of guns and trouble shooting, Ray

[jmoore]

This type carbine, yes?


I could not both measure AND photograph simultaneously, but basically, just used two calipers at the same time. The "outer" one established a plane tangent to the barrel OD, which is hopefully reasonably concentric to the bore, and adjusted the "inner" one until it read the same at the bottom and top of the sight blade. Some small room for error, but not more than 0.002- 0.003" per side.

About the thinnest walled barrel of which I'm familiar in a high powered centerfire rifle cartridge! 0.507" OD, 0.327" bore, so 0.090" wall thickness. Coincidence? Gotta be!



Right side. (as seen from the rear) 0.199" barrel OD to sight blade:



Left side, as above. 0.110" barrel OD to sight blade:



Raw numbers, I didn't even try to get them to come out the way they did.

[rayg]

Just thought of a possible reason why the bore may point more to the right then the sight on the carbine and that is that it has a much thinner barrel then a rifle. Possible with the left hand rifling and the initial flex of the barrel upon firing, it could cause the bullet to move left more then just drift. Don't know, but I know thin barrels will flex a lot more then thicker ones. Maybe if that initial flex is to the left coupled with the left hand rifling, it could make up the difference when using full power loads. Just a thought, Ray