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

[rayg]

I shoot 16grs 2400 powder behind a 205gr gas checked cast bullet in my berthier and Lebel long rifles with 31.5" bbls and get good groups at 50 yrds w/no flyers, but when I shoot the same loads in my 2 carbines having about 18" bbls and w/excl bores, about every other shot is a flyer about 6"-7" to the right.
Do you think the bullet is not stabalizing with that powder charge in the shorter barrels and would an increased powder charge correct the situation? Or is the powder not the right burn rate and I should use a slower or faster powder?
Ray

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[Patrick Chadwick]

Convention wisdom would suggest that for a carbine one should use a powder somewhat faster than for the corresponding rifle.
However, if you study the construction of the Berthier bolt you will see that it is at bottom still the same as for the Lebel, which was itself a modification of the Gras bolt. In other words, basically a blackpowder bolt with a small-bore head attached. And this head is neither integral (as on Mausers) nor screwed on (as on Enfields) but simply turned into a slot. In other words, it is woefully sloppy compared with later bolt systems designed from the outset for smokeless powders. It was an anachronism, even for its day.

As a result, a powder like Alliant 2400 is far too vivacious for this action. Although it may be plausible for firing cast or copper-plated lead bullets in a modern carbine, the pressure onset is too harsh for the old design. In non-technical terms, it is generating too much "whack" too early. The system is being subjected to a shock wave that rattles up and down the barrel several times before the bullet exits the muzzle. If the bullet exits the muzzle at the same instant as the shock wave hits it, the grouping will be poor and extremely sensitive to very small variations in the load, seating depth, neck tension etc etc which can produce flyers.

If this is indeed the major cause of trouble, then you should be able to improve matters by making a series of targets with loads varying over a wide range, right through from a minimum up to the maximum. Do not worry about position on the target, just measure the group sizes. As one can always have a flyer caused by personal error, make a graph with 2 curves.
1. A graph showing the group size against powder charge.
2. Then strike out the worst shot from each group, and then draw the graph again.

If you have done this very carefully - you really need to shoot all targets in identical conditions, which means ideally on the same day, in one long session - you will have two curves that do not cross and show at least two humps of bad grouping, with a valley in between.

The "peaks" are easier to see than the "troughs". As the peaks represent the worst loads, simply take a load that is midway between two peaks, and you will have a load that insensitive to small variations and is probably the best you can do with that powder. If you are still not satisfied, try again with a slightly slower powder*.

Patrick


* You are at present using a very fast powder with a very heavy bullet!

[Patrick Chadwick]

Do you think the bullet is not stabalizing with that powder charge in the shorter barrels

That is something that we on this forum cannot answer - but you can, by looking at the targets (which you have not presented).

If the bullet is not being stabilized, you will see shots all over the paper, and some of them will not be round, showing that they are keyholing. It does not have to be a crude as a real keyhole, where the bullet goes through the target more or less sideways. Even visibly elliptical indicates that the bullets are not being properly stabilized.

Patrick

[rayg]

Thanks Patrick, you've given me something to think about with the fast powder. The bullets were not keyholing. I only fired 4 rds with the carbine and the target shows two on grouping and one shot to the right with the 2nd off the paper way right. I shot the Berthier Rifle and Lebel rifles w/2400 powder In looking at the targets, I see two right flyers with the Berthier rifle when I used 19 grs of I-2742 powder. Also I see one flyer to the right with the Berthier rifle with 16-2400. The Lebel rifle is the first time I shot it. w/16-2400 had no flyers to the right w/ fair group. Possibly the flyers with the 2742 powder may give a clue on powders. In looking at some other targets I shot with the Berthier rifle, I didn't see any flyers using 17gs of 2400 only with the16 grs.

Sorry I didn't turn them, Ray

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[rayg]

Well forget the powder, I just bore sighted the carbine and the sights are off. With the sights center on target, the bore is right of the target which would cause the right hand shots. I also bore sighted my Lebel and Berthier rifles and the sights are right on. Maybe the sights were set different for the carbines shorter barrel to compensate for drift using full powder issue loads? Ray

[Patrick Chadwick]

Well forget the powder,

No, don't. If you refer back to my previous posts you will se that I recommended not worrying about the position on the target, but the group size and how it varies with the load. OK, the sights were really off target, and it is obviously useful if you make a correction to bring everything back in the black. But your original problem was the flyers - and that has nothing to do with sights. Unless, of course, the sight is actually loose!

So I repeat my recommendation to carry out the grouping test as I described.

Patrick


---------- Post added at 11:57 PM ---------- Previous post was at 11:54 PM ----------

Maybe the sights were set different for the carbines shorter barrel to compensate for drift using full powder issue loads?

Possible in theory, but in practice it would be hardly noticeable at 50 yards. Drift is a matter of external ballistics, not internal ballistics. It would depend on, amongst ther things, just how fast the bullet was rotating when leaving the muzzle. The sights were wrong, period. BUT just maybe, something else is wrong... like the barrel binding hard on one side of the channel - or even being loose! Or maybe the muzzle has a defect - asymmetrical wear, or a burr? Examine it under a watchmaker's eyeglass.

[rayg]

Well I just checked the rifling twist and it's a left hand twist. Possibly the bore on the short barrels has to point more to the right to compensate for the left twist of the rifling in the shorter barrel. Again this is the 2nd carbine with the shorter barrel I fired were the the shot went way to the right.
I never worry were the shots go as long as they group well. I've never had a old military rifle that didn't have adjustable sights that shot center. But this carbine is so far right that there has to be a reason why they set the sights like they did. Possible if I fired full velocity jacketed loads it would shoot on target. Maybe the short barrels with that left twist might have to be sighted different, Ray

[muffett.2008]

One of the things you are not telling us, is how and with what support, are you obtaining your groups.
Are you using a rest? front and rear? unsupported?
With a bity little carbine there is a tendency to 1. flinch- high shots, 2. lift your head-low shots, 3. anticipate the recoil-left shots(right handed) and 4. muscle the gun-right shots.
More information before you blame the tool.

[rayg]

Some good thoughts. I used a padded rest front and back. low kick with the low power cast bullet loads, no flitching at all. Great sight pictures and trigger control. Been shooting for many years. As stated, the carbine sights do not line up with the bore. The bore points to the right of the sights, thats why the shots go so far to the right. The shots are at least 6-7" right of center at only at 50yrds. The cabine is totally as issued with those sights made that way. Again this is the 2nd carbine I shot that would shoot way right about the same 6-7" with the same cast bullets.
There has to be a reason why they made the bore on the carbine to point to the right of the sights. The only thing I can think of is maybe the 17.8" (14"shorter then the rifle's bbl), carbine barrel with the left hand twist might shoot center when shot with the issue full power military ammo but the not with the low velocity cast bullets. Both the rifle's 31-1/2" barrels are bore and sight centered, Ray

[vintage hunter]

Are both front and rear sights offset to the left a hair or is it just the front sight blade thats off to the left? I've noticed the same thing withJap T-38 carbines (both sights offset) but they all pretty much shoot center w/ full power jacketed loads. Not sure this is your problem but some rifles are sensitive to where they are rested on the foreend, try resting it under the rear sight or as close to the magazine as possible. The front rest sensitivety is more noticeable on rifles with non-floated barrels but i've seen floated barrels that did'nt like being rested towards the forend tip.