Why is does my French Berthier 8mm carbine have flyers always to the right
:sos: 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
Suggestions for improvement
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
:wave:
* You are at present using a very fast powder with a very heavy bullet!
Overtightened or bent barrel (or foresight blade)
Quote:
Originally Posted by
rayg
There must be a reason the sights on the carbine were made to have the bore point to the right of the sight.
Rayg, you are assuming, quite naturally, that the rifle is as made. I think that this is something you need to check very carefully. There is one very simple possible explanation for what you observe - that the barrel has been overtightened at some time, and that is the reason why the foresight appears to be over to the left.
Simple eyeball judgement may not be adequate to check barrel alignment. One way of doing it is as follows:
1. Use a stable, flat tabletop or large sheet of glass as a surface plate.
2. Place a suitable block of hard wood or metal on the table, so that you can place the rifle upside-down and rest the base of the backsight on this block.* This is to ensure that the backsight base is parallel to the surface.
3. The front end of the barrel should also rest on a block, so that the foresight blade is not touching the table surface. Depending on the position of the center of balance of the carbine, you may need to weigh down the barrel so that everything sits stably. A wobbly setup will invalidate the measurement.
4. Now simply place an engineers square (or a suitable trued-up block) on the table surface in front of the muzzle, and on the bore line (i.e. central) and sight along it towards the foresight. The foresight blade must point vertically downwards. If it is visibly skewed, for instance so that the blade is to the left of six o'clock as you look at the muzzle, then the barrel has (probably) been overtightened. Or the blade is in a dovetail, and has simply been pushed over. Or - wierd but possible - the blade itself is bent.
Of course the answer may be that the barrel is bent! I hope not. But even that can be fixed.
Check it anyway.
Patrick
:wave:
*This will require folding the backsight leaf right over to expose the backsight base.
Check the crown - really carefully!
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
:wave:
