Beretta 391 instructions on shims

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opto55

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I am shooting a Beretta 391 Parallel competition and need to increase the cast off with shims. I am looking for the instructions to make this change but the stuff I see on the net is not specific enough. There are no instructions in the book. Where can I find this information?
Thank you.
 
I have two 391 Parallel Targets, an RL and an SL.

The Instruction Manuals that came with both (purchased about three yeas apart) are identical. Stock Drop & Cast Modifications are on p. 49 and p. 50.
The "DX" mark on the spacer and on the plate means "cast-off" (for RH shooters) and the "SX" means "cast on" (for Lefties) when you're looking at them.
(Turn them over, you have the opposite !) The different numbers on the (fibre) spacers and (steel) plates as provided are stock drop at heel in millimeters.
Depending on model, they range IIRC, from 40 - 65 in drop, but ALL are only a single value in cast, either on or off. depending which way they are installed.
Beretta warns that the corresponding drop & cast spacers & plates be installed as a pair.

If different cast off than that provided is required, Beretta recommends that "Stock drop and cast modification must be carried out by a competent gunsmith".

Of course, if you want to DIY, get a good set of calipers and start measuring the spacers & plates you have and make a new pair to achieve the fit you want.
The external & internal overall length and width of the fibre spacers are the same, but they vary in thickness from one side to the other and top to bottom. The metal plates are all identical in lenght and width, however the stock bolt holes through them are offset top to bottom and left to right depending on drop. The cast dimension (left or right) on each is located in the same place. To achieve more cast, the hole will have to be located just a fraction more to the left on the "DX" side.

From what playing around with shotgun stocks I've done over the years, I've found that as I've increased cast, I also need to decrease drop (as increased cast tends to "straighten up" your head, your eye position raises on the rib ... requiring a slightly higher comb ... i.e., less drop)

Good luck !
 
Play with the shims ... you basically want to be looking flat down the centre of the rib without having to "roll" your head over on the stock or having to crush your cheek down hard on the stock or raise your face of the stock to get the rib to flatten out under your eye. When you bring the stock to your face (not the other way round) and back it up with your shoulder you should get the proverbial "figure 8" bead position down the rib without having to adapt yourself to the stock. In other words, the "sight picture" picture, if you will, should be right there !
 
By all means, pattern your gun for Point of Impact ... before & after you make any change.

I do so on 4'x4' paper at 16 yards - at least 5 shots to ascertain if the gun is actually shooting where I'm looking. I put the pattern paper up and and draw a small dot roughly in the centre as a reference point. Not so much to "aim" at, but rather a quick reference to ascertain the centre of the paper. From 16 yards, load a shell, close the gun, mount it quickly and touch the shot off as if you were shooting at a going away bird or target. The key to doing this is a positive & rapid gun mount ... not "aiming" the shot, but rather replicating what you would do on a target or in the field. Of course this kind of patterning is very much dependent on good form and a repeatable ( time after time after time ....) gun mount. 1/16" of change at the comb (at 16 yards) yields approximately 1" of change at the pattern paper ... or if you prefer 1/8" to 2" . For this kind of patterning, I normally would use the target shells I typically use through a fairly tight choke like Improved Modified or Full. An average of 5 shots should give you a good average of POI ... and if not (as in your patterns are all over the place ) you need to work on the form, technique and mechanics of your gun mount. To achieve the results you are looking for, your gun mount has to be absolutely repeatable. If not, and you start moving your stock around, you will be just chasing your tail. You don't want to purposely aim the gun, nor do you want to have to adapt yourself to the gun to obtain a good sight picture down the rib each time. What you'tr after is to make changes necessary to either drop or cast to get the gun to "shoot where you're looking". Length of Pull and to a smaller extent pitch also have some impact on fit. A bit of reading on each of these facets of fit may well help you to understand how each affects pattern placement and how to fit the gun. ;)
 
Thanks again. You know what you are doing! I bought the gun used. There was no owners manual wit it. I am going to play around with drop shims and see what happens. Will have to order some from Stoeger and go from there. I will let you know what happens.
 
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