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Discussion Starter #1
Hello all:

I am a left hand shooter who just purchased his first Beretta 391. It's on its way to me now.

I understand how shims affect the cast and drop of my stock. SX is for lefties, DX for righties.

The 391 stock has a slight right hand cast.

Cole Guns has four listed:
42.5mm
40/45mm
50/65mm
55/60mm


What shim will give me the the most drop and most left hand cast?

50/65mm or 55/60mm?
 

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The most drop should result from the 50/65mm. I just bought a couple of those from Brownells.

I haven't noticed a change in the degree of cast with any of them. I think it's either right or left and doesn't vary with the drop selected. It's also never sufficent for me with a factory stock.

What stock is on it now? Factory sporting or trap? Aftermarket? Why does it have a "slight right hand cast"?
 

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Discussion Starter #4
Factory sporting.

From what I've seen and what Pacific Sporting Arms says its a slight RH cast.
 

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Discussion Starter #5
Looking at a shim online the 50/65mm is C-65-DX and C-50-SX

The SX side is for lefties and would result in 50mm of drop.


Wouldn't the 55/60mm result in greater drop?
 

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The most drop is ALWAYS the shim with the greatest difference between the two numbers, where the larger number is the top number. It doesn't matter what those numbers are. Look for the greatest difference.
 

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Looking at a shim online the 50/65mm is C-65-DX and C-50-SX

The SX side is for lefties and would result in 50mm of drop.


Wouldn't the 55/60mm result in greater drop?
Yes,it will result in either 55 or 60 mm of drop depending on how it is oriented. Also you can have 65 mm drop by properly installing the 50/65 shim.
 

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The most drop is ALWAYS the shim with the greatest difference between the two numbers, where the larger number is the top number. It doesn't matter what those numbers are. Look for the greatest difference.
I believe you may be mistaken about the difference statement.Read the instructions that came with the gun.
 

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I believe you may be mistaken about the difference statement.Read the instructions that came with the gun.
I am not mistaken. Forget the instructions. Look at the shim. The one that is thickest at the top and thinnest on the bottom will allow the most drop. It's geometry. Beretta uses different numbers on the shims depending on whether it's for a parallel stock or a sporting stock. You can use any shim on any stock. The difference between the numbers is all that matters.
 

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I believe you may be mistaken about the difference statement.Read the instructions that came with the gun.
I don't know what you are reading, but dicktax is giving you the correct information.

To get the most drop, use a 50/65 mm shim and stock washer.

Good Luck and Good Shooting!
 

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It’s the number at the top of the washer when installed that counts. 65mm equates to 2.6” of drop at heel (top of pad). 55mm =2.2” drop at heel 45=1.8” .

These are standard measurements and your gun will vary slightly depending on how the stock was inlet and finished. Each 5mm washer change will move the heel up or down on your gun by .2” or roughly 13/64” (halfway between 1/4” and 1/8”).
 

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Looking at a shim online the 50/65mm is C-65-DX and C-50-SX

The SX side is for lefties and would result in 50mm of drop.


Wouldn't the 55/60mm result in greater drop?
You're only looking at one side online.

Installed with the C-50-SX readable at the top, it will be cast left with 50mm drop.

Flip it over, spin it 180 degrees and install it with C-65-SX readable at the top and it will be cast left with 65mm drop - the most drop with a single shim.

It can be installed in only four ways; you'll figure it out. But with factory wood you also need the corresponding steel shim that goes in the butt, around the through bolt.
 

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On a side note, make sure the front and back washers #s match and the front doesn’t flip around when you are installing it. Don’t overtighten torque down the stock bolt, you can crack or twist the stock at the wrist. If you have s stock with a little hump or bump in that area, it is due to mixed washers or over torquing the stock nut.
 

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The drop created with the shims is not the best way to lower the POI. Since it is changing the angle of the stock to the barrel, most of the change is occurring at the end of the stock, and the height and pitch of the butt pad. Relatively little where the face contacts the comb. An adjustable comb is a much better solution for raising or lowering the
the POI. Tron is a good choice to install an adjustable comb.
 

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I am not mistaken. Forget the instructions. Look at the shim. The one that is thickest at the top and thinnest on the bottom will allow the most drop. It's geometry. Beretta uses different numbers on the shims depending on whether it's for a parallel stock or a sporting stock. You can use any shim on any stock. The difference between the numbers is all that matters.
You're only looking at one side online.

Installed with the C-50-SX readable at the top, it will be cast left with 50mm drop.

Flip it over, spin it 180 degrees and install it with C-65-SX readable at the top and it will be cast left with 65mm drop - the most drop with a single shim.

It can be installed in only four ways; you'll figure it out. But with factory wood you also need the corresponding steel shim that goes in the butt, around the through bolt.
Mr Campbell has it correct.You need to use the black plastic shim with the matching metal piece in the butstock.
 
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