Benelli Shotgun Shims Explained

A Benelli stock shim does not alter the barrel or the choke. It changes the angle of the stock relative to the receiver, moving the shooter’s eye, the shotgun’s effective rear sight, into a better position. Used correctly, the system can improve gun fit and move the centre of the pattern.

First principle: your eye is the rear sight

A conventional shotgun has a front bead but no rear sight. When the gun is mounted naturally and consistently, the position of your eye above and to the side of the rib determines where the gun points. The stock therefore needs to bring the gun to the eye, rather than forcing the head down to the gun.

Benelli’s shim system changes two main dimensions:

• Drop is the vertical distance between the sighting line and the stock. More drop lowers the comb and heel relative to the rib. For a consistent mount, that usually lowers the eye and the point of impact.
• Cast is the sideways offset of the stock. DX moves the stock to the right as viewed from behind the gun; SX moves it to the left.

Length of pull is a separate measurement, normally altered with a different recoil pad or spacer. A drop shim is not a length-of-pull spacer.

Installation order: drop shim → cast shim → stock → matching steel plate → washer → retaining nut. The stock sits between the front shims and the rear plate.

Drop

Benelli’s tables normally quote drop at heel: the vertical distance from the sighting line to the heel at the top of the butt. The plastic wedge moves the complete stock, so it changes the height of the comb where the cheek rests. The quoted number is not the thickness of the shim.

Measure vertically from the rib line to the heel. More drop moves the stock down relative to that fixed line.

What each drop-shim letter does

Across the common Z–D system, the alphabetical direction is consistent: Z gives the least drop, followed by A, B, C and D. Moving towards D lowers the stock and generally lowers the point of impact. Moving back towards Z raises the stock and generally raises the point of impact.

The number attached to a letter is not universal. Many standard-rib guns use 45/50/55/60/65 mm. Raised-rib schedules commonly read 50/55/60/65 mm for Z/A/B/C. Older parts catalogues often call the maximum D position 64 mm rather than 65 mm.

Z shim
Common example: G0204600

Least drop: ↑ STOCK / ↑ POI
Highest stock position in the common sequence. Click the image to enlarge.

A shim
Common example: G0136300

One step below Z: ↓ STOCK / ↓ POI
Commonly 50 mm normal rib or 55 mm raised rib. Click the image to enlarge.

B shim
Common example: G0136400

Middle position: ↓ STOCK / ↓ POI
Commonly 55 mm normal rib or 60 mm raised rib. Click the image to enlarge.

C shim
Common example: G0136500

More drop: ↓ STOCK / ↓ POI
Commonly 60 mm normal rib or 65 mm raised rib. Click the image to enlarge.

D shim
Common family example: G0136600

Greatest listed drop: ↓ STOCK / ↓ POI
64–65 mm normal-rib families; only where the model permits D. Click the image to enlarge.

Cast: DX and SX explained

Cast is easiest to understand from above, standing behind the gun and looking towards the muzzle. Benelli uses Italian abbreviations: DX for right and SX for left. The moulding may be reversible, so the marking specified by the manual normally faces the stock when installed.

Reversible cast shim
DX means right when viewed from behind.

DX / normally right shoulder: STOCK →
The butt and comb move right relative to the bore centreline.

Reversible cast shim
SX means left when viewed from behind.

SX / normally left shoulder: ← STOCK
The butt and comb move left relative to the bore centreline.

The steel plate is part of the adjustment

The front plastic shim creates the angle; the steel plate inside the stock must support the same angle around the stock bolt or recoil-spring tube. Some older guns use a separate right- or left-hand plate for each drop. Later systems use reversible plates with several markings, such as A-DX/B-SX on one face and A-SX/B-DX on the other.

For a C drop and right-hand cast, the matching set is C drop shim + DX cast shim + the steel plate oriented to show C-DX.

Front and rear form one matched system.
The front shims establish the angle; the rear steel plate supports it.

Multi-marked steel locking plate.
Match both the drop letter and DX/SX direction.

Common drop schedules

These are family patterns, not a substitute for the exact owner’s manual. Benelli’s own M2/M2 Speed and SBE3 manuals show Z–C at 50/55/60/65 mm, while Ethos and Montefeltro manuals show Z–D at 45/50/55/60/65 mm.

How to choose the next shim

1. Start with an unloaded gun. Check chamber and magazine visually and physically, and keep ammunition away from the fitting area.
2. Record what is fitted. Photograph the front drop/cast markings and the orientation of the steel plate before moving anything.
3. Check natural mount. With a safe direction and no ammunition present, mount the gun to a fixed reference without craning the neck. The eye should arrive naturally over the rib.
4. Pattern the gun. Benelli’s SBE3 fitting video uses ordinary birdshot at about 20 yards and asks the shooter to mount and fire as they would at a bird, rather than carefully rifle aiming the gun. Several shots are better than trusting one mount.
5. Change one axis at a time. If the centre of the pattern is high, add drop by moving towards C or D. If it is low, reduce drop by moving towards A or Z. If the fit needs to move right, use DX; if it needs to move left, use SX.
6. Repeat the same test. A useful all round reference is often around a 60/40 pattern, but the right blend depends on discipline, target presentation and shooter preference.

Move the stock in the direction the pattern needs to go.
Pattern again after each one axis change.

Z → D progressively adds drop.
The physical profile and exact millimetres depend on the gun family.

Installation

Recoil pad removal, internal stock inserts and supplied shims vary by model, so use the owner’s manual for the exact shotgun. The following are principles, not universal disassembly instructions:

• Unload completely before touching the stock.
• Use the drop shim, cast shim and steel plate specified for that model and stock.
• Match the drop letter and DX/SX direction exactly. Do not fit the steel plate by whichever orientation seems to sit most easily.
• On common systems, the selected marking on the front plastic shim faces the stock and the selected marking on the steel plate faces the buttpad, but verify this in the model manual.
• Pointing the barrel down while sliding the stock on helps the internal plate and stock settle squarely on the tube.
• Tighten the retaining nut correctly, refit the pad, and recheck the stock after the first few shots.

Common misunderstandings

“A thicker shim must raise the pattern.”

Not necessarily. The moulding is a wedge, and the labelled result is the stock angle. Follow the letter schedule: more drop means a lower stock and usually a lower point of impact.

“A C shim is always 60 mm.”

No. C is 60 mm on many normal rib shotguns and 65 mm on raised rib shotguns. The rib changes the reference line from which drop is measured.

“The steel plate is just a washer.”

No. Its offset hole and bearing angle are part of the geometry. It must match the front shim.

“DX and SX tell me which side of the gun the part belongs on.”

They describe the resulting cast: DX right, SX left. Many pieces are reversible and work by presenting the chosen face in the orientation specified by the manual.

Bottom line

Think of the system as a matched three-part hinge: the drop shim sets height, the cast shim sets sideways offset, and the steel plate locks both angles from inside the stock. Z is highest, D is lowest, DX is right and SX is left, but the part number and the model specific manual tell you what fits.

Pattern first, alter one variable, match every marking and pattern again. That turns a small bag of black plastic pieces into a useful gun fitting system! 

Sources and further viewing

• Benelli SuperNova owner's manual — official Z/A/B/C 50/55/60/65 mm drop-and-cast schedule for shim-adjustable versions.
• Benelli Nova owner's manuals and Benelli Nova 3 owner's manual — the Nova stock/receiver is an integrated unit and the manuals provide no receiver-to-stock drop/cast shim adjustment.
• Benelli M2 Field owner’s manual — official Z/A/B/C raised-rib schedule and matching warning.
• Benelli M2 Speed use and maintenance manual — official 50/55/60/65 mm schedule and assembly sequence.
• Benelli Ethos owner’s manual — official Z–D 45/50/55/60/65 mm schedule.
• Benelli Montefeltro Silver owner’s manual — normal-rib Z–D schedule.
• Benelli Super Black Eagle 3 owner’s manual — raised-rib drop/cast kit and assembly.
• Benelli USA: Super Black Eagle 3 Shim System — Adjusting Drop and Cast — fitter-led pattern-board demonstration.
• Benelli exploded parts catalogue (2014 mirror) — part-code/profile cross-check for legacy 12- and 20-bore families.
• Teuvo Louhisola Benelli stock-parts catalogue — current G088 compatibility and normal-/raised-rib values.
• ShopBenelli 12-gauge stock drop assembly kit — factory kit photograph used to cross-check real shim and reversible-plate shapes.
• ShopBenelli Ethos 12-gauge stock drop kit — factory kit photograph used to cross-check the real five-position family and multi-marked plates.

Z shim drop — 45 mm standard-rib reference

A shim drop — 50 mm standard-rib reference

B shim drop — 55 mm standard-rib reference

C shim drop — 60 mm standard-rib reference

D shim drop — 64–65 mm standard-rib reference

DX cast — stock moves right, viewed from behind

SX cast — stock moves left, viewed from behind

Drop at heel — rib datum and vertical measurement

Shim system components and installation order

Benelli Z drop shim photograph

Benelli A drop shim photograph

Benelli B drop shim photograph

Benelli C drop shim photograph

Benelli D drop shim photograph

Reversible Benelli cast shim — DX example

Reversible Benelli cast shim — SX example

Matched drop shim, cast shim and locking components

Benelli Z/C locking plate photograph

Pattern correction diagram

Benelli-style Z, A, B, C and D drop-shim family