The Very Comprehensive Malcolm Interchangeable Parts Guide

For more information on which Malcolm scopes fit easily on which vintage rifles, check out the Vintage Rifle Compatibility List

A comprehensive Malcolm Short Scope parts compatibility post!

This article will be divided up in a way that should allow you to jump right to what you have a question about. 

Vintage scopes are just as varied and unique as scopes are nowadays - including the mounting solutions. To try to simplify these scopes and show the compatibility of parts, I've divided this Post into four sections: Tubes, Blocks, Front Rings, Rear Rings. The section on Front Rings will also include information on recoil sliding.

I’ll be covering the parts included in four of our Malcolm scope kits, as well as a few accessories.


Scope Tubes


Scope Tube:

USMC 8X (Unertl)

Two Tone

18” 6X

17” 3X

Magnification

8X

6X

6X

3X

Length 

23”

18”

18”

17”

Notes

Haspope rib that allows scope to slide

Has brass finish on the ends

All black finish

All black finish


All four scope tubes have a ¾” diameter.

The scope tubes being covered here are : 

The four malcolm scope tubes in this article - a 3X, two 6X's, and an 8X

 

We’ve traditionally referred to the 17 & 18” scopes as short Malcolm scopes (they're definitely shorter than the long 30" Malcolm scope!). All four of these Malcolms have a 3/4" tube diameter. Most of the parts that work on one scope will work on the others, with a few exceptions. If you have a ¾” scope tube, it is likely that the rings that work on our scopes will work on yours as well.

When it comes to choosing a scope tube, the only real considerations are style, size, and magnification. If, for example, you were going to compete at the CMP - you’d probably use the USMC 8X scope on a 1903A1 rifle. If you wanted to build a reproduction WWI rifle with an A5 scope atop it, you’d want to go for the 3X or 6X all-black Malcolm scopes.

In the smooth-tube Malcolm scopes, the reticle is leveled by turning the scope tube with the locking collar loose. In the USMC 8X scope, the reticle is attached to an exterior locking collar, which can be loosened and rotated to level the reticle. The USMC 8X is also the only scope with a replaceable & customizable reticle - though you’ll want to take care not to drop your reticle when you’re installing the rings.

Deciding whether you’ll want the scope to slide, whether to install a return spring, or for anything else that goes onto the tube, please read further. 

Blocks

Block Types:

1903A1 Bases

½” 60 degree Bases

Cut(s)

Crescent

Posa & Crescent

Hole Spacing(s)

.560”

.860”

Blank (undrilled)

14mm (previous bases)

.860” (current)

Profile(s)

Fits 1903 rifle receiver profile

Flat or round


The blocks that attach scope rings to the rifle - in different lengths and heights

 

Before the picatinny rail became commonplace, rings would fix to standard mounting points on a rifle, or be machined on in other ways. Whatever these mounting points were called in the past, those attachment points now come in the form of blocks. Blocks seem a little strange if you're not used to them. The long and short of it is - these are like individual picatinny mounting points. And, much like a picatinny rail, you need to stick these onto your gun in a way that's stable and aligned with your barrel. Once the blocks are on your rifle, you can go ahead and attach the rings that hold your scope.

Posa and Crescent

A block showing the crescent cut on the left and posa cut on the right

The crossbolt of the ring determines which cut of a block you need, while the shape of the barrel or receiver decides the shape of the block’s profile. The crossbolt locks the ring onto the block, keeping it from sliding backwards under friction.

a posa cut crossbolt and the associated side of the block A posa cut crossbolt has a flat end, and fits into a straight groove on the block.
a closeup of the crescent cut on a block and the associated crossbolt A crescent cut has a bowl-shaped end on the crossbolt, to fit onto the crescent on the block.

Profile

The underside of different blocks, showing the shape of their mounting point

If your barrel is octagonal or if the receiver is flat where the block is attached, the block needs to be flat. You could get a curved-bottom block that will work just as well, but the fully-flat block will provide more friction. On the other hand, a round barrel or curved mounting point will require a curved block. Trying to make a flat block fit onto a round barrel will let the block wobble side to side, and provide no lateral support.

As long as your block is the same general shape as your mounting point, and your cut is the same as your crossbolt, you’ve got the right block.

Adjustments

three sets of blocks with different spacing between the front and rear rings

These scopes have adjustments that are built into the rings. This means that changing the distance between the rings (by changing where you mount the blocks) will alter your adjustment values. We tend to mount the blocks 7.25" apart (center to center), which causes the adjustments to be 1/4 MOA, and the numbers on the turret index to refer to whole numbers. Mounting the blocks closer will cause the adjustment values to increase, while a farther mounting results in finer gradations.


Three curved-bottom blocks showing the different block heights available

Blocks can also vary in height. Having a very tall rear block (under the adjustment ring) will move your effective range farther out. Having your front and rear blocks level will help you zero at closer distances.

Front Rings

Sliding, springs, and stopping

Front Ring:

Unertl

Short malcolm

Crossbolt 

Crescent

Posa

Rib width

⅛”

1/7”

Notes

Built to slide

Can slide or hold still

Will not fit on Unertl Scope 

Accessories

Fits 18SLR (and Spring)

Fits 17SLR and Locking Ring


the unertl and short malcolm front rings

The front ring is the ring without the adjustments, and is responsible for handling the force of the recoil. 

There are two ways to deal with recoil: 

  1. Hold the scope steady (as in a modern scope)
  2. Let the scope slide (to reduce the force, especially to the reticle). 

If your scope is built to slide, you'll need to pull the scope back into battery before each shot. Otherwise, your eye relief (and potentially your distance-to-bore) will change.

We have two front rings, one built to slide and one built to slide or hold still.

Unertl Front Ring

The Unertl scope with front ring, spring, and locking collars

The front ring with a tall 'hat' is the front ring commonly found with the Unertl and Malcolm Two-Tone scopes. It has a crescent cut crossbolt. This ring is built to allow sliding. It fits the 1/8" pope rib on the Unertl scope without any modifications. The plunger at the top of the ring has a trough cut to fit the 1/8" rib exactly. 

If your scope does not have a pope rib, you can install the 18SLR (1/8" sliding locking ring) along with this front ring to allow sliding on your scope. The 18SLR and the Unertl pope rib fit a Spring that pushes the scope back into battery, in case you don't want to have to move it every shot.

Short Malcolm Front Ring

the front of the malcolm 6x scope with front ring and locking ring

The front ring without a hat is typically found with the 6X and 3X A5-style scopes, and has a Posa cut crossbolt. It has a trough on the bottom that fits a 1/7" rib or rail. In the kit, these rings are combined with a Tube Locking Collar to prevent the scope from sliding. However, that collar can easily be swapped out for the 17SLR (1/7" sliding locking ring) to enable the scope to slide. Aside from having the rib on the bottom of the scope, this sliding mechanism will operate in the same way as the 18SLR.

The Spring

The spring will fit on the 8X scope perfectly, including the rib. It can also fit on the other ¾” scopes when combined with the 18SLR. If you need the spring or the sliding locking collars to fit other dimensions, they are quite easy to machine at home without altering the scope.



Rear Rings


Ring Style > 

Lyman

Unertl

Clickless Cage

Clickless Precision

Clicks

Yes 

Yes 

No 

No 

Lockable Turrets

Yes 

No 

Yes 

Yes 

Re-indexing Turrets

Yes 

Yes 

No 

No 

Crossbolt

Crescent

Crescent

Posa

Crescent


These are the rings that have the adjustment turrets. They do not manage the weight or movement of the scope during recoil, so there are no additional collars or rails to consider.

The adjustment values of the turrets vary based on the distance between the mounts. We use a 7.25” standard, following after the 1903 rifle. Mounting the front and rear rings closer will result in a larger adjustment value (⅓ MOA per click at 5.4”, for example), while mounting them farther apart will result in finer adjustments (and less overall adjustment range). 7.25” is a good balance between the two and allows for easier math.


lyman rear rings on the 8X unertl scope Lyman

unertl rear rings on the malcolm 8x scope Unertl

Clickless cage rear ring on a vintage rifle Cage

clickless precision mount on a malcolm 6x scope and 1885 rifle Precision


We have four rear rings available


  1. Lyman - Has clicks. Comes standard with the Malcolm 8X scope. Crescent cut bases.
  2. Unertl (Competition Mount)- Has clicks. Available as an upgrade for Malcolm 8X scope. Crescent cut bases.
  3. Clickless Cage - No clicks. Typically found with the Malcolm Short A5-style scopes. Posa cut bases.
  4. Clickless Precision - No clicks. Typically found with the Malcolm 6X 18" Two-Tone scope. Crescent cut.

When deciding on a rear ring, you’ll simply need to consider either what equipment you already have that the ring needs to fit (for example, a rifle with Posa-cut blocks already installed), or what style you’d like to go for (for example, the Unertl scope is typically paired with a 1903 for CMP competitions). Any of these rings will fit on any of these ¾” scope tubes.

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