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4 Aug 2014 - mkillebrew

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Remington Model 51 - 9x17

The Remington model 51 is unique in that it is a locked breech pistol in 9x17, which are usually direct blowback, or inertial, which rely on the mass of the slide to retard the action. Utilizing John Pedersen's momentum block delay system, when a round is fired, the lug on the block is engaged on the locking shoulder on the frame, forward of the hammer. As the slide drives itself to the rear, a ramp milled into the breech block lifts the momemtum block up into the slide, disengaging it from the shoulder. The momentum block contains the breech face and extractor on it, which is held firmly against the chamber face until the action is unlocked, whereupon extraction begins and the case is ejected by means of a spring loaded ejector attached to the frame. The momentum block much resembles, in function, the dropping breech block in the Walther P38, Beretta 92, and VZ-58. The ejector pivots down and out of the way so the slide can be removed from the firearm. Pedersen designed the model 51 to be detail stripped without use of any tools other than the firing pin. This becomes just of great novelty once the operator discovers that it instead requires three hands. To disassemble the slide is first held back to the takedown notch and the takedown pin is removed from the left side. At that point, the slide is retratcted and the barrel pulled on, to unlock the action, then the slide and barrel assembly slid forward while depressing the grip safety and pulling the barrel and slide apart. To remove the momentum block, the barrel is pushed forward and slightly rotated, locking into a groove milled in the slide to keep it stationary. The rear of the momentum block is lifted up, over its engagement surface on the breech block and is slid forward and off. The firing pin and firing pin spring then slide freely from the slide. The barrel is then unlocked and pushed forward until the recoil spring bushing lines up with the cut in the slide, and the barrel tilted up, locking the spring in place and allowing the barrel to be slid free. The bushing and recoil spring can then be removed at great velocity and lost somewhere in the general vicinity. The grip pannels slide off by depressing the button on the butt of the pistol then pushing on the grip safety retaining pin which has a detent in it, sliding it to one side which allows the grip pannel to be slid down. The pin can then be fully removed, freeing the grip safety which has the main spring captive. The hammer spur depresses this spring when in the cocked position, much like the design of the Browning 1911. The fire control group also shares traits of the 1911 in that the trigger moves directly rearward instea of pivoting, has a vertical disconnector, and presses on the legs of the sear which then pivots, releasing the internal hammer. This movement is blocked if the grip safety is not depressed, and the safety selector immobilizes the grip safety. The model 51, in addition to the manual safety, grip safety, and disconnect, also features a magazine disconnect safety.

Truncated writeup, featured on TFB

More historical information and other great pictures can be found here

Right Side:

Left Side:

Slide - Above Profile:


Slide with Takedown Pin Partially Removed:

Slide - Underside:

Slide - Underside - Locking System

Slide - Underside - Momentum Block Locked:

Slide - Underside - Momentum Block Unlocked:

Frame - Hammer in Cocked Position and Disconnect Protruding in Center:

Barrel Rotated into Takedown Notch:

Slide - Underside - Momentum Block Removed:

Momentum Block - Side and Underside:

Momentum Block - Side and Top:

Momentum Block - Breech Face:

Momentum Block - Top:

Momentum Block - Bottom:

Barrel Bushing Locked Into Takedown Notch:

Barrel Bushing Locked Into Takedown Notch - Barrel Removed:

Slide - Undersite - Stripped:

Slide - Underside - Unlocking Ramp:

Slide - Underside - Unlocking Ramp, Continued:


Recoil Spring and Spring Bushing:

Takedown Pin, Firing Pin Spring, and Firing Pin:

Butt of Pistol, Notice Detent Button at Rear of Magazine Well:

Grip - Locked:

Grip - Unlocked and Slid Down:

Grip - Reverse Side:

Frame - Field Stripped:

Inside of Magazine Well - Magazine Safety Protruding:

Grip Safety - Front:

Grip Safety - Side:

Rear of Frame - Grip Safety Removed: