Tube Guns - The beginning of the M66

[Ovenpaa]

Given the interest in Tube Guns I thought this might be of interest, it is the translation of the original document written by Robert Chombart explaining the origin and concept of the M66 rifle. I have included it as a document as well for download.

The beginning of the 66 - revised 3.pdf

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The Beginning of the C.G ‘Delta ‘Model 66 Light Tube Target and Light Tube Repeater Rifles by Robert Chombart.

In 2009, during a series of exchanges between Robert Chombart and Germàn A. Salazar on the subject of INCH actions and C.G triggers, Germàn expressed his views on the concept of a tube rifle in which the centre part or chassis, instead of being used as a receptacle for a foreign round action, would instead constitute the action in itself, allowing considerable savings in weight and cost.

Immediately enthused by the concept, Robert investigated the principle and eventually established some key points for consideration:

The Chassis Receiver, inserts and the Bolt

The chassis/receiver could only be made from light metal and the choice was simple. Only the 7075 T651 hi-tech Light Metal alloy would have the necessary characteristics to fulfill the static functions of both a conventional receiver and a central stock chassis.

For the important functions of bolting and barrel holding, the experience gained with the C.G Delta 59 Light Metal actions make the choice of this system the obvious one and the superior characteristics of the hardened tool steel inserts for the already designed C.G Model 59 Delta LMT and LMR would be used. This insert is fixed in a permanent and non-removable fashion and becomes an integral part of the receiver.

The more conventional bolt systems would not be adopted, instead a full diameter bolt with separate guidance was chosen. The C.G Delta bolt was designed for such a system and was an ideal candidate with the added advantage of using the same bolt design for the whole range of C.G Action Clear range of new front locking actions.

The functions of recocking and primary extraction are by using the hardened shroud (specific C.G) acting against a hardened ramp insert at the rear left of the receiver.

The bolt has been specially designed for the purpose. It is of the full diameter principle, with the lugs at the same diameter as the bolt body itself. This allows a full surface bearing of the bolt in the receiver bolt raceway and also of the Bolt head in the Bolting Insert.

The lugs arrangement is of the triangular (Delta) profile. This arrangement allow generous lugs bearing and shear surfaces, also a total lugs bearing angle not obtainable with any other arrangement.

The bolt is the same for all models of the range and it’s full diameter principle allows a perfect and smooth motion. Guidance is ensured by the bolt stop lever itself, which retracts out of the raceway automatically at the end of the forward bolt stroke, when the lugs are already engaged in the receiver counter-lugs, to permit bolt closure rotation. At the end of the rearward stroke, the bolt stop lever also activates the C.G inertia ejector for controlled ejection.

The bolt head is of 120° tapered silhouette, fitting very closely to a corresponding female cone in the rear of the barrel. With this and the counter-lug’s geometry in the receiver smooth feeding of the cartridge into the chamber is ensured regardless of the cartridge dimensions.

The bolt head shape allows the use of the wide extractor of the C.G INCH. An Inertia ejector of the well-proven C.G, C.G Quadlock and C.G Millenium principle is standard.

Rifle Configurations:

LTT (Light Tube Target) Available in .308 Bolt face, single feed only.

LTR (Light Tube Repeater) Available in .308 Bolt face with integral bottom metal to accept the AICS 5 and 10 shot magazine.

.223, PPC/Russian and Short Magnum bolt faces are planned.

Firing Mechanism: The firing mechanism is specific. Parts are fully machined and adjustable. The firing system can be powered by either the C.G Belleville spring discs stack or conventional coil spring with the C.G dual-tipped reversible firing pin of the INCH. Cocking is of the shroud principle with the shroud closed at the rear for safety and easily removable from the bolt with no difficulty and no specific tools. Protrusion is factory pre-set and need no further adjustment.

Triggers: The OEM trigger used on these rifles is the new Centra produced C.G Model 22 designed for the Remington however any aftermarket trigger intended for this fitting can be used. The fitting of the trigger is by means of the two cross pin and the pins are fixed by screws allowing easy removal of the trigger for adjustment or maintenance.

Hand grip: The standard AR type hand grip mounting would be used to allow the shooter a wider choice of different grips.

The Forearm: First, the thought was to use a tube thick enough to have a conventional Anschuetz accessory rail milled into however this was quickly abandoned and David Bonwick (Shooting Shed) helped to define the requirements to adapt for various disciplines.

The imperative then were:

• Rigidity and firm fixing to the Chassis/Receiver to bear full weight of the rifle when on a bipod or front rest.
• Ensure the correct convection cooling of the barrel.
• Ability to accept accessories specific to disciplines.

The fixing to the receiver was easy to ensure by mean of a closely toleranced register and 3 radial screws.

The convection air flux is ensured by 3 rows of large ventilation slots. The top of the tube is left solid to avoiding hot air mirage escaping directly under the aiming line. The forearm has provision for a mirage band to be fitted. The bottom of the tube is also solid with a row of tapped holes at 50mm centres to fix the front accessories.


The Forearm is built to allow the use of the rifle in various disciplines with the following options:

• A Target Rifle/Palma Forearm addition, of elliptic form for comfort and to allow the inclusion of a standard accessory rail milled in the centre. The rail ends short of each end of the Forearm addition and the external wings of the Tee slot are machined out of one end to allow introduction of the Tee Nuts of the hand stop, sling attachment, etc. The TR forearm addition is reversible to allow full use of the rail.

• A short accessory rail for the location of accessories capable of being moved along the forearm in 50mm increments.

• A Base plate, screwed under the forearm, capable of moving lengthwise in 50mm increments and designed to accept either:

• A wide (40mm) front bipod attachment point for F-TR.

• A front bag rider suitable for Bench Rest and F Open disciplines. The front bag rider being of an undercut design, 75mm wide with dual mounting points to allow either central or offset fixing to compensate for torque.


The Buttstock

This was another challenge as it was necessary to:
• Have it different, offering the maximum of adjustments.
• Be easily detachable from the Receive/Chassis, but also be firmly fixed.
• Be comfortable to shoot.
• Be easily adaptable to various disciplines and anatomies.

The elements are firmly clamped on a central tube interface. This interface is fixed to the chassis by a closely toleranced register and by a quick release latch situated under the receiver/chassis. This location was chosen for its accessibility and for it not protruding on the side of the chassis.

Buttstock adjustments:

• Cheekpiece adjustable in length by movement along the interface tube.
• Cheekpiece adjustable in offset by rotation on the interface tube.
• Cheekpiece quickly adjustable in height in 1,5mm increments by mean of a scaled rack.
• Buttplate adjustable in 3 ways; length, offset, cant.

For comfort the Wegu/GFT soft rubber buttplate was selected, this element has the advantage of having an integral height adjustment giving the 4th way adjustment and saving some more weight within the element.

A specific height adjustable Rear Bag Rider is an add-on for F-Class and BR shooting. Adjustments are ensured by mean of a rack system in 1,5mm increments, this operation is independent of the height adjustment so a shooter can both adjust the butt for optimal height and lower the rear bag rider so allowing bipods to be set lower in F Class and Bench Rest disciplines.


Conclusion

The first prototypes were built for the end of 2012 to prove the design and concept and the results were extremely promising from ergonomic, aesthetic and weight view points.

The rifle system is fully adjustable to suit the shape of almost any shooter, the looks of the rifle are a very personal thing however it has been greeted with very positive comments when viewed and handled, and weight wise it came in as expected:

Basic weights including trigger and excluding barrel and accessories:

LTT single shot rifle, complete 2850 grammes (6.29 pounds).

LTR repeater 2700 grammes (5.96 pounds).


Weights in discipline configurations:

TR/Palma/Match Rifle (LTT with Forearm addition +110grammes) 2960 grammes (6.53 pounds).

TR/Palma/MR, LTT with short accessory rail (+52 grammes) 2900 grammes (6.40 pounds)

F-TR Rifle, LTT with baseplate and wide bipod rail (+76grammes) 2926 grammes (6.46pounds)

F-Open/BR, LTT with base, 75mm front bag rider (+238grammes) 3088 grammes (6.82pounds)

F-Open/BR, LTT as above, with adj. rear bad rider (+134grammes) 3222grammes (7.11 pounds)

[paulbradley]

Thanks for posting this.