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The CG INCH Target Action
1°)-Starting from the material, the steels are classified as:
-Construction steels such as AISI 4110, 4340, 8620. Those are commonly used in action making. Those metals are either harden-able to some 42 HRC, or need surface hardening (carbo-nitridation).
42 HRC means a Rm of 114kgs/sp.mm, or 162000psi
-Tools steels. Those are highly alloyed steels, of higher specifications. The steel used for the CG actions and now the INCH is the Boehler-Udderlohn K600, Euro Norm 42NiCrMo16. This hi-Nickel-Chromium alloy hardens to 52HRC.
52 HRC means a Rm of 186kgs/sq.mm or 264000psi.
The Receiver, Bolt, andmost of the mechanical parts of the INCH are made from this Hi-Tec alloy. Its characteristics are toughness, shock, wear and galling resistance. One of its important characteristics is the total absence of warping unde r vacuum-quenching heat treatment. The steel has been designed for those characteristics, and this is the reason why we use it.
As an example, it is the most used steel alloy for Jet engines mainshafts.
In addition, the Receivers and Bolts are Electroless-Nickel plater with the added advantages:
-Absolute 100% corrosion resistance.
-Very low coefficients of friction (0,2-0,3 max.)
2°) The Bolt stroke. The rear locking system allow a considerable reduction of the Bolt stroke.
On the INCH, it is 85mm (3.346&rsquo), a reduction of some 20 to 30mm over all classic Short actions (Remington or Barnards are 105mm Bolt stroke (4.135&rsquo).
The loading port is 91,5mm (3.602). Remington 700 SA is 61mm (2.400&rdquo).
Moreover, this Lugs arrangement allow loading and firing of cartridges of a length up to the .338 Lapua Magnum, and easy ejection of fired cases of this size.
3°) The Firing System.
Shooters often considers an easy bolt lift as a primary necessity for a Target rifle? This can be valid when a rifle is not fired from the shoulder, as in Bench Rest for instance. But TR, MR or F-Class shooting need a very fast blow.
A) The light bolt lift can only be achieved by:
-A 90° Bolt rotation, this limiting the lugs to 2, with for consequence a small lugs bearing angle, often inferior to 120°.
-A long Firing Pin travel, always superior to 6,35mm (.250&rsquo), or still about .185 at impact on the primer.
-A long, heavy, low response pre-loaded coil spring of a force just sufficient to ensure the motion of the mass in movement and impact energy.
B) When increased accuracy is researched, the design factors to consider are:
-Increasing the Lugs bearing angle. This is achieved to the maximum on the Delta lugs profile, in which the total Lugs bearing angle is of some 170°, almost the perfect 180°, impossible to realise because of the necessary functional clearances. The 3 Lugs triangular truncated design imposes a bolt lift of 60°.
If this reduced Bolt lift by itself already imposes a different feel on opening, the advantages are a faster cycling and absence of constraints in regard to interference of the Bolt handle with sights location.
-Creating the conditions of a faster locktime. This impose 3 conditions:
-A lighter Firing Pin mass. The mass of the INCH Hammer is 52 grammes (1.85oz). The shorter Bolt allow also a shorter firing pin, thus reducing also its mass.
-A shorter Firing Pin travel. It has been here possible to reduce it to 3,9mm (.153&rsquo) in dry firing, or .102&rdquo at impact.
-A faster reacting spring system. A coil spring could be used, and this is offered also as an alternative, but the real solution consists in the use of a Spring Discs stack arrangement (Belleville Washers).
The patented firing pin system first adopted on C.G actions, then on the RPA 2000, Quadlocks,Quadlites and the HHE-Milleniums incorporates this imperatives. It has been redesigned specifically for the INCH, and bears now a double-ended firing pin tip, allowing aquick change in the unlikejly case of a FP tip break. It can be considered that the action always carries inside themechanism a spare firing pin, of the correct automatically pre-set protrusion.
On operating the Bolt, the Sear does not slide under friction on the cocking ramp, but a Roller ensure a non-friction re-cocking movement. A Nadella Thrust bearing also ensures friction-free rotation of the Bolt.
The CG INCH is about 99% backwards compatible with the Millenium action/stock system. Which makes it easy for people to upgrade to the INCH from the Millenium if they so desire. The other thing is we have available the fleXibloc (and incidentally for the Barnard as well). This system was developed by HHE in NZ, and further developed by Robert Chombart (CG - as in CG Millenium, RPA CG 2000 etc).
On the bedding block, we believe this is the best system of attaching the action to a stock, but we ultimately leave this decision to the customer and his chosen rifle builder. We do not use any other system on rifles we build for ourselves, or for standard factory rifles. We also believe that the "glass bedding" (epoxy bedding) is far inferior to this system (particularly when it rains!!). For the small added cost, we believe it is worth every cent. These blocks can be fitted either in a new stock, or any current one that a person likes, to convert over to the CG INCH system.
The function itself of the action is most excellent. One cannot begin to notice the big differences between the CG INCH rear locking system, and that of any typical front locker. The bolt throw is short - 85mm, which is between 20-30mm less than any typical front locker. This has implications with cheek piece modification, but most of all, it allows the cheek piece to be modified much less. I shoot with the action very close to the shooter&rsquoq face, so this is a real benefit and places the bolt handle in easy reach for cycling with no position disturbance.
The bolt handle lift and closing pressures are much the same as a Barnard, with the INCH bolt handle being very slightly shorter.
The firing pin travel on the INCH is only 4mm, generally at least 20% shorter than any other using a coil spring. The expected lock time is around 1,4 milliseconds.
The CG INCH design uses a hammer and pin tip, not a one piece firing pin. This means the largest moving part in the firing system, actually works on the firing pin tip, as a hammer, which is how the light weight and high speeds can be attained. The INCH uses the well proven and reliable Belleville washer system. These are high quality alloy steel units, not the sometimes used inferior carbon steel units acquired in mainland Asia.
The firing pin tip is reversible. It is a double ended unit, so if on the rare occasion it may break, another spare tip is available on the other end of the tip to use. This can be done on the firing point with only a 5mm Allen wrench.
The lugs on the INCH are external to the bolt shank, not inside of it. This means a much larger area (both radial and circumferential) for the lugs bearing, meaning a stronger action. It has been calculated up to 50 metric tonnes of force to press the bolt out the rear of the body.
The rear locking lugs have a hidden but very real advantage over front lugs: that of the way the force of the bolt face / case head operates on them. The closer the lugs are to the case head, the more the force is angled tangentially to the bore axis. This detracts from the ultimate strength of the action - the INCH has the lugs 100mm to the rear of the bolt face, giving very straight force lines, and therefore gaining the most advantage of the material strength. The INCH bolt is very heavy for this reason.
The standard CG INCH comes standard with the CG UNI trigger unit made by Tom Myers, from X-Treme Shooting Products in Cincinnati, Ohio,USA. Also now made by Centra Visiertechnik in Germany. They are a superb, albeit expensive, addition to the INCH. It is true that we could bring the price of the action down considerably if we used a lesser trigger, but the trigger and action are designed to be used as a system - not two items made to fit at some stage in the future (as some in Australia have found even at this early stage!). I notice you said "body and bolt" - all CG INCH actions come standard with the CG UNI trigger unit anyway.
Usually, any thoughts of pessimism about the claims for the CG UNI trigger go away shortly after the customer has used the unit!!
Camp Perry 2009 US National Matches general comment: The C.G-XTreme trigger has become the reference by which all the others are compared. Recent trips to the USA by the CG INCH manufacturers also showed the gaining momentum for interest in the CG UNI trigger.
The INCH uses a double register barrel tenon. The INCH is the only action with this feature. The idea of this being the threads cut on the barrel are never fully self centering (all threads are not self-centering), as the registers locate the barrel with the action bore axis, the thread only then having the job of tightening the barrel. Almost all other actions rely on the barrel thread to both locate the barrel concentrically and to tighten into the action body - this is not really a very good idea we believe.
The longer barrel shank is due to the shorter bolt travel from the rear located locking lugs. The system also allows barrel changes with no loss of zero.
One of the smallest, but biggest technical advances in the CG INCH, is that of the internal primary extraction. Action with a pin type bolt stop have a slot milled into the side of the bolt shank for a key that stops the bolt from falling to the rear of the action - and provides a secondary safety that stops the Bolt.
The INCH goes further than this and has a cam built into the rear section of this slide, so that opening the bolt makes the slot act against the stop key, giving close to 2mm of legitimate primary extraction, which is more than most. Almost all actions otherwise use extraction on the handle root - Barnard, RPA, Remington etc all have this feature. A softer material in the cross section (like 4340), cannot be used when dealing with high dragging forces like those in the primary extraction of the INCH.
Of course the CG INCH uses a narrow Sako style self-gripping extractor. This is a very simple system (but not simple to make!!!) in use and function. There are only 3 parts, and none are pinned or screwed to the bolt in any way - being held in place by spring pressure alone. These small extractors are extremely strong, and very positive, having been machined to fit the case rim curve, not just milled straight like so many others.