Weaver rail mount
A Weaver rail mount (Picatinny type) is a system to connect telescopic sights and other accessories to rifles, shotguns, pistols, archery bows, etc. which uses a pair of parallel rails and several slots perpendicular to these rails. The slots on a Weaver system are primarily used as a clearance of the locking screw that tightens the clamp to the rail. The slots in a Picatinny system serves as clearance for locking screws as well as a lock-bar to hold accessories in place and dramatically reduce recoil effects on scope alignment. Some Weaver-type accessories have a bar that fits inside the machined slots on the rails while many others do not. A Picatinny system consistently uses a locking bar. Older Weaver systems used two pieces mounted a distance apart from one another typically on the receiver of a rifle over the bolt opening where the bullet would be inserted and/or ejected. With a one piece rail, the system eliminates alignment problems of the two piece system than can put undue stress on a rifle scope and also eliminates alignment problems between the scope and rifle barrel parallels and bullet Point Of Impact (POI). Also the two piece system must be mounted to exacting tolerances to one another to ensure perfect alignment using a scope alignment device called Alignment Sleeves, while the one piece rail system remains consistent in alignment. The two piece type can be problematic when some rifles will not allow for the two pieces to be mounted due to metal thickness of the receiver or other issues of receiver length that will not allow for proper distance to hold the scope. In such cases a single mount is used and a smaller scope is mounted.
Differences between Weaver and Picatinny:
Picatinny and Weaver rail systems both have slots machined into the rail as a whole. One difference between the Picatinny rail and the Weaver rail is the size of these slots, although many rail-grabber-mounted accessories can be used on either type of rail. Weaver rails have a slot width of 0.180 in (4.572 mm), but are not necessarily consistent in the spacing of slot centers. This is most true with the two piece system.
The Picatinny locking slot width is 0.206 in (5.232 mm) and the spacing of slot centers is 0.394 in (10.008 mm).[1] Because of this, with devices that use only one locking slot, Weaver devices will fit on Picatinny rails, but Picatinny devices will not always fit on Weaver rails.[1] The other difference is that Weaver rails are continuous, while Picatinny rails are cut by the slots (like a dotted line) to neutralize expansion caused by barrel heating.
The lack of a locking bar on many Weaver-type accessories also lends to another alignment issue: Canting. Though this problem is not common it can be very problematic especially with scopes. Because scopes need to be mounted to a rifle in perfect parallel to the barrel and to ensure the cross hairs sit exactly where a bullet will go (POI), a small variation of even ¼ of one degree can cause massive problems at longer ranges. The locking bar holds the mount in a perfect 90 degree to the rail system where as a non-locking bar system can cant to the left or right. This canting (sometimes called jamming of surfaces) is caused by not matching the clamping surface perfectly to the rail. When tightened down, stress exerted on the base can cause the scope to be off from the POI by as much as several feet at 100-200 yards and gets progressively worse the further out the range goes. Lower grade materials used in manufacturing of scope bases, inconsistent design tolerances from one manufacturer to another and other factors can cause twisting stress and cause the mount to move out of parallel with the rifle barrel. The locking bar system allows for even stress to be distributed and prevent canting of the scope mount.
Another form of scope canting is caused by the rings themselves. Many Weaver-type mounts (including many Picatinny-type scope rings) and even the Redfield Type either have two or four screws on top of the scope ring that hold the scope in place. Both the Weaver and Picatinny clamp system has a screw side and a clamp side. With the two screw style, the ring usually aligns well but does not have the strength of the four screw system. Many times when tightening the screws of the four screw type, the scope can twist in place causing misalignment. Tightening the mounts in a “X” pattern and usually starting opposite of the outside clamp side; hold the scope slightly to the opposite side while tightening the screws usually allows for proper alignment of the scope to barrel parallel.
The Weaver rail can be used to mount the following on a firearm:
The Weaver mount is a development of William Ralph Weaver (1905 – 8 November 1975) and W.R. Weaver Co., founded in 1930 [2]. Now known as Weaver Optics, it has been a subsidiary of Meade Instruments Corporation since 2002.
In 2008 Meade sold the Weaver Optics brand. It is currently part of ATK's Security and Sporting division in Onalaska, WI .
[edit] References
- ^ a b Brownells - World's Largest Supplier of Firearm Accessories and Gunsmithing Tools
- ^ Article from Shooting Times about Weaver Optics.
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