In the world of rifle optics rails, there is some variation that can be frustrating at times. Most .22 rimfire rifles will have a fixed 3/8 inch dovetail to fix a rifle scope using 3/8 inch rings. Some European rifles use an 11mm slot that looks nearly identical to the 3/8 inch but is not quite interchangeable. Old Com Bloc rifles have a left-sided mount on the receiver, sometimes known as the Warsaw Pact rail. Thankfully, most rifles on the American market will either use a Weaver or Picatinny rail.
On the surface, a Weaver and Picatinny rail look similar and some mounts that use either of them can interchange. But that does not mean either mounting system is completely compatible with the rifle scope or mount of your choice. Follow along as we explore the history of the Weaver and Picatinny rail systems as well as their similarities and differences, so you only have to buy your optics gear once.
The Weaver Rail
Riflescopes have been available since before the American Civil War, but rifles were almost exclusively used with iron sights and never came with a scope mounting system from the factory. Scoping a rifle was a custom gunsmithing job until the early 20th century when companies began to release mounts to make the job easier. William Ralph Weaver came up with his Weaver rail in 1930 as he launched the WR Weaver Company.
The Weaver rail is a dovetail type mount that is drilled and tapped on the rifle receiver as usual, but the mount itself proved exceptionally strong when paired with Weaver rings. The locking screws that fastened the rings to the dovetail locked into corresponding rounded grooves. Most Weaver rails come with two to four grooves. This arrangement is stronger than competing Leupold and Firefield mounts of the day, ensuring the optic would be more difficult to knock from zero with abuse in the field.
Today, the Weaver rail is the go-to optics mount for most hunting rifles, but it is by no means the end-all-and-be-all. It certainly is not a perfect option. Weaver rings tend to cant the scope slightly from alignment with the bore if the locking screws are not torqued down incrementally. The shallow rounded slots are still imperfect in some ways. First, they do not truly lock the optic in place — the slots are simply a depression for the locking screws to run across. Second, the more manufacturers that came online to produce Weaver rings, the more variances there was in both slot and screw diameters.
The Picatinny Rail
Fast forward fifty years and optics were fast becoming the rule rather than the exception for both sporting and military applications. The Vietnam War had shown the weaknesses of the Weaver system, particularly from the standpoint of parts compatibility as the US Army simply used commercial equipment, particularly in their sniper program. In the 1980s, the Army sought to standardize the Weaver rail. The end result became the Picatinny Rail, named for the Picatinny Arsenal in New Jersey.
The Picatinny rail was adopted by the US Military with the rollout of the M4 Carbine. The primary improvement of the Picatinny rail over the Weaver rail is the number of slots were increased and each slot had a machined shoulder instead of a rounded groove. These shoulders interfaced with flattened sections on the optics mounting screws for a stronger lockup.
Since its introduction, the Picatinny rail has become popular on the civilian market as both an optics mount and a means of mounting accessories such as lights and foregrips.
Weaver vs. Picatinny
If you are holding a section of Weaver and Pic rail, the most obvious way to tell the difference is the in the machining and number of slots that lock the scope ring screws in place.
The Weaver rail will have usually have 2-4 slots and will be shallow and rounded with a diameter of .180 inch.
The Picatinny rail will have spaced slots throughout the entire section and will be machined squared, rather than rounded. The Picatinny rail will also have a more generous slot diameter of approximately .203 inch.
The biggest differences that you will perceive between the Weaver and Picatinny rail is not the rail sections themselves but what and how you mount to them.
Pic rails have the advantage of not being solely an optic-only mounting system. Sections of Pic rail are also used on handguards on rifles and dustcovers on handguns to mount lights and other accessories. With some exceptions, Weaver rails live entirely in the optics world.
Picatinny rails also have the advantage of usually coming in a single rigid section, while Weaver rails often (though not always) come in two separate pieces that need to be mounted to the rifle. This rigidity is advantageous, except in cases where the rifle can or should be loaded from the top of the magazine, where a long section of rail over the receiver can prevent the shooter from thumbing in new ammunition quickly.
The Weaver rail often lacks a sighting groove along the top strap of the scope bases. Many Picatinny rail sections on the market have such a groove, and that allows the user to use low-mounted iron sights, whereas Weaver rail sections tend to obscure any existing iron sights.
Picatinny rails have more slots and, thus, more mounting positions for scope rings. This will let you adjust the scope in the rings to get the appropriate eye relief.
Weaver scope rings will fit most Picatinny rails, although the smaller diameter of the locking screws means that the shooter will have to push the rings into their forwardmost position, so the round locking screw doesn’t walk around in the square notches. Picatinny scope mounts can’t work the other way around with a Weaver rail.
The Takeaway
Although the Weaver mounting system works well and comes on countless new and old rifles, the Picatinny rail was made as an improvement, and it shows. The Picatinny rail’s mounting slots are more rigid and allow for the flexible placement of scopes and other accessories. In addition, the ubiquitous Weaver ring will generally work on a Picatinny rail, while the reverse is not true. Whether you prefer one or the other, it is easy to justify having a section of Pic rail that is made for mounting on the rifle of your choice. You might thank yourself for it down the road.
