I know it's been beat to death, but here's another thread about Picatinny rails, Weaver bases, and choosing rings that "fit".
As when purchasing any item, in this case rings, I generally only use product reviews for any product as a trend analysis (favorable or unfavorable reviews with some sort of intelligable reason for either).
As for example when it comes to rings, many fail to grasp that the slots in a Picatinny cut base (.206") are larger than that of a Weaver slot (.180), and rings that are designated to "fit" both will not precisely fit both without some play in the Picatinny rail application as the smaller Weaver slotted base. When it comes to a multislotted base, the Picatinny base's center to center measurment is precisely .394, whereas it is reported that the Weaver multislotted bases can vary with the center to center spacing.
The Weaver sized cross lug / bar / mounting screw doesn't completely engage the Picatinny slot, needing the Picatinny rail application to have the rings securely bumped up to the "ridge" in opposing directions to avoid them from slipping or moving around in the Picatinny slot, or the addition of some sort of filling / bedding or shimming of the gap.
So when many mount rings that are able to "fit" both, they actually have space on the Picatinny slot causing problems and a bad review for a secure fit, especially on heavier recoiling firearms. This happens with lower end and top shelf rings alike that are advertised to "fit" both. Perhaps a better description is to fit a Weaver base, but can be ATTACHED to a Picatinny rail.
So many rings reviews have to be taken with a grain of salt, and condsidered when purchasing rings and / or base combinations.
The only true fit for a Picatinny rail is a ring that specifies that it will only fit a Picatinny rail. On the flip side, those rings will not fit into a Weaver slotted base.
For a quick analogy, much like you would expect a 15" tire to fit a 15" rim, a different tire dimension in width or height may rub or cause complications in other places, or not be mountable at all. Another way to look at it is if you have a 34" waist (a Weaver ring), you can fit into 36" jeans (Picatinny rail), but will have "play", though wearable. Likewise, you would not be able to fit into a 32" jean (much like a Picatinny ring will not fit a Weaver base).
So to wrap it up, a Weaver style ring will fit a Weaver base, and although may be attachable to a Picatinny base, will not be a perfect fit. This can lead to rearward and forward movement, canting, yaw, and other torque induced misalignments without the presence of the Picatinny recoil lug that completely engages all the surfaces of the Picatinny slot.
Even Weaver makes a specific Picatinny ring to fit the proper application.
PICATINNY SPEC DRAWING:
http://www.biggerhammer.net/picatinny/1913_specs.pdf
REV. A (just an additional measurment)
http://www.biggerhammer.net/picatinny/1913a_specs.pdf
I did a search for the Weaver base dimensions (even through the patent office) and could not find the full measurements of their slots, base width, or the angle of the hexogonal shoulders as a reference to se if there are more differences in those catagories from the Picatinny rail.
As when purchasing any item, in this case rings, I generally only use product reviews for any product as a trend analysis (favorable or unfavorable reviews with some sort of intelligable reason for either).
As for example when it comes to rings, many fail to grasp that the slots in a Picatinny cut base (.206") are larger than that of a Weaver slot (.180), and rings that are designated to "fit" both will not precisely fit both without some play in the Picatinny rail application as the smaller Weaver slotted base. When it comes to a multislotted base, the Picatinny base's center to center measurment is precisely .394, whereas it is reported that the Weaver multislotted bases can vary with the center to center spacing.
The Weaver sized cross lug / bar / mounting screw doesn't completely engage the Picatinny slot, needing the Picatinny rail application to have the rings securely bumped up to the "ridge" in opposing directions to avoid them from slipping or moving around in the Picatinny slot, or the addition of some sort of filling / bedding or shimming of the gap.
So when many mount rings that are able to "fit" both, they actually have space on the Picatinny slot causing problems and a bad review for a secure fit, especially on heavier recoiling firearms. This happens with lower end and top shelf rings alike that are advertised to "fit" both. Perhaps a better description is to fit a Weaver base, but can be ATTACHED to a Picatinny rail.
So many rings reviews have to be taken with a grain of salt, and condsidered when purchasing rings and / or base combinations.
The only true fit for a Picatinny rail is a ring that specifies that it will only fit a Picatinny rail. On the flip side, those rings will not fit into a Weaver slotted base.
For a quick analogy, much like you would expect a 15" tire to fit a 15" rim, a different tire dimension in width or height may rub or cause complications in other places, or not be mountable at all. Another way to look at it is if you have a 34" waist (a Weaver ring), you can fit into 36" jeans (Picatinny rail), but will have "play", though wearable. Likewise, you would not be able to fit into a 32" jean (much like a Picatinny ring will not fit a Weaver base).
So to wrap it up, a Weaver style ring will fit a Weaver base, and although may be attachable to a Picatinny base, will not be a perfect fit. This can lead to rearward and forward movement, canting, yaw, and other torque induced misalignments without the presence of the Picatinny recoil lug that completely engages all the surfaces of the Picatinny slot.
Even Weaver makes a specific Picatinny ring to fit the proper application.
PICATINNY SPEC DRAWING:
http://www.biggerhammer.net/picatinny/1913_specs.pdf
REV. A (just an additional measurment)
http://www.biggerhammer.net/picatinny/1913a_specs.pdf
I did a search for the Weaver base dimensions (even through the patent office) and could not find the full measurements of their slots, base width, or the angle of the hexogonal shoulders as a reference to se if there are more differences in those catagories from the Picatinny rail.
