XM148 was originally used on the M16 series rifles, and was later used by the US Navy's SEALs (under the XM177E2). It has a quadrant sight, but it is so delicate that it requires proper maintenance or it can be easily damaged. It uses an externally designed trigger and trigger handle, with the exposed trigger handle on the right side, allowing the shooter to directly pull the trigger with the right index finger.
At the same time this design also has the problem that it is easy to pull and shoot by mistake, and the trigger is also easy to be pulled off. In addition, the long trigger stroke makes it not suitable for use in the jungle of Vietnam. This design is too complicated to be easy to use in the wild. The shortcomings of maintenance eventually caused it to be replaced by the M203, with a similar conceptual design.