Many companies out there are offering what we refer to as "universal optic cuts" and do not require you to send in your optic with your slide to be fitted. As a result many of our customers have asked us why we require them to send their optic in with their slide at the time of machining. Let's try and shed some light on why we do what we do.
First, having a close tolerance fit means the forces during recoil are transferred to the optic body which has a much larger surface area, and much more support material than the mounting screws and the "recoil" lugs could possibly provide. The locating lugs are a small diameter feature that interfaces with an aluminum or polymer optic body. While they may support the optic under some conditions they alone will not stand up to hard use or pistol slide recoil over time. Additionally, on a majority of the optics you cannot machine the full diameter of the locating lugs due to the proximity of them to the front of the optic (especially important considering the slide moves both fore and aft). The original intent of the locating lugs were to aid in indexing the optic on non-reciprocating platforms for the ease of returning to zero when the optic is removed. Mounting these smaller optics on pistols introduces a tremendous amount of force on the optic. Just look at why Trijicon had to make a Type 2 RMR. I have personally witnessed PLENTY of optic failures and almost ALL of them have been due to sheared screws and locating lug holes that are deformed due to loose tolerances of the optic pocket.
Second, when you have an interference fit of the optic to the slide you will have a more precise return to zero if the optic is removed and re-installed (which many require you to do when you replace the battery). Fitting each optic to each slide absolutely means it takes longer to machine so just ask yourself this. Why would we spend more time on fitting your optic (which we don't charge any extra for by the way) if we didn't know it mattered? We want your optic to be as securely mounted to your slide as possible because one day you might just have to subject it to what is considered as "hard use" and we don't want it shifting zero or breaking off your slide due to sheared screws.
Now, one of the down sides to a precision fit optic cut is that if you ever have to replace the optic, your replacement may be a bit over or undersized compared to your original. Here's the thing: we don’t believe that counting on a replacement optic fitting the existing optic cut is priority vs the quality of the original fit of an optic to a slide. This is why we caution our customers to buy quality optics especially if this is a weapon they use for defense or duty (because it minimizes the risk of a failure and need of a replacement). Loose fit optics are a compromise. Precision fit is not.
At the end of the day we are trying to provide you with the most secure, precise fit we possibly can so that the work we do minimized the possibility of failure on a gun that one day be used to save your life or others around you. THAT is the primary reason we take such a hard line on this.
An example of the precision fit you can expect from us. No screws in the optic and still secure...