I am using the 2.75" most of the time; the same design is available in 4.5" and 6.5" You can PM IMADMAN on the forum here and he can make them for you; these are designed by the skilled Subscriber whom is a specialist in LCD's designing them for air pistols, etc. I find the 2.75" works so well I rarely would use the longer ones as it is quiet enough for my backyard. If I lived in an apartment complex maybe I would use either the 4.5 or the 6.5" oval version to be extra stealthy? For the quality, appearance, and price you can all 3 for less than buying a manufactured brand option so I highly recommend them!
These look like they were designed for the GK1 and work great! I am using them on my GK1 .25 tuned to 810 FPS.
Here are some more pictures: the photo's are of the 2.75", the 4.5" and the 6.5" oval versions.
View attachment 455820 View attachment 455821 View attachment 455822 View attachment 455823