i bought a 27mm ims reflector from him a few days ago to use... do i need a spacer? or is there already one in there i can use?
There is a spacer in the light that helps center the reflector. As pistolsnipe mentioned, the stock reflector is an IMS27.
It sounds like you have not opened the light yet. If you are open to some advice, here is a brief description of the steps to mod a Gladius with an XP-G.
The first step is opening the head. I have always heated the head for 15 minutes, or so on a mug warmer. After it is hot, I use strap wrenches to loosen the bezel. When it is loosened, open the head carefully. There is a small ball bearing in a detent that could fall out and get lost. Put the ball bearing in a baggie, or safe location. Set the head reflector side down on a clean surface, or put it into a baggie to keep things dust free. Remove the o-ring from the light body so that you can screw the head on and off without much trouble (you will see why later). Place that in the bag, too.
The next step is removing the stock Luxeon LED**. Use solder wick and remove the solder from the leads until you can get the leads bent away from the board. Next, while the board is still hot, grab the LED and give it a twist. I have a very low success rate in getting the emitters out in one piece. Remove the thermal adhesive under the LED and clean the area well with alcohol. **I like to leave the Luxeon star base in place because it is thicker than the stars that the XP-G LED's come on. It also makes getting the correct emitter height easier.
Next, prepare a 0.060" thick copper shim for under the LED to raise it into focus. The 0.060" thickness is a typical height for this mod. You need to do a dry fit to check for proper focus of the LED, and adjust the thickness of the shim as necessary. Clean the seat for the LED again with alcohol, and allow to dry. Once everything is clean, use Arctic Alumina (AA) to adhere the copper shim in the depression that the Luxeon sat in. Make sure that the AA is in a thin layer for best heat transfer. After the AA has cured, use more AA to set the LED in place observing the polarity of the LED.
Before the AA cures, screw the head onto the light to check the centering of the LED in the reflector opening. Adjust as necessary. Allow the AA to fully cure before you solder the leads to the board. Solder the leads back into place, check the LED anode/positive for continuity to ground to avoid any problems later. If all is OK, reassemble the light paying attention to the leads of the LED as you tighten the head***. Remember the o-ring and ball bearing.
***Usually, you do not have to remove any material from the reflector. But, if you get binding on the leads of the LED, remove some material from the reflector opening. The reflector on the Gladius is cheap plastic. Be very careful.
After the light is back together, insert batteries and fire it up. Be amazed. The strobe of the XP-G modded Gladius is absolutely disorienting so use caution.
This is a very DIY friendly mod. Take your time, and enjoy yourself. :thumbsup: