I have been using the “SLED” for a almost two years now, it’s a very handy device.
It is a simple modified clip that allows the a shooter to single load by inserting the round into the Garand’s internal magazine instead of inserting the round into the chamber.
There are two major benefits of using this contraption. First, feeding from the magazine reduces the risk of slam fire. Frankly I’ve never seen or heard of is happening to anyone at a match but it is a valid concern. Why I use a SLED is because it makes loading, especially one handed while in the prone position, much easier. Using the SLED can also allow the shooter to keep the rifle shouldered while reloading which can help keep a consistent position.
Once installed it is easy to use just push the round down into the magazine, then pull back on the charging handle. It’s important not to put pressure in the charging handle while inserting the round, else you give yourself a case of Garand Thumb.
I painted my SLED orange to help me notice when it is still in the chamber.
It’s important to remember to remove the SLED before the rapid prone stage. I keep a flat head screw driver in the front pocket of my shooting stool so when I forget, it’s not so hard to pop out.
Here is a quick video of how to insert and load the SLED.
And how to remove it.
If you are handy you can build your own see ray-vin for instructions. http://www.foundry.ray-vin.com/m1sled/m1sled.htm