Try taking the end cap off completely. If you have silicone oil or any other type of lube then try that on anything that causes friction against the bolt handle. If it doesn't become easier with the end cap off then you might have to sand the inside of the bolt handle (the part that connects to the cylinder) to make the hole wider.
When you take the end cap off you should put paper as a spacer on the end of the cylinder so when you tighten the end cap all the way it doesn't go in as far. This makes it so it won't put pressure on the bolt handle, making it lock in place.