Cutting barrels for a pen to shorten the length to fit your hand is a required skill when pen modding. Here are 3 different tools that are the most optimal
a pipe cutter, more recently famous within the last few years. there are flaws with using a pipe cutter though generally a pipe cutter is a great way to start a cut on a barrel after you measure and tape up the body and size you want to cut Although i do not recommend cutting an entire body with just a pipe cutter with out an x acto knife as it can be tricky to know when you are cutting too deep on hard plastic bodies and on soft plastic bodies they can get smashed in. Examples later down below
the 2nd tool i recommend after many years using it is a steak knife or a saw just make sure one side is flat and doesnt have teeth. otherwise you will be cutting the side you didnt want to damage the only problem with using a saw or a steak knife is that sometimes if you do not take your time cutting through slowly. the body can snap off and you might have a small chunk removed from the wrong side of the pen body.
The most consistent tool that you can use to cut pen bodies are an x acto knife they are sharp, make clean cuts and sanding the body after cutting takes less time. the only problem when using an x acto knife to cut is that, it takes a lot of energy and strength. you can sometimes slip and cut into parts where you didn’t mean to. although if you want to achieve the highest quality cut, practicing with an x-acto knife is the most optimal. Buying new blades after each body cut is fairly important as well, but it is a good price to pay for consistency and cleanliness.