I have gotten a ton of great info from Castboolits, but one topic that still is murky to me is gas checks. Lots of posts on them, but there seems to be two camps on whether you need them or not. I do not cast my own boolits, due to lack of time. I am trying to determine if I can launch a commercially available 170ish grain bullet at ~1700 fps (for rams in silhouette) without a gas check. Penn says their bullets can run up to 2000 fps without, and other companies say you need a gas check for lower velocities. What is the answer? I will be using a Marlin 336 with microgroove rifling. I would especially appreciate responses from those that are buying commercial bullets and are achieving this velocity or better. If I have to press on a gas cap, then I might as well just buy Speer JFP. Thanks!