Anvil, You are correct in your analysis of how the die works and remember that the demensions I gave are not carved in stone. I have found that a finer pitch thread on the internal function generally works better but it still takes quite a bit of effort to squeeze the top using a wrench. Also the dies are caliber sensitive, i.e, can't use a .458 drop to size a .452....would destroy the edge of the die. Takes me at least 4 hours to make the die,and that is if everything goes well, so if you are still in the "time is money" situation, swinglock's 189.00 price tag is not excessive. I am retired so it is not a burden to spend a lot of time on projects. I have used these dies for more than 3 years and have had no problems yet. One thing I have found that really surprised me when using FF sized bullets is how imperfect some of the premium barrels are. Try this, when you get a bullet sized very close, rotate the bullet one land/groove at a time. you will find that one or two orientations will fit a little bit looser than the rest...I mark the bullet with a sharpie as it comes out of the die to a refference spot and mark the barrel at the land/groove where the fit is the best(loose) and load the same way every time. I have achieved very good accuracy this way. I assume you are doing this for muzzleloading with smokeless powder.
Good luck with the build, it really is not difficult.
Mike