All of us hear that a case has to expand to let the bullet out and keep pressure down. Very common with BR rifles and tight chambers. (but is it fact?) But I have questions. I have been trying to imagine myself in the case at the moment of ignition. Does the entire case expand all the way to the mouth right now, leaving the bullet hanging free while the bullet is still in the case, or is it progressive, expanding the brass as the bullet moves out of the way? Kind of makes a guy wonder, doesn't it?
This brings up the hard crimp on revolver cases. Does the pressure expand it open before the boolit leaves? I hardly think so. I say the boolit has to force it open and if the lead is too soft the crimp will scrape/size the lead making the boolit smaller or leaving grooves that the gas can get into and cut the boolit. Making some tests today with cases that had both jacketed bullets and cast boolits shot from them, I found I could get a cast boolit back into the case that had the condom bullet shot from it, but could not get one in the case that had a cast boolit in it. There was still a lot of crimp left on these cases. This can only mean my boolit was damaged when shot! Does a harder piece of brass cause more damage and open groups?
Take a loaded cast boolit and remove it with an inertia bullet puller so you can see the damage and the amount of crimp left on the case. The crimp is almost exactly the same amount as is left on a fired case. Is this a cause for poor accuracy and barrel leading?
Maybe this is why I find hard boolits shoot better! Also a good reason for gas checks.
Does anyone consider this damage when they say to use softer boolits for "bump up". Is "bump up" enough to eliminate the damage from the crimp? I don't know! I want to make all of you guys think!
I was shooting water dropped WW metal for this test.
Starmetal, I await your thoughts, and I do respect them!