(the baffles having been moved forward, compressed by repeated firings, after first assembling my screenwire "donut" design, you NEED to have a 1" long pc of thick walled steel tubing, beveled on one end, to a concavity on its inside diameter. This is put on the floor, to protect the rear of the can, and the fragile threads in the aluminum rear endplug. You have to REALLY hammer the baffles to drive them back to the rear of the can, even if you DID WD-40 the insider rear of the can. Doing so, resting the rear of the can on a flat surface,is pretty likely to ruin the can's ability to align itself with the bore of the rifle.
In a 9" long 223 can, over the firing of the first 30 shots, you will install another 2" of screenwire donut baffles, due to compression of the orignals from firing. If you don't, you will have 2" of wasted space in the rear of your can, meaning it wont stay very quiet, for very many shots.