Niner4Tango gave you the load out of the Hodgdon book - 4.1 grains minimum and 5.0 max / you said you went clear to 5.3 grains .... but the load in Hodgdon's tables uses a Hornady XTP bullet not a Rainier bullet... and you were out of specs on that load ....
Rainier recommends you use a "lead bullet" recipe for their bullets or drop the load on jacketed bullets by 10 % meaning you should have started around 3.6 grains .....
http://www.rainierballistics.com/loaddata.htm
I'm not a big fan of Rainier bullets / the jackets are inconsistent - and on 180 gr bullet they may be + or - a couple of grains easy .... so you can't weigh the finished rounds you have and come up with any useful or accurate data on what you did. You need to pull all of the bullets / and reduce your powder drops ...
I load a lot of .40S&W for Sig 226's and other guns ( 1911's, etc ) - and I scrounge brass from the indoor range where I shoot. But I clean and inspect the brass carefully / I load to min specs / I primarily use Montana Gold bullets in 180 gr .....
Based on what you told us / I'm not sure you can rule out a double charge ...and I'm assuming you're not using a press with a "powder check die in it" verifying every drop on every round .... .45 acp is a very forgiving case / .40S&W is not. I also suggest you check every finished round / by hand / and use a case gague on each and every round as you box it up as well. You might have found a little crack in a case by doing that / or a dent or something that caused that case to give way ......