SPRINGFIELD - A federal jury yesterday found Michael A. Crooker guilty of a firearms crime that will mean a 15-year mandatory prison sentence. The jury, made up of eight men and four women, delivered its verdict shortly after 2 p.m. yesterday after deliberating about 10 hours during two days. Crooker, 51, formerly of Agawam, had been charged with being a previously convicted felon "causing a firearm to travel in interstate commerce." Crooker was accused of trying to mail an air rifle and sound muffler to an Ohio man in 2004. Air rifles are not considered firearms under federal law, but...