Problem with svt-40 need HELP

I have a SVT40 and its acting strange. I'v cleaned it up seriously, the gas system work prefectly, the ejection is good, BUT... If I put one single bullet in the magazine and shoot it everyhting works great, altough if i put more than one bullets, say 2, it would either slam fire or EVEN detonate the first bullet upon closure of the bolt! Kinda scary... I use CCI primers, and I reload...Using 42 gr of 4895 and 150gr Hornady bullets. But that's hardly the problem since its occuring upon closure of the bolt. Anyone can help? If i close the bolt with only one bullet in the magazine there's no problem at all...

Are the primers deep enough? As the bolt slides forward the firing pin probably dimples the primer, like on a Garand. At least it's a place to start.