300 seconds timeout with SSRS 2012 + Sharepoint 2013

Hello,

Using Reporting Services 2012 in SharePoint (2013) integrated mode, i'm hitting a 300 seconds wall when i run long reports.

The RS logs mentions a SqlException : timeout expired error .

Problem is, I have tried to search where this limit lies, but to no success so far.

IIS & Sharepoint : in every web.config, the executionTimeout value in the <httpRuntime> tag is at least set to 3600 seconds.

The reports have either no timeout or high values (1800 sec or more).

Reporting Services : use the default 1800 seconds timeout.

I'm really confused and any help would be greatly appreciated.

Thanks,