Saving/exporting sRGB Jpegs for printing

Hello!

I generate large files to be printed. Even though I set my resolution to 300dpi, then convert to sRGB then save as JPG. When I later open the file it shows as 72DPI at 4 times the size in inches, Yes, I know I have the same pixel count.

Doesn't PS CC 2014 save JPG at the 300 dpi set in the file, or do all jpgs default to 72?

I just don't want any variables that can confuse the service bureau that will be printing for me.

Thanks

Max