Today I picked up an old Sheaffer's fountain pen, piston filler any help identifying it would be apreciated... It is a great writer.....the nib says Sheaffer's M1 made in usa and the barrel is stamped
WA Sheaffer pen co.
Fort Madsen, Iowa USA
Made in USA

The nib and the clip both say Sheaffer's With the "S" and the nib has a heart shaped hole in it.

OH BOY, I question I can answer and actually feel I know something about..

What you have is a Sheaffer Tip Dip Cadet... 1953 to circa 1963 .. it has an open stainless steel nib that is interchangeable... I have 4 of them 2 F1 and 2 M1 nibs and they all write beautifully.
The pen fills from the front of the feed. If you look closely you will see a small recess at the front of the feed. Basically it looks like someone did not drill out a snorkel hole...
Just dip the pen into the ink just past that hole and press down on the plunger and wait about 10-20 seconds for the sac to fill.
Most of the TD and Snorkel pens that I have acquired need some work. This particular pen is real simple to work on. Normal repair requires a new sac and O ring. Both easy to do.
If you want more info on this pen go to Pen Hero - Sheaffer Tip Dip Info
I find Jim's site absolutely fantastic for Sheaffer information...

OK now that I have given you all I know... I don't doubt that someone else will come along with more info I don't have or to correct some mistakes I have made... I am also still learning...

OldGriz, Thanks. I had found the pen hero site lastnight, well, actually early this morning while I was searching for info, I figured it was a cadet from the pictures but you really gave me the info I needed. Thanks so much. Any way to tell the dates?
I have always loved the old pens, I just don't have a lot of them as I don't often know if they work etc I am somewhat gun shy to pick them up.
There is a repair guy in town here who I have seen on the board, Ron Meloche, I have emailed him for info on repairs and I haven't heard back from him. I am figuring he is out of town at a pen show or something. Once I am in touch with him and I know I have someone who can do repairs... look out...oh man I gotta start working on my pen alibis for my wife... uh yes dear a little old lady gave me that pen, and then her neighbor gave me these other twenty.... nah she'll never buy that. sigh... lol