Preparing large cherrystone clams I was tempted last week-end by Cherrystone clams.

They were large and with heavy shells.

Reading about them, there were supposed to eaten raw; I tried to open one of them with an oyster knife, and failed miserably.

So I tried steaming them, a bit like steaming small clams or mussel( shallots,garlic, white wine...) 

The problem I had is that one of them opened quickly and the other ones took more a lot time.

The result was that most of them were too chewy to be really good.

Other than improving my skill in opening clams (I can open oysters easily), how can I cook them so that all the clams steam properly ?

Maybe my pot was not big enough and they had no space to open (remove the ones already open)? 
Should I have them out of the fridge before so they were not too cold before putting in the pot?

Thanks.
An oyster knife, paired with the most common technique used to open oysters will fail you when it comes to clams.  You need a thinner bladed, clam knife...and you need to find the seam opposite the hinge side of the clam.  Another approach is cryo-shucking; that is, freezing for a short time in a traditional freezer...or even using liquid nitrogen, if it is available.  Large cherrystone clams can be steamed.  I prefer them raw...or opened, seasoned and baked, such as in clams casino.  If they are very large, approaching the size of quahogs, steam them open, chop them up and make chowder.