Can i go into a sporting goods store in pa , purchase a sks, leave the store with it and drive home to MD?

All SKS, except for the SKS-M and D models that take AK mags, are unregulated in MD. So there is no problem buying one from a dealer in PA.

well the dunham's store i went into , the "dude" behind the counter refused to sell it me because i was from MD. Dunham's doesn't have a custumer support number listed , should i call the store manager and find out if "dude" was misinformed, or if this is a store policy? What would one of you do?

Very similar to the whole thing with Sportsman's Guide in that it is apparent that being from MD is akin to having a big scarlet A on your forehead ("A" being for anti).  Dealers outside of MD (henceforth known as the United States) are scared to death that some politician or lawyer is going to come after them for some perceived infraction.

Therefore they just refuse to deal with us.

I'd just look for a dealer who understands the law........

Long arms are fine to purchase so long as they are not regulated.  Regulated would be "assualt rifle" (cringe) type guns like an AK, FAL, M1A, etc.  I've purchased several rifles and shotguns from PA and VA.

Depends on the dealer - some just want to keep it a simple as possible so they only sell to in state residents.  I recall a sign at a MD gun store a few years ago that said they would not sell to anyone except MD residents.  I think they have their head in the sand - but it's a little different from Sportsmans Guide - they know the rules in all the states - but they selectively make up their own special rules for areas they don't like