Drywall screws have been a staple of the theater trades for as long as I've been involved - 35 years, I have no doubt that I've driven and removed far more of these screws that all Haggis combined
with d-list tossed into the mix! I have some observations.
Drywall screws are different from regular screws in several aspects, The most important is that they are made from an alloy that is not affected by lime, (Plaster is highly corrosive.) The trade off
is that they are very brittle, In theater, the bits that protrude clear through a joint are trimmed by giving them a whack with a hammer, I'm sure you all have had a head break off of a long screw,
The design parameter assumes that a maximum of 1 inch of the screw is in wood, The remaining length is in plaster,Homasote, celotex, foam or what have you, A true drywall screw is black from the
phosphate coating.
A similar screw has been available for the past few years; generically called a deck screw, These are typically stainless, or galvanized or red.These are a lot tougher since they are intended for
wood/wood joints, (In theater we trim these with a giant dremel with an abrasive cut-off disk known to the rest of the world as a 4" weld grinder.) This is the screw you want to use.
Good old fashioned normal screws are still available (!) and are much stronger than drywall or deck screws. They need clearance and pilot holes and are a bit of a bother for model railroading
use.
The mental attitude you need to adapt is that only the pointy end needs to bite into wood, The shaft part stays loose so that the joint is tightened between the point and the head.
Don't place any screw closer than 1-1/2" from the end of a plank without drilling a clearance hole, I use 3/16 bit for all deck screw clearance holes and a 1/8" for all pilot holes, (Yes, I use three
battery drills when I am building something!) In shit-pine (SPF) you will not have a long lasting joint when a screw goes into end grain, Use better wood or reinforce the joint, One inch of deck
screw into wood is as long as the screw needs to be, Additional metal does nothing for strength, Want more strength, use a plumper screw.
Lag screws are ductile, They are intended for joints where shear strength is important, You need proper clearance and pilot holes.
Having said all that about screws, Damon Transportation (Previous layout) and Wabash∓Southern (Future layout) was/were shot together with 5mm X 1-1/2" furniture staples, The impact from an air gun
is so sharp that no clamps are needed and a new brace can be added right below a rivetized locomotive without shaking anything loose, Not to mention 50 times faster than a screw gun.
Christian