WHEN YOU GO FROM A 9 1/2 COIL TO A 4 1/2 COIL. DO YOU LOSE A LOT OF DEPTH. I CAN'T SEE MUCH DIFFERENCE. BECAUSE ALL THE COINS I FIND ARE ABOUT THE SAME DEPTH?
Yes, you would probably lose depth. But you enable yourself to get coins in trashy areas, close to playground equipment, in tight bushes and greater sensitivity to tiny targets. Most coins are in the top 4-6 inches, easily attainable with that small coil in most soils.
Excal 1000, Excal II, Sovereign GT, CZ-20, Tiger Shark, Tejon, GTI 1500, Surfmaster Pulse, CZ6a, DFX, AT PRO, Fisher 1235, Surf PI Pro, 1280-X, many more because I enjoy learning them. New Garrett Ca
As John said you will lose a small amount of depth but the ability to find coins and rings close to junk more than makes up for it. Add to this the lighter weight and ability to cherry pick in heavy brush where a larger coil won't go.
Surprisingly Garrett's small coils achieve incredible depth for their size although the larger coil has a definite edge. The little 4.5 inch Sniper for the 250 will get nearly seven inches in good ground and that's unheard of in general circles.