I think you can go into a safehouse and use the gun rack. Just pick what ever gun you want and add it to your controls. Then use the 1,2,3,4 button, 2 is for pistols. Or use Q,1,2,3,4, and bring up you weapon wheel and choose from there. I use 1 for Bow, 2 for pistol, 3 for assault rifle, 4 for sniper rifle. But all guns and ammo and selling stuff is inside the safehouse in the gun cabinet...After clicking on Buy and Sell, look to the top of the screen and choose weapons and go from there.