I love the Crosman 1300, it's an elegant gun, well designed, and constructed with minimal amounts of plastic. The grips are made from a molded plastic that has hand-laid colorant, no two sets of grips are alike. It's well balanced and fits my hand perfectly.
The only problem with the gun in my view is the trigger. The Crosman 1300 shares the same trigger design with at least the Crosman 130/137 that use the same valve components as the Crosman 1300. The valve arrangement and trigger design makes the trigger harder to pull the more the gun is pumped. Furthermore, the finish on the trigger components is very poor. This results in a long, gritty, and heavy trigger. The trigger weight on one gun I acquired was 5lbs at 3 pumps and 9lbs at 8 pumps. Not a lot of fun to shoot. However, with a little effort, the trigger can be brought in to the sub 2lb range with a short smooth pull.
Remove the grip frame and pull the valve components out the back of the pump tube, no need to remove the pump handle.
You will have to remove the trigger components from the grip frame by punching out their pins. The parts that will have to be rectified are the trigger, the sear, and the sear block. Specifically, their respective mating surfaces need to be smoothed and polished.
The trigger and sear do not appear to be hardened, but their edges where they mate are at least work-hardened as the parts were stamped out.
The finish on those parts is simply criminal, I can't imagine what Crosman was thinking. You will need something harder than a file to clean those surfaces up. I used a grinder, some Emory cloth, and finally a diamond hone. The surface doesn't have to be perfect, not even close, it just has to be smooth such that you don't feel any roughness when you run your fingernail lengthwise along the edge.
The sear block has a concave surface the interfaces with a hook on the sear. The surface finish on that face needs to be improved. The sear block is hardened for sure. I can't turn it on my old-timey lathe using HSS bits, but someone with a modern lathe might be able to clean it up with a modern high speed lathe and carbide bits. I just put the sear block in my lathe and kept at it with Emory cloth until the surface was smooth using the fingernail test. Be careful to preserve the geometry of the concave surface as that surface geometry is crucial for the proper operation of the gun.
At this point, I usually reassemble the gun and test the trigger to see if I can stop there, I really don't like messing with sear geometry as just a few missteps with a grinder can render the sear unusable. What I find most the time is that the hook on the sear will have a burr on its tip that causes the trigger to feel uncertain. If so, I remove the burr trying to preserve the sear geometry.
On this particular gun, I ended up with a trigger weight of 2.1 lbs at 3 pumps and 3.0 lbs at 8 pumps. I've acquired a few of these guns and their triggers are always a mess, I don't know why Crosman allowed this to happen. The late Crosman 130s and 137s have the same issues. I believe that poor triggers hurt the sales and now collectibility of these guns. With a little effort, they can be the sweet fun guns that they were meant to be.