Stevens 315 Light Primer Strikes

I have a Stevens 315 that was excessively hard to open with huge firing pin drag marks. I measured the firing pin protrusion at 0.100 and 0.154. I looked up a spec that said a 12ga should be .050-0.076 for protrusion. I shortened the firing pins so that they were right at the 0.076 number and centered. Inserting a pair of fired shells and pulling the triggers it is much much easier to open with no excessive firing pin drag.

After test firing I get light strikes and roughly a 50% ignition rate on the right barrel. It shot well (aside from needing to be Samson to open it) before I shortened the FP's. I was testing with AA's. The hinge is tight. I think I have plenty of protrusion, I don't know if the headspace is to large or how to measure it.

I'd like an opinion on either extending the firing pins to say 0.090 or I can shim the main springs to make it hit harder, or both. Seems like they hit plenty hard. I can see a faint mark on a shell that didn't fire correctly. Fired shells from the same barrel have good primer indent which leads me to think there is a headspacing issue and the shells are setting back after firing.

Any burrs built up on firing pin holes, causing drag? Not to be smart ass but dirt possible?

Throughly cleaned and deburred while is was taken complete apart to remove the FP's.

How do you know the firing pins were too long and the problem wasn't that the firing pin stops weren't too short?

Steve

Headspace is important.. Simple depth of rim counterbore in chamber.. A depth mike or even caliper, will tell you if it is .030 long (simply insert an unfired shell in chamber) measure from rear face of shell base to rear of barrel..... A proper gage can be purchased..

Excess head space, will require long FP protrusion... And in lesser amounts, actually increases recoil...

To correct on an otherwise tight action, counterbore is deepened and a ring fitted.. Good place for locktite..

As to drag marks.. There are parts that lift the hammers when cocking, or on cheaper guns... a type of rebounding hammer setup is used..

Properly rounded FP tips, are also very important..

The hammer lifters might need adjustment, or rebound assy (often part of hammer spring plunger) is incorrectly installed/fitted..

The FP tips dragging, will make it very hard to open... Stiff gun to begin with...

I don't know how the firing pins are retained in the 315 but I recently fixed a similar problem on 311. The fp's on the 311 are held in place by large head screws which also act as hammer stops. If the heads of these screws are to thick, the hammer is stopped before it can deliver all its energy to the fp. Shaving a bit off the head of the screw (either under the head or the top of it - depending on the overall size of the screw) fixed it.

A 315 is completely different than a 311. The firing pins have the mainsprings around them and don't rebound at all, compared to the separate hammers in a 311. The firing pins stop on the back of the cocking lever, which was stamped and coined in use which led got he excessive protrusion -- my theory at least. It was easier to file on the FP than to build up the back of the cocking lever.

I field checked the headspace with a new shell. A straight edge laid across the back of the barrel block showed the base of the shell, extractor, and barrels were all within 0.003 of each other. The extractor also fits very tight when it is locked up.

I think I'm going to try to put a spacer on the mainsprings to compress them further. It is easy to push the FP flush to the breachface.

I would not have shortened 2 parts, when 1 is at fault.

Sounds like you now have 3 parts to repair/replace. Adding parts seldom solves problems, on cheap guns that were designed to reduce parts count..

I do not know if it will make a difference, but when you shorten the FP's... you can screw up the relationship of the cocking mechanisim..

The mainsprings may have a little slack/be short, to allow FP's to slide flush with standing breech face. In effect the FP itself is the rebound system..

It sounds like the gun was excessively dry fired, thus allowing FP's to strike lever/stops and deform them/it

Deformed parts will not retract FP tips properly....

All I have are exploded views of that action...