Does anyone know if a new manufacture Model 70 firing pin spring will fit a Model 54? Or does anyone make a new model specifically for the Model 54?

I do not know the answer to your question, but I do know that there are two very different firing pins for Model 54's. The earlier one is a two piece affair similar to an M1903 Springfield. The later one is a one piece firing pin but is different from a pre 64 Win 70. I don't have a 54 laying around to look at the differences. Post which firing pin you have and maybe someone can help you out.

First picture, full assembly.



Next photo, just the head showing plenty of pin protrusion compared to the extractor.



Next is what happened when I tried firing some factory ammo. Barely a dent in the primer.



Now for the interesting thing. I just had this rifle rebarreled last month. The gunsmith provided the following three "proof" rounds. The dent in those primers does not match up with what I have and the brass is extremely clean. Something pretty fishy not that I look at it.



My thought is that the firing pin isn't being projected forward fast/hard enough. But now I'm wondering if there's a chambering issue instead.

The 22 Hornet uses a weaker spring than the other calibers. That is the later style. It is probably the same as a pre 64 Win 70. Make sure the firing pin is moving freely in the shroud without the spring; also make sure there is no crud inside the bolt towards the front. If that all checks out the spring would be the culprit. I should have that hornet info somewhere as I have read it before and owned a 70 and 54 Hornet in the past.

You might have a different gunsmith check the headspace.

I stripped the entire bolt to make sure there wasn't anything slowing it down. Then I tried firing a primed piece of brass and I still get the weak firing pin dent.

It does look like the hornet required a different firing spring than all the rest, so I don't know what the chances are I'll ever find one.

I paid enough for the work that I'll send it back to the smith that did the work and have them fix it.

What sbrmike said about having a different gunsmith check headspace.
Also, if you can get enough magnification, and you know what to look for, you may be able to determine if those "proof" rounds were hit by the same firing pin as the ones you fired or attempted to fire.
Both of those pieces of information might make the picture more clear.

If I paid a gunsmith to do what turned out to be shoddy and perhaps dishonest work, I'd be leery of letting him mess with it more. I get that in a perfect world he should make it right, assuming he did something wrong and he is capable of doing it right. But the world is not perfect. It might be better in the long run to cut your losses with that smith. Much depends on what you find out, his reputation, and your history with him. Just some thoughts.

As far as the Hornet Spring goes, I am going from memory, 25 or 30 years ago, when I was much more active in collecting. I am certain that you could order a pre 64 Win 70 Spring from numerous sources used or NOS or aftermarket and cut a coil or two off and be fine. You could try one full length but be ready for a pierced primer. I think a full length pre 64 Win 70 Spring is like 25 coils and the Hornet is the same spring cut to 23 coils, but that is going from memory.

Buy yourself a 22 Hornet NoGo or Field Gauge from Brownells or Midway and check the headspace yourself. He may have used handloads with the bullet sticking into the lands, which held the case head closer to the bolt and fired it; or they weren't fired in that gun, or I don't know what is going on, but something just doesn't look right there.

A field expedient would be to put two layers of electric tape on a new factory cartridge and see if the bolt closes. Add more layers until the bolt won't close; measure or compute the total added thickness necessary to cause a NoGo and report the results here.

ETA: Just use the bolt without the Striker Assembly installed. And don't try to make the bolt close as you can compress the tape and or virgin brass, just use slight fingertip pressure to close the bolt.

ETA: So much for my memory on the spring coil counts!! I may have it confused with another gun, i.e. M1903 Springfield and M1922 Rimfire version!

My pre 64 Win 70 Striker has 37 coils and is much more compressed than your striker, and is just about 2-3/8" compressed.

Still not much help but the Rifleman's Rifle says they used a special 39 coil spring for the newly adopted 22 Hornet in 1933.

Good news, crisis averted.

Per the headspace suggestions, I took a piece of the supposed fired brass and added tape to the back until the bolt was hard to close. There was clearly a headspace issue. As I really started watching every part of the action during cycling, I noticed the the bolt was slightly hitting the wood when closed. Sure enough, I took the barreled action out of the stock and everything works like it should.

So it looks like I have some stock sanding to do to get the bolt to close all the way, then I should be all set.

That is great to hear. It would have been upsetting if it was a gunsmith issue.