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Old March 25, 2014, 05:08 PM   #1
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Weak mainspring on a Pietta '58?

Broke this gun down several months ago in order to do some mods over the winter. I draw filed the italian stampings off of it and reshaped the grips to suit me. Was going to do some action work on it but never did and just took the parts out of the box and reassembled it about a week ago. (too many other projects right now)

Anyway, after making no further mods, the mainspring seems extremely weak. It will pop 3 out of 6 caps and the hammer force is definitely weak as it gets to the tail end of its travel. The parts just sat in the box for several months and it shot just fine prior to disassembling it. In every other respect, the action seems to work fine, timing is good etc. While I have not done so frequently, this is not my first time to tear down/rebuild a revolver. Never had a challenge like this before.

What am I missing here? Got any ideas?
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Old March 25, 2014, 05:43 PM   #2
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Did you remember to replace and tighten the mainspring set screw?
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Old March 25, 2014, 05:44 PM   #3
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1 dumb question and 1 recommendation:

Did you increase tension on the spring with the tension (set) screw? (this is the dumb question as that's kind of hard to miss)

I recommend you take it back apart again, fully, and put it back together again. I find that if it wasn't broke when I took it apart, but it doesn't work when I put it back together, I did something wrong in reassembly. I guarantee that hammer spring didn't wimp out on you. Something else is dragging in the works.
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Old March 25, 2014, 06:54 PM   #4
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Yes, I did tighten the mainspring screw. Is it possible to get it TOO tight?
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Old March 25, 2014, 07:37 PM   #5
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Another dumb question . . . since it worked fine before you took it apart . . . is the hammer binding anywhere in the travel? Pivot hole in the hammer clean as well as the pivot screw? If it's getting weak near the "tail end", I'm just wondering if it's binding up somewhere?

If it worked fine before it was disassembled and the main spring was fine then . . I don't see how it would be weakened by sitting in a box. I would take it apart, check each part - slide the hammer over the hammer screw to see that it pivots freely . . . check the hammer slot in the frame . . . reassemble and see if it still doesn't work. It's probably something very simple that you just aren't seeing . . . and that happens to all of us! Sometimes I concentrate on trying to figure something out so much that I overlook "the obvious". Let us know how it goes as it may be of great help to the rest of us somewhere along the way!

Good luck and hopefully it will be an easy fix.
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Old March 26, 2014, 02:57 AM   #6
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My personal opinion on the adjustment of the spring screw

I think it is possible to get it too tight.

Tightness is judged not by the difficulty with which the screw moves but by the action of the hammer. It should be tight enough to pop a cap every time but not so tight that it is uncomfortable for the shooter to cock the weapon.

Sorry if I am spouting stuff you already know.

Too tight springs wear the weapon early and are hard on the thumb.

I wonder if there is something wedged in behind the spring. A foreign object or something.

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Old March 26, 2014, 07:10 AM   #7
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I recently purchased a 1970 lyman/uberti remingtion new army, and had ignition problems with it. I noticed the last of the bit of hammer travel was balky even with heavy spring pressure. I found a burr on the spring where it meets the hammer and I removed it and polished the end. This made an improvement but did not eliminate the problem. Then I polished the hammer area where the spring rides, this eliminated the problem and at the range I got 100% ignition for 20 rounds with different caps. I was using ampco nipples.
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Old March 26, 2014, 11:55 AM   #8
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Check to see if the spring is fully seated in it's slot. If it is up a bit the spring could rub on the back of the hammer. It should only contact the roller on the hammer. That would make it harder to cock but not necessarily increase hardness of the hammer fall.

Also screwing in the mainspring tension screw will markedly increase the hammer fall if the screw is long enough to push on the spring. The older Piettas I have had did not have a functioning tension screw so you had to narrow the mainspring to lighten it. I just "tuned" a brand new Pietta Remmie for a friend and the screw regulates the mainspring beautifully. All the way out (no spring contact) and the hammer fall is too light to be reliable.
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Old March 27, 2014, 11:00 AM   #9
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Yeah Hellgate, When I initially installed the spring it was actually not fully seated in the slot - and it was a BEAR to cock the hammer. It is now fully seated and the tension screw is tightened all the way in, which should make it as stiff as possible, I believe. Just returned yesterday from some travel so have not had the time to fiddle with it yet. I will do so later this weekend and see what will come of it.

Appreciate all the replys.
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Old March 28, 2014, 08:01 PM   #10
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Longer screw or how about bending the spring?
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Old March 28, 2014, 09:39 PM   #11
44 Dave
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I have a small shim in mine to keep the spring up about an 1/8" from the bottom of the slot because the hammer would be on the very tip of the spring. It shouldn't be to hard to figure out what needs to be done, between the tension screw and spring placement to get a little more spring pressure.
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