Light strikes - K Frame *UPDATED*

[Black_Sheep]

Last fall I picked up a clean Model 12 no dash which apparently has an issue with light strikes. The first time I fired it at the range there was a couple of rounds per cylinder that FTF, often they would fire if I dropped the hammer on them again. Rounds with light strikes always fired when they were tried in another revolver so I don't think it's an ammunition issue. Subsequent range sessions using reloads with a different brand primer produced similar results. I detail stripped the gun, cleaned and inspected each piece for damage or abnormal wear and everything looked good. It wasn't very dirty inside so when it was lubed and reassembled there wasn't really a noticable improvement.

Today at the range the FTF continued. Rounds that functioned had deep, fairly well centered strikes, FTF rounds had shallow strikes. The attached photo shows the last cylinder full of ammo, 4 FTF and 2 that fired.

The only thing I can think of is the 49 year old mainspring is fatigued. Any other suggestions? I really like the gun but without 100% reliability it's not all that fun to shoot...

 

[RychenCop]

yea...change out the main spring.

 

[Bailey Boat]

Make sure the mainspring strain screw is firmly seated in the frame and if that doesn't cure the issue go with a new mainspring... 49 years is a long time.......

 

[Black_Sheep]

Make sure the mainspring strain screw is firmly seated in the frame and if that doesn't cure the issue go with a new mainspring... 49 years is a long time.......

The strain screw is fully seated and also appears to be unaltered. Are aftermarket mainsprings OK or should I go right to S&W for a replacement?

 

[RychenCop]

get wolff springs

 

[Bailey Boat]

The strain screw is fully seated and also appears to be unaltered. Are aftermarket mainsprings OK or should I go right to S&W for a replacement?

I personally prefer genuine S&W parts, not to say there's anything wrong with other makers....... just MY preference......

 

[PJGP]

Rounds that functioned had deep, fairly well centered strikes, FTF rounds had shallow strikes.

I am sure that the deep strikes you speak of are in fact the result of the case setting back on firing. The hammer nose then gets the primer pushed back against it. The shallow strikes are just that, but some times a primer agrees to go off!

Peter

 

[Black_Sheep]

I have a new standard strength mainspring coming from Wolff, I'll post the results once it's installed and I can get to the range. Thanks for all of the responses...

 

[Black_Sheep]

I replaced the original spring with the standard strength Wolff mainspring and still get an occasional fail to fire. Rounds that didn't fire showed light strikes on the primer again, each of them fired when I tried them in a Model 36. FWIW the FTF rounds all had CCI primers, every round with Winchester primers went BANG on the first try...

 

[GLV]

1 Be sure you are fully seating primers.
2 check the firing pin protrusion through the bushing.
3 Check the headspace.

These measurements can likely be found in Jerry Kuhnhausen's The S&W Revolver.

Last, I would recheck the length of the strain screw. Some lots of CCI primers do have hard cups.

 

[jimmyj]

Hi:
Anyone with the information:
What is the proper length of firing pin and mainspring tension screw???
Jimmy

 

[Nightowl]

Too much endshake can also be a part of the problem in that the primers are farther away from the firing pin. With no endshake, a full mainspring and full length main spring strain screw, screwed tight should make every primer of any make fire virtually every time, with room to spare.

 

[SaberOne]

Man Oh man. If that happened with mine and I couldn't resolve it quickly, it would be off to my preferred smith'. I know that my guy likes to install an extended firing pin when possible.

 

[Black_Sheep]

I'm not ready to give up yet, I'll compare the OAL of the strain screw with that from another round butt K-frame, check endshake as outlined in the S&W revolver shop manual and firing pin protrusion although I didn't see it covered in the manual.

One thing I failed to mention was an occasional "bind" in the action. I'm not sure of the correct name of the bar that blocks the hammer but if it was hanging up, could it possibly prevent the hammer from impacting the primer with full force? With a straight edge, it appears to be straight and it sits below flush in the sideplate so clearance shouldn't be an issue. There are no witness marks but it looks like it may be hitting the cylinder release. Thanks for all the tips so far, I appreciate the guidance...

 

[minconrevo]

The serious revolver competition shooters use Federal primers virtually without exception. Check what GLV suggests and you may find what's happening.

I have run into failure to fire (FTF) issues in well-worn guns with stretched frames. Normally this takes lots of hot rounds, but happens quicker in alloy or smaller frame guns.

 

[Bert Man]

Too much endshake can also be a part of the problem in that the primers are farther away from the firing pin. With no endshake, a full mainspring and full length main spring strain screw, screwed tight should make every primer of any make fire virtually every time, with room to spare.

10-4 on endshake. Very possibly endshake cylinder. Hammer nose strikes primer and cartridge case is moved forward slightly lessening force of the hammer's fall resulting in light strike failure to fire. May be more or less likely to occur with certain chambers and not others due to machine tolerances in cylinder/ yoke assembly. To check endshake cylinder take the unloaded weapon and drop hammer to fired position and hold the trigger all the way back. With the other hand try to move cylinder forward and back. If there is more than more than a slight amount of movement it is excessive endshake cylinder (normally an inexpensive repair with no new parts needed. If endshake is not an issue other posters gave good advice about mainspring/strain screw. It is possible that the strain screw was at one time shortened and then tightened back down and could also cause light strikes. Might also check that hammer nose protrudes far enough through bushing in recoil shield to make sufficient contact with primers. Hope you get it sorted out.

 

[Twist]

The occasional bind is possibly the cylinder rubbing against the forcing cone end of the barrel. This problem is a symptom of excessive cylinder endfloat. Check the cylinder for rub marks on the face closest to the barrel.

Excessive endfloat is easily fixed with some Ron Power Custom cylinder shims - Brownells have 'em.

 

[Ben Cartwright SASS]

I had FTF issues with an old 38/200 Victory. I totally cleaned it and still had FTF's.

I was using Factory Loads of whatever I could find.

The hammer nose seemed to be short (to me)
I went to Namco and got a new hammer nose, replaced it and it solved the problem.

I am starting to handload for it, I prefer Winchester primers

 

[bpeddicord]

I've had the same problem of light strikes with CCI and Wolf primers even in brand new revolvers. I now use only Winchester primers and haven't had any more problems.