Concerning bolt shroud gap/firing pin lug wear - Stoeger response in post 11

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stickhunter

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Hi,

I have a used Sako AV that I recently took apart to clean and lube. When I removed the firing pin assembly, I found significant wear on the lug that rides in a slot on the bolt body:





The width of lug that has been worn down is approximately 0.130"

When I noticed this wear, I realized that the gap I was seeing between the bolt shroud and back of the bolt body was not normal and the result of the wear allowing the shroud to move further back than normal under firing pin tension.

Here's the bolt cocked-and-locked with a > 0.1" gap that pretty well matches the wear:



Upon firing, the bolt gap is reduced, but not completely:



After firing, with no firing pin tension, I can move the bolt shroud in-and-out with my fingers and close the gap:



This wear seems very excessive for a rifle that doesn't appear to have fired many shots. I was recently testing out the trigger quite a bit and cycling the bolt --- I noticed a gritty feeling to the bolt lift and found a significant amount of metal filings in the action, so I now know where those were coming from.

Now for my questions:

1) Any ideas on why this lug is wearing? The raceway in the bolt body shows no damage, so I wonder if the metal was unusually soft - that lug has to withstand the pressure of the mainspring and any pierced primer gases. I'm really concerned that there is something misaligned or loose that is allowing the lug to ride partly out of the raceway and be ground away.

2) Is this repairable by depositing some new metal with MIG/TIG and reshaping the lug? Unfortunately, this era of Sako firing pin isn't meant to be broken down further, so it would be a chore to separate the shroud from the actual pin. With proper heatsinking and short weld times, could this be done to the firing pin assembly without ruining the spring or firing pin temper?

3) Any recommendations for who could do the job? I'm out West (Victoria), but happy to ship to someone with the proper setup and experience with this type of repair.

Much appreciated,
Stirling
 
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If you bought it used, I would think bubba altered it. I have seen some sako rifles with high mileage and never seen anything that worn. As for a fix - I would call WGP, stoeger, numrich, accuflite, and join the sako collectors forum to buy a replacement instead of trying to repair this one.

Mind you, you don't have much to lose, and it doesn't look terribly hard to fix.
 
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double gun said:
If you bought it used, I would think bubba altered it.
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If that's the case, I wonder to what end? The rifle had a pretty heavy trigger (6-7lbs) that wouldn't lighten with spring adjustment... could someone possibly have thought thinning the lug would reduce the mainspring tension and lighten the trigger? Well, I guess anything is possible! I must admit, I don't know how that wear could occur with the lug properly seated in the raceway since it should never cross the disassembly cut-out and contact a perpendicular surface.

I'll start calling around for parts, but based on past experience, I'm not too hopeful. I have heard of some people finding complete firing pin assemblies in the white --- the problem they encountered was how to separate the shroud from the pin so that it could be blued.

If this is not the work of bubba, I'm also concerned what will happen with the replacement part over time... I'd definitely look to constant inspection and maintaining lube on the lug.
 
It would be theoretically possible to rebuild the stud by welding... you need to find a tool & die man who knows how to do microwelding. It would likely have to be rehardened as well, or it will just wear down again.

It's difficult to say from the photos whether this is from wear & tear, or if somebody's tampered with it.
 
If it wasn't altered then maybe no lubrication and possible soft metal... Once it started, it would get worse with every operation of the bolt. I would recommend getting a new piece. I would suggest you contact Sako with your pictures and description and ask for their comment.
 
Thanks for the advice, everyone. The amount of shavings that I found in the action was no wear near the amount of wear, so I imagine this has been going on for a while. I've sent an email to Stoeger to see if they have any recommendation. Unfortunately, the sources that I've checked are sold out of AV firing pin assemblies.
 
Try first contacting Sako (directly :) ) to see if they have record of a batch of wring or bad heat treated pins. That's were i'd personally start.
 
Well, I think I may have found the smoking gun to this problem. Here are some pictures of the straight raceway in the bolt body, down which the firing pin lug travels during assembly/disassembly:





Notice the shiny sliver at the end? Curiously, this sliver is far enough down the straight raceway that it is actually within the circular raceway, and the distance from it to the front edge of the raceway about matches the width of the remaining firing pin lug. The sliver does not appear to be burr as I can't see/feel any grooves in front or behind it. Pushing a pin head down the raceway is stopped by the sliver, while dragging a pin head from behind the sliver doesn't catch anything and just drops down. So I'd describe the sliver more as a "step" than a burr, and possibly a result of the cutting operation for the straight raceway.

The rest of the circular raceway looks normal and dragging a cotton bud didn't show any snags. The only oddity (and it may very well be normal) is a scallop relief on part of the circular raceway that isn't involved during bolt lift/close (as shown in the second picture below):





The rest of the action shows little wear, except for the cocking piece camming surface. I initially thought this was the source of the filings, but I don't believe that to be the case anymore (and I do note that Sako recommends lube on this surface):



The remaining pictures are of the action and bolt. I don't believe there are any signs of abuse/damage in these pictures:

















As I mentioned, I was doing a lot of testing/adjustment of the trigger, and had probably dry cycled the action a few hundred times before I noticed the grittiness and found the filings. Initially, I thought all the firing pin lug wear was caused by my actions and lack of lube, but I'm now skeptical given (a) the amount of filings doesn't look like it would amount to anywhere near the missing lug material and (b) the step leads me to think that bolt assembly is the issue, and I hadn't taken the bolt apart prior to noticing the problem.

My hypothesis is that the "step" is a manufacturing defect, but there was still enough clearance to allow the bolt to be properly reassembled. Either this step contributed to the wear or upon subsequent disassembly/reassembly, someone encountered troubles inserting the shroud because it was hitting the step, and decided to (incredibly stupidly!) reduce the width of the lug so that it would fit the reduced raceway.

For the life of me, I can't imagine anyone filing away this lug, but I also don't see otherwise how such significant wear could have occurred. I now suspect the filingsI saw were simply smoothing out/wearing down the already cut away lug surface.

This is definitely going to be headed to Sako/Stoeger for an inspection and recommendation.
 
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I just received this response from Stoeger, so I think the prevailing consensus that bubba was at work is correct. BTW Stoeger was very quick to respond to my email --- now to source a new assembly.

Stirling;



I have seen this exactly once before (probably 10 years ago) and the damage was man made. If I remember the story correctly, a gun enthusiast “gunsmith”/machinist was attempting to lap the locking lugs and smooth the bolt travel of a Sako and ruined the cocking piece of the rifle. I don’t know if he got lapping compound where it didn’t belong or didn’t have any lube on the tabs that retain the shroud but the damage was exactly like this. If you bought the gun used in this condition, I’d almost bet money this is the same gun or the firing pin has been switched and this gun sold with the damaged firing pin. The only fix will be to replace the firing pin assembly.
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Just wanted to follow up with a conclusion (hopefully!) to this issue.

I was able to source a new firing pin assembly from Stoeger. Their parts person said they only stock L61R firing pins, but that they are compatible with the AV action. The new assembly arrived and I measured the lug width at 0.155" compared to 0.045" on my worn assembly.

Everything went back together easily and the firing pin protrusion ended up within spec. So things look good. I'll be keeping the lug lubricated with moly grease and checking it periodically to ensure no significant wear is occurring.

Here's some pictures comparing the old assembly (above) to the new assembly (below). Notice that the bottom of the new bolt shroud has less material than the old and the checkering is slightly coarser. Fortunately, function appears to be fine and there's no longer any gap between the bolt body and shroud when cocked.




 
blargon said:
Glad it worked out. did you swap the springs?
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No, I used the new assembly as-is. I haven't taken it to the range yet to verify operation, but I'm expecting the firing pin to work fine (fingers crossed). Removing the firing pin/spring to switch shrouds seems to be a mystery in the Sako world --- I've not seen a definitive answer on how it's done. You can see on the old assembly that there is a hole on the bottom of the cocking piece, in which a pin or headless screw binds the firing pin. The new assembly has no hole, so I have no idea how I'd go about separating the pin from the shroud.
 
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