Solving a Sako design fault

The Sako .22 P94S has a design fault in the bolt locking ring which can cause the bolt handle and locking lug to break off the bolt during opening. This problem is caused by a combination of a steep cocking cam and a stiff mainspring coupled with a design that has a stress point and one unsupported edge. The stress point is created by the sharp internal corner in the slot milled for the striker and safety plunger. This stress point can create (over time) a small crack across the base of the locking/bolt handle lug leaving only a thin wall on one side holding it together. Eventually this thin wall fractures with the amount of force needed to lift the bolt handle. As the photos show, I have redesigned the problem area and made a new locking ring from Chrome-Moly 4140 steel. A lot of work on both lathe and mill but a pleasing result. The only reason I did this is because no spares are available and I believe the design has been changed in later models. The rest of the rifle is in near new condition and justified the work. If you have a similar problem don't come to me!
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Show off! :pissed off: :thumbsup:

Very nice work @gundoc
4140 would have been hard going!
I made a set of front hubs to take vented disks and 4 pot calipers years ago when I "Tigerised" a Sunbeam Alpine.
Days of work but the bar stock was free :)

Hmm, @gundoc my ‘go-to’ .22 is an older Sako, you’ve got me worried!
How do I identify mine to know if it is the same model that you had to repair?

@Finnwolf don’t worry @gundoc can fix it:ORLY:;)

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Originally Posted by Finnwolf

Hmm, @gundoc my ‘go-to’ .22 is an older Sako, you’ve got me worried!
How do I identify mine to know if it is the same model that you had to repair?

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PM me a photo of the underside of the bolt handle area.

Well done Doc.

I flicked a couple of photos of my Sako .22 bolt to gundoc, much relief on my part when he assured me the bolt was not of the ‘fragile’ design, big thanks @gundoc:thumbsup:

Very nice work!
When I saw the thread title I was half expecting to see a photo of a howa :D

Nice work, I like making fiddly parts like this that itch your brain a bit.

Id love to see some progress shots and any of your mill/lathe setups if you took photos. I have learned a lot over the years by just watching people who are good at stuff do their thing.

Quote:

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Originally Posted by SixtyTen

Nice work, I like making fiddly parts like this that itch your brain a bit.

Id love to see some progress shots and any of your mill/lathe setups if you took photos. I have learned a lot over the years by just watching people who are good at stuff do their thing.

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The 4140 bar stock was about 4mm undersize to turn the locking ring in a concentric manner but as the two lugs are on one side I put a 2mm offset on the bar in a 4 jaw chuck and the resulting lump on one side was enough to mill the lugs. I marked out the rear face of the ring then milled away all the part that I didn't need in a 3 jaw chuck on a rotary table, taking the diameter down to just under the size of the front part. The main lug was then milled on both sides to the correct thickness with a 10mm end mill with a 1mm radius on the bottom edge. This process was repeated for the small guide lug, after which I marked out and milled and drilled the cocking cam and safety bolt hole. The milling head was then tilted 13 degrees and I milled and drilled the bolt handle mounting, then tapped it to M6. All finishing was then done by hand. Tungsten carbide tooling was used throughout. Sorry but I didn't take any photos of the set-ups.

A few years ago when I owned a Sako 85 Finnlight I discovered a limitation (perhaps not a design fault). Went on a very wet trip to Hauroko over 3 days everything was just soaked. Went home had rifle cleaned & dried out. Next trip bolt wouldn’t work properly, played around for a long time and eventually gave in. Took it to a clever mate and in no time he worked out how to take the bolt apart. Turns out that the stainless steel rifle and bolt had a non-stainless spring inside which had rusted up! Swapped it out for a stainless spring and still purring along with no issues 6-7 years later.