Hardness of gun bolt

[Robert Turner 1Participant @robertturner1]

I wonder if there's a gun enthusiast on the forum who can help…..

A friend of mine has asked me to modify the bolt of a Chinese-made SKS 52 assault rifle (don't worry, I am in Canada, and it's all legal). It's the square-section block that contains the firing pin, and as standard it is designed to prevent removal of the magazine if it is in the forward position. The mod is to mill off about 1.5 x 3mm off the bottom edges of the block.

Anyway, enough preamble… Does anyone know how hard this steel is? I will be milling with a 1/2" HSS end mill at about 1000 rpm max, on a Boxford with vertical slide. Does this sound feasible, or is the steel way too hard for that set up?

Any advice gratefully received.

[Robert Turner 1Participant @robertturner1]

[ronan walshParticipant @ronanwalsh98054]

Gun actions are recommended to be around 30 hrc minimum and can go up to the mid 40's for 416 stainless steel actions. Whatever the hardness of the action, the bolt is always slightly harder to prevent pick-up and galling. All that been said, i was told recently that some ruger actions are up to 50 hrc in hardness. Its very difficult to tell how hard a metal is until you try to cut it , its been tested,or you've been told exactly how hard the metal is by a supplier.

[Tony Pratt 1Participant @tonypratt1]

I would guess HSS at 1000rpm will be a no go, I would try a lot slower rpm or carbide.

Tony

[Oompa LumpaParticipant @oompalumpa34302]

File test first then if it passes that a small carbide cutter at high speed usually works. It is always a "suck it and see" exercise without definitive info. Which is usually the case with the Chinese made guns. You quite simply wouldn't believe how many Chinese made guns, of all types and Calibers I have scrapped. Not saying your friends is rubbish, just that the quality of production can be "variable"

graham.

[Robert Turner 1Participant @robertturner1]

Thanks for the advice, guys. I will get hold of a carbide end mill. My friend is under no illusions about the quality of his gun – I'm certainly not surprised that the global black market price of these things is only about $15. The materials aren't bad, but the tolerances are pretty loose.

[JohnFParticipant @johnf59703]

Robert, I am not familiar with this particular firearm or quite what you are doing and whether it will weaken a load bearing part of the bolt a photo might help BUT PLEASE EXERCISE CAUTION this is a major load bearing part of the gun and it must not be weakened in any way. Indeed any work of this type in the UK the gun would have to be re proofed at one of our national proof houses. Work on any load bearing part of a firearm deems the gun to be out of proof if that work does or may potentially weaken the gun. A bit more detaild than that but that is the Essenes of the rules of proof this side of the pond.

Think about the possible consequence if the bolt failed in service due to the work you have done ! Does not bear thinking about.

Back to your original question, yes the bolt will have been heat treated as will the action, most rifles are quite tough but again most can be machined one way or another . Graham's suggestion of a file test is probably the best way to determine if it's likely that you can do the work with your kit.

Regards John

[Rich2502Participant @rich2502]

As an ex gunsmith myself I would say it would be better to grind it out, problem solved. I looked on YouTube and theres a video of this mod. The bolt might be case hardened ?

PS. I don’t think its a load bearing part of the weapon, the part he wants to alter is a flange that just locks the mag in place. The locking shoulder on the bottom rear of the bolt takes all the load on firing.

Edited By Richard chucklbutty on 31/08/2014 18:44:03

[Robert Turner 1Participant @robertturner1]

Hi Richard

Yes, he already has a similar gun with the mod made. Having looked at the price of solid Carbide cutters, I was thinking grinding might be better. The bolt certainly isn't case hardened, but it is hard.

[ronan walshParticipant @ronanwalsh98054]

Posted by Robert Turner 1 on 31/08/2014 20:00:44:

Hi Richard

Yes, he already has a similar gun with the mod made. Having looked at the price of solid Carbide cutters, I was thinking grinding might be better. The bolt certainly isn't case hardened, but it is hard.

I priced carbide milling cutters in the local suppliers (a branch of cromwell) and in certain sizes they were cheaper than hss, both the same manufacturer (sherwood).

[JonParticipant @jon]

If you go a smaller size for milling cutter it will be cheaper. Decent carbide of the order 3/8" to 10mm more than ample to do any bolt without flexing.

Even the cheap Sherline will be more costly than the guns worth, charge him or scrap it.

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