Receiver Impact Damage?

[JFrisbee]

During my clean up and inspection of my 2nd SKS, I found Two Impacts at the of Rear Receiver, I'm not exactly sure what made these, however, I am thinking impacts from the bolt slamming into the receiver. Has anyone observed similar impacts on theirs? And, if it is caused by the bolt, is there an issue with this rifle? I am really new to the SKS and need to learn a ton more. Thank you.

[Boris Badinov]

The bolt doesn't travel far enough to impact the rear of the receiver well. Any impact from recoil occurs between the rear of the carrier and rear wall of the receiver cover. The two marks you see are from the original milling procedure. Early rifles don't have the two marks, later production rifles do.

[running-man]

I don't know that I'd say those are machining marks Boris. I've not seen those on other receivers in the past. I'd say they are clearly from some type of impact which the OP probably needs to get to the bottom of.

OP, what's the rear underside of the bolt carrier look like?  That's the only component that is even possible to hit the inside of a receiver on the rear wall like that. Perhaps it was fired with out a recoil spring?  But Boris is correct in that I'd also expect the receiver cover to take the brunt of damage. (This is where those stupid after market rubber recoil buffers go in fact, between the carrier and the receiver cover.)

Maybe post some photos of the various innards and we can piece together what happened.

[Boris Badinov]

Its common trait seen on receivers with the right angle corners.

Scroll down to the Early vs Late receivers section at the weebly link below. Early receivers have scalloped corners and the marks are not present. Later receivers have 90° corners and the marks are present. Possibly they are from recoil, and not from intial milling but you'll find those marks on receivers with the right angled corner cuts.  But they are nothing to be concerned with.


https://chinesesks.weebly.com/component-variations.html


Is the bolt even wide enough to make those marks?

[JFrisbee]

Its common trait seen on receivers with the right angle corners.

Scroll down to the Early vs Late receivers section at the weebly link below. Early receivers have scalloped corners and the marks are not present. Later receivers have 90° corners and the marks are present. Possibly they are from recoil, and not from intial milling but you'll find those marks on receivers with the right angled corner cuts.  But they are nothing to be concerned with.


https://chinesesks.weebly.com/component-variations.html


Is the bolt even wide enough to make those marks?

Yes, they match up.  not sure why yet.

[JFrisbee]

[Boris Badinov]

That's not the bolt. That's the bolt carrier. The bolt is the lower part that rides beneath the carrier. Both at made of very hard, tempered, carbon steel.






From yooper's site:






If it's caused by the carrier recoil, it's not causing any harm.

[JFrisbee]

Thanks. I get tired of correcting folks, not just with these. I know they sell the plastic spacers that you can add in, but I dislike those as they restrict the travel of the bolts/carriers in any rifle. If it is an issue, I'll hear it when I fire. Since i am new to the SKS, I would rather ask than apply my logic from other firearms just in case. After gunsmithing for 50 years, I still see new things!

[running-man]

Its common trait seen on receivers with the right angle corners.

Scroll down to the Early vs Late receivers section at the weebly link below. Early receivers have scalloped corners and the marks are not present. Later receivers have 90° corners and the marks are present. Possibly they are from recoil, and not from intial milling but you'll find those marks on receivers with the right angled corner cuts.  But they are nothing to be concerned with.


https://chinesesks.weebly.com/component-variations.html


Is the bolt even wide enough to make those marks?

Laugh, you know I've edited that weebly page more than once and many of those are even my photos, but I'm embarrassed to say that I never keyed in on the dimples on the late receiver innards.

Looks like in addition to the different angle the inner face is maybe 0.050" farther forward as well. Carrier bottom kissing that face makes sense. That it happens so frequently that you noticed it Boris likely means you are correct in that it's not a cause for concern. 


It's always nice to learn something new!

[Greasemonkey]

Just to throw it out, a weak recoil spring can allow it, weak gas piston extension spring, an over gased gas system, or the previous owner bump firing can all cause the receiver contact.

One thing I've noticed in the later models, the springs seem weaker than earlier ones and the gas system seems a little more violent in its operation. Maybe it's just me or it was my particular variants.

[Boris Badinov]

Its common trait seen on receivers with the right angle corners.

Scroll down to the Early vs Late receivers section at the weebly link below. Early receivers have scalloped corners and the marks are not present. Later receivers have 90° corners and the marks are present. Possibly they are from recoil, and not from intial milling but you'll find those marks on receivers with the right angled corner cuts.  But they are nothing to be concerned with.


https://chinesesks.weebly.com/component-variations.html


Is the bolt even wide enough to make those marks?

Laugh, you know I've edited that weebly page more than once and many of those are even my photos, but I'm embarrassed to say that I never keyed in on the dimples on the late receiver innards.

Looks like in addition to the different angle the inner face is maybe 0.050" farther forward as well. Carrier bottom kissing that face makes sense. That it happens so frequently that you noticed it Boris likely means you are correct in that it's not a cause for concern. 


It's always nice to learn something new!

I'm pretty sure the marks have been discussed elsewhere in the last two decades. It would have been years ago, but I recall seeing the comments made about the dimples-- maybe a off hand  comment in a thread about something else entirely? But I know I've seen it somewhere.

When I read the OP I began scouring my photo files for screenshots I might have taken from the discussion, but I could not find any. I tend to take a lot of screenshots and then never follow through  with organizing them into easily retrievable folders.