Bolt lug setback?

[Pofoo]

Can anyone explain this?
What are the symptoms?
How do I check for this.
Thanks in advance.

[Toxic Shock]

Bolt lug set back is caused when cartridges that generate too much pressure and bolt thrust cause the bolt lugs to form indentations into the lug recesses in the receiver. The type of firearm that is usually most susceptible to this are small ring Mausers that have been converted to calibers that are too powerful for the action. It can also be caused by unsafe, heavy charges in handloads.
The symptoms of bolt lug setback are shiny depressions in the face of the lug recesses that are typically pushed back around .004" You need to remove the barrel to inspect this area of the receiver. Sometimes, if you gently pull back on the bolt handle as you close the bolt on an empty chamber you can feel the bolt lugs fall into these depressions.
Bolt lug set back causes excessive headspace in the weapon. The sidewalls of the cartridge case can stretch near the head area, and if reloaded might cause a case head separation. A case head separation can destroy even a very strong weapon. Because of the lack of gas handling features on a small ring Mauser, a case head separation could be especially catastrophic with this type of rifle.
The way to fix bolt lug set back is to grind the bolt lug recesses on the inside of the receiver flush again. Do not try to machine them because the set back will have caused work hardening, and the recesses would present an interrupted cut. This will virtually guarantee chatter and an uneven surface with a boring bar. Then the receiver will need to be heat treated again, (the grinding will have removed the case hardening from the face of the recesses). Because the grinding operation will cause the bolt to sit back farther in the receiver, the root of the bolt handle may need to be built up with weld and reconfigured so that it will mate properly with the extraction cam surface. Then the barrel will need to set back, and rechambered.
It is almost always the case that a rifle with bolt lug set back is not economically worth fixing. However, if left with the set back, it is dangerous to operate. Because this problem is usually found on small ring Mausers that have been converted to 7.62 NATO, and are being fired with 308 Winchester (which is higher pressure), I'd recommend that if you are using this type of rifle, that you replace the receiver. Right now Sarco is selling model 1893 Mauser receivers for $20 each. the bolt from either an 1893, '94, or '95 will work in these receivers. (a Swedish 1896 bolt will not) This would be the cheapest fix available. Remember to always check the headspace whenever you swap major components on an action.

[Pofoo]

Would this have anything to do with having a loose bolt--forward and aft movement--when cocked and closed on a empty chamber?
I have this on a mdl 98 and a mdl 91 Mauser.

[pacrat]

Would this have anything to do with having a loose bolt--forward and aft movement--when cocked and closed on a empty chamber?
I have this on a mdl 98 and a mdl 91 Mauser.

If cocked and closed [in battery]. The cocking piece would be held rearward by the sear. And the striker/FP spring would be holding the rear of the bolt lugs against the frnt of the lug abuttments in the reciever ring. Having a round in the chamber would not change this.

[Pofoo]

If cocked and closed [in battery]. The cocking piece would be held rearward by the sear. And the striker/FP spring would be holding the rear of the bolt lugs against the frnt of the lug abuttments in the reciever ring. Having a round in the chamber would not change this.

Well, actually it does. The FN standard model/Chinese contract mdl 98 has a loose bolt with the chamber empty, cocked or not, but tightens up with a round in the chamber.
Not sure with the Argentine mdl 91 as to if it gets better with a round chambered. I'll have to check.