Locking Lug *Set-back* Photos

For those of you who hear the term: locking lug set-back. This is what it looks like.
Its caused by the locking lugs on the bolt *pushing* back into the lug race, that part
of the receiver where the bolt lugs cam into place to lock the breech of the rifle.

Pressure pushes back on the bolt face and depending on the metallurgy of the action
the surface of the lug race *gives way*. It compresses the steel into an *imprint* of
the locking lugs. The threaded part of the receiver was milled away to illustrate this
issue. This is where *excessive headspace* comes from. (one of the places).

This action is a 1895 Chilean Mauser that was re-worked to 7.62 Nato.
It literally beat the rifle to death.

https://images45.fotki.com/v1200/pho...SCF3134-vi.jpg

https://images41.fotki.com/v608/phot...SCF3133-vi.jpg

Woah! I wonder how long that took before that happened?

I picked up a bunch of 1914 and 1917 receivers early this year.

In going thru them was one Remington 1917 that did not look right.
Front ring was cracked and also had lug set back ???
I did a hardness test on it and it was about 25 RC
WOW, I really went over it and found about 7 areas that had scale yet ??
Dang thing must have been in a fire at one time and then someone barreled it up and shot it.

Set back like that happens, I have seen my share of pre 64 M70's, Mauser's both mil and commercial.
Most were almost blown up or really HOT loads shot thru them.

JW

Quote:

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Originally Posted by roverboy

Woah! I wonder how long that took before that happened?

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Not very much bluing wear so not that many rounds.

More detail here

http://castboolits.gunloads.com/show...to-conversions

https://www.gunandgame.com/threads/w...mausers.98629/

Where I see it most is with 98 Mausers that have been trued by lapping or turning that has been done to deep and cut thru the case hardening.

Same thing happens in No. 4 Enfields converted to 7.62mm NATO. Also in some wartime receivers in original .303 caliber if heat treatment wasn't correct. Inspection of lug seats in receiver is de rigeur during FTR. If rifle requires next size larger bolt head to correct headspace, but locking lugs on the bold body are undamaged, therein lies the clue.

Rifles in such condition are either scrapped or deactivated for Drill Service (DP stamp on butt socket).

The stuff night mares are made of!

Three44s

Dutchman - That's a good visual tool. Thanks for sharing that.

I suspect as that condition gets worse, the damage is accelerated. Sort of like when a revolver develops excessive end shake the cylinder begins to batter itself even more against the recoil shield.

Lug Set back can be deceiving.
If you check headspace on a rifle that has Set Back.
The headspace may read that it is within limits.
But that is because the bolt has not rotated all the way closed
Thus, the headspace gets Greater when the bolt is in the Fully Closed Position.