Angled locking lug and seat.

[Old Gunner]

Way I remember it from very old gunsmithing books, stuff I read fifty years ago, the mating surfaces of the locking lugs and their seats will almost always be inclined by a tiny amount, no real 90 degree angles even if machined that way to begin with.
Since with any locking recess one side is more supported by the receiver ring than the other proof testing pressures will tend to compress the less supported side and the locking lug will conform to that.
Also if lugs are lapped to fit theres a tendency for a slight angle to form.

Of course lugs don't have to be dead on at 90 degrees for strength otherwise interupted thread bolts wouldn't work.

First I heard of this was a response to questions about the appearance of the open sided right hand guide rib lug and its shoulder. So far every No.1 Enfield I've seen has a noticable, to me at least backwards inclination to the action body locking shoulder, or resistence shoulder as they call it.
Early works on the SMLE said this was natural and beneficial, since it prevented binding when opening the bolt after firing. The source said this inclination formed at the proof testing when final seating of lugs took place.

I suspect the angle increases over time with wear.

So I got to wondering about whether this sort of inclination is noticable with more modern action types, and if so is it considered beneficial.

Any other related information would be helpful.

 

[Al Nyhus]

The Gilkes-Ross 3 lug action has it's locking surfaces at a 45 degree angle.

http://www.rossprecision.com/products_action.htm

 

[alinwa]

The Gilkes-Ross 3 lug action has it's locking surfaces at a 45 degree angle.

http://www.rossprecision.com/products_action.htm

yeahh but......


dude's talking about the engagement surfaces "screwing together."

I've got one fairly customized Rem700 that tightens on the downstroke, otherwise all of my custom and customized rifles are true 90 to centerline.

al

 

[Boyd Allen]

Other than the 1917 Enfield, I am not aware of any modern, front lug actions that have lugs and abutments set up so that their engagement surfaces advance the bolt as it is being closed. I am not referring to primary closing cams.

 

[Old Gunner]

Other than the 1917 Enfield, I am not aware of any modern, front lug actions that have lugs and abutments set up so that their engagement surfaces advance the bolt as it is being closed. I am not referring to primary closing cams.

I don't think its intended in most cases, its just how most wear in.
The old books on the Enfield said it was more of a beneficial byproduct, which made the action slicker to operate.

I've seen several multi row lugs designs that appear to have a significant angle to the lugs.

I think Newton pioneered the Interupted thread lugs, at least in high powered rifles.

 

[John Kielly]

I suspect that the Ross straight pull, for one, was using helical lugs earlier.

 

[Old Gunner]

I suspect that the Ross straight pull, for one, was using helical lugs earlier.

Could be, I'll have to check the dates.
I think Ross later reverted to a simpler twin opposed lug for his straightpull rifles.

I saw the Weatherby Mark Five mentioned as having interupted thread locking, but I'm not familar with those rifles.

Doesn't the Remington 740 use interupted threads?
I worked on one years ago but I don't remember for sure.

Anyway it seems a slight angle doesn't adversely effect the solidity of the lockup.
I figure it also reduces drag on opening the bolt, probably why it was used with the straighpull and some autoloaders.

 

[msalm]

Some of the old BSA/Herter's actions, at least the BSA Majestic had a 5 degree 'slope' on the bolt lugs and seats in the action. That was one of my first actions I rebarreled years ago and I remember seeing it along with mention of it in the book 'Bolt Action Rifles'.