Trigger set up re Peter's 10 commandments

[RJW NZ]

lol, ok, I was reading Peter's trigger set up descriptions in our technical files and I see the part where keeping the striker knob from being loose/movable on the firing pin threads is important to keeping parts properly aligned and working properly.

I've just been examining and comparing how loose my various bolts are in their channels. What struck me is not so much the variables there, probably due to wear and tear over the years, some quite loose, and others like a Parker Hale target rifle with a non matched bolt but with very little side play, is the quite dramatic amount of free play in the vertical plane there is, as much a 5 times more than side play, and they're all similar, old and new, worn and un worn.

The question of the moment is that if its important to a correctly functioning trigger for the striker knob not to be loose on its threads, surely this other larger movement has a significant effect on correct trigger set up and function too?

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[Peter Laidler]

Mmmmmmmmm Good point....... Thinking out aloud, I suppose a worn bolt in a worn body would/could replicate a loose threaded cocking piece on the striker. The difference is that even a worn bolt in a worn body will be held 'tight' by the compressed striker spring (try it and see.....). Therefore, while the bolt will be 'tight' in the body after it has been cocked, the rotating sear will always rock a loose cocking piece to the detriment of the pull off.

This didn't affect us in service as we'd just scrap a rifle with a worn body. Yet another reason for a DP rifle that the average commercial/civilian shooter wouldn't immediately pick up on.

Maybe someone ought to list all the reasons for DP'ing a rifle that aren't obvious

[Bruce_in_Oz]

It is also not just the threads in play.

The parallel surfaces forward of the thread on both the striker and cocking pieces have incredibly fine tolerances. This short bearing surface is where it all should happen. The 1/4" thread stops the two parts separating and the retaining screw is there to stop rotation. SMLE striker dimension just forward of the thread: 0.250" Accept, 0.249" REJECT.The thread on the SMLE striker is another Enfield Bastard Special: 1/4" x 30TPI, Form angle? 56 1/2 deg. Cocking piece striker hole dimensions: 0.250" Accept, 0.251" REJECT.

Another source of problems could also be the striker hole in the rear of the bolt body. It too is fairly closely "toleranced" (.250L .252H). If it gets too enlarged, the relationship of cocking piece to sear will also go out of whack.

I don't have the drawings (yet) but I suspect that the figures on the No4 bolt components would be similar, considering the similar mechanical constraints.

Note also that the cocking piece and striker threads are indexed (qualified) so that when assembled to bolt and bolt head, which also have indexed threads, the whole thing lines up within a whisker.

And then there is much machinists fun to be had aligning the early Striker No1 with the Type 1 bolt head (the one with the safety notch cut into the rear of the thread).

No wonder these things cost a fortune to make, even given the wages of the day.

As a further note: After 1920, Lithgow made two "Grades" of bolt heads. The "new" model had a standard thread indexing, the "spares" variant was made with the thread advanced by between 9 and 13 degrees, to make up for face adjustment and thread wear in the bolt bodies. Of course, the thread indexing is referenced to a gauge drawing, which is a problem.