Barnard P tenon question

[Hybrid284]

Greetings

Beginner machinist here. Can someone more experienced than me please explain the Barnard P tenon...

On a removed barrel where I would have expected to see a thread releif cut there is a 2mm section of the shank turned to 27mm.

So I ask if and why this necessary or can i do my releif cut instead? The tenon drawings i have show this.

I also found this online about Barnard actions, and was unsure about this inner ring...

"A major design feature that we admire is the "twin shoulder" system whereby the barrel shank locks up on the forward receiver face as well as an inner receiver ring."

Thankyou for any assistance

 

[clowdis]

The "P" action has a couple of threads relieved in the front of the action simply to aid in threading the barrel. You can make an undercut on the barrel to clear action threads or just leave the shank unthreaded for a short distance. There is no "fitting" of the barrel shank diameter to the action thread clearance required nor is it specified in any of the Barnard shank drawings. The only manufacturer that I know of the specifies this type of fitting on some of their actions is RPA.

 

[DR_2297]

I generally turn tenon entire length to 1.058 and then come .100 from shoulder, plunge threading tool .050 deep and then side cut .030 in each direction to create a thread relief / undercut.

I don’t leave a larger diameter journal between relief and shoulder to register in the bore of the action. I let the pitch diameter of the mating threads align to themselves.

As a caveat, I am using a stand up threading tool flipped upside down to thread in reverse (away from shoulder) because I don’t trust myself to not get it out of gear before crashing into the shoulder….

 

[cb186]

I always turn a close fitting shoulder on actions that have a thread relief at the front of the action and then thread right up and slightly into that shoulder.
The overall length of the tenon is what allows for the double contact(twin shoulder).

 

[hpshooter]

Mauser 98's have two shoulders also. Some claim better accuracy cutting the tenon short and leaving a few thousands clearance at the inner shoulder. Information from past post on Mauser's on this site.

 

[jackieschmidt]

If you do decide to have the barrel seat on both locations, I would machine the tenon to where it fits dead on the action face while having .001 inch clearance on the inside Ring. When you torque the barrel, it will then just touch the inner ring as the major load is on the action face.

This is how I did my Mauser project. However, I did true the action so to insure that both surfaces were truly square with each other. Both being truly square with each other would be a critical factor in setting the barrel fit in this manner.