Gunsmithing Barrel lug fit

[Ratbert]

I'm curious to know if there is a consensus or objective argument regarding the fit of the barrel lug to the tenon. I've noticed that at least a couple well known gunsmiths will just thread a tenon all the way to the shoulder and let the lug just sort of "float" with little to no radial contact. I've seen other barrels where the tenon is machined to match the diameter of the lug perfectly and the threads extend into the barrel lug maybe 0.01" or so.

Obviously nicely machined and fit pieces give a warm fuzzy feeling, but at the same time I can see an argument for having the lug floating on the tenon so that only it's flatness/parallel properties influence the fit of the barrel to the receiver, not the concentricity of the hole. Turning the tenon to a single diameter and then threading the entire tenon should also be easier/faster and make fiddling headspace or pushing a chamber easier.

Thoughts? Advice?

 

[hero's machine]

Re: Barrel lug fit

You have taken the time to true the action and setup the barrel. Your setup is square......it would be utter basphemy to waste the opportunity to get the right fit now. The thread termination needs to be after the action side lug face....that's it. Threading to the shoulder is only asking to give up ridigidity and invite slop....and disaster if you hit the shoulder. Make your termination well shy of the shoulder, it will give you room to breathe and keep a good fit on the lug.

 

[Ratbert]

Re: Barrel lug fit

But that's sort of my point (at least on that side of the argument, I'm still trying to decide which side I ultimately come down on), the action has been trued and the barrel indicated in, but how much work has gone into making sure the hole in the lug is absolutely round, concentric, and perpendicular to the shoulder surfaces? The lugs are ground flat, but who actually takes the time to hone the hole through them? Could a loose fit, letting the shoulder and the threads of the action/barrel do their work to hold things be better than also trying to force the lug to be dead perfect? My first instinct is always to try and fit the barrel to the lug but I'm left wondering what exactly that helps and how exactly it could hurt.

Obviously I don't think it makes a HUGE difference either way, I just like to have an analyzed reason for the methods to my madness whenever possible.

 

[300sniper]

Re: Barrel lug fit

if you can absolutely guarantee that the hole in the lug is dead nuts square to the lug faces, then in my opinion, it shouldn't be a problem to have a snug fit. personally, i like to allow about a thousandth or two of breathing room between the tenon and lug bore. i also chamfer the front lug bore to allow for a radius at the tenon/shoulder junction instead of plunging the tool to put the radius below the tenon surface.

 

[hero's machine]

Re: Barrel lug fit

Rereading what I posted....to clarify, I was more focussing on the thread termination. The tennon to lug fit does not have to be a perfect fit, some clearance as sniper said is to your benefit.....I can't agree with threading the entire tennon. It's a wasted of time, invites more opportunity for a crash and removes strength.....I just can't see a reason.

 

[300sniper]

Re: Barrel lug fit

i prefer to use .300"+ lugs and thread about one full thread pitch under the lug. that allows me plenty of room to adjust the shoulder to time the barrel without having to chase the threads or cut a relief if the receiver needs to spin just shy of 360 degrees. with the thick lug, there's still plenty of room to avoid a crash.