I thought this was the case before this thread but I did more reading because of it and it seems in some cases smiths will cut the tennon threads a little smaller/looser on a pre-fit if they don’t have action in hand to validate fit. The perception I have is once torqued, that shouldn’t make a notable difference in performance. Don’t know how true that is.
Would love to hear
@LRI_Chad or
@Shooter71 weigh in on how they’d cut tennon threads for action in hand vs not and if the approach is different based on the action.
I've attempted to answer this a few times now. I return a day or two later and start over because my response emulates a labrador retriever attempting to walk in a straight line.
20+ years ago, while working for Nesika, I'd of told you that if the thread fit between the barrel and receiver isn't like a thimble on a micrometer, then the rifle is junk. Experience is not cheap, and the number of actions that we "stuck" back then while trying to do this borders on the absurd. -I was told to do something, so I did it. I also didn't know any better.
There were two major issues. Material selection and hardness (heat treat). 15-5ph stainless only gets to around 40 Rockwell C scale. Most ss rifle barrels (cut or buttoned) live around 30-ish C scale. The analogy I've settled on is that you are rubbing two pieces of chewing gum and expecting them not to stick together. Today (thankfully), we might barrel a Nesika 3x a year, and the experience from back then has taught me not to play with fire. For almost every other action out there, it's a non-issue. Thread them to a silky feel and send it. When the action is not in hand (Prefits or "Jebus nut guns" like the Ruger RPR, Savage, etc...), thread to a ring gauge and move on with your life.
As for accuracy: Again, 20+ years ago, I'd of died at the altar defending the idea of a minimal differential in pitch diameter as vital to rifle accuracy. I mean, c'mon:
-It's written on a stone tablet somewhere in the Middle East.
Today, it's not nearly as big a deal to me. We still do it, but if I'm going to be honest, it's because the gun community expects it, and I don't have the time to talk a dozen people a week off a cliff or spend all day defending myself on forums. The turning center I have here makes it an easy task, so it's of no consequence.
The truth is, on a 60* thread form, the flanks of the threads only load the joint for about 4 or 5 threads right behind the shoulder. The rest are along for the ride. Some work was done (two decades ago) to change this by using a "bent knee" type thread form where one of the threads (barrel) was kicked at an angle that intentionally caused the crest of the opposing side to bite into. The problem is that the risk of sticking the two pieces together increases exponentially. The practice never became popular in gun land (thank God!).
This is where I believe that fitting the barrel to a properly prepared receiver is a bigger deal than a lot of people might think. Ensuring the chamber, cartridge, and bolt face rotate on the same axis can only do good things. It is precisely why I have spent the better part of a half million dollars on a 5-axis mill for blueprinting receivers and bolts. The boutique "custom" actions should already have this, so we don't mess with them much.
-They better have it as it is what you are paying for.
I've had clients bring guns to me where the barrel work was atrocious. I've seen thread tennons so undersized that it's flirting with criminal negligence for fear of the thing shooting itself out of the receiver ring. Yet, a lot of those guns performed exceptionally well on paper.
The one thing I will say is comparing any of this to the bench rest world is a horrible mistake, and here is why: BR guys will often "hand snap" a barrel onto a receiver and go blast 5x down range and then smile over a small ragged hole. That's great, but where was it on the paper in relation to where the optic's reticle was pointing? The next question is where will it be tomorrow, in a week, six months, etc...???
Group Center and
Group Size are very different things, which is something to be cognizant of. If you play this game for any length of time, you will inevitably be confronted by a rifle that suddenly stops performing well. An experienced shooter will immediately start grabbing things and wiggle them to see if something has come loose. If it is a firearm that is used anywhere outside of the pampered firing line of a BR event, then the barrel/barrel nut
must be tight if you have any expectation of the thing shooting where you point it.
Hope this helped.
C.
