WarrenSmith wrote:
These two articles are intimating it can happen under certain conditions due to changes in manufacturing induced barrel stresses brought about by removing barrel material during the process of threading.
It's more a theoretical problem than a real phenomenon. I caught the part where dude claimed a bore @ muzzle was .0015 larger than bore at chamber. Yeah.......did he measure it
beforehand? Because my money says it was
always that way. In the video, other dude is comparing the bore diameter consistency of button rifled production AR barrels with cut rifled precision barrels. They're never gonna compare favorably, and there's a reason air gauging is done in the accuracy world, even with cut rifled tubes; bore size will vary slightly from one point to the next.
I routinely thread .30 cal sporters at 1/2-28. I caution people that if they're putting rounds down range at a rate that heats the barrel appreciably, the hoop stress could potentially cause belling of the thin walls. But again, these are typically hunting rifles.
5/8-24? Pffft. If it was gonna happen, it would definitely occur on short barreled machine guns. I've had my post sample .308 AR extremely hot after back to back mags, bore @ muzzle is still tight to a .3002" pilot bushing. If 5/8-24 were problematic, it wouldn't be the standard for .30 cal barrels from high end outfits. Look at Proof Research; they have the tenons pre-turned at .625" and left long. These are not cheap OEM-type button rifled tubes.
Let's face it; there just aren't that many barrels which can even take 3/4" threads. Not one sporter I can think of; many of them have to be cut back considerably and/or include a custom collar to interface with the brake or can because the barrel OD is barely enough for 5/8 threads.
Then there was that nonsense in article #1 about threading class 4 or tighter external threads for an interference fit. Any gunsmith who does that is bound to have a pissed off customer when they go buy a brake or DT suppressor and cant screw it down full, or worse yet, can't get it back off due to galling. If someone requests it, I'll do 3A, but a gauge muzzle threads at 2A and undercut all of them .050" so any muzzle device will go on. I've had to chase a couple of factory rifles that were threaded 3A or tighter because they wouldn't take a QD brake.
The most important thing about muzzle threading is axial alignment, which brings me to another eye rolling part of that article when they talk about threading between centers. Nobody calling themselves a gunsmith should be doing that for a weapon that is to be suppressed. Period, end of story. I explained in another thread, but bottom line is, to have properly concentric and axially aligned threads, you use a sized, perfectly true rod at least 4" long that indicates the last 1.5"-2" of bore. If home shop guys wanna thread their own stuff between centers, that's their business, but if a customer is paying ~$100 or more to have a barreled action done, it better be right. Sometimes it takes a little while to dial them in, but that's what we're being paid for! So if you walk into your gunsmith's shop and see some dinky lathe with a 1" through bore and no spider in sight, run, don't walk away from having him thread your barrel for a can.