Cold bore zero versus (very) Hot bore zero “test”

[Formidilosus]

@Formidilosus two questions:

1) With modern quality barrels, what then would warrant a thicker barrel contour short of a reduction in POI for mounting heavy things on the barrel, machine gun use, or added weight for recoil reduction?

It seems with modern barrels, most of the reasoning is tied up in anecdotes and myth, or misinterpreting results. Ie. An assumption that thick barrel contours are more accurate due to heat and etc, when in reality the shooter is likely just more accurate due to the increase in rifle weight.

The only real benefit that a thicker barrel provides is more rounds before barrel mirage causes issues with aiming. Of course a mirage band solves that. However, the thicker barrel also takes longer to cool and stop barrel mirage.

2) When using a suppressor, have you noticed any detriment in accuracy/barrel life due to heat with threaded barrels that have a smaller thread diameter paired with a larger bore? Thus having less “meat” at the muzzle and being more susceptible to heat.

No.

For example, I’ve heard threading something like 6.5 or 308 with a 1/2x28 reduces the mass at the muzzle to such an extent that the muzzle can swell and deform under heat (especially with the added heat of the suppressor being mounted over the muzzle trapping heat further). There is physically enough metal there to do the thread job but allegedly not enough to withstand the heat stress.

For this very reason (and for want of a bigger shoulder), I had a 6.5 threaded at 9/16x24 for the extra mass, then affixed a permanent 9/16x24 to 5/8x24 adapter for the convenience. Not sure if this is just a theoretical problem that creates extra steps or a realistic one.

It’s theoretical BS at best. Almost no one/no company that talks about this stuff has actually done legit testing and long term use for themselves.

Hope that was understandable. Would appreciate the insight.

It was.

 

[ddowning]

I'd think it's most likely a factor of chamber heat. Warming powder, when it's not a temp stable powder. It's not hard to test.

A lot of time ES and SD doesn't play out at distance like you think it would.

Just came across this. I hate talking to engineers about es and sd. I don't know what the explanation is, but Billy Goat is right. My best 243AI load ever had an es close to 50 fps. I shot multiple 10 shot groups under 3" at 776 yards. I had no chrono when I developed that load. When I bought one, I assumed the es would be awesome. Shooting over that magneto was eye opening. I have had this play out multiple other times to a lesser extent. If you put velocity variation in a ballistic calculator, the group is a lot shorter than the calculator says it should be.

I'm sure velocity variation with a load like that will show up at extreme distances, but it will be way out there before it gets as big as the calculator says it should, if ever. Obviously the best load has good es and positive compensation, but if I have to pick one, I'm picking positive comp. over es. You could possibly change my mind if you were talking elr, but I haven't played with that. I've never shot past a mile and rarely past 1000 yards.

 

[z987k]

The only rifle I've ever seen really go to crap quickly was a kimber, which we associated with heat and the really thin barrel. That barrel was quite hot after 10 shots. Group was massive and the mirage made any more firing pointless. It'd be interesting to do this test with that rifle.

 

[jmillr1]

What was the distance you shot at?