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?

 

[Anschutz]

That Tikka Master Sporter is a real shooter and not a bad looker. I've gotten my butt handed to me by an older gentleman with one of those at an XTC match. I think he had his in 6 Creedmoor shooting factory ammo.

Sent from my SM-S918U using Tapatalk

 

[donrleonard]

Late to this thread, brought here by some consistent patterning I’m seeing on my browning XBolt in 7PRC when firing 5 shots groups at 100yards: Two shots touching. Then two shots touching, about an inch high, followed by a (gulp) flier.






These aren’t cherry picked. These are my most recent three 5-shot groups, taken on two different days with the barrel being cold at the start of each string. The ammo was the same (Barnes LR 160gr factory).

They appear to me as though I have a sub-MOA gun when shooting cold bore for two rounds, about MOA for four. But in a shooting match when Im shooting a warm barrel I’m going to shoot about 1.5 MOA (or worse) after the 4th round.

I’m a late onset hunter, and will be the first to admit that those fliers might be pulled shots that come from the human factor—maybe shooter fatigue? I’m also a social scientist , which doesn’t make me a real one but tells me to be skeptical of anecdotal evidence across a small number of observations. But the consistency of this pattern on a fully supported rifle being fired from a bench makes my mind run to cold vs hot bore theory, which in turn brought me to this thread.

My one observation about the data Form shares at the top of this thread is that, for most rifles they tested, the “error” is not evenly distributed in a cone as one would expect if we are to believe that barrel heat is uncorrelated with group size. Some exhibit a strong horizontal (windage) error, while for many of the others there seems to be a tendency towards vertical (elevation) variation.

Perhaps these could be attributed to other attributes of the rifle, like bedding, or differences in muzzle velocity owing to ammunition variance.

But to truly test the cold/hot bore “myth” I would want to see the data for each individual shot and get a sense of whether the average point of impact and the standard deviation of the overall spread changes across rifles between shots 1-10 and shots 11-30.

Has the dataset been published? Forgive me if I missed it. I only read through the first 8 pages of comments.

 

[wind gypsy]

Late to this thread, brought here by some consistent patterning I’m seeing on my browning XBolt in 7PRC when firing 5 shots groups at 100yards: Two shots touching. Then two shots touching, about an inch high, followed by a (gulp) flier.

View attachment 776077
View attachment 776078

View attachment 776080

These aren’t cherry picked. These are my most recent three 5-shot groups, taken on two different days with the barrel being cold at the start of each string. The ammo was the same (Barnes LR 160gr factory).

They appear to me as though I have a sub-MOA gun when shooting cold bore for two rounds, about MOA for four. But in a shooting match when Im shooting a warm barrel I’m going to shoot about 1.5 MOA (or worse) after the 4th round.

I’m a late onset hunter, and will be the first to admit that those fliers might be pulled shots that come from the human factor—maybe shooter fatigue? I’m also a social scientist , which doesn’t make me a real one but tells me to be skeptical of anecdotal evidence across a small number of observations. But the consistency of this pattern on a fully supported rifle being fired from a bench makes my mind run to cold vs hot bore theory, which in turn brought me to this thread.

My one observation about the data Form shares at the top of this thread is that, for most rifles they tested, the “error” is not evenly distributed in a cone as one would expect if we are to believe that barrel heat is uncorrelated with group size. Some exhibit a strong horizontal (windage) error, while for many of the others there seems to be a tendency towards vertical (elevation) variation.

Perhaps these could be attributed to other attributes of the rifle, like bedding, or differences in muzzle velocity owing to ammunition variance.

But to truly test the cold/hot bore “myth” I would want to see the data for each individual shot and get a sense of whether the average point of impact and the standard deviation of the overall spread changes across rifles between shots 1-10 and shots 11-30.

Has the dataset been published? Forgive me if I missed it. I only read through the first 8 pages of comments.

Did you break position when shooting by chance? Twice over the course of 5 rounds maybe?

 

[mxgsfmdpx]

Late to this thread, brought here by some consistent patterning I’m seeing on my browning XBolt in 7PRC when firing 5 shots groups at 100yards: Two shots touching. Then two shots touching, about an inch high, followed by a (gulp) flier.

View attachment 776077
View attachment 776078

View attachment 776080

These aren’t cherry picked. These are my most recent three 5-shot groups, taken on two different days with the barrel being cold at the start of each string. The ammo was the same (Barnes LR 160gr factory).

They appear to me as though I have a sub-MOA gun when shooting cold bore for two rounds, about MOA for four. But in a shooting match when Im shooting a warm barrel I’m going to shoot about 1.5 MOA (or worse) after the 4th round.

I’m a late onset hunter, and will be the first to admit that those fliers might be pulled shots that come from the human factor—maybe shooter fatigue? I’m also a social scientist , which doesn’t make me a real one but tells me to be skeptical of anecdotal evidence across a small number of observations. But the consistency of this pattern on a fully supported rifle being fired from a bench makes my mind run to cold vs hot bore theory, which in turn brought me to this thread.

My one observation about the data Form shares at the top of this thread is that, for most rifles they tested, the “error” is not evenly distributed in a cone as one would expect if we are to believe that barrel heat is uncorrelated with group size. Some exhibit a strong horizontal (windage) error, while for many of the others there seems to be a tendency towards vertical (elevation) variation.

Perhaps these could be attributed to other attributes of the rifle, like bedding, or differences in muzzle velocity owing to ammunition variance.

But to truly test the cold/hot bore “myth” I would want to see the data for each individual shot and get a sense of whether the average point of impact and the standard deviation of the overall spread changes across rifles between shots 1-10 and shots 11-30.

Has the dataset been published? Forgive me if I missed it. I only read through the first 8 pages of comments.

Not enough information to make any assumptions here, sorry. 5 shots on a 7 PRC is nothing for "barrel heat" in the slightest.

 

[JGRaider]

First thing I'd do with groups like that is check the bedding/stock fit to make sure it's floated like it should be and not rubbing somewhere. Action screws as they should be as well.