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.

 

[donrleonard]

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

I broke position every time.

 

[donrleonard]

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

I haven’t rigged a thermometer up to it, but I can definitely say that after two rounds in quick succession (under 1 minute between shots),that fluted sporter barrel is definitely hot to the touch. Whether that’s “accuracy hot”?

 

[mxgsfmdpx]

I haven’t rigged a thermometer up to it, but I can definitely say that after two rounds in quick succession (under 1 minute between shots),that fluted sporter barrel is definitely hot to the touch. Whether that’s “accuracy hot”?

"hot to the touch" is subjective and means nothing. You shouldn't be able to hold your hand on the barrel for more than a second without it burning skin, that is a "hot" barrel. And even then, most browning barrels I've shot in these type of conditions show immeasurable POI shift from ice cold barrels.

Your data set is far too small and your barrel is NOT heating up enough to cause any type of POI shifts from 5 shots. The reason to let a barrel cool between shots is because of miraging affecting the shooter not "loss of accuracy" or "potential damage" to a bolt action system. Particularly not in browning bolt action rifles that I have seen, they are better than most, contrary to what many on Rokslide will say.

This post screams of a combination of shooter and rifle capability compounding on each other, especially with a 7mm chambering.

Verifying everything is in order with stock contact, action to stock, ring bases to stock, ring cap screws to bases, like @JGRaider mentioned is an excellent start if you still think it's the gun.

If you haven't yet, give this a full read through and apply it to your gun and start over.

Scope mounting to maintain zero

After multiple requests for an explanation of how to mount a scope in order to have the lowest possibility of loss of zero, a discussion of a scope mounting video, and the latest thread about scope bases and action screw coming loose, I took some pics of what I do with a rifle when I get it and...

rokslide.com

 

[donrleonard]

"hot to the touch" is subjective and means nothing. You shouldn't be able to hold your hand on the barrel for more than a second without it burning skin, that is a "hot" barrel. And even then, most browning barrels I've shot in these type of conditions show immeasurable POI shift from ice cold barrels.

Your data set is far too small and your barrel is NOT heating up enough to cause any type of POI shifts from 5 shots. The reason to let a barrel cool between shots is because of miraging affecting the shooter not "loss of accuracy" or "potential damage" to a bolt action system. Particularly not in browning bolt action rifles that I have seen, they are better than most, contrary to what many on Rokslide will say.

This post screams of a combination of shooter and rifle capability compounding on each other, especially with a 7mm chambering.

Verifying everything is in order with stock contact, action to stock, ring bases to stock, ring cap screws to bases, like @JGRaider mentioned is an excellent start if you still think it's the gun.

If you haven't yet, give this a full read through and apply it to your gun and start over.

Scope mounting to maintain zero

After multiple requests for an explanation of how to mount a scope in order to have the lowest possibility of loss of zero, a discussion of a scope mounting video, and the latest thread about scope bases and action screw coming loose, I took some pics of what I do with a rifle when I get it and...

rokslide.com

Thanks for your time, your knowledge, and for scrounging up this article.

 

[5811]

I've always wondered if maybe the barrel can get hot without shifting impacts but can the fore end of the stock get hot and flex more, maybe affect poi that way if its not free floated enough? Obviously some stocks would be more susceptible than others.

 

[mxgsfmdpx]

I've always wondered if maybe the barrel can get hot without shifting impacts but can the fore end of the stock get hot and flex more, maybe affect poi that way if its not free floated enough? Obviously some stocks would be more susceptible than others.

Not likely. Especially not from just 5 shots.

 

[walk2112]

I think once you confirm there’s no bedding, screw binding, scope mounting, or other rifle system setup issue… if the same results occur, multiple times in a row, and your technique is consistent throughout… this boils down to that barrel doesn’t like that load (bullet/powder combo) probably :-/, partially because of the vertical string nature of the dispersion.

I’m no bonified expert, but from what I’ve seen in myself and others many times if technique/positional inconsistencies exist (OTHER than rear bag vertical support) the dispersion has some significant horizontal component to it. I.e. not being square behind gun, head position relative to scope, follow through the recoil moments, torquing the forend, etc.

 

[wind gypsy]

I broke position every time.

Not uncommon for POI shift to occur more when breaking positions, that might play a part.

 

[donrleonard]

Not uncommon for POI shift to occur more when breaking positions, that might play a part.

It's a great point, and one that I need to drill on for hunting--staying in the scope, spotting impacts, and being prepared to take follow-up shots.

The thing that puzzles me is just how consistent it is. Two tight shots low, two high, and a random 5th shot inside of a 2" cone.

If my scope didn't have parallax adjustment I'd be more inclined to believe that it was from breaking position or some other shooter-induced error. But with good rifle support (sand on front and back) and good breath work between shots, these all felt like solid shots.

The notion of my rifle not liking the ammo is also another compelling argument. Here all I can say is that my rifle did not like Hornady CX or Terminal Ascent 155gr, but does seem to like Federals' new tipped fusion and this, the Barnes LRX 160gr.

Other shooting gurus, like Joseph von Benedikt and Cliff Gray, do commonly see accuracy open up after as few as two or as many as 5-7 shots. Given their vast experience, I can't help but wonder if there isn't some systematic variance in the 1-10 shot range inside these 30-shot strings that Form reported here.

Have the data been published yet? I'd love to run some sub-group analysis here.

 

[Jason Snyder]

Go test it. Shoot a 10 round string and number every shot. Let your barrel cool between each shot. Then repeat it without cooling. It’ll give you a pretty good idea of how, if at all, barrel heat is affecting your group.

FWIW I’ve had two lightweight rifles with pencil barrels that will rattle out a 10 round group with no ill effects. One is a 6.5 and the other was a .280 Remington.

 

[TaperPin]

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?

Do you shoot another rifle that doesn’t string shots vertically? If someone else shoots your rifle does it shoot the same? “Stable” rifle support is subjective as is how consistently the trigger is squeezed. How much pressure is applied through the hands or onto the shoulder has to be the same. For those who regularly shoot small groups it’s easy to assume the vertical stringing is rifle related. About once a year we’ll have a shooter with accuracy problems only to learn after 10 pages of responses the person has never shot a small group with any rifle.

Some rifles with some ammo will string shots one way or the other - the better a barrel is the less common this is. Often it happens with one brand of ammo and not others.

Probably the least common reason is in the barrel heating up - in 30 rifles I’ve had one and about once a year someone brings up a rifle that legitimately moves with heat. It’s not something that is universally true or false.