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

[donrleonard]

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.

Great idea. Challenge accepted!

 

[wind gypsy]

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.

Do they progress in the same direction?

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.

Not familiar with the Cliff Gray fella. I’m guessing they get a bunch of production guns that wear barrels that are not adequately stress relieved, carbon barrels that walk, etc so I’m sure it happens to a degree and I’m sure sometimes it’s not heat that is causing the issue as well but that’s what everyone is conditioned to assume.

 

[Macintosh]

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.

I am a little skeptical if its legit to call this “consistent”. If you did 10 separate 5-shot groups, all staying in the gun for the full 5-shots, and every group progressively “moved” the same way (ie 2 on poa, 2 higher, then a third even higher) Id say the stringing was consistent. But I see in the 3 examples you posted the 5th shot in one case is high, and in the other case it’s 180-degrees in the other direction, and in one case a tight pair is more offset horizontally than it is vertically. I may have missed it, but how many 5-shot groups had the consistency you are referring to?

It just seems odd that if its walking UP as it heats as you indicated, that the 5th shot would be up in one case, and then below the first shots in the other case (all the stringing Ive ever seen with older rifle or those not floated, etc stays in one direction), and that the pair in the one case would be offset horizontally. Im no expert but regardless of whether its heat or something else that does not point to a consistent shift to me.

 

[nephewjephew]

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.

I've chased my tail on a few guns like this. Not getting good (or confusing) 3 or 5 rd groups, chasing zero etc,etc. Shoot a 30rd group, I bet they all fall in the cone of the rifle. Once I started down this road I have had no problems (along with a scope that works). Its a great way to set a base line for the rifle and gives unbelievable confidence in the rifle system. More data to start with the better.

 

[donrleonard]

I've chased my tail on a few guns like this. Not getting good (or confusing) 3 or 5 rd groups, chasing zero etc,etc. Shoot a 30rd group, I bet they all fall in the cone of the rifle. Once I started down this road I have had no problems (along with a scope that works). Its a great way to set a base line for the rifle and gives unbelievable confidence in the rifle system. More data to start with the better.

I’m a big fan of more data. If the quality of shots are evenly distributed across a shot string, 30 shots is actually the magic number in statistics where the average (or central tendency) becomes meaningful.

Two reactions to this approach:

1. This is definitely the way I would do it if I was going to war (against varmints or humans). But as hunters we (and maybe/maybe not our rifle bores) are shooting cold for the decisive shot. This would be immaterial if the cone that a 30-shots string produces was indeed distributed as a cone. But in fact, many rifles in Form’s test demonstrated a clear elevation or windage bias to their “error” or drift. Some strings lined up vertically, some horizontally. That’s not a random cone. That is meaningful, non-random variation.

2. Until we have the shot-by-shot data, it’s still difficult to see whether accuracy opens up as more shots cycle through the weapon. As several others have pointed out, I still need to test more. And sadly I’m not the ideal candidate to be testing given my skill level (and pocket book!) But it appears to me that my rifle is more accurate in smaller shot strings (.5 moa for two shots, 1moa for 4, 1.5 moa for 5+). At least, that’s the hypothesis I have to test with more data.

I’ve got more ammo arriving today. Hope to get back to the range this week. Will follow up.

 

[nephewjephew]

If the quality of shots are evenly distributed across a shot string

Its more of a random numbers game. Say you have a gun that shoots 2 moa, and your zero is actually zero, as long as they all fall in that circle that's all that matters. The idea is not to get caught up in two were touching and the third was an inch high. Or 5 were in all an inch form each other and the next two were low. As long as they all fall in the cone of what that rifle can produce with that ammo. And a good way to figure that out is shoot a large group (30 seems to be the number). If you're worried about you barrel heating up, let it cool between shots. For shits and giggles try a 10rd group one hot one not, I was surprised in 3 different guns that it didn't matter at all (minus mirage).

This is definitely the way I would do it if I was going to war (against varmints or humans). But as hunters we (and maybe/maybe not our rifle bores) are shooting cold for the decisive shot

Who cares about going to war, don't you want to know what your gun can or can't do? Once you figure out what the gun is capable of spend the rest of its life shooting one shot groups for your "shooting cold for the decisive shot".

Once I decided to try this out for myself it instantly made sense. I had a clear picture of what to expect from the gun and the ammo. I could stop worrying about shooting groups and now I focus on shooting form field positions and getting comfortable at distance. Don't get over think it.

 

[E.Shell]

One thing to keep in mind when seeing a lot of vertical is that fatigue and shoulder pressure play into impact points, not just having a solid rest front and rear.

I often noticed students that initially shot well will begin to suffer vertical issues and high misses as the afternoon wore on and they accumulated fatigue. Their shoulder 'softens' and variations in shoulder pressure can be directly linked to vertical stringing

 

[Formidilosus]

I’m a big fan of more data. If the quality of shots are evenly distributed across a shot string, 30 shots is actually the magic number in statistics where the average (or central tendency) becomes meaningful.

Two reactions to this approach:

1. This is definitely the way I would do it if I was going to war (against varmints or humans). But as hunters we (and maybe/maybe not our rifle bores) are shooting cold for the decisive shot. This would be immaterial if the cone that a 30-shots string produces was indeed distributed as a cone.

They are distributed as a cone. 10 shots are not “data”. There is one gun that seemed to have shifted from hot to cold, so 3x10 round groups were fired.


This is a cone.

But in fact, many rifles in Form’s test demonstrated a clear elevation or windage bias to their “error” or drift. Some strings lined up vertically, some horizontally. That’s not a random cone. That is meaningful, non-random variation.

No, they didn’t. All you are seeing is random changes due to small sample sizes. When overlaid they just form a general cone.

2. Until we have the shot-by-shot data, it’s still difficult to see whether accuracy opens up as more shots cycle through the weapon.

Not correct. Each shot is a random event. You are trying to read tea leaves. Your vertical stringing is not barrel heat. And you do not have enough information to even say it even is stringing vertical.

As several others have pointed out, I still need to test more. And sadly I’m not the ideal candidate to be testing given my skill level (and pocket book!) But it appears to me that my rifle is more accurate in smaller shot strings (.5 moa for two shots, 1moa for 4, 1.5 moa for 5+). At least, that’s the hypothesis I have to test with more data.

Of course it is “more accurate” in smaller strings- that’s how groups work. You can just shoot two shots and claim it’s a quarter MOA rifle if you like?

 

[Macintosh]

...
1. This is definitely the way I would do it if I was going to war (against varmints or humans). But as hunters we (and maybe/maybe not our rifle bores) are shooting cold for the decisive shot. This would be immaterial if the cone that a 30-shots string produces was indeed distributed as a cone. But in fact, many rifles in Form’s test demonstrated a clear elevation or windage bias to their “error” or drift. Some strings lined up vertically, some horizontally. That’s not a random cone. That is meaningful, non-random variation.
...

I went back and re-looked at the targets. I'm not seeing the linear stringing, or even a "clear elevation or windage bias" you are referring to. If you are seeing something I'm not, maybe re-post the specific examples you're referring to. All I'm seeing is that all those groups are within the same cone, but the fringe of several groups has a shot or three that is outside the hot core...but in any 10-round group you will almost always see that--that's simply the "fringe" 5% or so of shots that fall more than 2 standard deviations or more from the zero, except in a 10-round group you would expect to only see less than 3 of these, so it almost necessarily looks linear...keep shooting and you'll see it's not usually linear.

20 and 30-round groups are not for "going to war". 20 and 30-round groups simply show you the cone that you can bank-on for any random single first shot. Perhaps to prove this to yourself you need to shoot a 30-round group all at the same target, all without coming off the gun so re-building your position doesnt affect the group, and just let the barrel cool between shots...with 2 minutes between shots that's 1 hour of your time, and you'd have a sense of the true cone of your gun so in the future you know if what you are seeing in smaller groups represents a change.