Apologies to the OP of you are not interested in this side bar. However, I am going to address below because myths and bad information cause more misses and frustration than all real world variables combined.
Because we’re not on a range face to face some clarity of how and why I say what I do. I work at a unique place. So far this year I have directly witnessed just shy of 400,000 rounds fired, 90% of those being recorded for score/time/group/zero. I have exceeded 60,000 rounds personally since Jan 1, and I’m on barrel replacement #8 I believe for rifles.
No no, hold on a second. I didn't say heat would cause the group size to increase, but heat most certainly does cause a POI shift. If it didn't then recording cold bore shots would be irrelevant, but it's not. I've seen rifles shoot up to 0.5 MOA shift from cold bore to not consistently.
From here on out I am speaking to rifles that have a solid bedding, barrels that are properly stress relieved, optics that correctly function.....
“Cold bore” shifts are a myth. What people think “cold bore” shots are, are almost always cold shooter. Now, CLEAN bore shifts can be, and are real. However, if a barrel is not cleaned, the cold bore shot will fall within its true cone. If it doesn’t- there most certainly is a problem with the gun system. This is not an opinion. Take the rifle out in in a vice or machine rest. Fire 30 rounds straight. Mark target. Let barrel completely cool. Fire one cold bore round. That round will land inside the first 30 shots. If it does not, there is something wrong with the rifle.
Then, fire 30 cold bore shots from the machine. Those cold bore shots will NOT form a “hole” in a different location. Those 30 cold bore shots will be statistically identical in size and location to the 30 fired back to back. If they are not there is stress in the system somewhere. I.E.- the gun needs to be fixed.
Since you believe that in a properly built rifle, with stress free barrel and bedding, there will be a cold bore shift- first shot of the day, but shot number 2 and all subsequent shots from the group will land in a different place on target, which means that we would have two separate groups on target if we repeated this multiple times- what is the mechanical reason that this happens?
Mechanically what causes a stress free system to move between shot number 1, and shot number 2?
So if we're dealing with a rifle that will produce mechanically 1 MOA, and the hot barrel causes an upward POI shift, then as the barrel heats the cone will trend upwards. It's not expanding in size but the MPI is shifting, causing the gun to "walk". If you can explain how I watched 30 well-maintained and tested rifles all exhibit this phenomenon this week I'd love to hear it.
I have no idea how “30 well-maintained and tested rifles” are so messed up that they all exhibit “walking” due to heat. I would start by changing brands/gunsmiths.
This is demonstrated in enough guns that I don't buy it being a flawed barrel or bedding in ALL of them. If it was irrelevant then why don't more competitive shooters run lighter barrels? The heavier barrels have more consistent harmonics, but they're not necessarily more mechanically more accurate than hunting rifles if the hunting rifles are allowed to cool.
This is incorrect. In large numbers stiffer barrels ARE more precise than less stiff barrels due to harmonics. The difference isn’t massive though, and in hunting rifles where true 2 MOA precision will kill every BG animals walking to 600 yards it doesn’t really matter. The difference in a number 1 contour barrel fired from a machine test, and a number 7 isn’t huge- around .2-.3 MOA for statistically relevant group sizes. That is swallowed up in errors in a 7-8lb rifle.
However, if you are a competitor than it does matter.
So at what point does 0.65 MOA stop being that as an average? If there mechanically a difference between shooting a 300 shot string with even barrel temperatures between shots, or shooting 100 3 shot groups that have a maximum spread of .68 and a minimum spread of .62? I don't see how your numbers add up claiming that 3 shot groups are a feel good but 10 shot groups aren't when either could be conducted the same way to the same standard. One group is an outlier. Ten groups is a pattern.
Yes, .65 MOA is an average of 5 three round groups, but it is not the size target that your rifle will mechanically hit. Shooting 5x3 round groups and averaging is only useful for comparing against other rifles shooting 5 three round groups and averaging. As far as useful information... not so much. Granted that is far better than the vast majority do, but grouping for practical purposes should be giving us information that feeds into our decision process for shooting. Mainly for determining probability of hits. Otherwise it’s ballistic and mental masterbation.
You have a rifle that averages .65 MOA for 5 three round groups. Now I know because of tens of thousands of test shots that I can use that info to hit targets and have a decent idea of what it’ll do. But for most, when they hear “.65 MOA” and they miss a 1 MOA target, what do they do? Did they miss, or is there something wrong with the rifle? How do they adjust and hit with the next round? What’s the probability of hitting with the next round? They don’t know and will most likely come to a wrong conclusion based on faulty information. Your rifle may average .65 MOA for 5 three round groups, but it will not on demand hit a .65 MOA target. That is not how it works. The reason you are averaging those 5 groups, is to eliminate the bad rounds that you don’t like. If it wasn’t, then you would just count the two worst shots from those 15 rounds, or come up with a probability of hit. I.E.- 90% of round fired will fall within 1.5 MOA (thats about the probability of your .65 MOA rifle is).
Unless you shoot all 5x3 round groups to the exact same target, same exact POA/POI and measure all 15 rounds (that would be a 15 round group then), you are not accounting for the reality of random variation within the cone of fire, and the fact that statistically the next shot is more likely to land close to the last shot, rather than farther away. It’s giving you a false sense of capability.
I'm really not sure how you got 1.5 to 1.7 MOA "on demand" when the rifle has demonstrated better accuracy at all ranges over the course of 500 rounds. I'd be worrying more about the ability to make accurate wind call for 99% of shooters than trying to claim that 80-90% of rifles are really actually 2 MOA rifles because they don't shoot ten round strings.
I’m not trying to claim anything. The vast majority of guns aren’t even 2 MOA rifles. On demand means just that- on demand. Hit “x” size target with a huge penalty if you miss. Now do it 10, 20, 30 times in a row. What size target will all of those shots land in? It isn’t .65 MOA.
I got 1.5-1.7 MOA, because I am talking about the size target the gun will mechanically hit with 95+% of rounds. Everything has a probability attached to it due to statistical variation. Everything. 30 shots, whether 10 three round groups on the same target, 6 five round groups, 3 ten round groups, or just 30 rounds straight is somewhere above 95% certainty. A single 10 round group is about 85% certainty that the 11th round will land inside the first 10.
Here is the data sheet from a random rifle I just pulled up that was tested at the worlds top ballistic research facility using very high quality match ammo. 3 shot groups were not logged because in their words “it’s waste of time”. But, because it was shot on an acoustic target, we did track the first three rounds of every 5 round group, and it averaged right at .9 MOA for 5x3 rounds.
This is the average of 5x5 round group fired at 100 yards, with discounting the worse group (facilities standard). With all 5 groups it averaged 1.44”. The barrel was cooled down to ambient temperature for each 5 round group.
Here is the same rifle for 3x10 round groups, cooled between each-
Same but 30 rounds straight (note starting and ending barrel temp)-
Now what do you want to bet that those 5x5 round groups did not land to the exact same point of impact on target? Do you think that the cold bore shots from each group landed in a different place than subsequent shots? Do you think that all rounds fired landed within the 2.72” thirty round group (since it’s the largest)?
Not hardly.
That barrel then had 15 more rounds fired through it to make 100 shots. All 100 shots are here-
The cold bore shots were not the worse, or best of any of the 100 rounds fired. Can you show where the cold bore shots are? Can you show the “walking” that occurred during the 30 shot group where the barrel temperature reached 240 degrees?
The real question is, is this rifle a .9 MOA rifle (5x3 round groups) or a 3.11 MOA rifle....?
Cont....
