There has been some discussion of this before, but I’m revisiting it now and will ask the question directly after having pondered it some and started some experiments:

Can we expect the first shot (or two+) from a clean, cold bore to have a different point of impact from subsequent shots in a string? And if so, why? What causes that phenomenon?

The answer might seem obvious: A clean bore doesn’t have the fouling caused by subsequent shots and therefore the friction between bullet and bore might be less. A clean bore might also have a residue of oil or solvent that would change the friction even more.
Or (and?) as a barrel heats up from firing, it might start to bend and warp, causing a POI shift for that reason.

The problem with both explanations is that neither seems to be universally true and therefore is unlikely to be the reason.

I have only started recording bullet velocities from clean bores, but when shooting a batch of Hornady 308 Winchester 155 grain A-MAX TAP ammunition yesterday, the first shot velocity was 2801 fps as recorded by a new LabRadar chronograph. The average velocity of the 14-shot string was 2808 fps, and the extreme spread was 76 fps. The first shot velocity was therefore right in the middle of all the shots. And not only was the rifle bore clean, it was slightly oily from a bit of protection applied a few days before, and which I deliberately did not remove before the session. The first shot also fell within the first five-shot group I fired at 100 yards.

The second explanation for the first shot outlier is that the barrel heats up and bends, and that causes a POI shift. At this point I’ll say that I’m not talking about “mountain” rifles with pencil thin barrels. This is about precision rifles with heavier barrels intended to deliver accurate results throughout long strings of fire. Bryan Litz has conducted experiments with such rifles and determined that even extended firing strings heat barrels slowly, and that they have little influence on POI shifts. A single shot or two at the beginning have almost no effect on barrel temperature.

Guidance to US Army snipers is to fire five shots before the start of a mission to avoid the clean bore effect, but it obviously would have no effect on barrel heating as the barrel would cool long before any shots were fired after moving into position.

I know that one member here (fritz?) has said that there no “cold bores,” only cold shooters, and it’s the failure to be in proper position behind the rifle from the beginning that results in first shot(s) POI shifts. I have certainly been guilty of being a cold shooter myself, but I’m wondering if clean cold bores could also cause POI inconsistencies as well. Even assuming similar precision rifles, could individual rifles vary: Yours isn’t susceptible to the problem, but mine is? Again, if so, why would that be?

Thanks for all thoughtful replies.

quote:

Originally posted by sigfreund:
...there no “cold bores,” only cold shooters,

The USAMU dosen't agree.

Cold bore miss excuse is just that, an excuse. Cold shooter has far more effect. Add making a wind call...

Don't buy into predetermined amount of shots to do this or that. How did they come up with 5? 4 is not enough, 6 too many. Crap, I only took 4 fouling shots, I'm most certainly going to miss

quote:

Originally posted by cas:

quote:

Originally posted by sigfreund:
...there no “cold bores,” only cold shooters,

The USAMU dosen't agree.

Thank you, but:
https://www.youtube.com/watch?v=gaIvWAi8eNA

On the other hand, a deputy who attended an LE sniper course last year came back and when I asked him about cold bore shots, he said everyone in the class experienced a POI difference, some as much as 2 inches at 100 yards. They were all experienced shooters (somewhat, anyway), and reportedly were all using reasonably decent rifles. So that’s the reason for my question: If, as in the AMU video, a POI difference is to be expected, what causes it? (And as a reminder, if it’s not a significant change in bullet velocity, what makes the bullet fly differently because it came from a clean and cold bore?)

My old GAP 308 would shoot the first round about 1 inch high and 1 inch left maximum without fail. After that, POI shift to POA and stayed very tight. I don't know if it's cold bore or cold me but it sure as hell happened. To the point I could predict it.

I'm shooting an M14 currently with a Krieger barrel and seems like the cold bore chucks rounds randomly in a 2 inch circle. (I'm still green on this rifle so I haven't developed a pattern for first shots yet.) Easy to blame that on the platform, but once that barrel is consistent it stays pretty tight as well. Here's my best 10 dot drill, (1 of 3 so far) that was shot after the range was called cold. That's the first 10 rounds after the delay. And the shots before it was called dead weren't "wandering." I'm fully ready to accept it's my lack of focus, I'm just not sure of that.

IMG_1752

Short answer -- assuming a modern precision bolt action rifle, using consistent ammo of high quality, with a quality barrel & chamber -- the shooter's actions have more effect on POI than the bore itself.

I do believe that some thoroughly cleaned bores have a slightly different point of impact, as compared to their fouled POI. But it's a relatively minor difference, especially compared to the technique errors that we shooters impart on the rifle.

I don't see cold-clean-bore POI shifts with my bolt actions with my normal cleaning. Which is pushing a few patches down the bore, after virtually every shooting session, using a mild cleaning/lube solution, to the point the patches cleaned most -- but not all -- of the barrel's carbon fouling.

Now if I see accuracy fall off, and I'm pretty certain the barrel isn't shot out, I will do some thorough cleaning -- for me. In my experience such accuracy issues have generally been due to a carbon ring. After cleaning with chemicals, brush, and patches, I may see a cold-clean-bore shift of 1/4 to 1/2 MOA for one or two rounds. But that's the only time I see the cold bore POI change.

Well, I'm not part of USAMU and I am definitely not a sniper; I'm just an ordinary F-class competitor.

It is well accepted in the F-class competition circuit that a thoroughly cleaned bore most always has a different POI compared to even a lightly fouled barrel. Indeed, we plan around that when we go to major competitions. We always want to know if the first match of the day has unlimited sigthers or if it's limited to two sighters, we want to know if there will be a blow off period prior to the first macth of the day.

It's pretty much a standard now that the very first match of the tournament will have unlimited sighters and that subsequent days will have a blow off period before the first match of that day. Knowing this, most competitors will thoroughly clean their barrels prior to the start of the tournament and will either do that every night, or just run a few patches through at the end of the day.

The blow off period is right after prep time; the targets are all pulled into the pits and on the signal from the MD, you have 1 minute in which to shoot as many rounds as you want into the impact berm. This also occurs on team match days. The astute competitor or wind coach will pick a terrain feature at which to aim to confirm the general area of impact. Usually a rock or a clump of dirt.

Most of us seem to experience a slight deviation starting with a very clean barrel; that usually disappears after a couple of shots. After shooting the first match it can be several hours before you shoot the second match and the barrel will be "cold" by that time. It will, however, remain fouled. Subsequent matches are always two sighters and the last thing we want is for changes in POI because of a cold barrel as these sighters are critical. In International matches, the sighters are convertible and thus become even more critical. Rememebr, you want to shoot as few rounds as possible in a string for international matches so if your two sighters are Vs or 5s, or you second sighter is a V, you can convert both or the second one and then only need to shoot the remaining 13 or 14 shots.

Most of the match rifles on the line are not affected by "cold bore," but they are susceptible to "clean bore."

Rimfire rifles are a whole different matter. POI shifts can take 5-15 rounds to cure after cleaning. It can take that long to cure POI isues after changing ammo types, too.

I've seen POI and accuracy issues with my AR15s when I switch between certain types of ammo. The most pronounced is to and from Hornady 73 ELD. I see the need for 5, sometimes 10, rounds for the POI shift and accuracy deterioration to go away.

This is why I believe shooting only one type of ammo in a rifle is important to its consistent performance.

******
On a little different note, it's easier to shoot a bolt action with precision than a semi-auto. Regardless of the type of semi-auto. Skills that make bugholes with a bolt action may produce shotgun patterns with a semi-auto. This becomes more noticeable with cold-shooter shots.

Furthermore, it's easier to shoot a low-recoiling round accurately than it is a higher-recoiling round. Anybody with experience in PRS-type competition knows this. Regardless of the keyboard commandos who state they can shoot their 308, 300WM, or 338LM "sub-MOA all day long, if they do their part", they are less likely to exhibit cold-shooter POI issues with a 223 or 6BR than with a 300WM.

A slight drift, but I have noticed a poi shift on the last round that locks back a semiauto gas gun.

I know this is a first shot bolt gun discussion but I thought it may have some relavence.

I typically define first shots as:
“clean cold bore” - the first shot from a barrel that has stripped of copper
“cold bore” - the first shot from a barrel that has been cleaned but NOT stripped of copper
“fouled cold bore” - the first shot from a barrel previously shot but not cleaned

The different rifles and calibers I shoot are 6mms, 6.5s, 7mms, 30 cals and .338s and none of them have a POI shift on any cold bore shot. This is not to say that a “cold bore shift” isn’t real as I do know good shooters who have experienced them, I just never have. I do think many times the shooter has more influence in the POI change as they mount the rifle and establish a cheek weld. Obtaining the proper position of the eye in relation to the scope reticle and the target with every shot, including the cold bore, takes practice. Learning to build a solid shooting position requires work/practice and shooting dot drills is an excellent exercise that will pay dividends.

My bolt gun has cold bore issues. It throws the first shot 1 min high. (Shilen barrel)
My 308 AR has a Krieger barrel and doesn’t do it.
Very well could be “cold shooter” but the same guy shoots both.

quote:

Originally posted by smithnsig:
A slight drift, but I have noticed a poi shift on the last round that locks back a semiauto gas gun.

I am interested in all POI shifts.

It’s not something that we hear much of these days, but at one time a significant complaint was that the first shot from a new magazine from autoloading pistols, especially 1911s, would not group with the rest. I read a comment from a then well-known author who claimed that that was a complete myth. I, on the other hand, could personally attest that it was absolutely true of the Colt “Combat Elite” I owned for a time in the late 1980s. At a distance of 10 yards or so, the first shot would hit a good 2 inches high and to one side as compared with the rest of the magazine.

Ten years ago I would have told you were crazy if you said your rifle had a cold bore shift. I might accept a 1/2" shift, but not more. I now own a gun that has an honest to goodness and consistent shift high right (1/2" right & 1.5" up) from a Caldwell Lead Sled. If you quickly shoot two follow-ups, it will walk in to the POA= POI on shot 3 or 4. If you keep it warm and do your part, it will group at 1-1/4" @ 100 yards consistently for the rest of the day. Take it out the next day and repeat.

This is one of my hunting rifles and it is frustrating to think your first 1 or 2 shots WILL NOT be POI = POA. In hunting, you need to have your first shot be true, especially when trying to make a long shot or ear hole a hog. So how do you sight in this rifle? First round or 5th round? Right now it is sighted in for shots 5-10 and I figure Kentucky since he on my first shot. Not ideal, but...

Sorry. No explanation, just my personal observations.

quote:

Originally posted by smithnsig:
A slight drift, but I have noticed a poi shift on the last round that locks back a semiauto gas gun.

I had this happen to me a handful of times last month, on a day that I was shooting well with one of my better AR15s. The 5th shot of some 5-shot groups were going wonky. I thought it might be something with ammo, or maybe issues with the mag lockback. Maddening, really. I turned a 1.25" 4-shot group at 320 yards to a 3.0" 5-shot group. Turned a 1.75" 4-shot group at 440 yards into a 3.75" 5-shot group.

Then I realized I was shooting with 10-round mags and half of my sheep-dip shots occurred in the middle of the mag -- not on the bolt lock back. OK, so unless my ammo was magically turning to crap every fifth round, it was me.

So...I stopped admiring my purdy 4-round groups on steel and shot at a consistent cadence and with consistent technique for all 5 shots. The next five rounds were 1.25" at 320 yards, with no yanked shots.

It always is possible that the bolt lockback influences the POI of the rifle, but it's my understanding that the bullet should be out of the bore before the bolt even begins to move backwards. For a properly functioning rifle. Which means the bullet is definitely down range prior to bolt lockback, or bolt moving forward to strip the next round from the mag.

At least in my case, last round flyers are caused by me.

quote:

Originally posted by fritz:
admiring my purdy 4-round groups ....

Gee; I don’t know how that could happen.



Two beautiful (for me) four-shot groups at 100 yards with Hornady Black 308 Winchester 155 grain A-MAX from a Tikka T3, then number five. I thought about blaming the two “fliers” at the left on the wind, but no, probably not.

Thanks for the reminder.

quote:

Originally posted by offgrid:
How did they come up with 5?

We loves our groups of numbers. Favorite is any number that ends in zero (10 fingers > base 10, and all that), but five is second best.

quote:

Originally posted by sigfreund:

extreme spread was 76 fps.

That's a big number. Guessing vertical spread approaching 24" or so at 1000yds.

quote:

Originally posted by offgrid:

quote:

Originally posted by sigfreund:

extreme spread was 76 fps.

That's a big number. Guessing vertical spread approaching 24" or so at 1000yds.

Yup. Wish I had someplace to shoot to 1000. Using local environmental conditions, I get a vertical spread of about 21 inches at 1K. At half the distance, 500 yards, it’s only a bit over 3".

What little experience I have with 1000 yards made it clear how things really change at such distances, but there nothing like looking at the figures to understand why. When I didn’t appreciate the effects of something like velocity spread I was often puzzled by the results I got: “Man—I know I broke that shot right (for once); why did I hit there?”

quote:

Originally posted by offgrid:

quote:

Originally posted by sigfreund:
155 grain A-MAX TAP
extreme spread was 76 fps

That's a big number.

I found Hornady's 155 grain loads to be quite accurate out to 200-300 yards. The little accuracy testing I've done beyond that is a bit inclusive, but I did not see the accuracy I obtain with Hornady's 168 grain loads.

I found Hornady's 155 grain loads to have much higher MV variation than their 168 & 178 grain ammo. As in the SD and ES numbers were at least double the values of 168 or 178. As a result, I shot a few boxes of 155, then didn't buy any more. As offgrid noted, the 155 loads will be susceptible to greater vertical variation at longer distances, due to their MV variation.

Your ammo choice depends on your use. If your distances to target are short and if you prefer a higher MV load, then the 155 ammo may work.

For me the first shot shift is a real phenomenon, but not 100% and not enough to matter for any hunting conditions I have within about 100 mile radius.

I realize the above doesn't answer your question much, but for a solution to it what I always did was to have some time on the bench before hunting season - as much as needed for sighting in. Then hunt with that gun without cleaning.

During the same session mentioned above, I also measured the velocities of 14 rounds of Hornady “Black” 155 grain A-MAX. The groups pictured were with that. The average velocity was 2770 (v. 2808 for the TAP) and the extreme spread was even worse at 82 fps.