There are a whole lot of military and police snipers that argue the cold bore stuff is bullshit.. They make one-shot kills all the time..

Clean bore is one thing (requires fouling to be consistent), but I think it is more shooter than anything else. I have never had issues with my first shot being a flyer, but I tend to take multiple, multiple dry fires on the range before I ever shoot my first round too...

I have never heard of snipers keeping record of their first snot dope and then have to make adjustments for 1st cold shot vs. 2nd warm shot.. Of course they are shooting people size targets not bulls-eyes so that may be why?

Been my experience as well.

I never realized this was even controversial. To be fair, I never really thought about the "why" of it - I've only observed the "what" of it.

"Significance" is a matter of context.  Such a shift is well within the accuracy range of most rifles.

Those talking about hunting have me wondering what kind of hunting they are doing if they expect to notice or care about a minor 1 MOA or so shift.

I was also taught about cold bore shots, and to log them.  I don't remember seeing a lot of shift, but we didn't mess around shooting at 100yds or 100m much in any of the formal training that I did in the military.

For SOTIC MTT, we pulled the M3A's off the rifles on the first day, and installed the Palma sights, which none of us expected. I don't recall at what distance we zeroed them, but I specifically remember shooting with them for at least a day, all day.

I know we did grouping exercises at 400m with the Palma sights.  You had to shoot 1.5 MOA consistently before moving forward in the course.  I still have the log book with those days, with my hits, and the M24 was surprisingly accurate at distance with Palma sights.


Years and years later, when training with the Finns, they did a practical experiment with a Sniper Instructor Course.  On the morning of Day 2, they told half of the class to practice dry-firing until their called simulated shots were within the POA sufficiently, while the other half of the class was told to go straight live.

Results?

The guys that dry-fired had POA = POI, and the guys that went straight live had initial errant shots that previously were chalked up to cold bore phenomenon.

I know within the benchrest community, they are fanatic about clean bore shots, versus fouled shots.

Here's what I think is going on:

With .308 and larger caliber rifles, the initial recoil impulse and torque on the gun is often substantial, even when shooting gas guns.  This settles in the position similar to a mortar tube, and changes the Natural Point of Aim IF you re-index loosely on the settled position and shoot again.  A gas gun will really make you pay attention to this if you get good enough to drive the .308 AR's to consistently shoot sub-MOA with them.

With smaller calibers that have less recoil, the phenomenon seems to be less pronounced to me, but is there if I haven't dry-fired.

With my .260 Rem AR10, and my 6.5 Grendel's, I expect POI to be POA with the first round, but will pay more attention next time out.

With a friend's Krieger-barreled .308 Iron Ridge Arms gasser, the POI was consistent for me from 1st shot throughout 2 weeks ago.  I was shooting loose out of the gate, even driving it hard, but as I got used to the gun, I was able to tighten the groups up.  I started at just under an inch, and finished with .738" for the last 5rd group.  I started with a 3rd group to see where POI was after re-mounting and bore-sighting his optic.  All of the groups were consistent in terms of POI.

Cold shooter. From what I've seen cold bore doesnt exist.

i think that's mostly the right answer but while i've never seen a shift in my precision rifles, i'll stop shy of saying it doesn't exist.

it's pretty common knowledge that especially in lightweight hunting rifles, you're not going to get through a 20 round string of fire before that tiny barrel gets hot and starts flinging rounds everywhere.   so heat CAN change the POI.   it's just a question of how much heat does it take and is there some difference besides the mass of the barrel and free-floated and proper bedding?    

or are we saying that those number 1 profile hunting barrels heating up is a myth?   my guess is if you could demonstrate those barrels being accurate during sustained strings of fire, the mil guys would love to swap less barrel weight for more batteries and ammo

I've seen more then a few people sight in a light weight hunting rifle with say half of box of ammo and a hot barrel then go back later and wonder why there off. When Im zeroing my rifles I'm not doing it with a barrel thas going to burn me its so hot.

No, not at all. I didn't read it like that. Thanks for the info, this is the discussion I was looking for.

So i decided to do just a little testing tangent to this topic over the past 2 days and here are the results, which admittedly are very small group sizes and anecdotal rather than a large controlled survey, but it's still interesting to me and could potentially support reconb4's cold bore theory.    specifically, it seems to show up on the chrono, but not on paper

net, i have two mostly identical rifles, one i call my match rifle and the other a practice rifle.  and i have 2 different sets of ammo, one that's a little light and the other a little more peppy, which i also call practice and match respectively.   Yesterday, I fired some practice ammo with both my match and practice rifles.  The groups are on the left.  POA was the 5/8" black dot.  Distance was 338 yards.  Today, I cleaned both guns and then fired my match ammo through both rifles.  I chronographed all rounds, but put the first 5 rounds from each rifle on steel, and the second 5 on paper, which are the right two groups.  POA was the 5/8" orange dot. (I dialed off, so i wouldn't screw up my POA)  I shot the groups round robin, so I'd estimate 10 minutes passed between the first five and second five on each gun, which gave it time to cool enough that the suppressor was barely warm.

After I clean, I usually see things start to settle in after 5 rounds, so that's why i just threw the first 5 of each on steel.  I would normally ignore those chrono results from the first 5 as well, but i thought it might be interesting for this discussion to include them.

In any event, all groups are under 1 MOA, but obviously the match ammo shoots a good bit tighter.  (the round over by the orange dot was poor trigger pulling on my part.)

So what's interesting is looking at the spreadsheet.   In every case, the cold bore is lower velocity than most of the rest of the shots.  If you throw out the cold bore first round (top row of numbers) from each group, the SD and ES tighten dramatically.   In fact, if you average across all the groups shown, the SD drops from 6.2 to 3.5 FPS when the CB is excluded, and the Extreme Spread drops from 16.5 to 7.8 FPS.  (bold numbers in bottom right)
After 6 rounds of fouling and 1 round to warm up, the last 4 shots are 2 SD and 4-5 ES for both rifles.   (shown in yellow)

And yet, there's no measurable shift on paper.  The cold bore shot on each was in the middle of the group.

(i cleaned the rifles differently.  the match rifle had a major issue in oklahoma last weekend so i've been cleaning the piss out of it for all week with just about any solvent i could find.  The practice rifle just got a dozen patches with butches bore shine this afternoon.  I think that is why the practice rifle settled down in fewer rounds)

Wow that is an impressive group 7/8" at 338 yards!  I have seen the same thing as you with the cold bore shot being slightly slower than normal, but still being in the group.  I had one exception to that when I left a little oil in the chamber which spiked pressure and speed on the cold bore shot.  That was obviously caused completely by my mistake.  It didn't cause me any trouble because I run way below max pressures, but it was a lesson learned so that mistake will not be made again.

Thanks for sharing the data!  I'm impressed with both your shooting and reloading skills I'd really like to get my velocity spreads as tight as yours.

Per my comments in the previous discussion on this subject:
http://www.ar15.com/forums/t_16_3/1252_Question_on_Cold_Bore_Shot__First_Round.html

There is one component that has been left out of this discussion:



I am assuming that a lot of the rifles being used in this discussion are "higher end rifles", which use quality materials and are assembled properly, so you will not see this issue. However there are a number of factory rifles where this can be an issue.

When we teach a LE Sniper Course, this issue has to be forefront throughout everything we do, because obviously for a LE Sniper, the first shot is usually the only shot that matters.

In the course we identify:
- Clean vs Fouled Bore
- Cold or Warm Bore
- Cold or Warm Shooter

To demonstrate these in the the course we:
- Clean vs Fouled Bore: after shooting on day 1, we tell the students to "clean the hell" out of their rifles that night. When they come back in the morning of day 2, we have them do a number of warm-up dry fire exercises. They then fire a single cold bore shot. The first shot is a "Clean Bore, Cold Bore, Warm Shooter" reference. We then have them shoot more rounds, noting each one. This demonstrates how the rifle is performing going from clean to dirty and how long it takes to "settle back in".
- True Cold Bore: we have the students after lunch on day 2 (no shooting for 1 hour) deploy from a starting point, move quickly to the firing line, and fire a single cold bore shot. They are told specifically they can NOT do any dry firing at anytime during the exercise. This is a reference for a "Fouled Bore, Cold Bore, Cold Shooter".
- Warm & Cold: throughout the remainder of the course, we have the students doing multiple exercises where they will fire "True Cold Shots", both the rifle and shooter are Cold. "Warm & Cold Shots", rotating, with the shooter cold and rifle warm, or the shooter warm and the rifle cold.

Per many of the comments above, the students come to appreciate that they will usually have little if any "Cold Bore Shift". However they will very frequently see a "Cold Shooter Shift". When they do the proper warm-ups, they will be able to consistently make Sub MOA first round shots.

By doing very thorough documentation throughout the process, the students get a very good understanding of how both themselves and the rifle system come into play.

Hopefully that all makes sense, if not fire away with the questions.

Best of Luck,
M Richardson

You and Agent Boone (Ret) must have written that course together.



 

Solid info as usual. Thanks.

Cold bore is cold bore.  Most rifles will shift slightly as it heats up. Even my AI does, ever so slightly however.  Maybe 1/4 moa.

Maybe 1/4? Thats not enough to even matter or measure in the real world.

So at what temperature does one experience a cold bore shot? If you have a cold bore shot deviation at 50 degrees, do you not experience it when its 70 degrees? Does your rifle constantly shift POI with each shot as it gradually heats up?

IME, with pencil bbls, I see shifts after 5-10 rounds, depending on the ambient temperature.

You can go from a 1.5-2 MOA group to 10 MOA in a hurry.

Very interesting topic of discussion, gentlemen.  Thanks to all for your input.  Don't know how I missed this
thread earlier but am glad to have stumbled across it tonight.

As a relatively new long range enthusiast, I appreciate the chance to learn something here.  Again.

The more you know...

This is almost every exactly how my AI PSR behaves with the 300WM barrel. First cold shot is .5mils high, second is .3 mils high, third shot settles on target at POA/POI consistently. This is a 26" barrel with a can, and is quite clearly from the barrel settling downward with heat. It only settles about half as much,  around 2/10 mil without the suppressor installed.

I did a little test last Sunday with my 7.62 PreditOBR with 175gr FGGM and surefire 7.62 SS can.     with a fouled bore, I shot some groups with my .223 to warm up and try to take my shooting out of the equation..   Shot one 4 round group. wanted 2 min shot another 4 round group wanted another 2 min.. until I had 5 four round groups.. (20 round box of ammo)   and the gun was nice and warm..  as all the groups where under 1moa, but seemed to shift about .2 mils to the right as the gun warmed up..   at 100 M

But in the first group all the holes where touching and I could not tell you which one was the first one..  I am leaning a little more towards it is a little both cold shooter and cold bore..  I think pretty much all rifles are going to shift some.. (some worse than others)  if an AI PSR and a LaRue shift i think everything is going to shift..  but in my little test it was more a creep than a shift

But with a bad barrel or thin barrel that dose not take the heat as well it will be more dramatic..

Has way more to do with clean bore than cold. Stop cleaning your precision rifle so often. Once every 500 rounds is good usually accuracy degrades after that but takes about 60 to settle in.

You are wrong. It is common military doctrine to obsess over clean rifles, but fouled bore is much more consistent and accurate. Try not cleaning for the next 1,000 rounds in your bolt gun. I guarantee 100-500 will be the most accurate part of the test. The "cold bore" effect will nearly disappear magically.

Cleaning actually destroys barrels too. Clean and live the bolt, wipe the chamber and run one or two cleaner patches without copper remover down the barrel to remove gun powder which attracts rust then patch dry. They will come out very dirty and they should. This will help keep all that wonderful copper barrel protection nice and clean. Think of the barrel as copper plated.

The military focuses on cleaning to ensure function not longevity.

A point on cold barrel vs cold ammo. Ammo temp is far more important in stringing than barrel temp BUT!! Putting 70 degree ammo in a 200 degree chamber for 3 mins while you get ready to shoot you heated the ammo thus the powder burns faster resulting in higher velocity. Test? Freeze some ammo. Shoot 5 rounds fast then the frozen without it sitting in the chamber guarantee the frozen ammo shoots under all the other rounds

X2 hence good data. Some rifles are inherently closer to poi on the first cold bore shot than others. I think barrel profile has a little bit of influence here too. The thinner whippy barrels have a higher rate of irregular cold bore shots than heavy barrelsin a solid bedded action. This can also reflect on the shooter. Wind body posture etc all is harder to control with light poorly balanced rifle.

Speaking of poor bedding a rifle that consistently shoots a round in a string of fire to a certain point of impact shift can be traced to a bedding problem torque problem or stock touching problem. I had a Burris scope once that the cross hairs would rotate as you shot. Then it would reset like a type writer. Torque is another player in poi shift. As the barrel and action heat up it gets a bit tighter. Now this is not my theory but it was explained by a gunsmith many years ago and makes a little sense. As the action cools back down it shrinks just a bit. Moving ever so slightly then the recoil sets it back into place.

What do the people with machine action rifles have to say on the subject?

I have 2 work guns.  My 700 has no discernible cold bore shift. My semi-auto always shoots 1/4-1/2” high right at 100 yards.

I regularly dry fire a few times before the first shot.

Hence Data collection. My RPR has little to no poa to poi shift either. But you go to my pencil thin  .270 it really shows up. Now that could be the bedding it's pillar bedded. Now we step over to the 7mag in the medalist stock it's aluminum bedded with accuglass. It's only about 1/4" right and maybe 3/8" high. And it is temperature sensitive the closer you get to 60 degrees the closer it gets to poa. The stock fits me so well it pretty much doesn't matter cold shooter cold bore.  Now I can upset that with a uncomfortable position. But my data says that reflects shooter. Now I go over to my  .243 with it's medium weight barrel. It will almost always shoot 3/4" high. No matter how warm I am as the shooter. But it's just a bedded stock.  Now I have a Remington youth mod seven with the pressure point on the barrel wood stock. It has a tendency to be high with either a 1/2" left or right fouled or not.

Now I have a 6.5 Grendel with the Adams Arms gas piston. It has a very distinct poi/poa shift and doesn't group as well as my Direct impingement grendel.  So that leads me to believe bedding plays a major role in cold bore fouled or not poi shift.

And another thing that has perplexed me for years is how the first round at lower velocity can be higher than the fallowing rounds at increased pressure and velocity. Then how your rifle gets hot the velocity stabilizes then it starts to loose some velocity the hotter it gets with increased extreme spread. It's kinda like there's a sweet spot temperature each rifle likes to operate at?

That's one of the reasons I would like to hear what the people with a machine barreled action have to say.