Cold Bore Shots - Any definitive Expert Articles?

[Romulus]

I've got a 260 AI barrel that really wants to shoot, but the cold bore when new was almost exactly 2 MOA low when I just started shooting it. 500 Rounds later the cold bore is 1 MOA low then it starts stacking.

I've been too busy to lug my chrono around since I shoot on the way home from work as it's the only time I can get to my medium range (740 yds) anymore. This of course would give me valuable information about the CBS and would give me REAL data for compensating for that first shot - AND I need to get that done. I am not comfortable just winging it by adjusting 1 MOA. I want to get better info or reduce the CBS.

I've considered HBN but my rifle shoots single digit ES that creeps into the teens after 8-15+ shots so I'm not wanting to change anything just yet. I figure I could keep it single digit or real low teens with more work, but this rifle is used for medium range mostly (inside 1000) and those stats will suit the field tactical discipline better than most loads.

I prefer articles and advice from career experts over the masses, but I do not disregard enthusiast experience, thus the very nature of a Forum.

Are there any definitive articles on Cold Bore Shots written by the leaders of the shooting community. I'd rather read from someone in the gunsmithing, f-class, BR, or HP communities over some tactical stuff since most of that shooting is honestly minute of man, 2+ moa targets, the reloading and prep is often grossly lax, data is not recorded regularly since it's literally field work (no chrono, indeterminate wind, non-permanent target record etc), and most of the culture is younger than the old wise men, but any solid article would be much appreciated.

In terms of personal experience -
[list type=decimal]
[*]How long does it take for a rifle to sit and return to a CBS? I understand this depends on many variables and I have not spent the range day to find out by shooting, taking time out, and then checking POI. I like doing tests but I just need a free day
[*]This rifle will be used in the "tactical" mode where I only get one or two shots. Do you have in-group success dialing out the CBS or have you tested/found that the CBS will not group without further compensation at longer ranges?
[/list]

Thanks for any links and any experience and especially good data.

 

[Michael Courtney]

We've thought about a careful cold bore experiment, but not done it yet.

We have had success minimizing velocity variations of follow-up shots by not letting the round cook in the chamber. The cartridge sits on top of the magazine with the bolt open until ready to fire, at which time the bolt is closed and the round is fired within a few seconds.

An alcohol patch between shots is another trick we've used when trying to minimize velocity variations between shots for laboratory work.

 

[M14AMU]

I could give a krap less about what a chronograph says! It's what shows up at the face of the target that counts!! : :

 

[Killshot]

Romulus, My Field Precision Shooting friends tell me they keep log books with data specific to their CBS (it's the first shot of the match and there are big points attached to it).

With past performance noted and condition variables documented, it's easier to know where you'll print that CBS each time. Typically the first shot of the day will be slower and print lower than subsequent rounds. It's all about knowing how much that is.

Obviously, getting this data takes time and patience as CBS mapping isn't as simple as normal group shooting/testing/chronoing. Note I'm talking about cold bore and not Clean Bore.
I imagine you'd need to wait until the barrel cools back down to the ambient temperature before firing additional "cold bore" test shots.

Good luck.

 

[Romulus]

Yes, I thought about clarifying that I was talking about Cold Bore and not Clean Bore. Thanks for the reply.

At my last match we had a cold bore at 550 to open the day. Out of about 30 shooters only a couple sunk it in the 4 point square and most got the 2 points. I got 2 and was about a 1/2 minute low :'( but considering the wind I was happy to get 2 points as most shots are worth just 1.

I guess I may lug my chrono around in the work truck to see if the CBS are consistently in some velocity band and then pop up to standard velocities. I like putting chrono and shooting data in excel, so over time collecting atmospheric/ambient temps,CBS velocities, and POI's I can build a better idea of how to compensate than just mapping where it hits on CBS. I've considered getting a magnetospeed just for the convenience but the POI shift has always put me off, especially in this case.

I've considered using a infrared thermometer to check the chamber temp to correlate with the target/chrono data lol. I know some may scoff at that idea but at least it's an easy data point to collect.

 

[Michael Courtney]

I could give a krap less about what a chronograph says! It's what shows up at the face of the target that counts!! : :

We've shot over a chronograph and mapped impacts at 500m. Slow hits low, just as the chronograph and ballistic calculators say. Likewise, fast hits high.

When we were shooting the data on lot to lot variations in H4831 (see: http://www.dtic.mil/dtic/tr/fulltext/u2/a572333.pdf ), the faster lots (C and E) consistently hit much higher than the slower lots (B and D). I was spotting for my daughter who was shooting, and after seeing where fast and slow shots were hitting, I could accurately estimate the velocity from where the bullet hit before I looked at the chronograph.

 

[fredhorace77]

We've thought about a careful cold bore experiment, but not done it yet.

We have had success minimizing velocity variations of follow-up shots by not letting the round cook in the chamber. The cartridge sits on top of the magazine with the bolt open until ready to fire, at which time the bolt is closed and the round is fired within a few seconds.

An alcohol patch between shots is another trick we've used when trying to minimize velocity variations between shots for laboratory work.

Michael ....for the record...who in the world is "we"....do you have a mouse in your pocket or does "we" have a name?

 

[Outrider27]

We've thought about a careful cold bore experiment, but not done it yet.

We have had success minimizing velocity variations of follow-up shots by not letting the round cook in the chamber. The cartridge sits on top of the magazine with the bolt open until ready to fire, at which time the bolt is closed and the round is fired within a few seconds.

An alcohol patch between shots is another trick we've used when trying to minimize velocity variations between shots for laboratory work.

Michael ....for the record...who in the world is "we"....do you have a mouse in your pocket or does "we" have a name?

As a senior in high school, I had a blue haired little old lady battle axe who taught English (and assigned homework) as if English was the only course we were taking. She would have gone ballistic if one didn't know about the "editorial we" and it's use.

I survived senior English, but I still feel twinges when someone uses a redundant expression or says something about "between A, B, and C" instead of "between A and B" or "among A, B and C". I'm not sure whether these twinges are remembrances of past education or post traumatic stress syndrome....

 

[Michael Courtney]

We've thought about a careful cold bore experiment, but not done it yet.

We have had success minimizing velocity variations of follow-up shots by not letting the round cook in the chamber. The cartridge sits on top of the magazine with the bolt open until ready to fire, at which time the bolt is closed and the round is fired within a few seconds.

An alcohol patch between shots is another trick we've used when trying to minimize velocity variations between shots for laboratory work.

Michael ....for the record...who in the world is "we"....do you have a mouse in your pocket or does "we" have a name?

I've co-authored many papers in ballistics. "We" includes my co-authors and colleagues at BTG Research and the United States Air Force Academy, and in this case some DoD contractors who need to remain unnamed because of various confidentiality and non-disclosure agreements.

Minimizing velocity variations related to cold/warm/hot bore and chamber temperatures is particularly important in the testing of armor, because when determining whether a particular bullet penetrates a particular armor, one wants the actual bullet velocity to be as close as possible to the desired velocity for the test. We've used many approaches to accomplishing this: Lapua once fired brass, cleaned in stainless media and meticulously prepped, Hodgdon Extreme powder weighed to 0.02 grains, sorting bullets for uniformity, match primers, careful barrel cleaning regimens, the alcohol patch mentioned above, and a laboratory procedure to achieve a consistent time interval between shots. The 2" thick (full length) barrels often used in universal receivers do not cool quickly and achieving a consistent barrel temperature upon firing is an important step.

You can find a lot of my (our) ballistics papers with the following Google Scholar search:

http://scholar.google.com/scholar?start=50&q=Michael+Courtney+bullet&hl=en&as_sdt=0,11

Sorry if the "we" offended you. It's my way of not taking too much credit for a body of work that lots of others have contributed to.

 

[fredhorace77]

Not offended at all...just was wanting to know. And thanks for the info. Some people's "we" is a handfull of wannabes hanging out at the coffee shop...other's are people that actually know what they are talking about. sounds like you have got a group that actually knows what they are talking about

 

[josh.rizzo]

I've actually found that "cold bore" is often a misnomer for "clean bore". Are these shots with a cold AND clean bore?

I found that there is such a thing as cleaning TOO MUCH. It wears out your bore faster and makes clean bore shots harder. If you just do 10 strokes with a mild solvent and a nylon brush and then dry with patches, that will get most of the crud out. I do this every couple hundred rounds, and not more often than that (except during break-in). There will still be some copper fouling, but it will reach an equilibrium and stay pretty constant through the life of the barrel. This will give you more predictable first shots than if you try and get it sparkling clean on the inside all the time. Some people also say this equilibrium of fouling will protect your barrel from wear, to an extent. I follow this cleaning procedure and I see no difference between my cold bore shots and the rest of my shots.

There are other reasons to clean your bore more than that. If it was exposed to particularly corrosive conditions, like salt water or something, then by all means clean the hell out of it. Some people also notice a velocity difference with sparkly-clean vs fouled bores and they may want to aim for the velocity from the clean bore, but thats all up to you.

Now if your bore is not sparkly clean and you still have a problem with cold bore shots, it may be a bedding issue. Try a DIY bedding job with Acraglas (or any other recommended bedding compound). I say DIY because you might want to experiment with how the recoil lug is bedded. Some people add a little tape to the front/sides/bottom of the lug and just bed the back (the side facing the shooter); some people just tape the sides/bottom and bed the front and back. The tape is just a spacer to allow room for heat expansion. [Please, excuse me if this is redundant info for anyone...] Now, I found that bedding it on ALL sides eliminated any POI shifts from temperature on my factory Savage 10, but you need to use a less-brittle compound like Acraglas or it will cause problems as the lug heats up (Bedrock from Midway had a problem with this method, as it was a very brittle compound). YMMV, but I would look at your bedding if cold bore is truly the issue.

That being said, some guns will just have cold bore issues by nature. In that case, refer to the rest of this thread, but that's my 2 cents.

 

[josh.rizzo]

Forgot to mention the more obvious: less temperature sensitive powders may solve your problem if your rounds are actually heating up in the chamber. Try not chambering until right before the shot.

I got an IR thermometer off of Amazon for cheap. They are great for diagnosing these things. http://www.amazon.com/Nubee%C2%AE-Temperature-Non-contact-Infrared-Thermometer/dp/B00CVHIJDK/ref=sr_1_3?ie=UTF8&qid=1390321517&sr=8-3&keywords=ir+thermometer

 

[josh.rizzo]

@dmoran

I do not use a borescope - I'm going off of what I've been told and what I've read. I do make sure that I eliminate any powder fouling - it's just the copper fouling that I don't fret too much (I do attempt to get most of it out, just not every little bit).

I think the results speak for themselves as far as consistent shots - I've virtually eliminated any cold/clean bore POI shift. However, your experience and expertise are welcome information. If what you are saying is true, then perhaps I'm doing more damage despite getting better performance?

Is it possible that there is a middle ground? Perhaps a light cleaning every 100 rounds and a thorough cleaning ever 300? What is your recommended cleaning schedule as someone who has seen a lot of bores through a scope?

EDIT: And I do believe this is relevant to the thread as I am still convinced that a lot of "cold bore" problems are actually "clean bore" problems. Significant ammo temp spikes notwithstanding...

 

[M14AMU]

PERHAPS....if you kept an accurate data book on TEMPERATURE some of those 'mystery shots' would go away!!

 

[johara1]

Cold and or clean to me at 600 yds. if i hold the top of a clay bird and i have the wind right it will break, The next shot i hold the middle and the same will happen. At 1K i hold the top of the black and it will be a ten. At 100 it will be in the group. This works the same with a fouler the day before the match, so it doesn't change the impact, from a clean one. This seems to be the rule now that i freeze them, both barrels have acted the same way…….. jim

 

[Michael Courtney]

- those who do not use a bore-scope at least periodically are only guessing at the truth

Have a look at the uncertainties in the muzzle velocities in the above graph. We achieve small variations in muzzle velocity with our thorough laboratory cleaning procedure without using a bore scope. Every 50-100 rounds we do the following procedure:

1. Wet patch with Hoppes Elite powder solvent
2. 50 bronze brush strokes with Hoppes Elite powder solvent
3. Remove all solvent with a few dry and alcohol soaked patches, then dry
4. Wet patch with Hoppes Elite copper remover, wait 15 minutes
5. 50 bronze brush strokes with Hoppes Elite copper remover (clean brush)
6. Remove all solvent with a few dry and alcohol soaked patches, then dry
7. Wet patch with Shooter's Choice copper remover, wait 15 minutes
8. Remove all solvent with a few dry and alcohol soaked patches, then dry
- Save first two dry patches removing Shooter's Choice
- These get carefully inspected with a good incandescent light source
- The amount of copper removed is judged from the "blueness" (hints of green)
- If there is too much blue on the patches, the whole procedure is repeated from 1.
9. Wet patch with Hoppes #9 Copper Remover
10. 50 bronze brush strokes with Hoppes #9 Copper Remover (black label)
11. Remove all solvent with a few dry and alcohol soaked patches, then dry
12. Wet patch with Hoppes #9 (traditional, yellow label)
13. 50 bronze brush strokes with Hoppes #9
14. Remove all solvent with a few dry and alcohol soaked patches, then dry
- Save first two dry patches removing Hoppes #9
- These get carefully inspected with a good incandescent light source
- The amount of powder fouling (carbon) is judged from the blackness (or grey) on the patches
- If there is too much grey on the patches, the whole procedure is repeated from 1.

Other important points are to always thoroughly clean every bronze brush after any brushing step. Replace loose or worn brushes. Clean the cleaning rod and jags between every step. Use a proper bore guide that fits the rifle well. Clean any solvents out of the chamber and crown as needed.

All the evidence suggests that the above procedure (esp. the patch inspections) produces good results without a bore scope. We've never tried it, but I wonder if we could pull out more copper (blue patches) and powder fouling (grey patches) with out procedure that would be passed with a bore score inspection.

I think improving our accuracy and muzzle velocity (consistency) further would require tighter chambers, case neck trimming, and sorting bullets by bearing surface rather than improving our cleaning procedures with a bore scope. When shooting matches, technique and wind are the bigger issues. When doing experiments, barrel temperature, chamber temperature and cooking time are the bigger remaining issues after we've done all our standard due care.

 

[johara1]

With all that brushing you better crown it every 500 rounds …….. jim

 

[Michael Courtney]

Never had a problem with crown issues. We are careful that the brush stroke is only long enough that the brush barely clears the crown with no room for the rod to rub. We are also careful to always clean extra solvent from the crown.

We've got a .223 Rem with over 5000 rounds and a 25-06 recently retired with over 3000 rounds. The .223 Rem still competes well, and the 25-06 competed well a few months ago, but was given as a gratuity to the owner of a very welcoming range facility that we use a lot. There was no visible degradation to the crown and only a small loss of accuracy that we attributed to throat erosion, as the lands had moved a bit and the rifle had seen its share of hot loads over the 3000 rounds. In addition to inspecting the crown and making inferences from retained accuracy, we have also shot high speed videos measuring pitch and yaw. Rifles with crown problems will have larger tip-off angles. Even our well worn barrels have tip off angles in the 2-4 degree range indicating that all is well with the crowns.

You might check out Alan Marshall's article on The Over Rated Crown. It originally appeared in Precision Shooting before its demise, but I think it is available now at the Long Range Hunting web site if you do a google search. I think abuse of the throat end (hot loads, non-use or misuse of bore guides, lack of cleaning, dirty ammo, and some or our unique experiments) ruins many more rifle barrels than effects of cleaning on the crown.

 

[LHSmith]

200 passes with a bronze brush??? Shirley you can't be serious. Do you also remove the brush at the end of every pass to protect the crown (as advised by some barrel makers). There are bore cleaning products that could reduce that scrubbing regimen by 10 fold.

 

[LHSmith]

We are careful that the brush stroke is only long enough that the brush barely clears the crown with no room for the rod to rub.

How is this possible?....the bristles either remain in contact with the crown (in which case you are reversing the direction while still in the bore) or the bristles clear the bore (in which case the rod contacts the crown). Whether you allow the rod to contact for 1/4" or 1", with a minimum of 200 passes every cleaning ....that a lot more rod contact that most seasoned competitors subject their crowns to.