Voici du site Sniper's Hide un post très intéressant sur le Break-in.
After many email requests I thought I'd repost the research I did on barrel break-in procedures. In addition I also added a short overview on Internal Ballistics 101 to help tie everything together.
This has been posted on many shooting boards over the years and has been modified as I uncover more information. This is a quick synopsis of my finding which has been generalized. I had lots of test results and data I looked through. It’s also not based on the opinions and hearsay. I set out to take an objective look of barrel break-in procedures. I wanted to find out if there was any hard fact evidence to support barrel break-in procedures or was it a waste of time. In the end all of the data I collected supported the fact that barrel break-in procedures are a waist of time and in some cases damages barrels. To research this project I spoke with a few metallurgists, originally three of our top barrel makers (Shilen, Hart and Rock) and have since talked with a handful of others including Bartlein and Broughton. I also talked with a few internal ballistic engineers and some our nation’s best gunsmiths.
A little back ground on myself. I have degrees in Engineering and Business Adminstration. I’m a data network engineer in real life. I’m an avid long range shooter and due to my knees gave up tactical competitions about 6 years ago. One of my hobbies is external ballistics and I enjoy reverse engineering new ballistic programs to see what ballistic models, mathematical calculations, formulas and algorithms the creator used. I have a pretty good knowledge on ballistics and long range shooting. By no means am I an expert, when I'm in doubt I talk with Bryan Litz. I have spent more time than I care to admit to trying to uncover the science behind the scene. With regards to this write up, I feel I've done a fairly good job with my research and conclusions. Though some may disagree with my finding which is fine.
Before blasting away at what I've written, offer insight supported by facts and test data and not hearsay or opinions. This is what I’ve tried to do. It’s ok to disagree as the more information we can get the better informed we are. Also remember my conclusions were the collective data from some of the best minds and subject matter experts in the business.
Back in the 2001/2 time frame I trashed a brand new Shilen stainless steel match barrel in under 400 rounds shooting moly coated bullets. Yes this was during the moly bullet craze and I jumped on the band wagon. Let’s just say I was not a happy camper. I live local to Shilen so after a few hand lapping jobs on the barrel which failed, Doug Shilen cut the throat section to see what was really wrong. The throat area showed the black moly ring of death which was so hard Doug could barely scrape it with the side of a flat head screwdriver. Let’s just say I’ll never shoot another moly coated bullet....ever!
After my new Shilen barrel was installed I set out to on a mission to understand this barrel break-in process and if I really needed it. After all this research my conclusion supported the fact that barrel break-in is a waist of time and effort.
Let’s talk barrel break-in shall we: I believe Kelly McMillan of McMillan rifles said it best, “This barrel break-in processes keeps us in business”. “This shoot and clean, shoot and clean every round or few rounds break-in process only damages your new match barrel and/or significantly decreases the barrel life”. Though I didn’t speak with Kelly on this subject I’ve read what he’s written and it mirrors my own findings.
Some barrel manufactures have now re-clarified their stance saying that a barrel break-in procedures helps to smooth the transition from the newly cut chamber into the throat area of the bore. Now there is some merit to statement except for the fact a cotton patch with bore solvent or bronze brush isn’t going to do squat to help remove any rough areas. Bullets passing down the barrel will help smooth the chamber/throat area. It may take just a couple of shots or it could take a lot, but it depends on how well the chamber/throat was cut and polished. Last I checked stainless steel and chrome moly steel is much harder than a cotton patch or bronze brush.
Speedy Gonzalez (Hall of fame bench rest shooter and one of the nation’s top gunsmiths) was a wealth of information as were the techs at Hart barrels. As Speedy says, “my $3000.00 video-bore scope doesn’t lie”. I've looked through lots of barrels at Speedy's shop while he was working here in North Texas. Looking through his bore scope I learned a lot and saw a lot of good the bad and the ugly when it comes to barrel and barrel maintenance. Speedy's video bore scope never lied. When looking through his video bore scope at the internal surfaces of trashed barrels, one thing we did see a lot of were cleaning rod marks. The cleaning rod marks showed too much cleaning with poor and improper cleaning techniques and equipment. This was also noted by the techs at Hart Barrels with regards to barrels they replaced.
There are probably less than a dozen individuals in the US that understand internal and external ballistic as well as Stan Rivenbark and Mike Rock. Stan is retired ballistic engineer from Raytheon Corporation and Mike Rock of Rock Creek Barrels. They both understood this whole internal ballistic equation more than all the others I talked with. This is because they worked on internal ballistics in their real lives, used state of the art test equipment to perform actual tests and record the actual data. They are true subject matter experts and both of their views points and explanations were very similar. A slight twist here and there and different approach but there test data and conclusion were the same. A lot of folks claim to understand all or part of the internal ballistic equation, but these people had the hard data to back up there statements and claims. I like solid test data and not opinions on what someone believes.
As I stated Stan and Mike Rock gave me some of the most detailed explanations on barrels and internal ballistics. Both were ballistic engineers and both have degrees in metallurgy (Stan has an masters in metallurgy); Mike was a ballistics engineer for the US Army for many years at the Aberdeen Proving grounds. When Mike worked at Aberdeen, the US Army used high speed bore videos with mirrors, thermal imaging and computers to analyze any and everything that happens when the firing pin strikes the primer and the round goes off. While working as a ballistic engineer for Raytheon Stan used similar equipment and processes to view and record internal ballistics though most of his work was focued around the .50 cal.
Before we begin take a step back and be objective. Ask yourself what you are trying to really accomplish by breaking in your barrel. What issues and/or problems inside the barrel need to be corrected or fixed? Now I do recommend cleaning your rifle after you purchase it to clean out all of the junk, oils and grease from the factory before shooting it, but also realize...
• 99.9% of shooters don’t have access to a quality bore scope to view the interior surface of their barrels.
• Without a bore scope to view the interior surface of your barrel what exactly are you trying to fix by a shoot and clean process?
• If there are burrs or machine marks from the machining process in the chamber, throat or barrel where are they located?
• Do the machine marks run parallel or perpendicular to the barrel finish?
• If there are high points and low points inside the barrel again where are they located?
• Does shooting and cleaning between rounds correct/fix all barrel imperfections if they exist? If yes how?
• Without a bore scope again you have no idea what the actual condition of the interior barrel surface
• So far if you don’t have honest solid answers to these first few questions and you’ve been performing a barrel break-in process you’re working off a SWAG (scientific wild ass guess)
Couple more questions while I still have your attention.
• Pushing a cotton patch with solvent or a bronze brush down the barrel will do what to remove a 416 stainless steel or chromemoly metal burr or machine marks?
• Last time I checked, 416 SS or CM is much harder than a cotton patch or bronze brush and is most likely impenetrable by most bore solvents.
• Yes it will remove copper fouling caught by the metal burr, but how will it remove the metal burr?
• How many shots will it take to remove the burr or imperfection and how will you know when the barrel issues have been corrected? Is it always x-amount of shots?
Let's take a few minutes to gain a basic understanding of internal ballistics and what really happens when you pull the trigger. This will also help you to understand why you don't want to clean after every shot.
High level view of Internal Ballistics 101:
When the firing pin strikes the primer, the propellants in the primer ignites. With this initial ignition there may or may not be enough pressure to dislodge the bullet from the case (this depends on neck tension and seating depth as well as a few other variables), if there is enough pressure to dislodge the bullet, it moves forward into the lands where it stops. As the primer ignites the powder, more pressure builds moving the bullet forward where it can stop again. Once there is enough pressure from the round going off, the bullet is moved down and out the barrel. All of this happens in nanoseconds (billionths of a second). Your bullet starts and stops as many as two times before it leaves the barrel. This is fact. Bet you didn’t know that…….neither did I!
Internal Ballistics on the brass case:
As the primer ignites the powder, pressure begins to fill the brass case. As the pressure builds the case expands to completely fill the chamber sealing off the chamber and preventing any gases from leaking around it. The pressure will also cause the brass case to move rearward pushing it flush against the bolt face. In addition the shoulder and neck area of the case will be force forward into the shoulder and neck area of the chamber. All of this pressure will have elongated and lengthen the total size and diameter of the brass case. As the bullet is moved down and out the barrel, the chamber and barrel pressure drops. The brass begins to cool and contract allowing the brass to be extracted from the chamber.
Internal Ballistics on the bullet:
As the bullet is forced from the case, it can only support a small amount of force. The force on the base of the bullet will cause it to expand. As more force is applied the bullet expansion will increase from the base of the bullet towards the bullet nose. Basically the bullet begins to stretch. In addition the bullet enters the lands and grooves of the barrel. The bullet will engrave itself to the lands and grooves as it proceeds through the barrel. The throat of the barrel takes on the majority of stress from the heat and pressure created from the firing of the round. This is why the throat area of the barrel is always the first point of barrel deterioration. Depending on the round being fired the flash point of the round going off can cause instantaneous burst in temperature upwards to 4000 degrees Fahrenheit and create a pressure spike upwards toward 60,000 PSI’s.
Why thorough cleaning between rounds is not good for a barrel:
Think of a car engine for a moment. Why do we use oil in the engine? To prevent any metal-to-metal contact as well as reduce friction between two metal (bearing) surfaces. Your barrel is no different from the engine. If you clean every round or every few rounds during your barrel break-in process or clean your rifle so well after shooting that you take it down to the bare metal, you’ve created a metal-to-metal contact surface for the next time you shoot the gun. So what’s the problem with this you ask? Just like your car engine, metal-to-metal contact will cause friction which can sheer away layers of metal from each surface. So if your bullet is starting and stopping as many as two times before it leaves the barrel, that’s two places for metal-to-metal contact to happen as well as the rest of your bore. Even though copper is a gilding metal it can still sheer away barrel surface in the bore when traveling at high velocities under extreme heat and pressures.
Remember it is these copper jacketed bullets passing down the barrel at high pressure and velocity that will ultimantly be the source of smoothing out those rough marks left by the chambering tool and machining process. The more bullets passing down the barrel will help smooth the barrel not cleaning it between rounds.
Cleaning between rounds especially thorough cleanings can take you back down to bare metal which can actually harm your barrel. In addition all this cleaning, done improperly with cheap bore guides and cleaning rods can scratch and damage the interior surface of your barrel. This was very prevalent in the barrels we looked at through Speed’s video bore scope. To preserve your barrel you need to avoid cleaning down to bare metal. A light wash of copper fouling in the barrel is not always a bad thing, as the copper fills in a lot of the micro groves left by the machining process. You don’t want layers of copper which effect accuracy, but filling in the micro grooves can be a good thing.
So what do we need to really take care of our new rifle and/or barrel?
According to Mike Rock and the other barrel manufactures agreed, all you need to avoid this metal-to-metal contact is a good burnish in the barrel. Some barrel manufactures will void your barrel warranty if you shoot moly bullets. This is not to say that moly is necessarily bad for a barrel, but it can be when applied to bullets. Never shoot moly coated bullets as they are bad juju for the throat of a rifle.
There are numerous ways to achieve a good burnish in your barrel such as just shooting a long string of rounds without cleaning. I like Mike Rock’s method and have been using it on all my match grade and factory barrels.
When Mike re-barreled my tactical rifle with one of his 5R barrels, I talked with him about my new barrel, any barrel break-in process and how to get the best performance out of my new barrel. This is what he had to say. When he makes a new barrel, he hand laps the barrels with a lead lap. Most if not all custom barrel makers hand lap their barrels. Mike takes his barrels a step further to provide a pre-burnished finish. He uses two products from Sentry Solutions. One product is called Smooth Coat, which is an alcohol and moly based product. He applies wet patches of Smooth Coat until the bore is good and saturated and lets it sit until the alcohol evaporates. The barrel now has loose moly in it. Next he uses a second product for Sentry Solutions product called BP-2000, which is a very fine moly powder. Applied to a patch wrapped around a bore brush, he makes a hundred passes through the barrel very rapidly before having to rest. He repeats this process with fresh patches containing the moly powder a few more times. What he is doing is burnishing the barrel surface with moly and filling in any fine micro lines left by the hand lapping. He then uses a couple of clean patches to knock out any remaining moly left in the bore. He also included a bottle of each product when he shipped my rifle back which is what I’ve been using on all my other rifles.
With the barrel burnished with moly, this will prevent any metal-to-metal contact during the barrel break in process. My instructions for barrel break-in were quite simple. Shoot 20 rounds (non-moly bullets) with no cleaning, as this will further burnish the barrel. Done! Now shoot and clean using your regular regiment of cleaning and if you have to use JB’s or flitz type products, go very easy with them as they can clean the interior barrel surface back down to bare metal removing your burnish. Never clean so well you clean back down to bare metal surface.
He said most of the cleaning products do a great job, don’t be afraid to use a brush and go easy on the ammonia-based products for removing copper fouling. Basically don’t let the ammonia-based products remain in the barrel for long lengths of time.
What’s my cleaning regiment you might ask? I’m not one who puts his firearms up without cleaning them; it’s what I was taught growing up. I'm also not one who wants to spend a lot of time and effort cleaning so my process is pretty simple but highly effective. I use only a Lucas bore guide and Dewey cleaning rods, something I learned from Speedy. Most other bore guides will allow your cleaning rod to flex inside the barrel which can scratch the barrel surface...not a Lucas bore guide.
I clean my rifles using WipeOut Accelerator and WipeOut foam. I use a few patches soaked in WipeOut Accelerator just to push the bulk of the gunk out of the barrel and then give it a shot of Wipeout foam. Let sit for 3-hours or so and patch it out. If I know it will be a few weeks before I get to the range or lease I’ll run a single patch of kroil oil down the barrel followed by a couple of dry patches. The process is quick and simple and works well for me. I have one barrel on my sons Win Featherweight where we need use a nylon brush with a little JB’s to get most of the fouling out as it’s a stubborn factory barrel. I’m considering using Tubbs Final Finish on this barrel.
For badly fouling factory rifles, I know of quite a few folks who have used Tubbs Final Finish with very good to outstanding results. TFF are lapping compound impregnated bullets you shoot down your barrel which can really help smooth out and polish a factory barrel.
I’ve used my buddies bore scope quite a few times to see just how clean my process gets my rifles. My Bartlein and Rock barrels hardly ever foul so I rarely if ever see any copper fouling in those barrels. My DPMS and Tikka both show very light and faint traces of fouling here and there after cleaning. I figure that fouling is just filling in some of those micro grooves as well as I know I have a good burnish in the barrel and I don’t give it a second thought as they all shoot lights out!
I hope that helps folks to understand what I’m trying to say.
Jeff in TX
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Ven 28 Déc 2012 - 21:46
