Barrel break-in do you or dont you?


Sep 10, 2006
This is posted with permission form a member of the "Texas Predator Posse" message board. Thought he made some interesting points and sounds like hes done some homework. Let the debate begin. :) I'm not weighing in one way or the 'tother. CL

"Barrel Break-in, internal ballistics, the use of Moly Coated Bullets and Fire-Lapping Compounds

Here's some research I did back in 2000/2001 time frame which I've updated here and there. This is not an end all, solve all paper on barrel break-in and internal ballistic, but it was written to give everyone a better understanding of what really happens when you pull the trigger.

Quick Note: This post has appeared on many hunting and shooting boards and web sites in the past and has be modified by myself as well as others who have asked permission to post it on there site. What prompted me to do this research was the fact that I unintentionally destroyed a brand new Shilen SS select match barrel in under 400 rounds shooting moly bullets.

I’ve spent a lot of time reading and talking with members on many different shooting boards about barrel break in procedures, shooting moly coated bullets and trying to fire-lap a barrel shooting impregnated bullets. Conclusion, what works for some, doesn’t work for others and some of the stuff out there theoretically, technically just can’t work. Being an engineer, when it’s broke or you don’t understand something you talk with real subject matter experts, use manufactures specs and schematics and look for real hard test data to support their conclusions. I’m not much for opinions and hearsay.

In the process of researching this subject I talked with 4 metallurgist, benchrest hall of fame shooter Speedy Gonzalaz, Doug Shilen at Shilen Barrels, Mike Rock of Rock Creek barrels, Stan Rivenbark retired ballistic engineer for Raytheon, and a couple of techs at Hart Barrels. Being an engineer I stuck with the folks who could give me hard facts and real test data to back up there claims. From a scientific/engineering point of view, all of the subject matter experts said pretty much the same thing.

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.

A lot of barrel manufactures state the need for a breaking in a barrel, but when you ask for actual test data they don’t have any. Then when I asked how they came up with their barrel break-in procedure, they said this is what they’ve come up with by testing lots of new barrels. For some reason they don’t like it when you keep asking re-clarifying questions they don’t have answers for. I’m not saying there not knowledgably barrel makers as they are. They build some of the top barrels in the country.

Some barrel manufactures have now tired to re-clarify there 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 this statement except that the fact a cotton patch 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 was cut.

Speedy Gonzalez was a wealth of information as were the techs at Hart barrels. As Speedy says, “my $3000.00 video-bore scope doesn’t lie”. Not to mention he’s local to me and I’ve seen lots of barrels in his shop that have been ruined by various methods…mostly moly bullets.

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 at Raytheon and Mike Rock of Rock Creek Barrels builds some of the best barrels in the country. They both understand the 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 approachs 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 real scientific 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 the most detailed explanations on barrels and internal ballistics. Both were ballistic engineers and both have degrees 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 Army used high speed bore videos with mirrors, thermal imaging and computers to analyze any and everything that happens when the firing pin hits the primer and the round goes off. When the primer ignites there is enough pressure to move the bullet forward into the lands. The bullet then 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 out the barrel. All of this happens in nanoseconds (billionths of a second). Your bullet starts and stops at least twice before it leaves the barrel. This is fact. Bet you didn’t know that…….neither did I!

Think of a car engine for a moment. Why do we use oil in the engine? To prevent metal-to-metal contact and reduce friction between two metal 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 sheer away layers of metal from each surface. So if your bullet is starting and stopping at least twice 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 metal in the bore when traveling at high velocities under extreme pressures. Cleaning with products such as JB’s and Flitz can clean so well they can take your barrel down bare metal. To preserve your barrel we need to avoid cleaning down to bare metal.

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. More on moly later.

When Mike rebarreled my tactical rifle with one of his 5R barrels, I talked with him about my new barrel, the 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. He then uses two products from Sentry Solutions, a product 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 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.

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. This will also help smooth out the transition from the chamber and throat area. 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, or better yet avoid them. Never clean down to bare metal

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.

Moly coating and Fire-lapping a bore

This is one of those topics that just doesn’t hold water in my book. You theoretically and technically can not moly coat a bore with moly bullets and the same holds true for trying to fire lap a bore with impregnated bullets.

Think about this whole process of treating a barrel with coated bullets logically for a moment. A bullet is only so big and when compared to the surface area of the inside of barrel it’s really very small. Now let’s take it a step further. The contact surface of the bullet that will come in contact with the inside of barrel is even smaller. So you want to treat the inside of your barrel with moly using a bullet with an extremely small contact surface. Folks it doesn’t take an engineer to do the math and see this is going to work as prescribed. This is like trying to wax your entire car with just a very tinny dab of wax and starting over at the exact same place each time you apply more wax to applicator. You just can't cover the entire car, but you get a nice wax build up at the starting point.

The same thing happens when trying to moly coat your barrel with moly coated bullets. You get a nice moly build up right in the throat area and not much moly beyond that

Fire-lapping could and probably would help factory barrels. It would help polish the throat area of the barrel as well as smooth out some of the rough surfaces that a inherent to factory barrels, but I see it as a waist of time with a hand-lapped custom barrel

Moly Bullets – Bad barrel Ju Ju?

When I first researched moly bullets in a barrel, I concluded they weren’t bad Ju Ju for barrels. I jumped on the band wagon with everyone else. I’m not sure where I went wrong as I faithfully used Walt Bergers cleaning method for shooting moly bullets. I toasted that new barrel in less than a month. Speedy Gonzales really helped me understand just how I screwed up and my mistake is something he sees all he time when looking through his $3000.00 video bore-scope.

The reason I ruined my new Shilen SS match grade barrel with less than 400 rounds of moly coated bullets was really quite simple once I understood what happened. When your round goes off, moly comes off the contact surface of the bullet in the throat area of the rifle and is bonded to the barrel due to the excessive heat and pressure. Were not talking coated or adhered to, we’re talking bonded to. In addition, add carbon fouling and some of the copper jacket from the bullet to the mix. Follow this up with another round and you’ve now embedded the carbon fouling and copper jacket between layers of bonded moly. This is the beginning of the black moly ring, which ruins countless barrels and is so hard; it can hardly be scraped off with a screwdrivers corner edge.

When I first research moly bullets there was no product that would dissolve bonded on Molybdenum Disulfide (MoS2) without destroying your barrel steel. However I have since read of some organic cleaners that now claim to dissolve MoS2, but won’t touch the copper or carbon or bonded on moly. Most cleaning products will remove loose moly from the barrel, but not touch the bonded on moly. Some moly users say they brush it out when they clean their rifles. Without looking through a borescope, how would you know? Doug Shilen at Shilen barrels cut the throat section out of my ruined barrel to see the specific damage once he determined it was toast. He could barely scrape the moly out with the sharp edge of a screwdriver on the barrel I ruined. I could have scrubbed with a bronze brush for days on end and I wouldn’t have touched it.

I think moly shooters have a better understanding now of moly coated bullets and how to clean their barrels without getting the black moly ring in the throat area. I also believe they use moly coated bullets for accuracy reasons more so than trying to moly coat the inside of the barrel. But there are probably more moly users who haven’t figured out the right way to work with moly and destroy their barrels much in the same way I did.

So to conclude, for all this barrel break-in non-sense (as I see it) all that is really needed is a good burnish in the barrel. Factory barrels may need more work or more rounds down the tube and some are so bad nothing can help them. A good custom barrel that has been hand-lapped should take little effort to settle in and shoot well.

There’s a lot more to this but I hope this sheds some light on the situation.



Distance is not an issue, but the wind can make it interesting!

Mathew 5:16
I have never broken in a barrel. My guns shoot great though.
I have a ritual, guess you could call it a break in.

-Clean the bore with Iosso very well (can not believe how dirty they are from the factory.

-Fire a round, clean barrel and let cool, repeat for 10 shots.

-Then fire for groups :grin:
When I get a new rifle whether a custom (I own six of them with shilen and Lilja barrels) or factory I shoot at least 20 rounds and have shot as many as 50 before cleaning. The bullets will break in the barrel. Even then I clean lightly and I agree with the article and I never use moly bullets. Great stuff, thanks for posting it. Of course it will not register with some because there is a lot of tradition and hear-say in the shooting world.