Barrel Break In - Some Views on Properly
( Discuss this article and other barrel break-in considerations here. )
The old and common adage “if something works, don’t fool with it” is perhaps nowhere so prevalent as in the world of manufacturing. Justifiably (in some cases) proud of their products’ reputation the ad men will loudly, and at some length, proclaim the virtues of their chosen raw material, even though it is in reality a common off-the-rack line item, and sold by the pound or the ton. The rifle barrel business is no exception. “4140 chrome – moly steel” does have a nice ring to it, and fits quite nicely into a promotional spiel.
On the other end of this equation we find the quality obsessed R and D type who will fine tune and continually “tweak” his metallurgical formulation on a batch to batch basis. Based on his lab testing and “in the field” performance Ernie Stallman, up at his barrel works in Bristol, Wisconsin is a classic example of this breed. Deletion of those alloying elements contributory to “burnout” has been a key factor in the renowned longevity and performance of his superior barrels. His unique specification alloy steel, hot rolled, quenched and tempered, machine straightened double stress relieved is, from the mill, anything but a line item. Double de-gassing, in the crucible, deals with austenite in vapor form. (NOTE: In simple terms, an austenitic structure would be a desirable characteristic in a casing for an artillery shell or grenade casing … this is the last thing one would wish to see in a rifle barrel). The double de-gassing eliminates 92% of this phase, as performed at the mill. We can note, at this point, that Badger Barrels specifically requests that no cryogenic treatment be performed on their product. Your new Badger Barrel has already received an in-house cryo-treatment. (at ? º below 0º F) the 8% austenitic structure is fractured and a subsequent “heat soak”, at 760º F. ensures refinement of a tough, ductile martensite grain structure. (NOTE: In simple terms, a martensitic structure would be a desirable characteristic for a truck axle, or a fine wrench). Volumes of material are available on this subject, for those interested. This is but a “thumbnail sketch”, in the broadest of terms, and should be regarded as such. To put this in a nutshell: stress relief, taken to a very advanced level, is a vital pre-cursor to deep hole drilling and rifling. This superior raw material, and superb precision machining practice implemented in a “for shooters, by shooters” company mindset combine to give us barrels that, in this scribes humble opinion, are far superior to that produced hitherto … anywhere, anywhen. As far as fine, accurate rifle barrels go, these are the good old days.
Jacketed Bullet Break In … Some Whys and Wherefores
In predictably infrequent discussions with Mr. Stallman, I’ve developed a healthy respect for his application of metaphor in discussing metallurgy, machining, and rifle barrels. I’ve also come to realize that he’s developed his unique and amusing syntax by way of illuminating dark and mysterious areas for his customers. Here are a few particularly interesting examples:
· Cut rifled - “Marble” - Since the grooves are generated by a chip forming process, a very tough, tenacious and durable material can be used. With proper stress relief practice, little or no stress is induced during the rifling process.
· Button rifled - “Clay” or “Bread Dough” the chosen raw material must have a certain amount of malleability, with work hardenability occurring as the button “irons” in the grooves. An unavoidable by-product of this process is a certain amount of included “hoop stress.” When excessive levels of this sort of stress is present we encounter a barrel that “won’t settle down.”
Well, this brings me to a point from which I can, safely and in sincerity, make a declarative statement … having a bore scope in one’s hand does not necessarily empower one with the ability to interpret, or understand, what one is seeing (or thinks he is seeing.) Quite a few hours should be invested in the inspection of as many barrels as one can get his hands on before making any claims whatsoever … and one should be shooting, cleaning, and inspecting these barrels as the curriculum evolves.
For an investment no larger than that involved in a scoped factory sporting rifle, one can procure a fine quality bore scope. This is great, a fantastic asset for any dedicated rifle nut. Sadly, there are those who, shiny new toy in hand and with no study or practice, don the mantle of expert (self appointed, what?). Beware their dissertations and extrapolations, unfounded in good technical knowledge. This is not to say that the application of these now readily available bore scopes hasn’t generated some really fine text … it has. (Read Brian Pearce’s excellent work “Barrel Break In … Pros and Cons” Rifle magazine, Wolfe Publishing, July 2004).
In brief, Mr. Pearce based his article on his jacketed bullet break in procedure (and research) with a new badger barrel C. Sharps ’74 Sharps as his test bed. He wrapped black and white pieces of tape around the bore scope recorded the radial orientation of “flaws” or perceived asperities and periodically examined them as the break in went forward. Through the progression he watched the referenced “flaws” disappear (Were they “flaws” or simply “contradictory marks” in the fresh lapped “soft and fluffy” surface?) His thought provoking and well written article is worth reading.
In counterpoint we should all simply remain aware that some bogus data has circulated as well, be it in text, chat room or rumor mill venue, that was generated by unqualified evaluation of visual imagery. Let’s let it go at that.
I’m going to pick up the shoot one round, clean, and cool between shots practice pre-assuming that the reader has the basic nuts and bolts of this procedure already under his belt. Let’s bat some of it’s finer, and perhaps not readily obvious, points around.
Jacketed bullets … can you “lap” a bore with ‘em? Well, not really. Some surface enhancement will take place with successive shots as the “fluff” is longitudinally burnished forward and any contradictory marks will disappear. In terms of machining process vocabulary this is not a lapping process. In point of fact, I think I’m shaky at calling it a burnishing process (where one expects the burnishing tool to be harder, and smoother than the workpiece). Suffice it to say that some re-orientation of surface micro features takes place longitudinally, on a breech to muzzle axis, and this is probably best defined as burnishing, albeit subtle, and very gentle.
What about all those “scratchy” looking longitudinal marks I see in these big bore (40 cal. and larger) barrels particularly the BPCR barrels? … The “scratchy marks” are there by design, the bigger the bore, the coarser the grit designated as final lapping grade. You’ve got to have room for bullet lube. The mirror finish, glass smooth surface you see in minty originals are the result of paper patching, which will polish a bore. Experience has shown that this finish will lead foul to a higher degree than the courser finish.
How does the jacketed bullet break in relate to the throat and leade area of my new or rebarreled rifle? Is this part of the equation? Yes, emphatically so … particularly in the custom alloy formulation of a Badger barrel. As stated before (“Big Five in Cartridge Rifle Accuracy … a Quality Barrel”, July 2003). This is a work hardening material, and demands sharp tooling. One thing anyone who works regularly with this material will observe is that, when cutting in an exterior dovetail, a tendency for this tough material to roll up a burr, or wire edge at the cutter exit surface; e.g., the downside of the cut. Now, on the exterior surface, removing this little bugger is a snap, you can bust it loose with your thumbnail. Well, suppose that the reamer used to chamber your new rig was a bit tired, and not perfectly sharp, or that it was also infed too slow, at too slow an R.P.M. The downside of the lands in the leade area can also roll off into these wire edge burrs. And gettin your thumb in there to snap ‘em off don’t seem practical, does it? While this particular “flaw” in a chambering job should not be encountered regularly, that is, the use of brilliantly sharp reamers being assumed, and with correct application of cutting fluid, feeds and speeds … Mr. Stallman nonetheless advises that he sees “problem barrels” with this flaw all too often. (And I don’t blame him for getting a bit aggravated about it, I would to!) You know guys, that a barrel maker can’t be expected to take responsibility for poor machining practice performed offsite, but apparently there are those that see this differently. That little rant executed, I’ll get back to the issue at hand … minor asperities in the downside of the leade. Remember you can snap these off, cleanly, can you but reach ‘em. The bullet jacket material on your break in slugs will engage these micro burrs and clean ‘em off. I view this as probably more critical to good performance than tidying up contradictory marks. I reckon a couple of matches takes perfect care of that issue.
I hope this has gotten your attention, and that you’re really focused on this text because there’s one more really critically desirable benefit accrued by correct jacketed bullet break in. That old saw “as the twig is bent, so grows the tree” applies, in principal. The title byline “Educating a Dumb Piece of Steel” will apply. And if you care one whit about the mechanical/structural characteristics of your barrel, for its’ entire lifetime, right down at a basic metallurgical level, well, that too will apply. I do believe that this is the first time this material appears in a firearms publication, and will do my best to present it in a coherent fashion.
Home Registration … What on earth does that mean? … Your new, fresh, “soft and fluffy” “dumb” Badger barrel has been double stress relieved and, you might say, is in a very relaxed and laid back condition (my kinda metaphor). Your shoot/clean/cool break in protocol will “wring” the barrel on its’ bore axis. The drag coefficient of a jacketed slug, by its very nature, induces a more violent action. This is exactly what we’re after controlled violence, correctly applied. (A bit like our current global situation, what?) The one thing we distinctly, and emphatically do not want during this phase is heat. Keep things as cool as you can, and reap a substantial and lasting reward. Methodically wringing the new barrel, and its’ subsequent “snap” back to “home registry” on bullet exit are the basic curriculum of educating your dumb barrel … it will only have to be taught this once and, from an accuracy stand point, it is a lesson well learned. After Home Registry is established you will be able to shoot extended, rapid fire groups, with no changes in point of impact. Should you disregard the recommended protocol, and overheat the barrel during it’s initial training phase, the insulative quality of your fore end will cause localized excess heat on the lower radius. This will most certainly lead to a barrel that, ever after will unkink, and “walk” its’ groups. Remember, by keeping temperatures low, that at an almost mystical internal level (martensite crystalline structures settling comfortably into a ferrite matrix) your new barrel is settling down for a long hard career of good work. By patiently and correctly applying the break in procedure, you are taking responsibility for the final metallurgical refinement of a piece of brilliantly engineered and formulated American alloyed steel. I would ask at this point: Do you really want to second guess the fellow that engineered this material, and than created your great barrel from the raw billet? … I for one intend to meticulously and diligently follow my manufacturer’s instructions on break in, I reckon he knows what he’s talking about.
Footnote: Hoping that in some small way I’ve been able to illuminate a hitherto dim and murky area, I’ve got a little bit of additional cautionary advice. There are a couple of other ways that one might involuntarily induce unwanted stress in a fresh, new barrel. Actions like the ’74 Sharps and flat-spring high wall require substantial dovetails on their lower barrel flat or radius, for lever and action spring and fore end blocks. A good, very snug fit is the ticket here. Overtight fit-up, requiring lots of force to drift blocks into place is just asking for trouble. A “stress raiser” in this zone could very well see a flawless chamber neck pulling out of round upon heating. Likewise, interference fit in front sight dovetails should be precise, not overtight. Obviously, any drilling and tapping operations (for fore ends or scope blocks) should be well tooled and characterized by precise depth control leaving adequate barrel wall on completion. “Involuntary gas ports” can be a source of some embarrassment.
Remember, any new rifle barrel will benefit from proper jacketed bullet break in.
Ernie Stallman … Thanks for the hours on patiently “wringing this out” and your invaluable input in putting this together. Particular thanks for your unique metaphor.
Dave and Skip at Buffalo Arms: Thanks for your bottomless well of patient advice, freely distributed to all the great players in this great game, newcomer and old pro alike. Thanks particularly for the great brass and your sage advice “work with the chamber”.
Dave at Pacific Tool and Gage: I know we drive you nuts with all the wacky, off the wall, variegated chamber specs. Maybe someday we’ll come close to standardization (but I wouldn’t hold my breath.) For the time being, thanks for the great reamers.