Electropolishing & Fire Lapping

When I first came on board as the Armorer for the Army Reserve Marksmanship Program I machine rest tested 135 A2 National Match uppers. The results made my jaw dropped to the floor. Only 39 of them would shoot MOA. I seriously questioned my sanity in getting talked into accepting such a project given the hand I had been dealt. 96 of those uppers were very sick! On top of that, we had no replacement barrels and our budget couldn’t afford that many barrels at one time.

On taking throat gauge readings and bore scoping those 96 it was immediately obvious that hardly any of them were really shot out. They just weren’t shooting well. Either those 96 barrels were born bad or something else was wrong with the guns that kept the barrels from giving the accuracy they were born with. I briefly toyed with the notion of sending some of the barrels back to their manufacturers to have them go over them and see what was wrong.

The Army Reserve contracted with a competing team for maintenance support and it was obvious that the uppers had a hodgepodge of barrels on them. The uppers were serial numbered so I contacted those folks and asked if they could provide a list of what brand of barrels were on what uppers by serial number. I was told they kept no such records, removing any hope about getting support from the barrel makers. I called them "mystery barrels" and the phrase seemed to catch on with the shooters.

This also convinced me to keep good records, which has been one of the keys to my success in research and gunsmithing along with my experiences as a shooter using government firearms that flat weren’t built right gave me the motivation to try extra hard to help my shooters. Given my lack of funds and the need to get the uppers shooting better I instituted my "Upper Quick Fix Program." The program combined hard work and ingenuity using low cost methods.

One part of this was covered in "The Relationship Of Barrel Extension Diameter To Accuracy In The AR-15" (March and April 2013) about properly mounting the barrel extension in the upper receiver. My initial attempts involved the use of Green Loctite #620 to coat the barrel extension and the inside of the upper receiver during assembly. That alone resulted in an 18.6% average reduction in group size. Best of all it didn’t costa dime other than a lot of man hours of labor on my part.

Since I was getting paid a very modest flat rate rather than a normal hourly stipend that was a real good deal for the Reserves. I later improved the process to add thin shim stock around the extension in combination with the Loctite, doubling the effectiveness. Later, I worked with BAT Machine on an improved match barrel extension in incremental sizes replacing skinny, low-bid stock extensions and shim stock.

Using the improved processes and parts I am currently realizing about an average reduction in group sizes of 35% compared to normal rushed assembly techniques practiced by other gunsmiths in the AR business. Another fix was "Gas Tube Alignment" (March 2014) based on finding uppers with gas tubes either in contact with the float tube or not in alignment with the bolt carrier key, resulting in fat groups and lots of fliers. Again, the only cost to fixing the problem was sweat and long hours.

In "AR-15 Upper Quick Fixes: Match Bolt Carriers" (May 2014) there was some fiscal expense to substituting these for regular carriers, second in cost after electropolishing. The average accuracy gain was 8.8%. Since that article was published I have been further improving the alignment of the bolt carriers using Anti-Tilt Pads, shrinking groups an additional 14%. Combined with the match carriers, total accuracy gain is about 20%.

When I started getting budget money I included electropolishing the bores of poorly performing barrels along with fire lapping. During my decade as Team Armorer, I fully cut the group sizes of the guns in half and every one of the uppers would shoot sub-minute with preferred ammo. Electropolishing As I was bore scoping those 96 sick uppers I noticed a fair number of them were rough as a cob.

You flat can not pick a good barrel just by eyeballing barrels with a bore scope, however, you can identify a barrel that is likely to shoot poor. Examples are when you see pitting, especially near the crown. Another good predictor of poor performance is when the lands at the back of the barrel in the throat area are uneven in their start points. This is usually an indication of cleaning rod damage and it allows bullets to tip off center when starting down the barrel.

Such a bullet will be boogered and will never straighten itself. Heavy fire cracking at the back of the barrel can sometimes point to a barrel soon to go out. Another less reliable indicator are barrels that appear rough like some of the ones I was identifying. Don’t get me wrong, I have had some really fire cracked and ugly looking barrels shoot well but their percentages in the whole population would have been less than ugly barrels that shoot poorer than average.

The theory is that the rough barrels tear at bullets and tend to foul more, degrading accuracy. Barrels that are poorly

broken in also exhibit some of these tendencies and I don’t think there was much attention before I came on board as Armorer to proper barrel break-in. Some barrel makers lap their barrels one or more times in an effort to polish out some of the roughness to try to eliminate these potential problems. Such barrels normally cost more but shoot better. I break-in every barrel I sell or install. You can throat gauge this, air gauge that, and gauge something else.

You can look in bore scopes till your eyes bug out but the only way to know if a barrel will shoot is to shoot it! Whether in a machine rest or from the bench rest with sand bags you must shoot it to know for certain what its current capabilities are. Barrels never got the memo that they are supposed to quit performing at some arbitrary round count. Nor did they get the word that when they grow ugly they are supposed to start shooting fatter groups.

They are very much individuals and don’t necessarily follow our expectations. I selecting barrels for various treatments by shooting them on a machine rest and not because they were just ugly. Then I chose some of the ugly ones to try fixing by electropolishing or fire lapped. Back in the early 2000s there were two ways to polish rough bores that hadn’t been factory lapped. The first was called electropolishing and was done by Black Star down in Texas.

They used an acid in the process and the environmental police just made it so costly for them to store and dispose it that they are no longer offering the service. Having a barrel electropolished at the time likely ran 1/2 to 1/3 the cost of replacing a barrel. They also purported to perform the polishing in such away as to end up with a gradual taper to the bore. It would be slightly fatter at the breech end and more constricted at the muzzle.

It has long been a barrel accuracy theory that such a taper enhances grouping performance. I only sent a few of my very worst barrels on the trial run and they came back improved. As I became more confident with the results I increased my shipments. I ended up with a very noticeable 18.9% average improvement from the process. You could easily see in the bore scope how polished and smooth the finished product looked. Electropolished bores seemed to foul less and clean up considerably easier.

In 2005 Sierra came out with their 90 grain boat tail bullet for the AR- 15 and I started evaluating it in early 2006. The jacket on the bullet was too thin and I discovered that many of them would blow up on the way to the target. Sierra still credits me for being the first reliable reporter of the problem but before long nearly everybody that shot the bullet had the dubious experience.

In trying to make the bullet work I considered Black Star’s electropolished smoothed bores and hoped that the process might also make barrels more "Sierra friendly." I had just received shipments of barrels for 90 grain loads and split each shipment in half, keeping one as a control group and sent the others to be electropolished. These barrels consisted of 1:6 twist Douglas stainless, 1:6.5 Krieger chrome moly, and a mix of 3 and 5 groove polygonal 1:6.5 Pac Nors in both steel types.

Since we were new to 90 grain bullets I also split a shipment of 1:8 Walther stainless barrels purchased to shoot 80 grain bullets. Part of the results were expected. The incidence of thin jacketed 90 grain Sierra Match King blow ups went down but didn’t cease. I also found polished bores allowed me to use 0.3 more grains of powder. The surprise was no accuracy improvement over non-electropolished barrels.

This was the first time I had send brand new barrels to Black Star instead of poorly-performing mystery barrels. The conclusion I came to was that the electropolishing process was an effective repair tool but a waste of money except for lowering Sierra 90 grain bullet blow ups and making cleaning easier. It is a moot issue now but most barrel makers will void any warranties if a barrel is electropolished. Fire Lapping As with electropolishing, fire lapping likely voids any warranty.

After exhausting ammo, assembly, and tuning tips, contact the barrel maker for their suggestion before resorting to fire lapping. Since I was dealing with mystery barrels I had nothing to lose. Fire lapping was about a third the cost and doesn’t involve shipping a gun or barrel. Purchase Final Finish bullets from David Tubb Superior Shooting Systems (davidtubb.com and load accordingly. The bullets are coated with an abrasive.

Starting with an immaculately clean bore, fire the most abrasive first and work your way down towards the finest, cleaning between each 10 shots of the fire lapping process (every time you change abrasives). At the end you clean again and test. My results averaged again in accuracy of 19.3%, almost the same as electropolishing. I have never proactively fire lapped a bore and based on my lack of success in doing so with electropolishing I doubt I ever will. If it ain’t broke, don’t fix it.

I have fire lapped about a hundred barrels and don’t recall of a single one shooting bigger groups afterward. I think that is a fair endorsement of the process. If you buy a quality barrel from a conscientious manufacturer that does a proper lapping job before it leaves the factory you shouldn’t find yourself in a position where you have to do the barrel maker’s job with abrasive bullets. After having tested several hundred

barrels and keeping good records I have discovered which barrel makers get it right at the factory and I only buy barrels from two makers now. Since switching to those two manufacturers several years ago I haven’t had to resort to fire lapping a single barrel! Make no mistake, you are sanding off metal during fire lapping. You can measure this in terms of throat erosion. I have seen some fairly scary increases in throat measurements taking readings before and after fire lapping.

Just like regular throat erosion from normal shooting, this is extremely variable by individual barrel. The button rifled barrel maker camp swears up and down that the steel they use is every bit as good as the steel in cut rifled bores. After having fire lapped a bunch of both I tend to question that assertion as a number of other people have. On average, I see way more forward throat advancement from fire lapping button rifled bores than I see with cut rifled ones.

I have also seen more need to perform the fire lapping to button rifled bores. I believe fire lapping can shorten the life of a barrel but to what degree depends on each barrel’s own characteristics. One of my shooters once said about barrel longevity, "If a barrel isn’t shooting well why would I want it to last along time in the first place?" I will take an improvement in accuracy over long barrel life every time without hesitation.

I have heard of a few people advocating fire lapping to replace a normal barrel break-in. I have never tried it but am hesitant. Fire lapping will obviously move the throat forward more than a conventional 10 shot break-in and recommend that first. After a conventional barrel break-in give a barrel at least 200 additional rounds of "seasoning", cleaning frequently. Avoid getting the barrel hot during that initial period of service.

It often takes that long to shoot off gas port burrs, finish the burnishing process, and wear down the angular tool marks from the reamer at the back of the barrel. Sometime after that 200 round seasoning, call it an extended break-in period, is the time to determine if a barrel is shooting badly enough to warrant afire lapping. For you grown ups with AR-10s, Final Finish bullets are also available in .30 and other calibers.

You can also get .22 LR ammo loaded with fire lapping bullets in case you get a rimfire with a rough bore. Army Contracting stuck the USAR Shooting Team with some dedicated .22 LR uppers on a low bid purchase one time. They had barrels on them made by some folks who normally made muzzle loader barrels. They were rough as a cob and I fire lapped every blessed one of them.

The fire lapping, in connection with a lot of other work, resulted in a 31% reduction in group size which still didn’t make them "good" but it did make them "better". The folks that make the regular fire lapping bullets also make a throat maintenance bullet. The idea is to fire one or two of these rounds for every 100 rounds of normal ammo. As a military armorer that wasn’t practical because the guns were normally issued out and distant from me.

I talked to the smart guys at Superior Shooting Systems and they suggested that I fire ten of the throat maintenance bullets as guns cycled through my shop for routine maintenance or work. I would clean the gun and then shoot a group or two with known ammo lots, then clean it again and fire ten throat maintenance bullets, then clean a third time and retest with the same lots of ammo as the first group.

The second test firing would always show a spike in accuracy even with good barrels that had been lapped at the factory when new. I performed that before and after test numerous times and am absolutely sure this works. I performed the throat maintenance on chrome lined bores that had already eaten through the chrome at the throat and it worked just like non-lined barrels.

I was always reluctant to use the whole fire lapping process on a chrome lined bore for fear of eating through the chrome prematurely Conclusion I think that somewhere early in our educations when we professional gunsmiths are taking "Gunsmithing 101" we are ingrained in the notion that if a gun isn’t shooting right to suspect the barrel first. Perhaps that is a good idea with some firearms designs but not necessarily with the AR-15.

I don’t want to the impression I fire lapped or electropolished every one of the barrels on the 96 uppers that my initial machine rest tests identified as being sick. Some uppers just responded to simpler fixes, however, I did end up with a large sample size that were either fire lapped or electropolished to have good statistical confidence in my results and the improvement percentages. A few professional gunsmiths steer away from fire lapping because it offends their sensibilities.

The technique doesn’t require an expensive four or five figure price tag for specialized equipment, nor is it controlled by a fancy CNC program. You don’t need to take a course at a community college or professional trade school in order to perform the process. Perhaps worst of all, even their customers can do it just as well. Isn’t it our job to make guns shoot better regardless of the method used? Techniques that occasionally take us out of our ivory towers aren’t necessarily a bad thing.

My goal, as always, is to help you achieve your goals. I hope this and my other articles help make ARs shoot better. In the mean time I am going to wear a disguise every time I am around any barrel makers as I suspect I have ruffled a bunch of feathers in their camp. Perhaps I had better do likewise when around my fellow professional gunsmiths because I have likely alienated a few of them also for suggesting a method as "crude" as fire lapping. So be it.

I mentioned in one of my previous articles that in former lives I have been a Tax Assessor, State Game Warden, and Drill Sergeant so I am used to having few friends and making people angry. AG