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About Factory TC Barrels

By: Mike Bellm

Part 1. Important points to consider regarding Contender barrels.

     Based on 23 years of barrel work, most of it reworking thousands of TC factory barrels, this page deals with basic concepts about various vintages of factory barrels as well as barrel by barrel considerations. Must reading before buying a barrel or having a barrel reworked.

     I am not a TC historian or collector. And dates of various barrel productions are at best recollections. Anyone that cares to correct me on the years of introduction of various features is welcomed to do so. What is important are the physical features of various vintages of production and how they may effect your decisions on buying factory barrels and/or having them reworked.

     General Points:

     BASIC POINT, inspect any barrel for pitting inside before investing any time and money into reworking it. I have had quite a few barrels pass through my hands that were badly pitted, and while I have re-chambered quite a few of them with good results, it is only prudent to start your customized barrel project based on a good interior. It is too easy to swap barrels and inspect barrels at gun shows, etc. to not start with a good barrel. And if buying a barrel online, ask for inspection privileges and the right of refusal if the barrel is pitted.

     Not knowing exactly where to start, let's start with current events that suggested this page.

     Lug Type and Locking bolts:

     From the introduction of the Contender in 1967 until about 1983, factory barrels had under-lugs that were flat on the bottom. Then somewhere around 1982-83 TC added an extra step on the bottom of the lug that increased the thickness of the lip below the locking bolts, thus making the lug a bit stronger and less prone to being bent down under the load of high intensity cartridges.

     It was sometime in about this same time frame that TC also went to the two-piece locking bolts. If a barrel has the one piece bolt, by all means change it out for two-piece locking bolts.

     The flat bottom lugs do not have the strength that is needed to be reliable with the higher intensity, larger diameter chambers. One might re-chamber one of these early barrels in .44 Magnum to .444 Marlin and get away with it. Certainly in the early days of hot rodding the Contender, this was done, and we got away with it... most of the time. But with the abundance of later production barrels with the stepped lugs, why take a chance?

     The flat bottom lugged barrels are ok for modest chambers, but larger diameter chambers loaded to the maximum the frame will handle should be done in barrels with the stepped lug. Where is the dividing line? Hot cartridges based on .225 Win brass and larger, including .444 Marlin and the various wildcats based on it and cartridges based on the .307 Win. case.

     Unless you overloaded the barrel, the flat bottom lugs should hold up ok to things like .30/30, .35 Rem., and probably 7-30 Waters. I still have a .250 Savage barrel I made years ago with the flat bottom lug... sprung & now loose on the frame.


     The earlier barrels were 10," and with few exceptions there really isn't much that is advised for these. Most of them are a step backwards when re-chambered to a larger capacity case. Some examples are .22 Hornet or .218 Bee re-chambered to .223 Rem., which is ill-advised in my opinion for a 10" barrel, .44 Mag. to .445 Super Mag or .444 Marlin, etc. .222 Rem. is marginal in 10" barrels and gives mixed results. It is still a bit more capacity than advisable in a 10" barrel.

     The .30 Herrett and .357 Herrett are best left as is in 10" barrels. I do extend the necks in these chambers to use full length .30/30 cases untrimmed, but this is mostly to shorten up/correct the throat in these barrels

     Things that do work in 10" barrels include re-chambering .22 LR to .22 Mag., .22 LR to .22 Hornet or .218 Bee.

     I re-chamber quite a few .357 Magnums to .357 Maximum in 10" barrels, and this does work out well. It is one 10" re-chamber conversion I do recommend.

     I also re-chamber 10" .32-20, .32 H&R Mag, and .30 Carbine barrels to my .30 Bellm 1.4" long cartridge for Illinois handgun deer hunters.

     Note: 10" barrels that have the front sight soldered on will not fit into the spindle bore on my lathe and must be run in an adapter in the steady rest. This adapter leaves marks where set screws hold the barrel and adjust it to center it up. Two marks are below the wood line, one is above. If you want to keep a barrel with the fixed front sight pristine, it is best I do not re-chamber it. Most of the octagon barrels are best left as they are.

     Rifling Configurations:

     Early production barrels were made from blanks produced by outside contractors, and generally were excellent barrels. These were typically 6 groove barrels, while TC still uses 6 groove .22 cal. barrels, both for .22 LR, the rimfire Mag. and .22 centerfire. The 6 groove 7mm, .30, and .35 cal. barrels were generally of better quality than the ill conceived 8 equal land and groove barrels that TC produced in house starting sometime in the early 80s I believe.

     Somewhere along the way during this period, there were quite a few .44 Mag barrels that were produced with groove diameters .440" in diameter.... yes, meant to shoot .430" bullets. I will repeat. There were quite a few barrels made with groove diameters .010" oversize! I have not seen any for awhile, and I do not recall now if they were 6 groove or 8. Seems to me they were 8 groove. If you have any doubt about an older barrel, just drop a .44 bullet down into the chamber and push it forward against the throat with a pencil or other soft object. Then hold it up and look through it from the chamber end into the light. If you can see a significant amount of light coming through the groove areas, I would suggest slugging the barrel to see what its groove diameter is.

     I have re-chambered quite a few of these to .444 Marlin in the past with no complaints about accuracy, but given a choice, I would suggest your .445 Super Mag or .444 Marlin customized barrel have a groove diameter closer to bullet diameter. Might be a good thing.

     Both the 6 and 8 groove .44 Mag re-chambered to .444 Marlin have been extremely accurate, often out shooting "varmint" calibers like .223 Rem.

     The 6 groove .30 caliber barrels had 1-14" twists and are what Don Bower recommends for his .30 Alaskan cartridge. He shoots bullets up through 165 gr. through this slow twist at long ranges, and it does well. Reports suggest that with heavy bullets at closer ranges like 100 yards, the heavy bullets may not be stabilized yet since these barrels are reported to sometimes shoot tighter groups at 500 yards than they do at 100. I have re-chambered quite a few of the 6 groove barrels to cartridges like .308 Bellm, and so far as I know, they do extremely well. I do note that when test firing these re-chambers, the 6 groove barrels will take about 3 gr. more powder to produce the same pressure indications that I get from the 8 groove barrels that followed. Said another way, the more recent 8 groove barrels will not take charges as heavy as do the 6 groove factory barrels and custom barrels with narrow rifling as well. More on the 8 groove barrels later.

     The 6 groove .35 caliber barrels will run pretty close to .358" groove diameter, but the later 8 groove .35 caliber barrels are undersize more often than they are close to on size. Most I see run as small as about .356" to .357" groove diameter. Usually the 8 groove barrels shoot ok, but there have been a few that were not overly impressive, one of which had a groove diameter under .357" as I recall.

     There were 7mm TCU barrels made with the 6 groove rifling also, and these usually give outstanding accuracy when re-chambered. These barrels were chambered in a drill press and often show severe misalignment of the chamber to the bore. But in my re-chambering process, this is fully corrected.

     Summarizing the earlier production barrels, the 14" barrels made from 6 groove blanks and having the stepped barrel lugs are some of the best candidates for re-chambering. After the transition to the stepped lug barrels, TC also later went to the two-piece locking bolts. Thus you will find later transitional production stepped lug barrels with one-piece locking bolts. So if for example you are looking at one of these barrels with the one-piece locking bolt, plan on spending some money for replacing them with two-piece. You might bargain for a lower price on the barrel or pass it up if the price is on the high side and it has the one-piece locking bolt that you will want to replace with the two-piece locking bolts.

     What is the big deal about one-piece locking bolts? If the lock up is pretty snug, they are harder to unlock. The two-piece are made so that the roller cracks one side loose before the other. Also, the one-piece bolts had more of a tendency to unlock and let the barrel fly open when fired. Don't ask me why other than that.... they just work better.

     Later production 8 equal land and groove barrels started in the mid 80s sometime and appear to be phasing out since the 1997 fire at the TC plant. These barrels have equal land and groove widths which do displace more bullet metal and give very strong evidence of raising pressures compared to results from "normal" barrels with rifling narrower than the grooves. This seems to be more apparent in the 6.5 TCU barrels, the 7mms, and the .30s when re-chambering to high performance rounds at the top end of what the Contender frame will handle. I have not noticed a problem with .35 caliber barrels and larger, but .35 caliber may warrant looking at more closely. I re-chamber factory barrels for .375x.444 types and .444 Marlin with outstanding results and no apparent pressure problems.

     The quality of these barrels varies quite a bit. Most are pretty good, but some are pretty shoddy with rough and sometimes wavy interiors. Yet when properly re-chambered, they will produce outstanding accuracy. If you have an eye for a quality barrel, do inspect barrels for roughness. Given a choice of barrels with one having the smoothest finish inside, usually you are better off with the smooth one.

     8 equal land and groove barrels are what you will encounter most often since they have been in production nearly 20 years during the rise of the Contender's popularity. On the one hand, they represent the worst in Contender barrels. But on the other hand, they are predominantly what I have refined my re-chambering techniques in, and the results speak for themselves.

     Twist rates in the 8 equal land and groove barrels remained the same except for .30 cal. which went from 1-14" twist in the 6 groove barrels to 1-10" twist in the 8 groove barrels. Thus you might expect better accuracy at ranges under say about 200 yards with the heavier bullets in .30 caliber.

     Reloading manuals suggest that earlier TC .22 centerfire barrels had a 1-14" twist rate. If this is true, then the twist rate was also changed in the .22 center-fires since TC now publishes 1-12" twist as standard for .22 center-fires.

     Post fire/recent production barrels are showing up with narrow rifling and wider grooves like "normal" barrels. In Contenders, I have only seen a few of these in .30 caliber so far, and they are good looking barrels that by all rights should shoot along with most custom barrels if the chamber and crown are "right."

     Comments about the .22 caliber barrels. In all vintages, they generally are pretty good. Some are a bit rough, but overall they are pretty good. Twist rate for the centerfire barrels and .22 Magnum barrels from back about the time TC started making their own barrel blanks to date is 1-12," which while faster than optimum for .22 Mag and .22 Hornet is borderline for heavier bullets in .223 Rem. barrels, apparently more so in handgun lengths than carbine lengths.

     .22 LR blued barrels are a softer steel, but the stainless barrels may be the same as centerfire barrels. I have not seen a difference that I can put my finger on. .22 LR barrels have a smaller groove diameter that is supposed to be in the .222" to .223" diameter range. Twist rate is 1-15." Thus, between the tighter groove diameter, softer steel in the blued barrels, and the slower 1-15" twist rate, re-chambering .22 LR barrels should be limited to .22 Magnum and some of the smaller cases like .22 Hornet to .218 Bee.

     .22 Mag barrels have the same 1-12" twist as the centerfire barrels and can be re-chambered for any .22 centerfire suitable in the Contender.

     Groove diameters of both rimfire and centerfire .22 barrels vary quite a bit. I do run into a few centerfire barrels that are oversize, but most are pretty close to on size and give excellent accuracy.

     I have left out some calibers like the relatively rare 6mm TCU, TC Custom Shop barrels, .41 Mag, 10mm, and 45/70 barrels. The 6mm TCU’s have the equal land and groove rifling, but are ok to re-chamber. 10mm barrels are ok and make excellent .38/40 barrels. Custom dies for .41 Mag re-chambers are hard to come by. .45/70 presents no viable re-chambering options, but both older .41 Mag. and all .45/70 barrels need to have the throats lengthened for better accuracy. In fact, .45/70 factory barrels have no throat.

     General comments about all vintages of TC factory barrels.

     A big percentage of factory barrels show rather severe indications of misalignment of the chamber to the bore which can often readily be seen by simply observing the point in the throat where the throat section of the chamber reamer stopped. Quite typically, it will be evident that the reamer cut deeper on one part of the barrels circumference inside and shallower opposite this.

     If the barrels are placed between centers in a lathe, the misalignment of the chamber from the center of the barrel is also quite evident, as is warpage of the barrel. Visualize a child's jump rope with the middle swinging wide of the ends. This is what you see when turning many of the factory barrels between centers.

     Throughout all the years of barrel production, even the best vintages of crowns on TC factory barrels have been quite lacking in execution, meaning, it is not the style of the crown that matters so much as how it is done.

     When re-crowning factory barrels, I see the factory cut at the crown often off center from the bore and sometimes very badly out of square with the bore.

     If a barrel shoots well as it is, the crown is not adversely effecting accuracy to an appreciable degree. But for best accuracy, it is highly recommended that the crown be centered with the bore and cut squarely to it. You may assume it comes from the factory done this way, but take your barrels to any good machine shop and start taking actual measurements of run-out, and it is quite apparent they are in need of improvement if custom work expectations are to be met.

     Straightness of the un-tapered handgun barrels is usually best, though there are some exceptions. The worst cases of warped bores I have seen have been in the tapered carbine barrels.

     Comments about Specific Chambers in Factory Barrels, applies primarily to production barrels, but the same designs are used in TC Custom Shop barrels.

     Much of the following discussion focuses on the chamber throat, or lack of one entirely. Since knowing what a throat actually is, is critical to understanding what I will present, let's describe it.

What a Chamber Throat Is.

     In normal applications, the throat is nothing more, nor less than an area in the barrel immediately in front of the chamber neck that allows the bullet in a loaded round to project out into the rifled part of the barrel. For this to be possible, the rifling must be cut away. Thus, the throat is actually the groove diameter of the barrel with the rifling cut away.

     For best accuracy, the groove diameter of the barrel should be enlarged very little if at all, and then only enough to allow a bullet to fit in it. This insures that the shank of the bullet is supported and guided as it is forced into the rifling. To do this, the area in front of the chamber neck must be a cylinder, not a cone. If it is a cone, then only the loose fit of the case neck in the chamber neck gives any alignment and support of the bullet as it enters the rifled part.

     With at least several thousandths of movement possible in any random direction at the case neck, even if the bullet is centered in the rifling at its nose, as in seating bullets out to the rifling, the base of the bullet can still deviate in any direction out of alignment with the bore, and thus enters the rifling at an angle, canted, cockeyed, or whatever term you relate to that means it did not go in straight.

     This throws the bullet out of balance and accounts for much of the inaccuracy in all barrels. This is not my dreamed up hypothesis. In addition to my own observations, it is also confirmed by a nationally prominent scientist and shooter, Harold Vaughn, in his highly technical book "Rifle Accuracy Facts." In his book, Vaughn went so far as to measure the actual amount of bullet dispersion at the target caused by specific angles of "cant" of the bullet as it enters the rifling. The straighter the bullet enters the rifling, the greater its potential for hitting in the same place as the bullets fired before and after it.

     The taper cut on the ends of the rifling, also known as the "leade," helps center the bullet as it enters the rifling, and the longer this angle is (presumably within limits), generally the better the leade guides the bullet straight into the rifling.

     Regarding the case neck in its role of aligning the bullet with the bore, the forces involved pushing the bullet into the rifling are much greater than a thin little brass tube, the case neck, can offset. Only in tight necked chambers with case necks outside turned to give a loaded case neck diameter that is a tight fit in the chamber neck can the case neck do anything to positively align the bullet with the bore. But conversely, a closely fitted steel cylinder in front of the chamber neck, the throat, CAN offset the effects of misalignment in the case neck... and the chamber itself, for that matter. Theoretically, the chamber could be at a right angle to the bore, and the throat would align the bullet with the bore, as it is supposed to.

     The throat is where its at. Yet this is probably one of the very least talked about, least understood aspects of all we think we know about rifled firearms. When was the last time you read anything about throat DIAMETER in any popular shooting publication anywhere, IF EVER. Everyone talks about overall cartridge length and seating depth, but no one is talking about the actual DIAMETER of the throat, let alone some of the design issues I will be discussing below.

     Cutting a minimum diameter throat with a long leade angle and aligned with the bore will do more to improve the accuracy of TC barrels than any other single factor.

     With what the factory puts in the barrels, this is the reason for the need to always when rechambering, choose a case that is longer than the existing one. The new chamber should always cut out as much of, or preferably all of, the factory throat.

     With the above in view, let's talk about specific TC barrels. The focus is on the most common factory production barrels, but many of the chamber designs mentioned apply also to TC Custom Shop barrels, which while somewhat better than production barrels still leave a lot to be desired. In my opinion, special order factory barrels is a more accurate description based on everything I have seen in hundreds of custom shop barrels I have reworked over the years.

     .22 LR chambers. Usually aligned with the bore fairly well, abrupt leade angle on the ends of the rifling.

     .22 Hornet. Misalignment is usually not a problem since all but .22 K-Hornet re-chambers result in going to a large diameter chamber and allow me to lathe bore out the existing run out. Hornet throats are short and cone shaped, and thus the throat cannot support the shank of the bullet as it engraves. Many of the Hornet chambers are cut too deeply and require fire forming the shoulders forward so the case can be head spaced on the shoulder instead of the rim, due to the rim cut being too deep.

     .223 Rem. Throats are usually fairly short, larger in diameter than optimum, but in these barrels are also some very, very severe cases of the chamber throat being offset from the bore so far that the throat section of the reamer does not even cut the tops of the lands in about half of the barrels circumference in front of the chamber neck. This misalignment problem is compounded in tapered carbine barrels with warped bores.

     7mm TCU. The majority of these barrels were produced during a period of TC production where chambering was done in a drill press with the reamer held rigid in a drill check and the barrel held in a fixture that did not compensate for variations in the barrel's external diameter or for curvature in the bore inside. Thus you will find a big percentage of 7mm TCU chambers very definitely offset from the bore. The chambers were "stabbed" AT the bore, not aligned with it. During the period when Elgin Gate's 7mm Int'l Rimmed cartridge was vogue in silhouette circles, I re-chambered a lot of 7mm TCU barrels to this long necked, necked down .30/30 cartridge. When test fired, most of these barrels would show a definite "jog" on the necks of fired cases at the point where the old remaining TCU neck ended and the longer Int'l R neck continued forward. The neck I cut followed the bore. The factory TCU necks were usually "stabbed" off center. Case necks showed an obvious ridge on one side and a bit of a depression opposite this ridge. If you happen to have one of these barrels I re-chambered, take a close look at the case necks. You will quite likely see what I am talking about.

     7-30 Waters. These barrels do have a throat in them, and they are some of the very best barrels TC makes. Not only is the cartridge itself the best overall factory round suitable for the Contender, some of these barrels deliver outstanding accuracy as is. But there have also been a few problems, one vintage of which pertained to the Muzzle Tamer brakes. If you have a 7-30 Hunter barrel that does not shoot well, the brake may be the cause. My advice is often to not re-chamber a 7-30 Waters barrel if it is quite accurate unless squeezing another 150 fps or so out of it is that important.

     Most of the rimmed rounds such has 7-30 Waters above, and .30/30 below, have rim counter-bores cut too deeply to headspace on the case rim without more headspace than suitable for good case life. With new brass, steps should be taken to fire form the shoulders forward before loading for actual use. After fire forming, cases should be correctly sized so that they headspace on the shoulder. Factory ammo will undergo some unnecessary stretching when fired in these chambers.

     .30/30 Win. This one is either a curse or a blessing, depending largely on when it was made. Older barrels have a throat in them and usually shoot just super, but for at least about the last 7 or 8 years, TC has been chambering .30/30 barrels using reamers that produce a .050" overly long chamber neck and NO THROAT AT ALL. There is a slight angling or chamfer on the ends of the rifling, but there is no throat in them. Consequently, the .30/30 barrels usually shoot pretty poorly. Of all the barrels, to me, the .30/30s with no throat are most desperately in need of re-chambering of all the barrels TC makes. The inherently accurate .30/30 is reduced to lever action rifle 2" and larger groups at 100 yards.

     .357 Magnum. Older barrels had an actual throat. It was on the short side, but it was much superior for accuracy to the .4" long forcing cones that TC has been putting in these barrels for at least the past 7 or 8 years. This revolver type forcing cone is .4" long. In a cone shape, it goes from about .380" past the mouth of the case down to bore diameter, which is under .348" in the factory 8 groove barrels, and thus does nothing to align the rear of the bullet to head it in the same direction the nose of the bullet it going. Re-chambering these barrels to .357 Maximum does cut out most of the long forcing cone, though some does remain. The Maximum chamber does permit cutting some new throat in the barrel, and accuracy from the re-chambered barrels has been quite improved. However, the best .357 Maximum in a re-chambered barrel will be from one of the older .357 Magnum barrels with the short throat. This is the one to look for.

     .357 Remington Maximum. This one is a real travesty. .357 Maximum is a totally outstanding cartridge. It is inherently VERY accurate. With its small diameter case, you can run pressures the same as you would in a .223 Rem. barrel... in the 55,000 psi range. Because of the high expansion ratio of its large bore compared to chamber volume, the fastest of rifle powders and slowest of pistol powders are what it shines with... 2400, 4227, WW296, AA1680, etc. This makes it exceptionally well suited for use in handgun barrels even as short as 10." And in a 10" barrel, it is simply the best long range factory round for game there is. Unfortunately, this round has been given all but a death sentence by SAAMI and Thompson/Center. From day one of its introduction, TC has used a chamber configuration that has NO THROAT, but rather a revolver type forcing cone that is .4" long. In a cone shape, it goes from about .380" past the mouth of the case down to bore diameter, which is under .348" in the factory 8 groove barrels. I do try to constrain my language, but in this case, saying this is simply dumb is being as kind as I can be. It has all but destroyed one of the very best Contender cartridges there is. Remington no longer produces factory .357 Maximum ammo, but commercial loading companies such as CNC Cartridge (ph. (618) 435-2855) and The Old Western Scrounger are two I know of that do supply commercially loaded and/or custom loaded .357 Rem. Max. ammo. To get decent accuracy from these barrels, it is nearly always necessary to re-chamber them to something longer than 2" long to get rid of the forcing cone. 1.610" plus .4" = 2.010." Do you see now what we are dealing with?

     .35 Rem. These barrels do have a throat, and some of the .35 Rem. barrels have been extremely accurate. However, due to not understanding how to correctly adjust the FL size die, .35 Rem. probably causes more people more problems than any of the other barrels. Making cases out of .30/40 Krag brass and cutting a proper depth rim counter-bore in the end of the barrel solves much of the trouble shooters experience with this one, but correct FL sizing cases is still a must. The stronger, rimmed .444 Marlin brass used to make .358 Bellm and .358 JDJ cases cures most of the problems associated with managing .35 Rem. barrels.

     .375 Win. Big Bore is a pretty good round in the Contender, although its range is somewhat limited. I do not recall much information about accuracy from it, nor at this writing do I recall much about the factory throats other than the typical random degrees of alignment of the chamber to the bore. I have re-chambered quite a few of these to .375 JDJ or .375x444 Marlin, same cartridge, with outstanding results. Re-chambered correctly, they can be exceptionally accurate.

     .44 Magnum. This one, too, has suffered the injustice of the revolver forcing cone chamber which was started sometime in the early to mid '90s. For re-chambering to .445 Super Mag, which is quite popular now that Starline is supplying brass for it, the older .44s with the short throat are best. Newer .44 Mags have the long forcing cone, and the best cure for these is .444 Marlin which is long enough to cut out all of the cone and permit a proper throat to be cut. .445 Super Mag leaves some of the forcing cone in the chamber, but cuts out enough of it to give good accuracy from the new chamber.

     .45/70. As noted above and repeated here, .45/70 chambers have no throat. Bullets must be seated quite deeply in the case, and there is nothing but chamber neck and case neck to support the bullet when it engraves. These barrels do need to be throated.

- Mike Bellm

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This article reprinted with permission of Mike Bellm and
Warning: All technical data mentioned, especially handloading and bullet casting, reflect the limited experience of individuals using specific tools, products, equipment and components under specific conditions and circumstances not necessarily reported in the article or on this web site and over which The Los Angeles Silhouette Club (LASC), this web site or the author has no control. The above has no control over the condition of your firearms or your methods, components, tools, techniques or circumstances and disclaims all and any responsibility for any person using any data mentioned. Always consult recognized reloading manuals.