The Los Angeles Handgun, Rifle, Air Pistol, Hunter/Field Pistol Silhouette Club
Return to the index to LASC

A wide range of bullet casting information


Why Re-Chamber?

By: Mike Bellm

     Why Re-chamber a Factory Barrel?

     If you own a 14" or longer Contender barrel in 7mm, .30 cal, .35 cal, or .44 cal, you really should consider re-chambering it to a cartridge based on .444 Marlin brass!

     Why would someone want to re-chamber in the first place when the factory has so many offerings?

     1) The thin brass for all of the larger diameter chambering such as 7-30, .30/30, .35 Rem., and .44 Mag, is by design meant to operate at pressures less than 40,000 psi. The .375 Win. is the only large diameter factory cartridge meant to operate at pressures above 40,000 psi, yet you need higher pressures to get maximum allowable performance from other calibers.

     .375 Winchester is too hot for the Contender, IF WE ACCEPT 45,000 psi AS THE MAXIMUM SAFE PRESSURE FOR CARTRIDGES LARGER THAN 3/8" DIAMETER, but smaller than .45/70 (see Note 1).

     If you start loading 7-30 Waters, .30/30, or .35 Rem. to 50,000 psi or thereabouts, which is approximately the SAAMI max. for .375 Winchester, you will most likely find yourself troubled with extraction problems and potentially a stretched frame.

     So how does the .375 Win get away with these kinds of pressures? It is the 1) straight sidewall, combined with 2) the strength of the heavier brass in the .375 Win. case itself. But, wildcats on this case require custom dies.

     Heavy and strong .444 Marlin brass lets one operate at nearly these same levels safely, and common .308 Win. type dies afford the first parameter, that of the straight sidewall for my .444-based cartridges.

     The rim of the .444 Marlin is another plus. Rimmed cases simply work better and easier.

     2) However, the other all important reason to re-chamber is to cut a longer chamber to get rid of the misaligned or poorly designed part of the old factory chamber. I've thoroughly examined thousands of T/C factory barrels, both Custom Shop and production barrels. The majority are seriously deficient in the throat area (see Note 2). Once a new precision chamber throat is cut in the barrel, ahead of the factory's chamber throat, you WILL get outstanding accuracy from virtually all barrels without a factory muzzle brake, and most of the barrels with the factory brake, the only noted exceptions so far are isolated instances with 7-30 Waters Hunter barrels.

     .444 Marlin brass is the only readily available quality brass that gives all these benefits in one neat package: 1) strength, 2) length, 3) compatibility with standard dies for straight sidewall cartridges, 4) a substantial rim, and 5) an economical price.

     Chambers that utilize full length .444 Marlin brass are long enough to clean up all factory chambers. .444 Marlin brass is THE brass to use for all calibers 7mm and up. (With a little extra work it is also preferred for .25 and 6.5mm, and, yes, I chamber for 375x.444 aka 375 JDJ).

     Plus, my series of chambers use common .308 Win-type dies with a very minimal body taper to reduce thrust back to the frame. 7mm-08, .308 Win, and .358 Win. dies used to form and load my 7mm Bellm, .308 Bellm, and .358 Bellm are far more economical compared to custom dies required for most of the various other wildcat chambering’s available. Any full length size die sets are fine, but may not size the web area of the case small enough. If this occurs, simply run cases through a .444 Marlin size die which usually sizes much smaller than common 7mm-08,.308 Win., and .358 Win. dies will. Using the .444 die only when required permits a quasi neck size/"shoulder bump" when leaving the web area as fire-formed to the chamber.

     NOTE: UNLESS you use a .444 Marlin size die in addition to the standard size die, I must have the size die you will use so I can match the chamber to it. This also means you may end up with a bulgy web area, since most common dies are meant for larger factory type chambers. If you want a close tolerance web area in the chamber, you must use a .444 Marlin size die with it to size back to near new brass web dimension.

     .444 Marlin, of course, uses standard .444 Marlin factory ammo or standard .444 Marlin dies to reload.

     This is how you get the full maximum potential for accuracy, trajectory, and energy from your Contender. And, using standard dies, you do it very cost-effectively, transforming your factory barrel into one that out-performs many high priced custom aftermarket barrels. Performance, that's why you should re-chamber, and because of the experience I have re-chambering thousands of factory barrels and the way I go about it, I should be the one to do it for you. Why settle for less, especially if you get less and pay more elsewhere?

     Note 1: I've fired thousands of rounds of 45,000 psi factory ammo (.250 Savage, .300 Savage, .444 Marlin, etc.) in Contenders for nearly 20 years and test fired with one primary frame for nearly 10 years before any signs of stretching appeared. 45,000 psi IS OK in the Contender when brass meant for this pressure range is used.

     Note 2: T/C chamber throat deficiencies: To varying degrees, the majority of T/C's chambers and chamber throats are misaligned with the bore. Anyone with at least one decent eye can readily see the misalignment when they are shown what to look for. Most of T/C's throat diameters are much greater than is required for top accuracy. Current .30/30s have no throat, only an overly long neck and a chamfer on the ends of the rifling. The .30/30 barrels give very mediocre accuracy in factory form. Most .357 Mag, .357 Maximum, and .44 Mag barrels have a revolver type forcing cone instead of a cylindrical throat section which is required to support the shank of the bullet as it engraves the rifling. The throats I cut are of minimum diameter for accuracy, moderate length, and centered with the bore. They are done as a separate precision operation without any interference from forces produced cutting the body of the chamber. THE THROAT IS THE MAIN ELEMENT TO ACCURACY IN ANY BARREL. Yet it is so commonly neglected, even in most custom barrels.

- Mike Bellm

Top of Page

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.