.358-378 RG

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The 358-378 RG, or 358-378 Real Guns, is a .358" caliber large capacity, full length magnum wildcat cartridge. Based on the commercial .378 Weatherby Magnum cartridge, the .358-378 RG was developed for hunting big and dangerous game, intended to offer broader bullet weight and type selection than available for .375" caliber cartridges and to provide an increased sectional density over a .375" bullet at the heavy end of the bullet weight spectrum for greater penetration. The cartridge was designed by Joseph D'Alessandro and was documented in a series that first appeared on . The first article was posted March 2002 and the series concluded in November 2002.
Development Notes
The original drawings and dimensional specifications were produced with RCBSLoad, the initial internal and external ballistic performance projections were made with QuickLOAD. Actual development of the cartridge, internal and external ballistic data collection and assessment were accomplished with an Model 43 chronograph utilizing strain gauge technology. Internal, external and terminal ballistics data were collected during live fire tests. The development firearm was a Ruger No.1 Tropical .375 H&H, modified for this purpose by Dennis Olson of Plains, Montana. The barrel installed on the Ruger was a 26" Lilja chromemoly steel unit contoured to match the original No.1 Tropical barrel and refit with all carried over hardware including: quarter ramp, barrel band and front sight. The twist rate is 1:12" as optimized for heavier bullets. The muzzle of the barrel was threaded for a muzzle brake to make the rifle more manageable during long range session, however, the brake has not been required in normal use or more typical range sessions. No other modification of the Ruger was required for proper function. even the breech block extraction radius remained as original.
Clymer produced the .358-378 RG reamer as specified in drawings provided by Real Guns, Inc. The reamer was straight flute, fixed pilot and made from M7 high speed steel. Only a finisher was required to produce the prototype and a number of production rifles. There were only a few necessary accommodations. Brass thickens as it is necked down, so the neck portion of the chamber was cut 0.002" larger at 0.3840 than typical for .358" caliber factory cartridges. While case length also increases as larger caliber cases are necked down, case length for the .358-378 RG is the same as all other members of the .378 Weatherby family of cartridges. Since virtually all factory brass is produced to minimum length specifications, trimming to bring a newly formed case into spec has not been required. Additionally, most of the taper is removed from the .378 Weatherby case when formed into the .358-378 which reduced overall case length.
Producing a .358-378 RG case is a two step process. It is first cold formed in a .358-378 RG sizing die then final formed by firing in a rifle chambered for the cartridge. Fire forming completes the reshaping of the double radius shoulder and it expands the case to .358-378 RG larger body diameter. Weatherby or Norma cases tend to be hard at the shoulders and work harden quickly so cases are annealed after first firing. CH4D produced the custom sizing and seating die to developer's design and Clymer reamer drawings. A less expensive way to form the case would be with a neck-sizing die from RCBS or Redding.
The Ruger No. 1, with a 1" barrel shank, is 0.060" smaller in diameter than the Weatherby Mark V, however, no problems surfaced in terms of chamber or barrel distortion during test firing of several hundred heavily charged ammunition. Additional pressure margin can be added by turning the inside of the Ruger receiver to a larger diameter and increasing the diameter of the barrel shank. This has not been necessary. Cartridge case life is very good, 10 - 15 reloads, with annealing, before retirement is reasonable.
Virtually anyone who has hunted with, or developed, high velocity magnum cartridges knows that locating suitable bullets is a difficult task. The .358-378 RG is no different in this regard. Muzzle velocity of 200 - bullets falls in the 3,300 - which presents a problem in selection of an appropriate bullet in this weight range. Most of these bullets are intended for moderate 35 Remington, 35 Whelen and 350 Remington Magnum cartridges operating in the 2,400 - muzzle velocity range. Accordingly, bullet designed impact velocity, as specified by their respective manufacturers, is in the 1,800-2,500 ft/s range. A typical 200 - .358-378 RG handload is still pushing at and well above the maximum intended impact velocity. While bullet velocity criteria is typically and routinely obtained from bullet manufacturers tech or engineering departments, an example of this type of data for .358" bullets can be found at .
Even at heavier bullet weights the bullet suitability problem persists. Lead core bullets can routinely reach , Swift A Frame bullets can reasonably achieve 3,050 - , and very heavy for bore Woodleigh softpoints come in at approximately . Long-shank low-density Barnes Triple Shock velocity performance is somewhat less. The best overall performance, in terms of expansion, weight retention and penetration came from solid copper alloy bullets such as the , and HV bullets from .
Measured pressure for loads as indicated above were in the 62,000 - 65,000 PSI range. For practice loads and smaller game, deer and larger pig, hard cast gas checked bullets at 2,200 - work very well. There are made from RCBS 35-200-FN moulds using wheel weight hardened with 50/50 alloy.
As a note on originality, there are few combinations of parent case and caliber that are truly original, not because of a lack of creative effort, but rather as a byproduct of the constant independent cartridge development undertaken by firearm enthusiasts. Within the context of the .358-378 RG, the now-defunct Hollywood Gun Shop produced a .358" necked down version of the .378 Weatherby many years ago. That version had, however, an angular shoulder in place of the Weatherby double radius form. An improved version of this cartridge could be made from the .416 Rigby. The .358-378 RG, when optimized to an individual firearm's chamber, on the case shoulder and not the belt. This renders the belt passive in function. The beltless Rigby would provide the capacity of the Weatherby case without the need to cut into a gun's chamber to accommodate the belt.
Dimensions
In comparison to the parent case, the .358-378 RG maintains the same case and overall assembled cartridge length. The 0.348" neck length is shorter than the "one bullet diameter" rule for cartridge design, but more than sufficient to adequately retain the bullet and assure accuracy. In addition to necking down a .378 Weatherby case, the .358-378 RG can also be made by running a .338-378 Weatherby Magnum case through a full length .358-378 RG sizer and necking up this case to seat a .358" bullet. The latter approach is less preferable, as the neck material thins with expansion and chamber fit would not be as close as necked down .378 Weatherby brass. Case capacity, made by either method, is just under of water, however, is more typical for net capacity with a seated bullet.
Actions recovered from donor firearms for conversion are those offered in 416 Rigby. Examples of these are: magnum length Mauser, No. I and magnum length M77 Ruger, CZ 550 magnum length, and others. Remington 700 magnum length actions can be utilized, but require a modified extractor due to bolt face constraints and magazine box and feed length. even when modified, cartridge overall length will be limited to less than optimal. The magnum length Model 700 action and magazine length limit the Remington Ultra Mag cartridge series to 3.600" with little margin for error. A CZ 550 Magnum action has the potential of enough bolt travel and magazine length to chamber a 3.750" .505 Gibbs round with room to spare. A Ruger No. 1 cartridge overall length, in regard to bullet seating and subsequent cartridge overall length, is only limited by the length of the throat ahead of the chamber as cut by the chamber reamer.
Usefulness
Like the 375 H&H and its big brother the .378 Weatherby, the .358-378 is, hard hitting, and very accurate. Sub-MOA 3 shot group size in bullet weights above 225 gains is typical. Changing over to the .358-378 RG is an economical conversion on rifles where applicable. When this conversion was done in 2002 the total cost for firearm ($680), quality gunsmithing services ($420), custom reamer and dies ($300), and Lija match grade barrel ($230) was a little over $1,600. Gunsmithing cost included: chamber barrel, cut extractor groove, duplicate Ruger barrel contour, drill and tap new barrel for Ruger quarter rib, move front sight and barrel band to new barrel, install brake, blue barrel to match receiver. Priced today, the rifle cost is approximately $300 more, reamer and dies remain approximately the same and gunsmithing services have increased by approximately $40. A used Ruger No.1 could shave hundreds of dollars from the cost.
Unlike most mid-caliber magnum rounds, the .358-378 RG is quite flat shooting. As an example, a Sierra boattail driven at with the assumption of a 6" kill zone has a point blank range of and a drop of less than 12" at . Even a light for bore bullet of this type carries of kinetic energy at . Heavy high sectional density bullets like the 310 Woodleigh driven at with the same criteria can be zeroed to a point blank range, dropping only 4" more at and terminate at with of kinetic energy.
There are some drawbacks in utilizing a cartridge of this size in addition to the additional care required when making bullet selection. Recoil, while quite manageable, is heavy. Muzzle blast, with brake in place, is very loud and the shock wave from muzzle blast is directed closer to the shooter. All 26" of barrel length is necessary. Cutting back barrel length even to 24" will result in a loss of nearly for most loads. An increase in barrel length to 28" or more would result in a substantial increase in velocity. Brass is costly where $53 - $56 per box of 20 is typical for Weatherby product and Norma brand runs a few dollars more. Bullets are somewhat of a bargain for this heavy of a cartridge. Premium hunting bullets run approximately 80 cents each, simple one piece jacketed hunting bullets half that amount and hard cast bullets can be produced for as little at 3 cents each when using tinned recycled wheel weight material. The big case capacity consumes large quantities of expensive slow powder when loaded for optimal performance and accuracy. Re22 and Re25, H1000 and Retumbo and 7828 are some of the more useful powder for this application.

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