This article is reprinted here by permission of Wolfe Publishing Co. 
It originally appeared in Handloader, November 1993 and is the product of over 2 years of testing.

375 Hawk/Scovill

Dave Scovill

IT HAS BEEN nearly three years since Bob Fulton, owner of Hawk Laboratories (Bob has since sold Hawk bullets & they are still available) forwarded a custom Mauser he had chambered for a .375 wildcat based on the .30-06 case. Originally the rifle was chambered for the 375 Whelen. Bob wasn't happy with the performance so he ran a .375 Whelen Improved reamer into the chamber in an effort to increase case capacity and boost velocities a bit. That didn't prove to be what Bob was looking for either. The last effort was to run a 9.3x62 reamer into the chamber moving the shoulder forward and increasing the shoulder diameter to .454 inch. Preliminary loads suggested that was just the ticket and Bob was able to achieve some impressive ballistics with his Hawk bullets weighing from 235 to 300 grains.  (for more Hawk History Click Here)

When Bob called and outlined the series of events leading up to the final cartridge design, it sounded like the big game cartridge I had been looking for. On paper it was capable of generating something close to 4000 foot-pounds (ft-lbs.) at the muzzle of a 24 inch barrel treading heavily on the heels of the 338 Winchester Magnum.

To get some idea of the pressure that Bob's loads were generating I ran them through the Powley Computer for Handloaders and projected those figures to the Powley psi Calculator. From my calculations 62 0 gains of IMR 4064 under a 235.grain roundnose Hawk bullet would produce about 2660 fps at about 46000 psi. Bob reported using 63.0 grains of IMR 4064 for about 2700 fps. Energy tables converted that velocity to 3805 ft-lbs.  (The Barnes Manual now contains preasure tested data for the 375 Hawk/Scovill)

If a cartridge can be described in terms of energy potential a 250 grain bullet would require 2620 fps to produce 3812 ft-lbs. and a 270-grain bullet would be moving at 2520 fps to harness the same energy level. Since these energy figures were based on 46,000 psi it seemed that Bob's brain-child capable of producing about 2800 fps with a 235-grain bullet 2700 fps with a 250 grain bullet and up to 2600 fps with a 270-grain bullet, while remaining within the pressure limitations of the .30-06 case.

For comparison purposes the 9.3x62 Mauser factory load pushes a .366-inch 286-grain roundnose bullet at about 2350 fps (depending on barrel length) with a maximum average chamber pressure of 49300 psi. According to Norma 62.0 grains of IMR.4320 behind a 232-grain bullet in the 9.3x62 Mauser wall generate 2640 fps.

When Bob's rifle arrived I grabbed a handful of PMC 30-06 cases necked them up to .40 caliber and then shoved them into a 9 3x62 full-length sizing die moving the shoulder back just far enough to establish positive headspace in the chamber. The final step was to neck the case back up to .375".

Based on preliminary load data that Bob had been using, I fireformed a few cases and sent them off to Bill Keyes at RCBS. Shortly thereafter Bill forwarded a set of .375 Hawk dies.

In firing a few more test loads it appeared the cases were stretching a bit at the web. just in front of the extractor groove. The problem, if you want to call it that was that the standard 9 3x62 case measures .4765" to .4785" at the web and the 30-06 case measures from .4618 to 4698 inch according to SAAMI specifications. The difference was not serious but it did cause an unsightly bulge at the base of the case that may contribute to stretching and ultimately separation. By that time however I had been able to approach 2700 fps with the Hawk 250-grain roundnose bullet and just over 2800 fps with 235-grain bullets from Speer and Hawk.

Not long after I returned the rifle to Bob I mentioned the .375 Hawk to Mark Hendricks and suggested that it would make a versatile big game cartridge depending on which bullet weight was used. Mark took the dummy round I had made up with a 270 grain Hawk roundnose and headed home. Later he called to tell me that he had ordered a new reamer and he would make a rifle for testing. At that point we decided to incorporate a few minor changes in the chamber design, holding the maximum diameter to .470" in the area just ahead of the extractor groove, formalizing the chamber length and adopting the 17 degree, 30 minute shoulder angle that is common to 9.3x62 and the 30-06. (Interestingly it depends on which resource you check for the 9.3x62, some show the shoulder at 25 degrees. CIP drawings indicate 17 degree is standard).

Shortly thereafter Mark forwarded a custom VZ24 Czech Mauser with a Brown Precision synthetic stock Timney Sportsman trigger 25-inch Shilen barrel PME rear sight and a Jaeger front ramp fitted with a brass bead. All the metal sported a parkerized like finish that seemed fitting for a no-nonsense field piece. On the barrel Mark had inscribed "375 Scovill," and that was the name Bill Keyes put on the second set of dies that RCBS made for the slightly revised case design. (Hawk/Scovill would be a more accurate name)

In reality, the only reason for the second version is that you need to know which reamer is used to chamber the rifle since cases sized in the .375 Hawk dies will not fit the .375 Hawk/Scovill chamber. We also designed the freebore length and throat angle to fit the Hawk 250 grain and 270 grain roundnose bullets (seated to an overall length of 3.185 inches), which have an ogive shape that is similar to the Hornady 270 or 300 grain bullets.

Whatever you choose to call it the375 Hawk or Scovill or .375 Hawk/Scovill (H/S), the ballistics are the same but the chambers are slightly different including the throat angle and freebore length. Informed readers will also note that the overall design of this cartridge is similar to the 375 Brown-Whelen although the 375 H/S has about 10 percent more powder capacity than the run-of-the-mill 375-06 or the .375 Whelen and about 5 percent more than the .375 Whelen Improved.  (The 375 H/S has the advantage of a shoulder that is conducive to smooth feeding, most "improved" cartridges have sharp shoulder which introduce feeding and other potential problems).

Working up loads in Prescott, Arizona can be an exercise in futility. The summers are dry and hot while the winters are cold. Loads that worked out fine in the cooler months turned out to be some what hot during the warmer periods. For example 61.0 grains of H4895 produced 2835 fps with the 235 grain Speer bullet from the Hendricks rifle in August of 1992 and 61.5 grains from the same lot powder produced 2782 fps in February. It also serves to show that you must take any load data with a grain of salt and establish prudent maximum loads for the individual rifle and the season. Bob’s rifle would handle about one grain more powder with any given bullet weight to match velocities obtained in Mark’s rifle.

Where possible I attempted to establish load data using an overall loaded length allowed the bullet to be seated up to the cannelure for Hornady 270 and 300-grain roundnose bullets. Hawk bullets do not have a cannelure and the 235 grain Speer bullet is slick as well. The 285 grain Speer Grand Slam can be seated out about 1/16 inch short of the cannelure for an overall loaded length of 3.175". If the action can accommodate the .30-06 length cartridge, most of these bullets can seated out to 3.3" or so, but the freebore must be increased accordingly. Also note that the 270-grain Hornady Spire Point is seated deeper than their 270 roundnose bullet, although the overall loaded length for the Spire Point is longer than that listed for the roundnose.

I used H-4895 from the start in the 375 Hawk and .375 Hawk/Scovill. It is the powder by which all others are judged in terms of velocity and accuracy with all bullet weights from 210 to 300 grains. A good second choice is Reloader 15 followed by AAC 2495, AAC 2015, and IMR 4320. In most instances top loads are compressed somewhat depending on seating depth required for the individual rifle.

A few loads are listed for Reloader 12 but it proved to burn a bit too fast for optimum performance. Other powders that might be suitable for the 375 H/S include BL-C2, H-335, H-350, and IMR 3031. They are listed for a variety of bullet weights for the 35 Whelen in the Hodgdon Data Manual No. 26 and should work well the 375 H/S. Of those powders that I did not work with BL-C2 would appear to have the most promise. Suggested starting loads for the .35 Whelen with these powders would also be a good place to start in the .375 H/S working up one gram at a time to make sure all the details like seating depth are ironed out before things have a chance to get out of hand.

I started out using .Remington 30-06 brass in Bob's rifle and switched to PMC .30-06 cases just before the rifle was shipped back. Winchester 30-06 brass was used in the final stages of testing with Mark's rifle in an effort to determine what effect case capacity might have on top loads. Loads that will cause slightly excessive pressure in PMC brass will pass with flying colors in Winchester cases at least for the lots of brass I used. Most shooters however will have to fine tune these matters depending on what cases they use. At this point I will probably stick with Winchester cases since they seem to have less lot to lot weight variation and they go through the case forming process with ease. To date I have fireformed 205 cases including those from Remington, PMC, and Winchester, without a single loss. The final discard criterion usually crops up when the primer pockets get slightly loose after the case has been reloaded six or seven times with progressively warmer loads.

Some might like to simply neck the .30-06 case up to .375 inch, pour in a reasonable case forming powder charge seat the bullet so that it engages the lands when the bolt closes and pull the trigger.  Another method is to neck the case up to .40 caliber and then run it back into the full-length .375 H/S sizing die adjusting the shoulder location so that it produces a positive headspace in chamber. I've done it both ways and the results are fine. Suggested case forming loads are listed in the table.

In full-length sizing fired cases I adjust the die just short of touching the case shoulder usually about 1/32 inch short allowing the unsized portion of the case neck to help center the case as it enters the chamber. The same sizing technique nas been used with a variety of bottle necked cases from the .22-250 Remington to the .30-06 and I am reasonably sure that it contributes to improved accuracy when it is not prudent or smart to seat the bullets up against the lands in an effort to center the bullet in the chamber throat. In theory a neck sizing die should help improve accuracy as well, but in sporting rifles I have never been able to prove that it shows any improvement over partial sizing.

During load development I ran into a stumbling block with the Barnes 235-grain X-Bullet. Starting out with 56.0 grains of H4895, 5.5 grains below a respectable maximum with the 235 grain counterparts from Hawk and Speer pressure signs indicated a redline load. I called Randy Brooks at Barnes and asked if he might like to shoot the rifle and investigate the matter. Randy agreed that something wasn’t right and offered to take on the project, assuming Eric Pedersen the Barnes ballistician, could squeeze my rifle into his workload.

A few days after Eric received the rifle he called to tell me that he had loaded 58.0 grains of AAC 2015 to reach 2770 fps and 58 grains of H4895 to produce 2790 fps using an overall loaded length of 3.14 inches with the 235 grain X-Bullet. That was essentially the result of seating the bullet off the lands, effectively giving the bullet a short run at the rifling to produce a more acceptable pressure curve.

When the rifle was returned to Prescott, I tried 58.0 grains AAC 2015 in PMC cases with the 235 grain Barnes X-Bullet and decided reduce the load by 0.5 grains for a hunting load. The PACT Professional Chronograph registered 2756 fps at 65 degrees Fahrenheit.

That fall I used that load to take a 240-pound Utah 4x4 Muley and a Montana doe antelope at. 262 and 412 paces respectively. My friend Kent Sawyer used the same load to dump a Utah doe mule deer at 25 yards. The exit wounds in all three animals were similar, demonstrating consistent performance for the X-Bullet at a variety of ranges. None of the bullets were recovered.

My rifle range is an impromptu setup on public land. The target is backed up by a dirt hillside that is about the consistency of soft rock. Based on the condition of recovered bullets the jackets on Speer, Hornady, Nosler, and Swift tend to break or crack when stopped so abruptly in that hard earth. Conversely the soft Hawk jackets hold together exceptionally well and rarely crack or tear. I have yet to recover a Barnes X-Bullet because I am too lazy to excavate the hillside in an attempt to find one.

I shot a lot of three shot sub MOA groups with Bob Fulton's rifle using Hawk and Speer 235 grain bullets. The Hendricks’ rifle is just as accurate. Either rifle is capable of holding three shots around an inch at 100 yards with al the bullets tested.

Based on Eric Pedersen's independent tests at Barnes and the results of shooting nearly 1000 rounds through two different rifles, I am reasonably convince that the .375 Hawk/Scovill is operating within the guidelines suggested for the .30-06 case in the neighborhood of 50000 CUP or 60000 psi. Top loads listed in the table generally produce about .001" or slightly less expansion of the case head just in front the extractor groove on PMC or Winchester cases. I tried a couple of loads that boosted that figure to .002" but they were tried on a very hot day. The same loads would probably be acceptable on a cool October hunt, but you must be the judge of pressures in your rifle. None of the loads listed produced more than .001" expansion at the case head in Mark's rifle. Extended use of maximum loads however would cause progressive expansion and eventually sloppy primer pockets.

The idea of working with a heretofore unknown set of variables in a wildcat cartridge can be a nerve racking affair. To keep the chance of a mistake with new combinations of powders and bullets to a minimum I usually started out with a new powder using the Speer 235-grain bullet. Once the operating levels with that set of variables was established I switched to the next heavier bullet weight and started over. It la slow arduous work assuming you don't want to blow a primer or wreck a rifle.

As each powder began to reveal its burning characteristics with a particular bullet weight and design it became easier to predict how that powder would perform with the next bullet. All went well until I started working with the 260 grain Nosler Partition. I unceremoniously seated the bullet to an overall loaded length of 3.185 inches over 50 grains of AAC-2015 and blew the primer. In subsequent loads overall loaded length was reduced to 3.10" with that bullet and pressures and velocities were normal. When the Swift A-Frame bullets arrived they were seated to 3 l0 inches as well since they are very much like the Nosler Partition in design. Both are very tough and the cross section, or partition, is just behind the area that initially engages the lands. Where bullets of conventional design without the partition tend to give as they take on the lands the Nosler Partition and Swift A-Frame apparently don't -- neither does the Barnes X-Bullet.

To compound the problem with the Swift A-Frame and Nosler Partition bullets they have a short ogive radius and carry a lot of weight behind the cannelure. The temptation is to seat them out in an effort to get more powder in the case. Unfortunately that system doesn't work when the jacket is unyielding and the bullet is seated too close to the lands. The result is a pressure spike that causes all sorts of problems.

For a more complete discussion of the problem. I can only refer you to the Hornady Handbook of Cartridge Reloading, Third Edition page 13. The same information was reprinted in the Forth edition, page 14. Peak pressures depend heavily on the freebore and the throat angle in the chamber as well as the distance the bullet travels before it engages the lands.

One unexpected result was to find that all the bullet weights from 210 to 300 grams shot to approximately the same !.mint of aim. On one afternoon 55 shots were fired with a selection of loads and bullets weighing from 220 to 300 grains using the same aiming point on the target. The resultant group measured 3.6 inches. The widest dispersion was with the 270 to 300 grain bullets that shot about 1.7 inches left of the point of aim. The lighter bullets 220 to 250 grains shot pretty much where the crosshairs intersected the target. Later the 210-grain Barnes X-Bullets shot exactly to the point of aim at 2934 fps while the 300-grain loads shot 1.7 inches left and a bit lower at nearly 2400 fps.

Accurate Arms Co. lists their AAC-2495 as similar to IMR or H4895. From the tables that may be true, and it may not be. In the 375 H/S as with any wildcat case used in a custom chamber don't assume that any powder is similar to another until you have a chance to prove it in the rifle in question. In this rifle with the Speer 285 grain Grand Slam and the Hornady 300-grain roundnose bullets, H4895 and AAC-2495 appear very much alike but with lighter bullet weights some variations show up. Remember however that it took over 2.5 years to fire all these loads under a variety of weather conditions and some spurious factors may come into play over time-- like inadvertently switching primers from one lot to another or a dramatic change in the temperature and humidity from one week to the next.

I tried to stick with Winchester WLR primers throughout especially after switching to Winchester .30-06 brass. Once in awhile t us d CCI 200 and Federal 210 primers to see if they produced unexpected results, but pressures and velocities remained normal for the powder charge and bullet used. All top loads however, with all powders and every bullet design was sparked by WLR primers in Winchester cases.

Time precluded working up maximum loads with all the possible powder and bullet combinations. For example, loads listed for the 220-grain bullets are working loads, but these bullets are designed for moderate velocities in the 375 Winchester and 38-55 WCF. They might come apart if you whack an elk in the shoulder at something over 2600 fps.

The 250 grain Barnes X-Bullet was used with Reloader 15 only. Reference loads for the 250-grain Hawk and Swift A-Frame are suitable for the Barnes X-Bullet assuming you observe the proper overall loaded length requirements.

Loads approaching 2500 fps with the 285-grain Speer Grand Slam may, for all practical purposes be considered very near maximum. The one load listed for AAC-2495 is a good working load in the Hendricks rifle. That is you can hunt anything on this continent with it although it is a bit below a prudent maximum.

Top loads with the 300 grain Hornady roundnose sneak up on 2400 fps with all the powders listed. Of the lot Reloader 15 showed remarkable shot to shot consistency. Some velocity variations were less than 10 fps for five shots. At 2397 fps the big bullet packs nearly 3840 ft-lbs of muzzle energy.