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Shooting Illustrated

Shooting Illustrated
March 2005
Home Grown

By Bryce Towsley

Unlike most of the American big game hunting public I have always been a fan of .35 caliber rifles. Physics is physics and big bullets simply hit harder. The downside, even in cartridges like the .35 Whelen, has been a trajectory that is too curved by today’s magnum-loving standards. But when Remington brought out the .300 Ultra Mag in 1999, I saw an opportunity. Even though they had plans for a family of cartridges based on the parent case, I knew it would be a long wait for a .35, so I built my own.

I decided to keep it simple and necked the .300 RUM case up to .358 with no other changes. It maintains the same body taper, the same 30-degree shoulder and the same datum line for headspacing. The only difference is a larger, slightly shorter neck and the resulting shorter shoulder. I called the new cartridge the .358 Ultra Mag Towsley (UMT).

The .358 UMT shoots flatter than a 7mm Remington Magnum with a 160-grain bullet or a .300 Winchester with a 180-grain bullet. In the .358 UMT a Nosler Partition 225-grain bullet at 3,225 feet per second that’s zeroed for 200 yards is only 5.72 inches low at 300 yards. The .300 Win Mag with the same zero is 7.60 inches low at 300 yards and the 7mm Rem Mag drops 7.24 inches.

The .358 UMT with a 250-grain bullet produces 5,388 foot-pounds of muzzle energy. That is over 1,000 foot-pounds more muzzle energy than the .375 H&H 300-grain factory load. The .358 UMT has more energy than the .416 Remington 400-grain factory load at any range, including at the muzzle. At 100 yards it still has more energy than the .375 H&H has at the muzzle and at 200 yards it retains 3,676 ft-lbs, almost as much as the .338 Win Mag has at the muzzle.

I conceived this to be a gun that would be lugged for miles up steep elk mountains or through the muskeg of Alaska. The weight needed to be balanced between heavy enough to shoot well under field conditions and light enough to not be hateful at the end of a long day. When fitted with a Leupold Vari-X III 3.5-10 scope in Leupold two-piece mounts, my custom Bansner rifle weighs eight pounds. This is on the light side for a rifle chambered in so powerful a cartridge, but due to an excellent High Tech synthetic stock design the recoil is very manageable for an experienced shooter. Most people who shoot the rifle for the first time remark at how the kick was a lot less than they anticipated.

I wanted a rifle suitable for hunting elk, big bears, moose and the larger African plains game in all the differing terrain they live in. I wanted it to shoot flat so it could handle long shots, but also to hit hard and penetrate deep for big and tough game. What I found was a rifle that works for everything. I have used this gun while chasing a diversity of big game from whitetails to brown bears. It’s been to Africa with me twice and has accounted for game ranging from a 600-pound waterbuck to a diminutive red duiker. In a few days I am taking it to Montana for mule deer. Admittedly it’s more rifle than I need, but it’s so accurate and shoots so flat, it just makes sense. Dead is dead, “overkill” is a misnomer.

As wildcats go, this one is simple to make. One pass of a well-lubed Remington case through the RCBS sizing die’s tapered expander button expands the neck from .30 to .35. The case is usable and accurate right out of the gate, but fireforming with the first load insures the neck is centered and concentric with the case. The expanding process shortens the case by about .018-inch so I square the new case mouths and trim to 2.820-inch. I chamfer the case mouth and load it.

The big case works best with heavy bullets weighing 225-grains to 250-grains. The limiting factor in overall cartridge length with any of the Ultra Mag cartridges is the rifle’s magazine. The maximum workable cartridge length in this gun is 3.675-inch and that determines the bullet seating depth.

The .358 UMT is not a particularly fussy cartridge to load for, except that it does favor specific powders. I initially thought it would work best with powders like 4350 or 4831, but they actually proved to be a bit too fast. IMR-7828 was by far the best powder tested, but H-1000 also works very well in some loads. With big charges of any powder a hot primer is important; I use only Federal 215 primers.

A few years back I sent the gun out to Barnes Bullets and as a favor they did a series of load developments in their laboratory, where they could measure chamber pressure. The SAAMI spec for the .300 Ultra Mag cartridge is a mean average pressure of 65,000 PSI, which we used as a guideline. Their choice for a “best hunting load” turned out to be mine as well. With a 225-grain XLC Coated X-bullet, they found that 98-grains of IMR-7828 produced 3,100 feet per second and sub-inch groups. I experimented further and found that I could easily take this bullet up past 3,200 feet per second without pressure going too high, but when I did accuracy deteriorated slightly. In the end I settled on exactly the same load the Barnes Lab Rats said would be the best. Recently I substituted the new Barnes Triple Shock 225-grain bullet for the coated X-Bullet. Muzzle velocity with 98.0-grains of IMR 7828 is 3,164 feet per second and the average three shot group measures .6-inch at 100 yards. This was the first load I tried with this bullet, and I quit experimenting right there. It’s hunting season right now, maybe when I have a little more time I’ll see if I can take the velocity higher and still maintain the accuracy.

Another bullet that proved excellent is the Swift 250-grain A-Frame. When teamed with 97-grains of IMR-7828 it exits the muzzle at 3,114 feet per second. Accuracy is nearly one hole for the best three-shot groups and always averages less than one minute of angle. The steep ojive profile of this bullet allows it to be seated out almost to the rifling lands while the overall cartridge length remains short enough to fit in the magazine. With this heavier bullet, the mouth of the case must be crimped into this bullet’s cannelure or those in the magazine will migrate out of the case under recoil and fail to chamber.

With 102.0-grains of H-1000 powder, the Nosler 250-grain Partition has a muzzle velocity of 3,029 feet per second. The best 100-yard group was .5-inch and the average is just over one inch. The Nosler 225-grain Partition achieves velocity of 3,225 feet per second with 99.0-grains of IMR-7828 and 1.15-inch average accuracy.

One thing that must be kept in mind is that this is a custom rifle built by Mark Bansner and fitted with an excellent Krieger Barrel. In another gun with a different barrel these loads may prove to be too hot.

Most of the .35 caliber bullets on the market were developed for cartridges like the .35 Whelen and are not meant for velocities this high. This cartridge absolutely requires a premium bullet for any big game, as even some excellent game bullets act like varmint bullets, blowing up on impact.

Probably the best all around bullet is the 225-grain Barnes. I used it on big and tough game like gemsbok, kudu and zebra. Out of a dozen or more shot into big game, only one bullet failed to exit and that was a finishing shot on a gemsbok. It hit a lot of bone and was pretty beat up, but still weighed 170.5 grains. The X-Bullets always killed effectively and clearly expanded on shots as long as 450 yards, or on game as small as an 80-pound springbok. But they still penetrated enough to exit on a zebra hit in the shoulder from 30 yards. The new Triple Shock Barnes is showing a lot of promise and is impressive at the range. I haven’t shot any game with it yet, but the Barnes folks tell me that the terminal ballistics will be much the same as the old X-Bullet.

The Swift A-Frame opens up very quickly and transfers a lot of energy, but doesn’t penetrate as deep as the Barnes. This is to be expected with a wide-expanding lead core, bonded bullet. Of course, penetration is relative. I shot the elk-sized waterbuck in the chest as it stood looking at me from 250 yards. I found the bullet under the hide in front of the hindquarter. I didn’t measure the distance, but that bullet went through a lot of waterbuck. The average weight from the three A-Frame bullets I have recovered from game is 228.3-grains. The lightest hit a nyala in the spine with a finishing shot at 30-yards and still weighed 218.2 grains. All of the recovered bullets were expanded to slightly less than two calibers and averaged .667-inch.

I am currently working on a .416 UMT that will take over where this gun leaves off. After that I may take a look at the other direction with possibly a .270 UMT or .257 UMT. Let me know what your thoughts are by contacting me through Shooting Illustrated at shootingillustrated@nrahq.org.

For information on building a .358 UMT rifle contact:
Bansner’s Ultimate Rifles
261 E. Main St.
Adamstown, PA 19501
717-484-2370
717-484-0523 Fax
www.bansnersrifle.com

Loading Data tested in the Barnes Ballistic Laboratory
.358 Ultra Mag Towsley

Bullet

Powder & Charge

Velocity
FPS

Accuracy
100 yds

Pressure
Psi

Barnes 250-grain X-Bullet

IMR-7828
91.0 grains

2,889

-

56,900

Barnes 250-grain X-Bullet

H-1000
98.5 grains

2,887

1.75

56,500

Barnes 250-grain X-Bullet

RL-25
90.0 grains

2,965

1.25

58,900

Barnes
250-grain Solid

H-1000
98.5 grains

2,887

-

51,200

Barnes
250-grain Solid

IMR-7828
91 grains

-
-

48,700

Barnes 225-grain X-Bullet

RL-25
98.5 grains

3,048

1.25

60,300

Barnes 225-grain X-Bullet

H-1000
101.1 grains

2,990

1.25

59,400

Barnes 225-grain X-Bullet

IMR-7828
95.0 grains

3,039

0.5

59,100

Barnes225-
grain X-Bullet

Ram Shot Magnum 103.0 grains

3,045

N/A

58,600

Barnes 225-grain X-Bullet

MRP
96.0 grains

3,058

1.1

58,100

Barnes 225-grain XLC Coated

IMR-7828
98.0 grains

3,100

.75

N/A

Barnes 180 grain X-Bullet

MRP
101.5 grains

3,408

1.5

59,000

Barnes 180 grain X-Bullet

RL-25
106.0 Grains

3,398

2.0

58,700

Barnes 180 grain X-Bullet

IMR-7828
102.0

3,341

1.75

59,100

Nosler 250-grain Partition

H-1000
102.0 grains

3,029

1.2

61,400

Nosler 225 grain Ballistic Tip

H-1000
104.0 grains

3,011

2.0

57,300

Re-published with permission from the Shooting Illustrated March 2005 issue.

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