.375 Remington Ultra Magnum

History

During 1999 Remington Arms introduced their .300 Remington Ultra Magnum, an extremely powerful cartridge based loosely on the .404 Jeffery cartridge case design blown out to maximum dimensions. In the same year Remington announced that they intended to introduce both a .338 RUM and 7mm RUM, both arrived on the market in 2000. Following this, Remington made another statement in the year 2000 of their intention to introduce a .375 caliber RUM. The .375 RUM was released in 2001 and is the largest of the Remington Ultra Magnum cartridges.

The case design of the .375 RUM is the same as its 7mm and .30 caliber counterparts. These three cartridges differ from the .338 RUM in that the .338 has a slightly shorter case for the sake of a comfortable cartridge overall length (COAL) within the limits of the Remington M700 rifle magazine.

Since its introduction the .375 RUM has had a mild following. Firing a 300 grain bullet at around 2950fps, the .375 RUM is a potent cartridge.
 

Performance

The .375 RUM is an extremely well-balanced cartridge coming to within 50fps of the .378 Weatherby. The prominent factor of this bore diameter is versatility. Larger bores can prove more emphatic on heavy game, however the medium .375” bore excels in a wider range of roles, generally producing lower recoil combined with flatter trajectories. Having said this, both the RUM and .378 Weatherby lean towards the extremes. Recoil is now more noticeable than the smaller .375” magnums while powder consumption is higher. The advantage of the RUM and .378 Weatherby can be found in their ability to anchor heavy animals quickly.

When used on lightly built game the .375 RUM is an emphatic killer out to moderate ranges. But at extended ranges the heavy .375” projectiles require some body weight resistance (150kg / 330lb).

As a large thin-skinned game cartridge the .375 RUM is simply excellent and can make use of a very wide range of bullets. Both the RUM and .378 Weatherby can used with great success out to ranges of up to and beyond 600 yards with select bullet designs.

As a heavy game cartridge the .375 RUM can be viewed as light but fast in the same manner as the .243 or .25-06 relative to larger bodied deer. By selecting appropriate bullets the RUM can produce excellent performance but does its very best work at close ranges where energy is high. On extremely heavy game the RUM can be used to drive very long and heavy bullets deep into vitals as a means to achieve reliable killing.

Regarding the Remington M700 rifle chambered in .375 RUM, the stock design was never all that good in this chambering. The stock pitch was fine, however, as a tool handle it was altogether too small. The plastic stock model was, to be blunt, ridiculous. Realistically, this should have been placed on the Sendero stock. But alas I am sure the many opinionated gun rag writers and less than five hundred word internet bloggers would have found fault with such a design as they sit behind their lead sleds. The one aspect of this rifle that I have not been 100% sure of, is whether Remington’s M700 action is truly optimal for this level of thrust. Nevertheless, regardless of any differences in action thickness between the well trusted CZ 550M and the Remington M700, the locking lugs of the M700 are no smaller than the CZ (actually slightly larger). My own M700 rifle mated to an HS Precision PST014 stock has certainly never let me down. However, I have never overloaded this rifle.
 

CZ bolt (top) compared to the M700 bolt.




CZ and M700 locking lugs side by side. CZ bolt diameter is 17.8mm, body plus lug diameter 24.23mm, lug width 10.84mm. M700 bolt diameter is 17.66mm, body plus lug diameter 25.09mm, lug width 11.17mm. 

As always, steel based epoxy bedding is a key factor as a means to enhance accuracy and maintain stock integrity. A light and crisp trigger is also very important at this recoil level. Those who build a rifle with a generously wide forend and utilize a barrel of sufficient heft (all up weight 11.5lb or heavier) will find that it is possible to experiment without a muzzle brake. In lighter rifles recoil can simply be too high without a brake and can at times cause concussion headaches.

For the sake of posterity I will state here that I taught myself the critical aspects of shooting technique utilizing an unbraked Remington BDL rifle chambered in .375 RUM weighing around 9.5lb. My pet accuracy loads consisted of a 300 grain bullet at 2950fps along with a 225 grain load to 3225fps. By focusing on sub-minute accuracy, this rifle amplified the smallest of human errors. I learned how to shoot well and also learned the importance of developing a transferable skill set. I have never questioned my shooting skills since and find any arguments to my methods simply laughable. These lessons are now taught in my book, The Practical Guide To Long Range Shooting.

 

 

Factory ammunition

Remington currently list just one factory load for the .375 RUM consisting of the 270 grain soft point at a mild 2900fps. Gone is the 300 grain Swift A-Frame which was also loaded to very mild velocities of around 2700 to 2760fps. For some time Remington utilized the Hornady round nose projectile for this loading, however I do not know if Remington are still able to obtain this seeing as the Hornady RN bullet has recently been discontinued. The wide frontal area of the Hornady bullet combined with its basic conventional construction made it immensely effective at producing fast kills on lean game out to moderate ranges, suitable for game weighing up to 320kg (700lb). Put simply, it was a good bullet for a wide range of deer species. I would hazard at a guess that this load listing may soon have to be altered.

Barnes, Nosler and Double Tap also list ammunition for the RUM. I have not tested any of these as factory loads but have tested the component bullets. Readers are advised to be extremely wary of Barnes LRX load claims which utilize the RUM in a very poor manner, adopting the absolute opposite approach to that taken by the likes of Sierra and Hornady. The Nosler Accubond loads also have severe limitations in the RUM. These topics are covered in more detail within the hand loading section of the .378 Weatherby text and also with my Long Range Cartridges book.
 

Hand loading

Brass for the .375 RUM is still readily available and can also easily be formed from .300 RUM brass. Top velocities for the .375 RUM are achieved with powders in the H4350 (ADI 2209) range. Mild loads can be created by using slower burn rate powders such as H4831sc (ADI 2213sc). Those who wish to duplicate the .375 H&H can utilize full charges of H1000.

Using full charges of H4350 velocities for the 26” barreled .375 RUM include 3150 to 3250fps with 225 to 235 grain bullets, 3200fps with 250 grain bullets, 3150fps with 260 grain bullets, 3100fps using 270 grain bullets, 2950fps to 3000fps with 300 grain bullets and 2700fps with the 350 grain Woodleigh and Sierra projectiles.

The RUM is a very long cartridge; the chamber design features a good deal of freebore, much like the Weatherby magnums. Generally speaking, the magazine length of the M700 is suitable for most projectiles however long range bullets such as the Rocky Mountain and SMK require the longer Wyatt magazine box (gunsmithing required) to keep the ogive out of the case neck. Alternatively, a CZ or Mk V action may be used. These help the hand loader get closer to maximum OAL’s of around, or longer than 100mm (3.937”).

Due to the fact that this cartridge produces very similar velocities to the .378 Weatherby readers are referred to that text for a full discourse on hunting projectile performance. There is little more to say here other than to remind readers that on very large animals this cartridge works best with the toughest of premium projectiles combined with high impact velocities. Shot placement also has a highly pronounced effect. Depending on the angle of the animal, a 4” change to the point of impact can make a pronounced difference as to how fast an animal goes down. Full proficiency requires both good rifle accuracy combined with an ability to visualize outcomes from various angles. This can take a good deal of time and practice.

 

Closing comments

The .375 RUM is a wonderful cartridge. While the .375 Ruger is an extremely versatile cartridge, the RUM runs more towards the extremes finding its strengths when it used on very large body weights. This cartridge may not boast the same bullet weights as larger bores but is nonetheless well balanced and an absolute pleasure to use.
 

Another bull instantly down with the RUM. This was the rifle which I used to teach myself the finer aspects of
shooting technique.




The Woodleigh 300 grain PP Weldcore bullet, having taken on around 600kg of beef at an impact velocity of around 2900fps.This does however push the limits of this 300 grain bullet design. If used on heavier game at these speeds, there is a risk of over expansion and deflection. On heavy, dangerous game a homogenous bullet design can prove more reliable.

 

Suggested loads: .375 RUM					Barrel length: 26”
No	ID		Sectional Density	Ballistic Coefficient	Observed MV Fps	ME Ft-lb’s
1	FL	Remington 270gr RN	.254	.253	2870	4937
2	HL	235gr Speer, Barnes TSX, Woodleigh	.239	.301	3200	5342
3	HL	270gr Speer BTSP	.254	.429	3100	5760
4	HL	270gr Barnes TSX*	.254	.326	3100	5760
5	HL	300gr Sierra BTSP	.305	.475	2950	5796
6	HL	300gr Woodleigh PP*	.305	.380	2950

 

Suggested sight settings and bullet paths
1	Yards	100	236	272	300	325
	Bt. path	+3	0	-3	-6.3	-9.8
2	Yards	100	170	279	317	350	375	400
	Bt. path	+3	+3.8	0	-3	-6.4	-9.5	-13.1
3	Yards	100	165	283	323	350	375	400
	Bt. path	+3	+3.8	0	-3	-5.5	-8.3	-11.5
4	Yards	100	227	260	300
	Bt. path	+2	0	-2	-5.2
5	Yards	100	150	268	308	350	375	400
	Bt. path	+3	+3.6	0	-3	-7.2	-10.3	-13.8
6	Yards	100	220	254	300
	Bt. path	+2	0	-2	-6

Sight height 1.6” (Scope).

* Loads 4 and 6 considered as close range loads in order to ensure high impoact velocities on heavy game.
 

No	At yards	10mphXwind	Velocity	Ft-lb’s
1	300	13.2	1876	2109
2	300	9.1	2287	2729
3	300	6.4	2454	3610
4	200	3.7	2529	3832
5	300	6.1	2383	3783
6	200	3.3	2471	4067

.375 RUM	Imperial	Metric
A	.534	13.56
B	.550	13.97
C	15 deg
D	.525	13.34
E	.405	10.3
F	2.387	60.63
G	.359	9.12
H	2.850	72.4
Max Case	2.850	72.4
Trim length	2.840	72.1

 

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