7mm Remington Ultra Magnum

History  

Inspired by the Lazzeroni proprietary cartridges, Remington introduced the 7mm Remington Ultra magnum in 2000. The 7mm RUM is based on the .300 Remington Ultra Magnum (1999) which is in turn based on a grossly modified version of the unbelted 404 Jeffery’s case. The RUM was designed to produce ultra high velocities to meet the growing demand for long range hunting rifles and cartridges.

Since its introduction, the 7mm RUM has achieved a mild following among long range hunting enthusiasts. That said, it is a chambering which hunters generally eventually move away from due to short barrel life.
 

Performance

From a 26” barrel, the 7mm RUM typically achieves 3450fps with 140 grain bullets, 3275fps with 160-162 grain bullets and 3175fps with 175-180 grain bullets. Velocities ‘should’ in theory be higher than the 7mmSTW which has the same case length but a much narrower body resulting in less case capacity. Nevertheless, the law of diminishing returns relative to overbore capacity dictates that the RUM only achieves around 30fps higher velocity than the STW when both are hand loaded to optimum potential.
 
Ultimately, only so much energy can be pushed through a 7mm orifice. A car engine is no different, a small 4 cylinder engine can only produce x amount of energy based on its cylinder bore capacity. Regardless of advanced methods of forced carburation, beyond a certain point, the engine suffers excessive wear, the valves burn out, bearings cannot take stress loads and so forth. The 7mm RUM is identical to a high performance race engine in every sense.
 
To optimize performance of the 7mm RUM, Remington engineers produced a chamber design utilizing .400” (10mm) free bore. This free bore acts as a gas expansion chamber, maximizing velocity due to a longer pressure curve. The case itself is designed for a working pressure of 65,000psi however, brass is brass and case life is not that high.
 
Due to the long free bore, bullets featuring short bearing surfaces must go through a phase during firing where the bullet is neither engaged in the case neck, nor guided by the rifling, literally free of control. Often, projectiles engage the rifling slightly off center resulting in poor accuracy. Some rifles appear to be forgiving of bullet design, producing acceptable accuracy with 162-168 grain bullets while others are only capable of producing optimum accuracy with either the 175 grain SMK or 180 grain VLD, neither of which are available as factory loads.
 
Custom, short throated 7mm RUM’s can and do produce extremely dangerous pressures with mild loads (89 grains powder). Such configurations generally have to be loaded to exactly 65,000psi pressures tend to be in the region of 70- 80,000psi when the cartridge is loaded both below and above optimum pressure having a window of only one or two grains powder leeway. To this end, it is most in-advisable to adopt a short (.200”) free bore configuration.
 
Barrel life of the 7mm RUM is extremely short due to hot gas erosion which occurs at the start of the rifling, the carefully cut leade which guides the projectile into full engagement of the bore. Used in the same manner as a standard hunting or target cartridge, barrel life is generally approximately 600 rounds. Barrel life can be extended up to and beyond 1000 rounds by allowing the RUM to cool to ambient temperatures between shots and cleaning (powder residues only) between 3 shot strings, however in the field this is often impractical. A few die hard fans of overbore cartridges insist on minimal practice and minimal field usage as the key to long barrel life in the Ultra Magnums however, any placed competitive shooter would suggest, that the key to successful shooting at long range is practice and not with a different rifle/cartridge.
 
The Remington factory rifle barrel contours and lengths are also detrimental to the performance of the 7mm RUM. The M700 SPS has a light contour barrel which overheats quickly and is too short at 26” for optimum performance. The 7mm RUM is better served with a heavy contour barrel of a minimum 28”, driving 180 grain bullets at 3200-3250fps. Remington do produce one heavy barreled rifle, the Sendero, but with a 26” barrel. These factors are unfortunately market driven.
 
Difficulties aside and where accuracy allows, the 7mm RUM is an outstanding performer on medium game, producing absolutely emphatic kills out to 800 yards and clean kills out to and beyond 1000 yards at which range speed of killing is dependent on target resistance to aid bullet expansion. The one limiting factor, is that at point blank ranges, the 7mm RUM often fails to generate hydrostatic shock, resulting in dead running game. This type of performance can be a major frustration to mountain hunters, losing dead run game to ravines.

   

Factory Ammunition

Remington factory loads include the 140 grain Core-Lokt Ultra at 3425fps, the 150 grain Swift Scirocco at 3325fps and the 175 grain A-Frame at a mild 3025fps. Unfortunately, Remington do not produce a load capable of producing fast, clean killing at long ranges.
 
The 140 grain Core-Lokt Ultra has replaced Remington’s initial load for the RUM featuring the 140 grain traditional Core-Lokt which surprisingly, managed to hold together at RUM velocities and produce excellent performance on lighter medium game. The new core bonded bullet is better suited to a wider range of body weights and to some extent, less prone to producing excessive meat damage. BC of the Ultra is .409 which is of curse counterproductive to the design premise of the RUM however; this bullet produces fast killing out to 350 yards.
 
Remington’s 150 grain Scirocco load is a spectacular performer on medium game, producing best results inside 400 yards (2600fps) and clean but slightly delayed killing as velocities approach and fall below 2400fps, having the same limitations as all core bonded bullet designs. The 150 grain Scirocco is adequate for use on deer weighing up to 150kg (330lb) but can tackle heavier animals, especially as velocity approaches 2600fps and below. The 175 grain A-Frame is an excellent bullet for tough, heavy bodied game. Again, as has been re-iterated throughout the 7mm texts, regardless of muzzle velocities, the 7mm bore produces limited wounding on large heavy animals. The A-frame produces cross body penetration on large, heavy bodied game but hunters should always be mindful of the  limitations of the caliber.
 

Hand Loading

 
Brass for the 7mm RUM is available from both Remington and Nosler. Suitable powders include H1000, Retumbo, H50BMG while US 869 is perhaps the optimum powder for this cartridge. Bulk density is a concern when hand loading the RUM and both H1000 and Retumbo can sometimes pose problems due to under filling, causing high shot to shot velocity deviations which greatly reduce accuracy beyond 600 yards. These powders must be loaded to full pressures to produce optimum results. At the other extreme, H50BMG is extremely course, much the same as short grain rice and full velocities are only achieved with compressed or near compressed loads. Due to its course nature, H50BMG has the potential to cause significant abrasion within the throat area of the bore. U.S 869 suffers none of the above problems.
 
From a 26” barrel, the 7mm RUM produces 3450 with 140 grain bullets, 3350fps with 150 grain bullets, 3300fps with 154 grain bullets, 3275fps with 160-162 grain bullets, 3220fps with 168 grain bullets and 3150 to 3175fps with 175-180 grain bullets. 

Although the 7mm RUM can achieve sizzling velocities of 3450 to 3500fps with 140 grain bullets, most produce fairly slow killing at close ranges. On impact, the hide of thin skinned game becomes as hard as bone. Entry wounding is violent however, having lost much energy against the hide, eliminating any potential shock transfer, the animal remains conscious throughout this trauma. The animal may run anywhere from 25 to 100 yards before succumbing to blood loss.

In the 7mm RUM, the only truly reliable 140 grain bullets are the Partition and core bonded designs which include the 140 grain Accubond and 139 grain InterBond. Even the well constructed 139 grain SST fails to produce emphatic killing when used on light bodied game inside 100 yards. At longer ranges, conventional 140 grain bullets produce more uniform performance however the throat erosion caused by high powder charges and excessive heat outweighs all benefits. Bullet jump and loss of concentricity is yet another problem.

150 grain conventional bullets produce much the same results as the lighter 140 grain bullets in the 7mm RUM. Again, bullet to bore concentricity is often lost during ignition while performance on game is less than spectacular at close ranges. Of the conventional bullet designs the 154 grain SST will sometimes produce acceptable long range accuracy and fast killing. This bullet works well alongside the 154 grain InterBond as a dual loading, the SST for long range work, the IB for close range hunting.

The 160-162 grain bullet weight is realistically the lightest bullet weight suitable for the RUM regarding both accuracy and killing. Two very forgiving bullet designs are the 160 grain Speer Hotcor and Speer BTSP.  These bullets tend to produce excellent accuracy in the 7mm RUM and can be adapted to hunting light to medium weight game, the Hotcor for close range work, the BTSP for longer range work. The BTSP has a BC of .519 which is not exceptionally high but from a muzzle velocity of 3275fps, produces clean killing out to 740 yards.

Hornady produce three very good projectiles, the 162 grain BTSP, the 162 grain SST and the 162 grain A-Max. The 162 grain BTSP Interlock is a basic bullet suitable for hunters on a limited budget. This bullet is extremely effective and spectacular on lighter medium game, producing faster kills at close ranges than other conventional bullet designs driven at velocities above 3200fps. BC is .514 and the Interlock tends to produce best performance at impact velocities above 2200fps (600 yards) but is adequate out at 720 yards as velocity approaches 2000fps.

The 162 grain SST is one of the best bullets available for use in the RUM. Its only limitation is at point blank ranges where it occasionally fails to impart hydrostatic shock due to the increased target resistance associated with ultra high velocity, though wounding is thorough and killing usually only slightly delayed. At 3100fps (90 yards), the SST comes into its own, rendering wide wounds and exit wounds of up to 3” in diameter on medium sized game. The 162 grain SST is not well suited to heavy bodied game at close ranges but at long ranges, beyond 600 yards, this bullet is perhaps the optimum choice for large bodied game. BC of the SST is .550 and although this is lower than the likes of the A-Max, this bullet should not be over looked as it offers performance which other bullet designs cannot duplicate. Maximum effective range for the SST is up to and beyond 1000 yards depending on target resistance.

The 162 grain A-Max is an excellent hunting bullet. As has been reiterated throughout the 7mm magnum texts, its one limitation is that if used at close range on large bodied medium game, wounding can be shallow with shoulder shots. As an all-round load, the A-Max must be used with care. With time and experience, the A-Max can be used to great effect not only for dedicated long range hunting, but as a general purpose medium game load. As a long range hunting bullet, the A-Max has no peer, no other bullet is able to produce the same level of consistently wide wounding at velocities as low as 1400fps, equating to a whopping 1450 yards in the 7mm RUM.

Nosler’s 160 grain Partition and 160 grain Accubond are both good performers in the RUM. The RUM chamber design seems to work very well with the Partition and in some instances, the Partition can produce greater accuracy than 160-162 grain boat tail bullet designs. Although the Accubond has a high BC of .533, the Partition is the more violent of the two at all ranges. Both are good projectiles for use on larger bodied medium game however for both light and heavy bodied medium game, the Partition is a much more spectacular killer. That said, the Accubond produces much less meat damage. The Accubond tends to produce fast killing inside 360 yards with a reduction in speed of killing as it falls below 2600fps. The Partition continues to produce wide wounding out to ranges of around 675 yards (2000fps), producing emphatically fast kills at intermediate ranges.

Berger’s 180 grain VLD is extremely well suited to the long bullet jump of the 7mm RUM, producing optimum accuracy. Performance on game at both close and long ranges out to 1000 yards is outstanding and the 180 grain VLD can tackle a wide range of game weights. 

Note: Update 1 Jan 2011. Berger have recently thickened the Jackets on the VLD line of projectiles due to concerns from hunters that the VLD was suffering mid air bullet blow up (perhaps due to aggressive twist rates in custom rifles?). The new 180 grain VLD is very stout and can produce pin hole wounds on light bodied game at all ranges, regardless of ultra magnum velocities. This problem can be minimized by annealing the ogive. Place the VLD projectile in a pan of water with only the ogive exposed and heat the ogive with a blow torch duplicating the traditional method for annealing brass. The annealing should be aggressive, as to cause a permanent color change. Accuracy is unaffected providing care is taken. When used un-annealed, the new style 180 grain VLD is more suited to heavy bodied medium game at extended ranges, filling its own niche.
 

Closing Comments

The high cost of ammunition coupled with excessive throat erosion/ limited barrel life has limited the popularity of the 7mm RUM to dedicated long range enthusiasts. The RUM can be a lot of fun but its idiosyncrasies can lead to a level of frustration which eventually outweighs any benefits.  

Note: Recently, I discovered that a worn RUM can be revived. Please follow the link below to be re-directed to 'how to break in a rifle barrel'. At the bottom of this article is the stub article, 'Reviving a 7mm RUM'.

How to break in a rifle barrel
 

Suggested loads: 7mm RUM					Barrel length: 26”
No	ID		Sectional Density	Ballistic Coefficient	Observed  MV Fps	ME Ft-lb’s
1	FL	Rem 150gr Scirocco	.266	.515	3325	3682
2	HL	160gr Partition	.283	.475	3275	3810
3	HL	160gr Speer Hotcor	.283	.504	3275	3810
4	HL	160gr Speer BTSP	.283	.519	3275	3810
5	HL	162gr SST	.287	.550	3275	3858
6	HL	162gr A-Max	.287	.625	3275	3858
7	HL	180gr VLD	.319	.684	3175	4028
8	HL	180gr VLD *	.319	.684	3175	4028

 
 

Suggested sight settings and bullet paths
1	Yards	100	175	318	360	400	425	450	475
	Bt. path	+3	+4.1	0	-3	-6.6	-9.3	-12.3	-15.7
2	Yards	100	175	309	351	375	400	425	450
	Bt. path	+3	+4.1	0	-3	-5.2	-7.7	-10.7	-13.9
3	Yards	100	175	311	353	375	400	425	450
	Bt. path	+3	+4.1	0	-3	-4.9	-7.4	-10.3	-13.5
4	Yards	100	175	312	355	375	400	425	450
	Bt. path	+3	+4.1	0	-3	-4.8	-7.3	-10.1	-13.2
5	Yards	100	175	315	358	375	400	425	450
	Bt. path	+3	+4.1	0	-3	-4.5	-6.9	-9.6	-12.7
6	Yards	100	175	318	361	400	425	450	475
	Bt. path	+3	+4.1	0	-3	-6.4	-9	-11.9	-15.2
7	Yards	100	175	308	352	375	400	425	450
	Bt. path	+3	+4.1	0	-3	-5	-7.5	-10.3	-13.3
8	Yards	100	175	315	357	375	400	425	450
	Bt. path	+3	+4.1	0	-3	-4.5	-6.9	-9.6	-12.6

 
 

No	At yards	10mphXwind	Velocity	Ft-lb’s
1	400	8.7	2578	2214
2	400	9.7	2479	2184
3	400	9.1	2522	2258
4	400	8.8	2542	2294
5	400	8.2	2580	2394
6	400	7.2	2658	2540
7	400	6.8	2620	2742
8	400	6.8	2620	2742

 
Notes: Loads 2, 3, 4 work well in finicky rifles. Load No 4 duplicates trajectory of 162gr Interlock, another good economical, hard hitting load.  * indicates a load with scope set at 1.8” high.


 

 

	Imperial	Metric
A	.534	13.56
B	.550	13.97
C	30deg
D	.525	13.3
E	.322	8.17
F	2.387	60.62
G	.287	7.28
H	2.850	72.39

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