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7mm Practical


The 7mm Practical is a cartridge of my own design developed between the years 2010 and 2011.

Having witnessed very short barrel life with the 7mm RUM, yet also having enjoyed the excellent power levels of the RUM, I set about exploring whether it would be possible to obtain the same or similar velocities from a smaller case capacity. One of the major downsides of the 7mm RUM is that it is very much overbore and requires excessive free bore (bullet jump) to reach full velocities. I had already experimented with a half throated 7mm RUM and found this combination to be potentially dangerous due to pressure spikes with mild loads (powder bridging / detonation). Only so much energy can be squeezed through a 7mm orifice and I determined to work towards developing a maximum power wildcat cartridge design, one that would not suffer diminishing returns or have to utilize excessive free bore. The cartridge had to be a simple design, easy to work with and without requiring an extremely long magazine. It had to be practical.

During this period of research I was already aware of and had tested the 7mm STW, an excellent cartridge which Remington adopted but soon discarded in favor of the 7mm RUM. The STW had only one fault, the need for a longer than factory length magazine box if seating long match style hunting bullets close to the lands. For a time I contemplated the possibility that the STW (8mm Remington Magnum parent case) may well be the limit, but I also suspected that the case might still be a touch overbore. Either way, the issue of magazine length prompted me to look towards a shorter case.

Over the years, several hunters have necked the .300 Winchester Magnum case down to 7mm, I was certainly not the first to do so. Some claim that the 7mm-300 Win Mag is nothing more than the 7mm Mashburn however this is not quite true.  The 7mm Mashburn Super Magnum wildcat was based on the .300 H&H case, blown out and necked down - not the .300 Winchester Magnum. The Mashburn was designed by Art Mashburn during the mid to late 1950’s. Warren Page, editor of Field and Stream magazine put the cartridge into the public spotlight when he adopted Mashburn’s chambering and discovered its ability to comfortably launch a 160 grain bullet at 3200fps using the powders of the day. Page very much wanted Remington to adopt the Mashburn but instead Remington opted to standardize Les Bowman’s .338 Win mag necked down to 7mm, the now famous and very useful 7mm Remington Magnum.

Although the Mashburn never met fame the concept stayed alive - but only barely. During the mid 1990’s through to more recently, powder manufacturers have developed ultra-slow burning powders well suited to this case capacity. After studying the case capacity of the Mashburn, its similarities to the .300 Winchester Magnum as a parent case and reported velocities along with the occasional but hard to find anecdotal notes regarding the 7mm-.300 Win Mag, I settled on the .300 Winchester magnum necked down to 7mm as a basis for my wildcat case design.

The design premise for my version of the 7mm-.300 Win Mag was to obtain maximum power from the 7mm bore without excessive wear, suitable for the volume of shooting (practice and hunting) I prefer from a long range rig (approximately 12 shots per week on average). The cartridge was to be used for hunting light to medium weight game from point blank, out to true long range distances. Since its adoption, the case capacity is what I consider to be optimal for a balance of efficiency versus effective power at extended ranges. To obtain a chamber reamer, I sought the services of Pacific Tool and Gauge.

I also took the opportunity to incorporate a long neck into the cartridge design. This was achieved by simply extending the neck area of the chamber forwards and allowing cases to grow rather than continually trimming. The shoulder angle was also changed from 25 to 30 degrees. Had I selected a 40 degree shoulder, I would have arrested case neck growth.
There would be no need for special dies or special operations when reloading for this wildcat. The cartridge was designed to utilize a basic and generic 7mm Magnum neck and seating die.

Bullet jump was to be dictated by a separate throat reamer so that each rifle could have its throat cut to suit its magazine box thereby minimizing bullet jump. That said, the wildcat was too long for some of the less than generous magazine boxes found on several long action rifles. Ideally, minimum magazine length is 91mm (3.583”).

The wildcat was also designed in such a way that it would utilize an easily sourced parent case. The belted .300 Win Mag case design is easy for gunsmiths to work with, without need of custom head spacing gauges. The Smith can use standard 7mm Remington Magnum gauges to check fit. Furthermore, fire forming loads utilize the belt, giving the belt a second purpose. To this end the belted cartridge design is advantageous and in no way troublesome. Better still, full power fire forming loads have proven extremely accurate. These can often be used for long range shooting although the point of impact (POI) can in some rifles differ from formed cases. A second option is to utilize fire forming loads at closer ranges, loaded with controlled expanding bullets as part of dual loading. A third option is to simply utilize Trail Boss powder at an 80 to 100% fill ratio for low pressure, low wear fire forming loads.  

Finally, I had to come up with a name for the wildcat. I chose the 7mm Practical based on the premise for the design. After building the first test rifle, load development soon proved that the 7mm Practical was a potent cartridge, meeting my every expectation. The wildcat did however fall slightly short of the RUM by around 50fps. The first Practical rifles featured 28” barrels while the RUM typically utilized a 26” barrel. Nevertheless, the loss amounted to an effective range decrease of 25 yards. 

After building and testing my own rifle, we commenced building rifles for clients, utilizing the expertise of True-Flite NZ to supply and fit their excellent barrels. All of the rifles produced gave sub .3 MOA accuracy which was outstanding. But as more time went by, the Practical began to show stiff chambering and sticky extraction with continually neck sized cases. I had just worn out a .308 Winchester barrel using 60 Hornady cases, neck sized from start to the end of barrel life and saw no reason why the Practical could not do the same - back to the drawing board.

After exploring where the tight spot in the chamber lay, it was found to be occurring at the case body in the area of the shoulder junction - but not the shoulder itself as this sprang back nicely after each firing. I contacted PTG and we re-designed the Practical body dimensions in the same manner as the .284 Shehane, the slightly wider dimensions allowing more room for both expansion and hopefully - spring back. I was greatly concerned about potential accuracy loss but something had to be done to keep the wildcat a simple proposition for end users.

The 7mm Practical Revision B reamer design was and is the basis for the final 7mm Practical cartridge design. The first rifles were produced in December 2011. The final 7mm Practical design has proven to be extremely accurate. The extremely small change in cartridge body dimensions also resulted in a slight increase in power.  This allowed end users to adopt shorter 26” barrels and still remain within 50fps of the RUM. That said, a few rifles have produced greater velocities than the RUM.

The Practical was designed to do what its name suggests, to provide a simple, practical cartridge for precision long range hunting. The Practical also excels at closer ranges with suitable bullet designs. The Practical is in no way as efficient as such wonderful cartridges as the .308 Winchester, but as a long range hunting cartridge the magnum has great strengths, producing optimal magnum performance.

Since my first online research article charting the development and performance of the 7mm Practical, the cartridge has unexpectedly grown in popularity worldwide.

7mm rem mag and Practical for web

7mm Remington Magnum at left, Practical on right.


From a 26” barrel, the 7mm Practical loaded with 160-162 grain bullets produces velocities of between 3225 and 3275fps with the occasional rifle producing sweet spots as high as 3315fps. Sweet spots for 180 grain bullets are between 3100 and 3150fps while the 190 grain Matrix likes to be driven between 2950 and 3000fps. These velocities are generally on par with both the 7mm STW and 7mm RUM. The Practical definitely proves that there is no great need for the barrel killing 7mm RUM design. The same can be said of the 7mm STW, achieving maximum potential power without need of excessive free bore.

The 7mm Practical produces around 150fps greater velocity than the 7mm Remington Magnum (averaging past client rifles). That said, some 7mm Rem Mag rifles will produce muzzle velocities of 3125fps with 160-162gr bullets which closes the gap to around 100fps. It is therefore important to remain realistic as to the potential of the Practical. The 7mm Rem Mag is in its own right an excellent cartridge design. The Practical also recoils more than the Rem Mag, especially in occasional rifles capable of delivering up to 3315fps with 160-162 grain bullets. The small gains of the Practical really only come to the fore when shooting at extremely long ranges, displaying excellent wind drift characteristics.

The 7mm Practical is best suited to light through to mid weight game species but is also able to tackle larger game species with select bullets. The high velocities of the Practical can be used as a means to maximize wound trauma at extended ranges with minimum wind drift. The Practical cannot however fire the heavy bullets that prove so effective in the .300 and .338 magnums when used on large bodied game.

vital wounding at 1125 yards WL

Liver wounding at 1125 yards (see video).

Happy practical shooter WL

A happy Practical owner with a Pitt Island ram

Throat wear is approximately .1mm / .004" per 400 rounds - providing the throat is kept polished to close pores within the bore steel. Barrel life is approximately 1000 to 1200 rounds. All client rifles are going well apart from one rifle which showed more aggressive wear from long and fast shooting strings without attention to throat care. This rifle showed a growth of 1mm (40 thou) over 700 rounds and was beginning to lose accuracy. Fortunately, a session of re-lapping of the throat revived accuracy to full potential. There was still enough mag length (M700) to work with - mag length versus throat wear being something to keep in mind during COAL planning.

Most shooters tend to think that abrasive polishing will literally wear the bore down but the opposite is true when it comes to throats. It is very important to keep the pores in the steel closed as is the same in other engineering practices such as stainless food grade vessels and stainless marine.

Reamer notes

The 7mm Practical Revision B is a no throat reamer design, meaning that a separate throat reamer must be used to cut the lead. This allows the gunsmith to set the COAL to suit varying magazine lengths, the shortest suitable magazine length being 91mm or 3.582" internally.

In some instances, shooters have opted for fixed lead reamers.

If running a fixed lead reamer in the 7mm Practical, a good versatile bolt face to lead measurement would be 73.08mm or 2.877". This gives max COAL's of around 92mm or 3.622" with the A-Max and 92.2mm or 3.630" with the 190 grain Matrix. But again, it is important to check your magazine length to make sure it can handle cartridges of this length.

Putting the above into layman's terms, if approaching PTG or any reamer maker, you can set the throat length for a long magazine rifle (as opposed to the original no throat design) by including the statement: Please include free bore, bolt face to lead is to be 2.877". This comment can be placed during the order process.

Free bore is therefore .2043"

There have been some reamers created with lead (free bore) built into the single reamer. On occasion this has been left up to PTG to determine, resulting in a default .188" free bore. This is not far off my suggested figure and not really enough to negatively effect velocity potential in a meaningful manner. Individual bore tolerances would have as much effect. So I think PTG have done OK with this 7mm generalization. This free bore also allows room for throat wear- an added plus well worth considering!

As a reminder, less free bore should be employed if for example, employing a Howa action which is right on the limit for minimum magazine length. Either use my no throat design and separate throat reamer or if using a reamer that features lead (what end users call the throat), set the bolt face to lead measurement at 2.836".

All of the measurements given here are with regard to allowing the shooter to seat close to the lands. Some folk may wish to adopt a little more bullet jump. For example, it is no great trick to get Berger bullets to shoot with 40 thou or more jump. In fact more often than not the Berger bullets do much better with increased jump. If we take this a bit further and look the .188" free bore reamer, max COAL with the 168gr VLD is around 91.6mm or 3.606". The Howa / Vanguard (mag length 91mm or 3.582") feeds smoothly at a COAL of 90.2mm or 3.551" with a resulting bullet jump of 1.4mm or .055.

Gunsmiths please note. It is important to check the reamer supplied. There has been one instance so far of a gunsmith  receiving a no throat reamer and neglecting to utilize a secondary throating reamer, resulting in immensely high pressures. Always check. A second note for gunsmiths is to not get too tied up in the minimal head space game. The Practical does very well with generous head space (use 7mm Rem Mag gauges) and is all the better for it. If the chamber is made too tight it may have the negative result of making neck sized brass difficult to chamber long term. Remember, the hand loader has a belt to work with, there is no need for the same approach as is taken with such wonders as tight neck / neck turn .308 Winchester reamers. If you want your job to turn out a sub quarter MOA shooter - Let it breathe!

7mm Practical Revision B reamer drawing WL


Hand Loading

Brass for the 7mm Practical can be obtained from readily available .300 Winchester Magnum brass. That said, Nosler brand (and therefore possibly Norma) features heavy neck walls. The Practical derives a good deal of its accuracy from the tight neck reamer design. Unfortunately if heavy walled brass is used, this tends to jack up pressures and ruin accuracy. To date, Winchester brass has proven to be the best fodder for the Practical followed closely by Remington.

Suitable neck dies include the Redding .300 Win Mag neck bushing die fitted with 7mm neck bushings, Forster 7mm Remington Magnum neck dies and the Hornady 7mm “Magnum” neck die. The Forster die has a 25 degree shoulder angle therefore it cannot fully size the neck shoulder junction of the Practical however this is not of great concern. A small portion of the lower neck (junction) can be left unsized without posing any negative effects.

If full length sizing is required, a .300 Win Mag or .338 Win Mag die can be used with the decapping spindle assembly removed. The shoulder dimensions are of no concern here, the die being used to decrease case body diameter.
Hand loading practices are straight forwards without any special processes. The .300 Win Mag case is necked down, primed, charged, a 7mm bullet is seated. The first shot forms the case, the hand loader simply continues neck sizing.
As previously mentioned, throat polishing is an important aspect of barrel longevity. But further to this, while case necks are at their shortest prior to growing, it is possible to collect carbon in the neck area of the chamber. If this carbon builds up, chamber neck dimensions are reduced, lifting pressures and ruining accuracy. It is therefore extremely important to occasionally clean the neck area of the chamber with a bronze brush and solvents. A simple test is to pass a projectile fired through a fired case neck. If the projectile passes easily into the neck, all is well. If the case pinches the projectile, there is a problem with either carbon build caking or heavy walled brass.

The very best powder for the Practical is H1000 (ADI 2217). Retumbo (ADI 2225) also works extremely well, along with other similar burn rate powders.
The best twist rate for the Practical is 1:9. The newer 1:8 and 1:8.5 twists should be avoided as these can limit the versatility and ease of bullet selection that allows the Practical to live up to its name. The same can be said of deliberately long throating for a single bullet style unless the rifle is primarily designed for target shooting.
Below are typical maximum COAL’s based on a chamber cut for the M700 action, the original COAL based on the 162 grain A-Max as a dummy round.
  • Amax: 92mm (3.622”) (chamber based on this bullet as dummy round)
  • Berger VLD: 92.1mm (3.626”)
  • Berger 180gr Hybrid: 93.9mm (3.697")
  • Hornady SST & InterBond: 90mm (3.543”)
  • Hornady Interlock: 89.6mm (3.528”)
  • Sierra ProHunter & GameKing: 88mm (3.465”)
  • Nosler BT: 90.1mm (3.547")
  • Nosler Partition: 89.6mm (3.527")
  • Nosler Accubond: 90.5mm (3.563")
  • Barnes TSX: 89.1mm (3.508")
  • Swift Scirocco: 90.9mm (3.578")
  • Matrix 190gr VLD: 92.2mm (3.630”)

Basic case specifications are as follows:
Max case length: 2.657 (67.5mm)
Case trim length: 2.645 (67.2mm)
Neck length for the Practical when trimmed is .289 (7.3mm). Several shots are required before cases will grow to the ideal 2.645 length.

Tested load data for 26” barrel. Be aware; short throated rifles may produce dangerous pressures with maximum loads.  Approach maximum loads with extreme caution.
Bullet weight Powder Start load Maximum Velocity
160-168 H1000 76 79.5 3275  
180   73 76 3150  
190   71 74 3000  
The 7mm Practical can be hand loaded to perform well at both close and exceptionally long ranges. The Practical is also able to make use of lower BC hunting bullets in such a way that effective range is greatly enhanced.  As an example, the Practical loaded with either the 160 or 175 grain Nosler Partition bullet works exceptionally well at close ranges,  maintaining very wide wounding out to ranges of around 550 yards, wounding steadily tapering off thereafter with a maximum effective range of around 850 yards. 

The Practical has an effective hunting range of around 1400 yards with the 162 grain A-Max bullet. With the heavy Matrix VLD, its effective range for wide wounding on larger bodied deer is around 1000 yards.

Further notes on bullet performance can be sourced by studying the 7mm Remington Magnum , 7mm STW and 7mm RUM texts within the TBR knowledge base.

My Practical

My 7mm Practical. Remington M700 action, True-Flite barrel, HS Precision stock, Warne base, Leupold rings and Sightron SIII 6-24 x 50 Mil Dot scope. So many wonderful adventures.

Closing comments

Inspired by the excellent performance of the 7mm Mashburn Magnum, the 7mm Practical is a simple, effective wildcat. The Practical is a joy to work with, a potent wind cheating hard hitting cartridge which delivers on all fronts. I do not believe this is a cartridge for those new to extended or dedicated long range shooting; the 7mm Remington Magnum is more than enough gun for most folk. But for those who shoot long and have the skills to extrude maximum accuracy from their rigs, the Practical is an honest cartridge that achieves its goals of reaching maximum velocities from the 7mm bore without need of excessive free bore and without excessive barrel wear.

Those who wish to build a 7mm Practical will need to obtain a reamer or reamers from pacific Tool and Gauge (USA) and approach a reputable gunsmith to initiate a custom or semi custom build. Reamer export is no problem for PTG.

New Zealanders can contact True-Flite NZ directly for rebarreling and reaming operations.

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