The 7mm Practical. A Practical Magnum.

By Nathan Foster 21^st Sept 2010.

Background

As the evening set in, the wind gradually subsided until the air was almost still.  At a distance of 1149 yards sat a lump of papa clay, round and about twelve inches in diameter, protruding from a cliff face.  I dialed the appropriate elevation into the Leupold scope sitting atop the 7mm Remington Ultra Magnum and when the wind finally subsided, I fired.  A puff of dust appeared three feet below the rock.  I adjusted and fired again, this time the bullet struck wildly high and to the left.  Three more shots went down range- nothing.  It would seem that the rock was going to live for another day.

Examination of my Ultra Magnum revealed that the throat had worn out, thereby rendering the barrel as scrap material at the young age of just 420 rounds.  To some extent it was my fault because I have a tendency to fire slow but steady strings at long range. I thoroughly enjoy plinking at long range but the 7mm Ultra Magnum is not a plinking cartridge.  




So there I was, goodbye long range destroyer, goodbye death star, goodbye meat seeking missile.  What to do, what to do? 
 

Above:  The day the RUM died.  

The greatest aspect of the 7mm RUM had been its ability to produce potentially wide wounding out at 1000 yards, an altogether different factor than being able to hit a target at 1000 yards.  I really didn’t want to lose this level of performance but I also didn’t want to have to go through a barrel swap every six months.  I have to admit, I am quite a fan of the 7mm bore for use on medium sized game.  I could have utilized the .300 RUM as my ‘pet’ long range cartridge due to its slightly milder wear (better case to bore ratio), but I am not a great fan of the increased recoil when attempting to duplicate the down range performance of the seven, nor do I like muzzle brakes due to the noise- especially when hunting with a pointer or retriever dog.  Suppressors are effective at taming recoil but I am a sucker for long barrels and extra velocity when it comes to long range work.

I sat down and had a look over my previous notes, the experimentation I had done with past rifles. I wanted to work out a comfortable maximum power level for the 7mm bore that would not cause excessive wear.  It was also clear that above a certain point, not only did the 7mm bore suffer diminishing gains, there reached a point at which there were no worthwhile gains in velocity, only wear.

 There are a group of cartridges that all achieve approximately the same velocities, the 7mm STW, the 7mm Dakota and the 7mm RUM.  One of the strangest aspects of the 7mm STW and RUM, is that to be able to cope with the high charges of powders these cartridge cases contain,  both need approximately 10mm (.400”) freebore (bullet jump) to ease pressure or put another way, to house gas expansion.  It is the freebore that gives these cartridges their very last few feet per second but it comes at a cost. The first problem is that of bullet to bore alignment.  A projectile like the 168 grain Berger VLD fired in the RUM, must go through a phase where it is neither guided by the case neck or engaged in the rifling, literally free.  If the bullet enters the bore even slightly off center, it becomes unstable and in-accurate. The 7mm RUM can be short throated but this creates other problems. 

I built (via True-Flite),  a half throated 7mmRUM in 2008 and although it produced desirable accuracy, I later discovered a problem which I could not resolve.  I was achieving best accuracy at the highest pressures; case life was in the region of four to five reloads.  Later in the year, I obtained a quantity of 168 grain VLD projectiles at a good price.  I decided to start testing with a mild charge of 89 grains Retumbo, but rather than producing low pressures, this load locked the bolt up and blew the primer out of the case. I double checked my loads and it happened again.  After this, I increased the load by two grains and pressures dropped considerably, however I still had to increase the charge another grain for best accuracy and this load was right at the limit, reducing case life to the afore mentioned 4 to 5 loads.   Unfortunately, my  cunning short throated RUM plan was flawed.  I would have to stick to maximum pressures and shortened case life. In 2009, True-Flite altered the throat of the RUM back to factory specifications, I went back to the 180 grain VLD and left it at that.

The cause of high pressures with low charges was quite possibly due to uneven ignition.   The high charge of powder combined with the large air space surrounding the powder, could have allowed the primer flash to burn over the top of the powder. It may have even spread the powder around the case (like atomised fuel).  So rather than a slow, controlled burn, the primer flame ignited all of the powder  at once, generating huge pressures. Whatever the case, when Remington Engineers designed the 7mm RUM, they certainly understood the need for a gas expansion chamber which was created in the form of the freebore.

A second problem with the 7mm RUM is that the high charges and large amounts of hot expanding gas, erode the throat of the barrel in an excessive manner.  The power of the RUM is fantastic however the negative performance is a concern.  I had a hunch that a slightly smaller case might actually be able to achieve similar results (less than 100fps difference) without excessive wear.  The question was- what would be the optimum case capacity.

After a period of research and looking at various case designs, I theorised that the .300 Winchester Magnum might be the optimum case capacity for launching 7mm bullets at the highest possible velocities without excessive wear or other associated over bore problems.  I was not alone either. 

Over the years, many hunters have necked the .300 case down to 7mm. A very early example is the 7mm Mashburn Super Magnum wildcat, based on the .300 H&H case, blown out and necked down.  This cartridge 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 the .300 Winchester magnum necked down to 7mm.  A handful of shooters (mostly U.S) currently utilize personal  variations of this wildcat and while it may seem an oddity, it is a highly practical design.

The 7mm Practical

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 is intended to be used for hunting light to medium weight game from point blank, out to true long range distances. The case capacity is what I consider to be optimum for a balance of efficiency versus effective power at extended ranges.

The 7mm Practical has other user friendly  advantages.  These include a long neck, longer than is found on the Win and Rem magnums, both old and new designs from the 2.5" magnums through to the WSM/RUM’s, many have a neck length of up to 6.8mm at best.  The longer neck helps bullet to bore alignment immensely.  Rather than trim the brass, for the first several firings, the brass is allowed to grow until it reaches the desired length (see notes below).

There is no need for special dies or special operations when reloading for the Practical.  Simply use a standard 7mm neck die and 7mm Rem Mag seating die and get straight into maximum performance. Bullet jump is dictated by the separate throat reamer and each rifle should have its throat cut to suit its magazine box thereby minimizing bullet jump.

The Practical has a 30 degree shoulder, duplicating the WSM/RUM shoulder angle as opposed to the parent .300 Win Mag which has a shoulder angle of 25 degrees.  The idea behind the change in shoulder was to assist positive head spacing at the shoulder with hand loads and to some extent, it was hoped that it would encourage case neck growth based on my experience with the RUM and WSM’s which seem to display rapid neck growth.   To be honest, I do not know if the change in shoulder angle actually made any difference.  It’s certainly not a point worth pushing.

The Practical is also intended to make use of an easily sourced parent case.  The belted case is also easy for gunsmiths to work with, without need of custom head spacing gauges.  The Smith can use standard 7mm Rem mag  go and no go gauges to check fit. In this way, the fire forming load utilizes the belt and gives It (for once) a useful purpose while consecutive loads are head spaced at the shoulder for optimum accuracy.

Above all, the Practical was designed to do what its name suggests, to provide a simple, practical cartridge for precision long range hunting.   Don’t get me wrong, the Practical is in no way as efficient as something like the excellent .308 Winchester.  If I had my way, it would be mandatory for every licensed western hunter to own a .308, the arms officer would give you one after he or she ticked the last box. For 50 cents, you could upsize  to the .30-06.  No, the Practical is relevant to the pursuit of optimum magnum performance.

Pacific Tool and gauge made the reamer for the Practical as well as the separate throat reamer.  The reamer was perfect, as can be expected from PTG and the turn around time was incredibly fast, certainly beyond expectation. True-Flite NZ Ltd (Gisborne, New Zealand) blueprinted the M700 action I used as the platform for the build and fitted a button rifled barrel of their manufacture along with a PTG recoil lug and Barnard extractor.  The stainless steel barrel has a twist rate of 1:9”.   I also used this opportunity to trial True-Flite’s new 6 groove 7mm barrel which will eventually be offered along with the current 4 groove canted land design.  Three weeks later, I was lucky enough to have a client want to try the Practical using True-Flite’s 4 groove canted land barrel.  Results were as can be expected from True-Flite, simply outstanding for both rifles.  Show off bastards.


 
 
 
 
 The 7mm Practical
Max case length 2.657 (67.5mm)
Trim cases to 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.
 

Above: the 7mm Remington Magnum (Left) beside the 7mm Practical.

Test rifle

• Rifle: M700 action (trued). 
• Bolt fitted with Barnard Precision extractor (very nice extractor, finished the project off perfectly).
• True-Flite Ultra Match  28” No.4 fluted (same contour as Lilja). 
• PTG recoil lug. 
• HS Precision (AKA Sendero) stock. Rifle is bedded full length of action and knox (i.e the barrel parallel).
•  Leupold 4-12 power scope, retro fitted with target turrets.   This will eventually be replaced with a higher power scope and canted base however;  the Leupold has kept the rig more compact and portable than expected.
• Standard M700 trigger set 2lb. 

Note: The 28” barrel was chosen for two reasons, the first was to minimize recoil by extending weight forwards, the second was to ensure maximum velocities- especially if my calculations and predictions turned out to be wrong, I didn’t want to say goodbye to those RUM velocities!  I must point out, I hunt with a 20” barrelled .308 as well as the long barrelled magnums.  I find that both configurations have their strengths and weaknesses.   Generally, I do prefer a long barrelled rifle, even for bush hunting.   To some extent, my preference to the longer barrels probably comes from growing up with the .303 SMLE (25.4” barrel)  and Swede (sporterised to 24” barrel).

Components

Winchester .300 Win Mag brass
Federal 215 Magnum primer (*also 210 standard primer)
ADI 2217 (H1000) and ADI 2225 (Retumbo) powders.
Hornady 7mm Magnum generic neck sizing die used for reloading . This die has a 30 degree shoulder suitable for the 30 degree angle of the Practical.  I tried to use my Forster 7mm Rem Mag bench rest neck die but it had a 25 degree shoulder and bumped the case shoulder before all of the neck was fully resized. This caused difficulty chambering rounds.

No special care was taken with the reloading steps.  Any intermediate experienced hand loader using normal reloading practices can duplicate these results.

Max COAL’s

• Berger VLD: 92.4mm (3.633”)
• Berger 180gr Hybrid: 94.2mm (3.708")
• Amax: 92.3mm (3.633”)
• Hornady SST & InterBond: 90.3mm (3.555”)
• Hornady Interlock: 89.9mm (3.539”)
• Sierra ProHunter & GameKing: 88.3mm (3.476”)
• Nosler BT: 90.4mm (3.559")
• Nosler partition: 89.9mm (3.539")
• Nosler Accubond: 90.8mm (3.574")
• Barnes TSX: 89.4mm (3.519")
• Swift Scirocco: 91.2mm (3.590")

All test loads were seated 1mm (40 thou) shorter than the max COAL.  Bullet seating experimentation will be carried out at a later date.
 

Test loads

Bullet	Powder	Charge	Av. Velocity	ES Fps	Group	Comment
180 VLD Hunting	ADI2217 (H1000)	74	3075	40	1.990
		74.5	3100	21	1.075
		75	3152	23	.520	left cartridge in chamber waiting for wind gusts, heat caused increase in velocity and vertical disp. It is possible that the Group ‘should/could’ have been .3”
		75.5	3155	14	.300	Very good
		76	3160fps	60	1.6	Near max. Note the plateau in velocity of 3150.  Cannot seem to go past this with 2217/H1000.  Case life still OK.
180VLD Hunting	ADI2225 (Retumbo)	75	3144	49	.720
		75.5	3168	79	1.625
		76	3170	7	.740	Near max, safe

 
 

Bullet	Powder	Charge	Av. Velocity	ES Fps	Group	Comment
168VLD Hunting	2217 (H1000)	75.5				Yet to test
		76*	3220	7	.155	Excellent, good light game long range load *Fed standard 210 Primer used in order to lower ES.
		76.5				Yet to test
		77				Yet to test
168VLD Hunting	ADI2225 (Retumbo)	75.5				Yet to test
		76	3210	60	.275	No good at 1000 yards due to velocity deviation. Change of primer or .2gr incremetal load development needed
		76.5	3226	17	.420
		77	3346	45	.770	Near max, safe

 

Bullet	Powder	Charge	Av. Velocity	ES Fps	Group	Comment
162 SST	ADI2217	75	3200	60	1.000
	(H1000)	75.5				Untested.  Suspect sweet spot
162 SST	ADI2225 (Retumbo)	75				Untested
		75.5				Untested. Suspect a sweet spot.
		76	3273	5	1.000	Shame this won’t shoot better.  Need to experiment with seating depth.
		76.5	3333	50	1.6
		77	3330	34	1.4	Safe load, no max pressure signs.  Note plateau in velocity at 3330fps.

 

Bullet	Powder	Charge	Av. Velocity	Dev. Fps	Group	Comment
162 Amax	ADI2217 (H1000)	76	3200	12	.275	Fed 210 Primer.  Taken goats out to 1130 yards with this load, very effective
		76.5	3230	15	.78
		77	3275	14	.320	Good load
162 Amax	U.S 869	85	3200	2	.7
		85.5	3230	19	1.2
		86	3250	5	1.2	Poor groups may well be associated with excessive fouling.  A lot of rounds were fired prior to these groups (testing effects of bipod versus sand bag versus day bag). Retest at a future date will confirm.

 
Fire form load: 140gr ProHunter, 73 grains ADI2217. Velocity 3127fps, deviation 10fps. .5mm jump (20 thou), Groups size .460 for 5 shots.
Tables above will be updated if and when I have an opportunity to test. Some changes will also occur as the barrel and throat wears in. Round count at the end of the above testing was just under 100 shots. Velocities and loads will change by .5 grain and 50fps as the bore wears in.

 

Some conclusions

The case has plenty of powder capacity, no charges were compressed. I designed the Practical to have a separate throat reamer so that clients could match the COAL to their available magazine lengths. One could easily build this on, for example, a Winchester M70 action with a magazine length of 92mm, can use a shorter COAL and still have plenty of case capacity for the same or similar velocities.

I believe that the Federal 210 primer is perhaps better than the 215 Magnum primer for lowering extreme velocity spread in order to reduce stringing out at 600 yards and beyond.  The 28” barrel ensures the powder is burnt without loss of muzzle velocity.

So far, the numbers (extreme accuracy) look thus for the 7mm-300Win Mag with 28” barrel:
162gr 3250fps (Confirmed in second rifle)
168gr 3220fps
180gr 3120fps

The upper limit for this rifle (sub .6MOA  accuracy/ case life) appears to be:
162gr 3270fps
168gr 3226fps
180gr 3170fps

Averages are:
162gr 3250fps
168gr 3220fps
180gr 3150fps

The average velocities listed above are approximately 125fps faster than a 7mm Remington Magnum of the same barrel length.  I have been able to duplicate the velocities of the 7mm RUM with 162 grain bullets but am slightly behind with the 180gr VLD.  Ultimately, the Practical is producing 7mm RUM performance with 16 grains less powder. Yes, I have had to use a long 28" barrel but this itself has paid dividends in terms of decreased recoil while allowing me to use mild loads with excellent case life.

My last three RUM barrels achieved 3180fps with the 180VLD from  26” barrels which is a theoretical 3250fps when corrected for a 28” barrel (35fps per extra 1” barrel).  This is approximately 100fps faster than the Practical's average speed.  The 7mm RUM's extra 100fps is not (to me) worth the problems of barrel wear and load inflexibility and finicky accuracy with regard to the excessive bullet jump.  The 7mm RUM also produces extra recoil from the powder charge alone, producing significant recoil when loaded with a small felt wad rather than a projectile.  Case life was always poor in the RUM, regardless of its 65,000psi design parameters and regardless of throat length.  When the primer pockets weren’t expanding, the case necks were splitting, regardless of annealing.   In the Practical, I may yet achieve higher velocities with the 180gr VLD and match the RUM.  There is still great room for experimentation with powders and seating depths.
 
One last odd aspect is that ADI2217 (H1000) and ADI2225 (Retumbo) appear to be almost identical in burn rate in this cartridge. ADI 2217 produced several accurate loads as well as low ES, a generally excellent powder.

I Have already completed a second rifle in 7mm Practical (M700 SS Laminate) for a client and the above load data produced the same set of results in that rifle. Both barrels are of a completely different rifling design yet pressure, velocity and accuracy relationships appear to be identical.  A third Practical is to be started this week (20^th Sept 2010).

A look at the bedding on the M700 SS Laminate featuring our MatchGrade bedding compound.

I absolutely love this cartridge and rifle configuration.  Recoil is mild (for a magnum) and the cartridge seems to be (dare I say it) inherently accurate. I don’t believe my version of the 7mm-.300 is the ultimate or the be all end all, it is simply my version.  I have seen other versions and talked to the gun owners about their wildcats and each is equally happy with their design. 

The Practical has been fantastic in the field;  it is a great feeling to have a cartridge which has the legs to tackle a vast range of shooting situations in a reliable, repeatable manner. The HS stock is a brilliant design, especially the long forend with its extended sling stud which helps make the rig an easy, low carry when climbing.  The HS stock absorbs recoil and is ergonomically perfect for me.  The M700 action is great from the stand point that it is so easy to work with- the KISS principle, making accuracy tuning very predictable.  The quality of the True-Flite barrels speak for themselves.  The  two True-Flite barrels tested  both shoot .3 as an average with 'good' loads, smaller groups with care.

Both rifles are now sighted in with hunting loads producing  .155” (my rifle with 168gr VLD @ 3220fps) and .122” ( second rifle with 180gr VLD at 3116fps).  The VLD has performed flawlessly on target and on game. I usually load the 180 grain VLD in my big sevens as these work very well on heavily shielded Boar if a close range shot is required. Nevertheless, due to supply problems in New Zealand, I am currently using the 168 grain VLD while awaiting the next shipment of 180 grain bullets. No problems have been encountered with the 168 grain VLD in regard to penetration on game.

Update 4th Dec 2011: I have recently switched to the 162 grain Amax at a mild 3200fps due to changes in the VLD bullet design, poor fragmentation at low velocities / long ranges. the 1130 yard video clip below has further details.

Above: 162gr A-Max wound channel at 1km.

Belated update 2012:

In late 2011, I made some very small changes to the body dimensions as I felt the Practical was not working well long term for ease of reloading.  Progressive neck sized reloads were getting tighter, unlike other cartridges I have here which have been neck sized permanently.  So I tweaked the body dimensions a thou wider all around- apart from the neck, I held back on the job orders we had till I had it right, then we went ahead and made the next batch of rifles for customers.  The customers since have ranged from guys wanting long range climbing rifles (light weight, 26" barrel etc) to guys wanting extreme accuracy out and beyond 1000 yards from heavy barreled rigs.

The current reamer designation as of Jan 2011 is: 7mm Practical Revision B.

Velocities for this reamer are:
26" barrel gives 3225fps-3275fps average with the 162gr A-Max and 3100-3150fps with the 180gr VLD.
28" barrel gives 3315fps average with the 162gr A-Max and around 3200fps with the 180gr VLD.

Of course, variations can be wider, slower bores, faster bores, differences in throat lengths etc.

regarding my own part working with the newer reamer.  I worked up a load for myself at 3313fps with the A-Max that was very accurate over the sand bags.  But to be honest, I didn't like it, minute changes in hand hold tension or body position (field positions) opened the groups up.  So I went back to my old 3200fps load again, though to get the same acccuracy as before (old chamber), I had to seat 10 thou off the lands. Now I am under .250" off the sand bags, shooting under a half minute off the day bag or with the bipod, hand over the top of the scope (hold that forend article).  My rifle is 11.5lb and I believe it is too light (unbraked) to be any good at 3313fps, not to mention any potential extra throat wear.

Now, regarding barrel life.  I am still only at the 400 and something round count.  The throat has grown .1mm / .004".    The client rifles are going well apart from one client who is also a local, a friend. He has put 650 rounds through his rifle, the throat has grown 1mm / 40 thou. I found that his strings are shot fairly fast, I shoot a lot slower.   We also discussed differences in cleaning.  I polish my bore with abrasive paste after every shoot, even if its only 3 rounds fired. Rather than wearing out the bore, I find that this keeps the pores in the steel closed. My friend did not do this, atleast not to the same extent. Most folk 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.  I also use 600 grit scotchbrite every few sessions.  I actually use a Norton grey colored pad. 

In the rifle with the worn throat, my friend re-polished the throat, a full re-break in session going through the scotchbrite grades and fine polishing stages (see barrel break in article). The loads were reworked and the rifle taken back to the range.  All is well, the rifle is shooting straight and there is still enough mag length to work with- mag length vs throat being something to keep in mind during the initial build.  So to a great extent, the user has a great deal of control over barrel life of the Practical.

The new reamer dimensions are helping with continued neck sizing without any need to FL size with a custom die. Continued neck sizing is a breeze. However, for those who really want to play it safe, the body dimensions can easily be bumped back with a .338 Win Mag or .300 Win Mag FL die.

There are now quite a few 7mm Practicals in NZ.  The cartridge is also being utilized in Canada while a few U.S users are starting to play with this reamer design as opposed to the standard 7mm-300. I would like to point out though, I get emails each week from hunters wanting to build Practicals for use on large bodied deer, Elk and bear at long ranges.  Guys, try to follow my basic rule. If 90% of your medium game weigh 90kg / 200lb or above, consider a .30 cal or heavier caliber if need be. If 90% of your game weigh less than 90kg / 200lb, the 7mm's are a good choice.

The 7mm Practical is a good long range whitetail/Sika cartridge.  It works well on Red/Mule deer with the annealed 168 grain VLD or especially the (prefferably annealed) 162 grain SST and can be adapted for example to suit Elk hunting by using the 160 or 175 grain Partition driven at 3300 or 3100fps and used out to roughly 800 yards. A meplat trimmed 180 VLD (diameter 70 thou) is another option for heavy bodied deer. The trick here is to undertand strengths versus limitations. The sevens prove useful on larger bodied animals with careful bullet selection.  By the same token, if you read through the knowledge base, you will see countless examples of where many 165-180 grain .30 cal bullets are too stout for lean game, again requiring fore thought into appropriate bullet construction and selection.

But until a 180 or 195 grain A-Max hits the market, the Practical cannot make use of the sleek 162 grain A-Max as a single load for use on all game up to the size of Elk. With such demands, I would far rather recomend the .300 Win Mag with the 208 grain A-Max driven at 2800fps or faster than the Practical. Trajectory and muzzle velocity isn't everything so try to always keep this in mind.

 

Above: The 168gr VLD at 3220fps.   The poor goats always get it. This little fella was taken for dog food, just a moderate range shot.



Above: goat shot at 508 yards with the Practical.

If you would like to build a 7mm Practical, please contact me at Nathan@ballisticstudies.com.

For international readers, a reamer may be purchased from PTG, to be used by a smith of your choice.  The chanber print is provided below, please quote the drawing number 30120 Rev B to PTG when ordering.

Above: a Borden actioned 7mm Practical mated to an Accuracy international chassis with True-Flite barrel.

Below are three video clips of of the 7mm Practical in action.  The first clip is an intro to the cartridge, shooting a goat at 508 yards and a quick autopsy to see how the 168 grain VLD performed.  In the second clip, a small porker pig is spotted at 770 yards just on dusk.  The Practical absolutely flattens it on the spot. In the final clip, I shoot another goat but this time, at 1km. The clip ends with an autopsy, looking at the performance of the 162 grain A-Max.