Home Forums Hunting & Shooting Long Range Hunting 7mmx300WinMag

I'm running RCBS for my Mashburn

Dober

how does the accuracy of the mashburn compare to a 7mm magnum and a 300 win mag? Would like to get good velocity and between .3 and .5 inch accuracy...

does reaming the barrel require that the gunsmith take it off?

how many dies do I need...a form die and a 2 die set..??

are there gains to be had by neck sizing?

Could a 7mm weatherby on a remington 700 classic be reamed out to mashburn specs?

Is a detachable magazine for a remington 700 going to be big enough to take these shells?

has anyone here seen this guy calls it the 7mm practical.
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.


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: 92.1mm (3.625�)
Amax: 91.7mm (3.610�)
Hornady SST: 90.1mm (3.547�)
Hornady Interlock: 89mm (3.503�)
Sierra ProHunter: 87.6mm (3.448�)
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 (20th Sept 2010).

Imartin:Excellent post and very cool cartridge. I enjoyed reading that....you've reinvented the 7mmMashburn Super with a shorter neck

I'll take the 162 at 3150fps from a 24" spout please.

Hold the fluff...............

The Mashburn did that 60 yrs. ago albeit with different powders. Art Mashburn built Warren Pages first Betsy in 1950 +/-.

Geehee, the wheel is invented again.

Pretty tough to get excited about a l/a duping s/a performance.

Especially when wearing a belt................

Or having to employ 4 extra inches of barrel when other cartridges will get you there with 24".

Tough crowd...but encouraging to know that a few folks still shoot....................(grin)

Mark Penrod will be converting a Model 70 Classic Stainless (currently a .300 Bee) to the Mashburn.

Rifle hits USPS this weekend.

hey bob here is that guys website if you want to see his other stuff.
http://www.ballisticstudies.com/Resources/Articles/The+7mm+Practical.++A+Practical+Magnum..html

Can't disagree with that......... Once it leaves the spout,doesn't matter whet engine got it there......

I'd cite that handy/dandy prior to launch,is very easy to discern however..............(grin)

Stick: Yes I have made a habit of that over the years...an old favorite 7 Rem mag,now long gone and "worn out" was trimmed to 7.25, scoped, made by Butch Searcy....notwithstanding the handicap of the heavier M70 action....I used it everywhere through the 80's and back then it was unique,as there were fewer ways to get them "lighter".....with H&H box and .285 groove 24" Krieger,it did 3125 with 160's;3275 with 140's and carried like dream.

There have been two or three others similar.....

It is easier to "get there" today,but with all that the Mashburn is 7.9# with 6X Leup on board...not contemporary "light" but at 61 years of age I ain't complaining yet....maybe soon

Too easy to have the cake and eat it too...to be making concessions.

Ringin' bells is what it's all about...............

You should be!!!!!!!!!!!

Ha! Not me!

I don't know how you're still able to get around, being a year older than me and all