Shoot your own Wildcat

Breathes there a handloader with initiative so dead, that never to himself has said, “This is my very own personal wildcat.” The consuming ambition of any serious  and loader/wildcatter has often been to develop a custom concoction that would outperform what’s available. Something faster, more powerful more accurate and more efficient than anything else in his chosen calibre. Alas, today meeting this goal has become much
more difficult, there are aren’t many gaps left in the picket fence of factory cartridges, hence little room for experimentation. But this doesn’t dampen the enthusiasm of the fanatical wildcatter.

One of the ultimate vanities of the handload experimenter is to end up with a cartridge named after himself. But if you choose to follow this path you want the cartridge to be something that fulfills a certain need and is different enough to garner the interest of your contemporaries.

A good many of the better wildcats of yesteryear ended up being adopted and legitimized by one or another of the ammunition factories. These include the .257 Roberts, the .25-06 and .35 Whelen, and in more recent times the .338-06 and 7-30 Waters. Jim Carmichael  hit the jackpot when Remington adopted his 6.5/308 wildcat and renamed it the .260 Remington.

Aussie gun nuts may not have been quite as prolific as their American counterparts, but in thepast they whumped up a number of wildcats on the .303 and other available brass. More recently, Ted Mitchell succumbed to the temptation and developed his .358 Mitchell Express based on the 8mm Mauser case. He even went the whole hog by getting personalized brass made by Bertram carrying his own headstamp.

I heard the siren call of the unconventional back in 1987 when I developed my 7mm Harvey Magnum, a wildcat I’m still playing with today. In developing the new cartridge, I did nothing more radical than to simply neck up the existing 6.5 Remington Magnum case to shoot 7mm bullets without any other change. Nor was I very ambitious, all I wanted was a short case that needed little work done on it, with sufficient capacity to drive the 160gn .284 bullet at 3000fps.

The 6.5 Remington Magnum cartridge was designed for short- action rifles long before
the Winchester Short Magnums were ever dreamed of. Bill Marden built the rifle. I sent
him a Brno Mauser 98 action and he fitted a Shaw barrel and put together a die set. A
figured walnut stock was obtained from Keith Tyack, fitted, shaped, bedded and checkered
by Bill Howarth, who fitted a Jantz Model 70-type wing safety and adjustable trigger.

He also attached a new bolt handle and checkered the bolt knob. The end product is a classic rifle with shadowline cheekpiece and rosewood fore-end tip. It not only looks elegant but is nicely balanced.

As a cartridge the design is sound. The 6.5mm Rem. Mag. neck may be a bit short, but proved adequate. The original body shape was just tapered enough that it didn’t need to be “improved”, and together with the modest 25 degree shoulder angle contributes to the 7mm HM feeding as smoothly as the original 8mm Mauser round.

The short-action Remington Model 600 carbine that the 6.5 Remington Magnum was designed for required that the cartridge overall length be held under 71mm, but I had Bill
Marden long- throat my rifle so that it would handle cartridges with an overall length of
78mm. Bullets weighing from 120 to 150 grains are seated level with the base of the neck while the longer 160 and 175-grainers don’t extend below the case shoulder.

I had hoped that the cartridge would prove accurate, and it did. However, due credit must be given to a good barrel and precision gunsmithing by Bill Marden. I won’t suggest this wildcat – even though it can and has produced ragged one-hole groups for three shots at 100 yards – is necessarily more accurate than a 7mm Remington Magnum would be with similar barrel and loads.

Velocity is pretty good with all bullet weights even though I envisioned this rifle as a  genuine one-load big-game outfit based on a 160gn spitzer bullet at 3000fps. I didn’t expect to quite get maximum 7mm Magnum velocity out of it, and I have other faster 7 em-ems that will propel 160gn bullets at greater speeds. But I had it in mind for medium to long range work on deer up to the size of elk, African antelope and that kind of game.

Initially, back in the 1980s, I worked up loading data using a variety of slow powders including AR2209, IMR 4350, AR2213 and H4831. Of them all, AR2209 seemed best suited with bullet weights from 120 to 160 grains. It wasn’t until 2005 that I carried out additional load development work using AR2213SC, Re-19, and Re- 22. By this time I realized that my 7mm HM was producing ballistics comparable to those of the 7mm Remington SAUM and 7mm WSM using similar powder charges. This is because in the
new short-action 7mms the bullets intrude deeper into their more capacious cases taking
up more of the powder space.

Some good loads in the 7mm HM drive the 120gn Sierra at 3315 fps, 145gn Speer spitzer at 3155fps, 150gn Core-Lokt at 3115 fps, the 160gn Woodleigh at 3000fps and the 175gn Sierra at 2890fps. A top load uses 61gn of AR2209 behind a 139gn Hornady SST, which yields a startling 3265fps. But this load is near maximum, so my working load is 60gn of AR2209 for 3190 fps.

Dropping 75 foot- seconds was not noticeable in the field.

Once upon a time, I took the rifle topped with its Swarovski A series 3-9×36 scope to New
Caledonia – twice. It accounted for three rusa stags over normal distances and one at very long range way across an open valley. I didn’t own a rangefinder in those days and guesstimated the amount of holdover needed as being about 4 feet. The first 140gn Sierra hit him solidly and he staggered but was still on his feet wobbling about, when I launched the second bullet which dropped him. When I reached him I found both bullets had hit within a hands breadth in the centre of his chest. Obviously, there was a lot of
luck involved, but it did show what the 7mm HM was capable of.

Last year I was on a hunt for red stag when I spotted a 12- pointer standing, quartering away from me at the upper end of a gully about 250 metres away. With a hold just behind the shoulder, I shot, and the stag took a few steps and dropped to the ground. The 160gn
Woodleigh bullet exited the off shoulder. So I had achieved the kind of accuracy, velocity and performance on game that I desired. What more could I want.

Perhaps I should have stopped there. The velocity I’m getting is equal to that I’m getting
from my 7mm WSM, so my wildcat was an unqualified success. But is the wildcatter ever completely satisfied?

There is space for more powder, and it’s no problem to get 3000fps with the 160gn bullet. But in this rifle the best combination of accuracy and velocity seems to be about 2965 fps. However, I was curious to see if I couldn’t gain just a tad more velocity or at least the same velocity with a bit less pressure using two new powders – Winchester’s Supreme 780 and Reloder 25.

For starters I stuffed 65gn of Supreme 780 behind the 150gn Remington Core-Lokt and got 3115 fps with relatively milder pressure than my previous loadings of 59gn of AR2209 and 63gn of Re-22 which clocked 3080fps and 3030fps respectively. My conclusion was while there was very little gain in velocity and accuracy, the lower pressure made it worthwhile.

This encouraged me to try 62 grains of Supreme 780 behind the 160gn Woodleigh and
59gn with the 175gn Sierra. Muzzle velocities were 2960fps and 2835 fps.

Reloder 25 was next up. A 65gn charge behind the 150gn Core Lokt clocked 3000fps; 64gn with the 160gn Woodleigh turned up 2880fps; and 62gn with the 175gn Sierra Boattail got a strong 2855fps. Again with mild pressures and nary a sign of tight extraction. But Supreme 780 seems to offer a slight edge with bullets from 130 to
160gn which leaves slower burning Re25 as the best choice with the long 175 grainer.

Many charges of slow powder, even the finer granulated ones, often turn out to be too bulky or the case. All loads of slow burning powder were trickled into the 7mm HM case very slowly through a funnel with a long drop tube achieved from 84 to 100 percent load density. You’ll be amazed at how much powder you can get into the case by this means, together with a little gentle tapping of the case on the bench-top to settle the charge.

Each charge was increased one grain at a time and the diameter of the case head  measured on the rear of the belt after each firing with a blade micrometer. In general, if the case head expands by as much as .001”; in any dimension, you can nearly bet that pressures are excessive for that load in that gun. I personally, prefer to keep working loads under .0001” expansion, and recommend such a standard to the conservative handloader. One tip: make a mark with a felt-tip pen on the new case and take the  diameter reading at this point each time. Write down the measurement, prefereably to four decimal places. The round is then loaded, fired, extracted, and re-measured across the same mark, and the reading is compared with the pre-firing measurement.

If no pressure signs appear, the charge is increased and next heaviest charge fired and so
on, until some degree of case head expansion occurs. When I strike a load that gives .0005” belt expansion, I stop tight there, drop back one grain of powder and fire ten rounds. If none of that series shows as much as .0005” expansion, I call this my maximum load and reduce that charge by another grain or two for a safe working load.

Fortunately, the handloader’s obsession with wildcats never diminishes although it may lie
dormant for a while, and I learned a lot from this project. I am pretty sure that my pet wildcat is not going to be adopted by Remington Arms any time soon or achieve the same degree of fame as the 7mm-08. Nonetheless, I’m completely satisfied with my wildcat 7mm Harvey Magnum. It’s a real pussycat to load for and delivers very satisfactory performance with modest amounts of powder. What more could any wildcatter ask for?

This article was first published in Sporting Shooter, September 2010.




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Nick Harvey

The late Nick Harvey (1931-2024) was one of the world's most experienced and knowledgeable gun writers, a true legend of the business. He wrote about firearms and hunting for about 70 years, published many books and uncounted articles, and travelled the world to hunt and shoot. His reloading manuals are highly sought after, and his knowledge of the subject was unmatched. He was Sporting Shooter's Technical Editor for almost 50 years. His work lives on here as part of his legacy to us all.