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Rocky’s Reloading Room |
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The 25-308 has the same relationship to the .25-06 (left pair) as the .308 has to the .30-06. |
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Making cases is a simple as sizing 7-08 cases (left) and loading. Fully fireformed case is at right. |
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Expansion of fired cases is measured just ahead of the web, at the maximum case diameter. A high quality micrometer and a practiced hand are required. |
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Many powders work well in the .25-308. The author uses these for light-bullet loads. |
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The .25-308: An Easycat By Rocky Raab
A varmint hunter could spend an entire lifetime shooting standard cartridges and be completely satisfied. Millions have. But for a few, there comes an itch - an indefinable but undeniable and irresistible itch – for something… different. Those few suddenly find themselves crossing an invisible border from handloader to wildcatter.
A wildcatter is the ultimate handloader. He has to be, for no factory makes ammunition for his gun. The wildcatter truly has to roll his own. In the most extreme cases, wildcatting means designing a cartridge from scratch, making drawings for the construction of chamber reamers and loading dies, finding someone who’ll do such one-off custom work, then waiting and waiting for the precious items to be delivered. He’ll be paying through the nose for it, too. All that just to get the tools to begin the work! Now there are cases to reform, sometimes laboriously. Lathe work, neck turning, hand work, annealing and goodness knows what else. Sometimes lots else, as unforeseen problems are almost inevitable and results unpredictable. Suddenly the whole thing seems a whole lot less fun than what we imagined.
Kinda like having the fire sprinklers go off at an orgy, isn’t it? But what if there were an easier way, a simpler project, a way to get into the wildcat game without spending your whole life and life’s savings? What if there were an “easycat?” Pull your chair up a little closer, my friend. There is one. One that not only lacks and hidden booby traps but is a delight to shoot as well. It’s the .25-308, originally known as the .25 Souper.
As you might guess, the .25-308 is simply the .308 Winchester case necked down to .25 caliber. The .308 case was the subject of intense wildcatting efforts since the moment it was released to the civilian world in 1952. Handloading legends like Fred Huntington, Warren Page and others took .308 brass still smoking from Winchester’s laboratory and went straight to their reloading benches. In no time at all, .308-based wildcats from .22 to .35 caliber were proliferating. Commercial cartridge companies have since legitimized such outstanding performers as the .243, the recent .260 Remington, the 7mm-08 and the .358. Other eminently useful wildcat calibers on the .308 case, such as .22, .270, .338 - and .25 - have remained little-known.
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Knowing when to stopI determine relative pressure by measuring case expansion at a point just ahead of the case web. I use an electronic digital micrometer that reads to 0.0005”. I measure each case at three points around the circumference, then average all the readings for every case in a test string, usually five cases. In my rifle, extraction is easy, the edges of fired primers are just slightly less rounded and primer pockets stay tight for at least five loadings when the cases expand to no more than 0.4710”. That’s my working maximum. I strive for loads that average 0.4705” as everyday hunting ammo. That way, I know I won’t get sticky extraction or other problems when I can least afford it.
I will make a few powder recommendations. After testing more than 50 powder and bullet combinations, I found that the best extruded powders are IMR 4350, 4064 and 4895, Alliant RL-15 and -19 and Hodgdon Varget. Best spherical powders in this cartridge are H414, AA2520 and WW760. I suspect (although I have yet to try) that H380, BLC-2, IMR4320, as well as several of the VihtaVuori and Ramshot powders may also be excellent. Like most cartridges based on the .308 case, the .25 Souper is just about omnivorous. In this way too, it really is an easycat.
What’s it good for? I use mine for long-range work on prairie dogs, rock chucks and coyote, all with the mentioned 75-grain bullets or the excellent Nosler 85-grain Ballistic Tip. I haven’t killed a deer with it, although that’s only because the deer haven’t cooperated. When I carry it for deer-sized game, I load the 100-grain Speer softpoint or a few of my hoarded trove of wicked Nosler Solid Base softpoints. Bullets up to 120 grains are an option if I were going to tackle game bigger than deer, but frankly, I’d almost certainly prefer the superb Barnes 100-grain X-bullet for its enhanced penetration. Actually, I’d use a bigger gun.
How good is it? On prairie dogs, fox, coyotes and rockchucks the Hornady 75-grain VMax is definitely a red mist performer. Way out around 450 steps, prairie dogs are either helicoptered many feet in the air or blown into pieces. Closer in and it’s raincoat and squeegee time. If you will allow me my addiction to alliteration, even the porkiest pasture poodles are popped to projected pieces. Rawhide-resembling rockchucks are reduced to red remnants. Slinking song dogs are swatted to spectacular splatter. OK, enough of that.
Beyond raw performance, the rifle is a joy to shoot. Recoil is mild enough with 75-grain loads that a snug hold on the forearm keeps the target in view through 12X magnification. Hundred grain loads come back a bit firmer, but even an arthritic Leprechaun would find it comfortable to shoot. It’s just about identical to the .243.
Which leads to one final question: If it uses the same case, the same bullet weights, fits in the same rifles and betters the .243 by only 100 fps or so, why bother? To which I could begin a discourse on improved case-to-bore expansion ratios, improved bullet rotational radius and other esoterica. The real reason, of course, is obvious to dedicated TVHM readers. I built mine because the quarter-inch bore has always fascinated me. Because it’s just a little bit different. Mostly because with a .243, I can’t quite scratch that darned itch!
Published in The Varmint Hunter Magazine #41, January 2002 |
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But why call it Souper?
The .25 Souper was originally developed by P.F. Lambert of Washington, D.C., according to Speer’s Reloading Manual for Wildcat Cartridges (Number 4), published in 1960. (Incidentally, this rarely encountered jewel is one of only a few reloading manuals solely for wildcat cartridges ever published.) Despite my voracious readings about reloading over the past 45 years, I cannot recall ever finding a single other reference to Mr. Lambert. But if the only contribution he ever made to wildcatting was the .25 Souper, he deserves accolades. The cartridge is a winner. Why Souper, as he named it, instead of Super? Beats me - unless you’ve seen what it does to a varmint!
Ok, let’s assume at this point that your interest is piqued – you’re starting to feel a tiny itch somewhere just out of reach. How easy is this easycat? You’ll be happy to know that the good ol’ boys at RCBS not only list reloading dies for the .25-308, they have them on the shelf (#56145). Instead of a six-month wait and a hefty custom die charge, you can get a set in a week or so for well under a hundred bucks. Prefer to neck size? A Redding .243 die with the proper diameter sizing inserts takes care of it. Barrel blanks in .25 caliber are easily found in either blue or stainless and with any twist rate you might prefer. Chamber reamers may be a bit less common, but are by no means a custom proposition. Any good rebarreling service should either have one in stock or will know where to get one without difficulty. In a pinch, a good gunsmith could chamber a .25-308 with a .243 reamer and a separate neck/throat reamer. (I’m neither a gunsmith nor a machinist, so forgive me if I oversimplify there. But it can be done.) Any .243 or .308 rifle can simply be rebarreled to .25-308 with no other modifications. No changes required to the magazine, feed rails, or bolt face. As I said: easy.
Making cases is just as simple. Simply run new or once-fired 7mm-08 or .260 Rem. cases into your .25-308 sizing die. That’s it. Depending on the exact dimensions of your rifle’s neck, you may be able to use .308 brass without neck turning, at least some brands. In my rifle, I can use Winchester .308 brass with no problem, but Federal brass, especially their match brass, gives me necks too thick to chamber without neck turning.
It’s certainly possible to use .243 brass, but I strongly recommend against it. Because the .25-308 and the .243 are visually indistinguishable, there is a very real danger that one of the larger rounds could accidentally find its way into a .243 rifle. If the .243 rifle’s chamber neck were oversize or worn, the round might even chamber. Trying to force a .257 bullet down a .243 bore is certain to result in a nasty surprise. No such problem with a bullet smaller than the bore. Stick to necking down, especially where the dimensional change is as small as this one.
What about loading data ?
OK, we have a rifle, we have cases and we have reloading dies. All we need now are recipes for loading. There are three ways to obtain such data: find it, compute it or develop it. In the case of the .25-308, two of the three are easy.
Finding published loading data may be the toughest of the three options. There aren’t many sources that list the .25-308. The already mentioned Speer Reloading Manual #4 is not only a collector’s item, but it is based on components that are either obsolete or have since been modified. It is available on disk as an option to the excellent RCBS Load software, however. References to the round in more modern literature are rare. Layne Simpson published some loading data in an August, 1986 Shooting Times article on the .308 cartridge family. But the situation isn’t really a problem, as we’ll see in a moment.
Computing load data is as easy as point and click. You merely need a copy of Wayne Blackwell’s indispensable Load From A Disk software. (See my review) The program contains a database of factory cartridges from which it derives suggested loads. Simply use the .243 or .260 case and change the bullet diameter in the calculations. Simple. By the way, the data is derived from case volume, as measured by water capacity. To measure this, weigh a fired case. Then carefully fill the case to the brim with water and weigh again. The difference in weight is the gross water capacity. In my cases, the gross water capacity averages 53 to 55 grains. Filled to the shoulder/neck junction, the average is 50 grains.
A reference to P.O. Ackley is in order at this point. When Parker Otto was doing his famous experiments, he reported that his best creation was the .250 Savage Improved. That round showed the most improvement and produced the greatest efficiency of all his projects. Ackley firmly stated it was the optimum case size for the .257 bore. The .250 Savage Improved has a case capacity of 50 grains of water, measured to the base of the neck. The .25-308 is therefore identical in case capacity, and should duplicate the .250 Savage Improved on which P.O. Ackley so rightly doted. He liked the Souper, too!
Finally, we have the option of developing data from scratch. To do so, we take data from as similar a round as possible, carefully and gradually adjusting powder charges. With the .25-308, there are two approaches. We can start with data for the standard .250 Savage or for the .243. Because the .250 Savage uses identical bullets from a smaller case, we can safely start with .250 loads and slowly work upwards. The .243 uses an identical case, but with slightly smaller bullets of the same weights, so here again we can start with slightly reduced .243 loads and work from there.
How do we know how far to go? Some years ago, I read about some ratios of cartridge efficiency that can be applied. (I wish I could find that article, I’d love to give proper credit for what follows.) The rules of thumb are:
1. If bore size and bullet weight are constant, potential velocity varies at one fourth the percentage change of the case capacity.
2. If case capacity and bullet weight are constant, potential velocity varies at one fourth the percentage change of bore diameter.
3. If case capacity and bore diameter are constant, potential velocity varies at one half the percentage change of the bullet weight.
Don’t panic! We’ll take this slowly, and it doesn’t require calculus to compute, I promise. Let’s start with rule one, based on changing case capacity alone. The standard .250 Savage has a gross case capacity of about 46 grains of water. The .25-308, as we said, has a gross capacity of 53 grains. Thus, the .25-308 has about 15% greater capacity. Potential velocity, according to the formula, should be about one fourth of 15% greater than the .250 Savage. Using a 75-grain bullet as an example, most manuals show that the .250 Savage can reach 3,300 fps with several powders. If we multiply 3,300 by 0.0375 (one fourth of 15%), we get just about 125 feet per second. The .25-308 should get about 3,425 fps with the same bullet (also assuming loading to the same pressure).
Now let’s look at the second formula, base on identical bullet weight and case volume but different bore diameter. We see that .257” is about 6% larger than .243”. Therefore we should obtain about one fourth of that, or 1.5%, greater velocity over the .243. The .243, coincidentally, also gets 3,300 fps with a 75-grain bullet. Add 1.5% to that and we get 3,350 fps. Interpolating both results, if we again load to the same pressure, our .25-308 should therefore give us a muzzle velocity of between 3,350 and 3,425 fps. Call it 3,400 fps even. That’s what we’ll shoot for in our load development.
Out of curiosity, what will happen if we elect to develop data for 100-grain bullets in our 25-308? We see that a 100-grain bullet is 33% heavier than a 75 grainer. Using the third formula, one half of that difference is about 16.5%. If we now subtract that amount (because a heavier bullet will be slower), we should get about 83.5% of 3,400 fps, or 2,840 fps. Call it 2,850. Again, that’s our target value for load development. Ok, the computationally challenged can open their eyes again. Whew!
At this point, you might expect me to provide some actual load data. Sorry. Because there are so many variables in rifle, case and die dimensions (even with an easycat), I don’t feel it’s prudent to do so. I will say that my actual results with normal, not-quite-max loads gives almost exactly the numbers developed above. My loads with the 75-grain Hornady Vmax or hollowpoints have a comfortable muzzle velocity of 3,400 fps. Loads with the 100-grain Speer softpoints deliver 2,950 – about 100 fps higher than the prediction, but I have no complaints! |