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Thread: .375x.284 Winchester Wildcat

  1. #1

    .375x.284 Winchester Wildcat

    A couple of years ago I started a project to build a rifle chambered in a .375x.284 Winchester. I had paper-whipped the internal ballistics on QuickLoad, and it looked good 'on paper'. I was going to build it on a Mauser 98 action, (actually a Turk '38 Mauser), but I was looking to ultimately put it on a Swiss K-31 action.

    I bought a hand-full of Turk '38 receivers a few years ago for $10 each, so this was the action I would start with. Also, I was starting fresh with my relatively new lathe and mill, and if I buggered the action up, it wouldn't be too painful on one of these cheaply acquired actions. I am a self-taught gun-maker, and this was only the third rifle I had made 'from scratch'.

    Let me clarify that "gun-maker" term before anyone gets too excited. I did not ever, and do not now, have any intentions or plans to make guns for, or repair the guns of, other people. I am not a gunsmith, and I would not present myself as such. However, I have some hand-skills, and I am tired of "professional" gunsmiths telling me what I want, or telling me "that's not a good idea", or telling me that I have to wait 6 to 18 months for them to get around to the project I 'don't want to do'. The only realistic solution was to do it myself, and I am very pleased with the first few of them I have made.

    For those that might not be familiar with the .284 Winchester parent case, it has two "socially redeeming characteristics". First, it has a "magnum" diameter body (nominal 0.501"). That means more case capacity in a "standard length" case. Second, it has a "standard" rim diameter (0.473" nominal). THAT means a "standard" bolt could be used without having to modify the standard Mauser or K-31 bolt face.

    I wanted the extra case capacity to drive a .375 caliber bullet fast enough to deliver 2000 ft-lbs to 300 yd, as well as keep the muzzle energy below 3400 ft-lbs and the trajectory to about 12 inches of total vertical deflection. I really LIKE the .308 Winchester case, but it just didn't have enough capacity to do what I wanted. QuickLoad said that the .284 Win's case could. So...

    I ordered an Adams and Bennett barrel from MidwayUSA and a .375x284 Win reamer from Pacific Tool and Gauge. When I got the reamer, I chambered, threaded and installed the barrel on the Turk action. I had already drilled and tapped the receiver for scope mounts, and installed the mounts. Once the barrel was on, I bought a 'scope off EBay and a Hogue "Overmolded" stock from Midway. It was 'a rifle'.

    Here is a picture of some .375 Wildcats I have been 'playing' with:

    Here are a couple of pictures of the action of the finished piece:

    Here are the relevant spec on the case and rifle.

    Barrel length = 26.0" (1:12" twist)
    Case capacity = 68.56 grains of water
    Case capacity with 260-grain Accubond seated 0.648" deep = 50.4 grains of water
    Overall Cartridge Length = 2.900"

    Optimal Barrel Timing Charge (node #6) = 47.38 grains of Accurate 2495 (100.5% of case capacity)
    Estimated Muzzle Velocity = 2388 f/s
    Muzzle Energy @ 2388 f/s = 3291 ft-lbs
    Estimated Chamber Pressure = 46,985 PSI

    Trajectory when sighted in for a 6" target:
    ...................................Impact ........ Retained
    Range . . . Elevation . . . Velocity . . . . . Energy
    100 yds . . . 2.9" . . . . . . 2225 f/s . . . 2858 ft-lbs
    125 yds . . . 3.0" . . . . . . 2186 f/s . . . 2757 ft-lbs
    150 yds . . . 2.6" . . . . . . 2146 f/s . . . 2659 ft-lbs
    200 yds . . . 0.3" . . . . . . 2069 f/s . . . 2471 ft-lbs
    205 yds . . . 0.0" . . . . . . 2225 f/s . . . 2452 ft-lbs
    241 yds . . .-3.0" . . . . . . 2006 f/s . . . 2324 ft-lbs
    250 yds . . .-3.9" . . . . . . 1993 f/s . . . 2292 ft-lbs
    300 yds . . . 10.1". . . . . . 1918 f/s . . . 2124 ft-lbs

    The total vertical deflection is 13.1" instead of 12", but I can live with that. In more than 50 years of hunting, I've only shot two animals beyond 300 yd, and the vast majority were below 200. If I really need to shoot at something at 300+ yd, I can 'hold over a little'.

    2124 ft-lbs at 300 yd is nice. There's nothing in North America including coastal brown bears that can slough off 2000 ft-lbs and more. AND, .375" is a pretty big hole even without "mushrooming". Things were looking up. However, right away I had feeding problems.

    The rebated rim of the .284 Win case was a problem.

    I was cycling cartridges through the action, making sure every cartridge fed properly. They didn't. A single cartridge loads fine from from the Mauser's magazine, but load two in and it's a problem. Three is OK but four is not.

    The problem was the rebated rim of the .284 Win case. As the cartridge on the left side of the magazine is picked up by the bolt face and pushed forward, the bullet starts to rotate "up" into the chamber over the feed ramp, meaning the head rotates "down". When it's about half way up the feed ramp the rim moves just far enough 'down' that the bolt moves over it and hits the case's body about one-third the way forward of the head. That means jam. And jam it did.

    The cartridges on the right side of the magazine - numbers one and three - fed just fine. I had to figure out what was wrong between the feed ramp, rails, and follower, and fix it. The "wide body" of the .284 Win case caused both ramp and rail problems. In the end I had to remove considerable metal from both the feed ramp and the rails. Now it feeds smooth as silk.

    I made reloading dies by modifying a set of .284 Win dies. All that was required was reaming the neck to proper diameter and making a new expander ball. I loaded up 20 cartridges with 260-grain Accubonds, and a variety of charges of Accurate 2495 powder.

    It sucked. I was all over the paper. It was very discouraging. I took it home and redid the muzzle, being as careful as I possibly could. As I was reinstalling the barrel on the action, I happened to grab the 'scope. It 'rattled' around. Shiit muslims. The whole problem had been the scope bases shooting loose. Dang! I loaded some more cartridges and headed back to the range.

    It shot better, but it wasn't great, and it certainly wasn't acceptable for a 'hand made' rifle. Try as I might I just couldn't get it to be consistent. Some loads and groups would be "good" (MOA-ish) and the same load would be crap the next time I shot it. I was pulling my hair out.

    As I was preparing the rifle for shipping to Colorado where I was going on an elk hunt, I pulled the Hogue "Over-Molded" stock off. Shiits again. The forearm of that stock is as flimsy as a reed. I could, using only my index finger, pull the forearm away from the barrel by at least an inch with the barreled action fully mounted in the stock! The setup I used at the bench (a Lead Sled) rested the forearm on the bench. That stock will not 'make the cut'.

    Certainly the stock was a significant problem, but it wasn't the only problem. I had another wildcat (.338 caliber on an 8x57 Mauser case) that had that stock on it, and it shot well-enough. HOWEVER, I had a third wildcat that I had made (8mm bullet on .376 Steyr case) that had a very stiff fiberglass stock on it that shot 'like a house-afire' (sub MOA with any bullet I chose). Therefore I knew I was capable of making a barrel that could shoot.

    I started looking at other bullets. In the running was the 235-grain Speer Semi-Spitzer, the 260-grain Accubond, the 270-grain Speer BTSP, the 300-grain Hornady SPBT, and the 300-grain Accubond. The 300-grain bullets have really nice ballistic coefficients, and because of their weight, carry 2000 ft-lbs out to 300 yd easily.

    The problem with the "light" 235 was that it's BC was so poor that it couldn't get 200 ft-lbs out to 300 yd without running the muzzle energy (and attendant chamber pressure) up higher than I wanted it. The trouble with the "heavy" bullets was that muzzle velocity was so low that at 300 yd, the impact velocity was in the ragged edge of what the manufacturers recommended as the minimum at which the bullet's terminal performance would consistently be as designed.

    I'm not one to trust manufacturer's numbers without actually testing them. None of their numbers - except weight. If I was going to get this all worked out, I would have to test these bullets at the impact velocities their BCs predicted.

    Below is a chart I put together comparing the internal and external ballistics of the bullets listed above.

    To refresh some memories, I want this cartridge to:
    1) Deliver 2000 ft-lbs to 300 yds,
    2) Have muzzle energy less than 3400 ft-lbs,
    3) Have total vertical deflection of less than 12 inches (above line-of-sight plus below line-of-sight), and
    4) Have impact velocities at 300 yds that are high enough to expect "good" (as-designed) terminal performance.

    You'll note that it is not difficult to get 2000 ft-lbs out to 300 yds with this cartridge and keep max chamber pressures modest. However, when you start trying to get to a specific timing node, (barrel harmonics), it gets a bit more difficult. I could go to a faster node, (and get less drop at 300), but that would mean upping the muzzle energies up over 3400 ft-lbs. Way over in some cases. Since as I said above, I have taken only 2 shots at big game in my life that were over 300 yds, and the VAST majority of the shots I have taken have been near or less than 200 yds, I'm not inclined to beat myself up ALL the time for the rare possibility of a 300+ shot.

    The color coding goes like this:
    Green is "good"
    Yellow is "note"
    Red is "bad"
    White is "neutral"

    Those 1700-ish f/s impact velocities were making me nervous. I would have to see for myself what the terminal performance was going to be at the predicted impact velocities for each bullet. It turned out better than I expected.

    I got into QuickLoad (QL) and loaded the files with my "standard" loads for each of four bullets. That gave me the predicted impact velocities at 300 yd. I then got QL to give me some powders and charges that would produce muzzle velocities equivalent to the 300-yd impact velocities with my standard loads. I loaded up 3 rounds each of each of the four bullets with the reduced loads. I used one each of the four bullets for impact testing, and ran all three through the chronograph. I measured the depth of each bullet's penetration into phone books. The results are below.

    The 300-yd impact velocity for the 260 Accubond was 1861 f/s. I used 23.1 grains of BlueDot (61% of case capacity) at an estimated chamber pressure of 37 kPSI. The actual impact velocity of the bullet used to determine penetration was 1847 f/s.

    The 300-yd impact velocity for the 270 Speer was 1827 f/s. I used 28.2 grains of H4227 (63% of case capacity) at an estimated chamber pressure of 27 kPSI. The actual impact velocity of the bullet used to determine penetration was 1839 f/s.

    The 300-yd impact velocity for the 300 Hornady was 1733 f/s. I used 27.0 grains of H4227 (63% of case capacity) at an estimated chamber pressure of 28 kPSI. The actual impact velocity of the bullet used to determine penetration was 1725 f/s.

    The 300-yd impact velocity for the 300 Accubond was 1687 f/s. I used 25.3 grains of H4227 (64% of case capacity) at an estimated chamber pressure of 28 kPSI. The actual impact velocity of the bullet used to determine penetration was 1701 f/s.

    Penetration Depth was:
    260 Accubond -- 6 3/4th inches
    270 Speer -- 6 3/8th inches
    300 Hornady -- 6 1/4th inches
    3000 Accubond -- 6 5/8th inches

    Here's what thing's looked like:

    The penetration box with rod inserted 'til it stopped.

    The recovered 260 Accubond and 270 Speer with an unfired bullet next to the remains of the fired bullet:

    The recovered 300 grain bullets:

    While the medium was dry newsprint, the disruption is significant enough to indicate clearly that impact velocities like these will "work" to produce good terminal performance for all of these bullets. Furthermore, I really like the Accubonds. I don't mind the Speer and Hornady, but the Accubonds are very good. I really wouldn't mind using any of the four bullets on anything in North America up to coastal brown bears.

    Last edited by gitano; 13-12-2010 at 17:51. Reason: Correct rim diameter from .437" to .473" grammar and typos

  2. #2
    What a brilliant post! I'm not sure I understand all the details - I mean "timing node"? WTF?

    I could read this sort of thing all day as it really appeals to me. The idea of using larger calibres in smaller cases isn't something that we see a lot of in this country. Making your own rifles is very impressive too, you clearly have a very good idea of what you're doing! Keep us updated on how you get on with the rifle. I assume you're building it because you want something unusual that will throw a heavy bullet for large game without the recoil and unpleasantness that goes with the regular large calibres? It certainly looks good.

  3. #3
    Great write up Paul, and very interesting, but the timing node thing is beyond me I'm afraid
    Good luck with it in the field though, looking forward to hearing how it turned out.


    njc110381 small case big bullet, .300 whisper ?

  4. #4
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    Bonnie Scotland
    Sounds really useful Paul.

    But... just out of interest and bearing in mind the feeding problems (in a gun that you might look down the barrel at a big Bruin with ) why the .284 case and not the '06? or shorten the barrel 2 inches and mibbee use an '06 Ackley.... just out of interest, you understand.

  5. #5
    The timing node references are in the context of barrel harmonics (not theory) and their effect on a rifle's precision (theory). The empirical data collected so far substantiates the theory, but there are those that are almost violently opposed to it. It has worked repeatedly for me "in real life", so I continue to use it. Essentially it takes advantage of the fact that we know the mechanics of harmonic motion in a cantilevered beam (unless it's in a full Mannlicher stock, a barrel is a cantilevered beam) and attempts to time the departure of the bullet at one of the harmonic nodes. The theory being that the bullet leaves the barrel when the barrel is "vibrating" the least.

    Quote Originally Posted by njc110381
    I assume you're building it because you want something unusual that will throw a heavy bullet for large game without the recoil and unpleasantness that goes with the regular large calibres?
    In large part, but the 'large game' isn't too big a deal. In my youth, I worshiped at the "Speed Uber Alles" altar. As I have aged, I have come to appreciate the values of "slower, but bigger around". Slow and big around are much more pleasant to shoot in every aspect, including recoil. And there's nothing "wrong" with shooting "deer" with "big around" bullets.

    Quote Originally Posted by Tamus
    But... just out of interest and bearing in mind the feeding problems (in a gun that you might look down the barrel at a big Bruin with ) why the .284 case and not the '06? or shorten the barrel 2 inches and mibbee use an '06 Ackley.... just out of interest, you understand.
    I do understand, Tamus, and those are reasonable questions.

    The BIG answer is that I don't "like" the '06. That is a PURELY emotional perspective. I believe that the '06 is a great cartridge, and that the '06 case is an excellent case to use for a wildcat platform. But I don't like it. The primary reason is that in the US, it's practically treason to say ANYTHING that even SUGGESTS that the '06 isn't the best cartridge that ever graced this planet, and that if you use anything else you're either too stupid to know better or a freak with "magnumitis". So it isn't the cartridge I don't like, it's the people that worship it, and I don't want to confused with being one of them. Does that mean I care what other people think of me and the tools I choose to use? In a word, "Yes". In the same light as: if I found a t-shirt that was made of fabric I really liked but said "I Love Osama Bin Laden". I wouldn't want people to think I liked OBL, and I don't want people to think I'm one of the sycophants of the .30-06.

    There are a couple of small, practical details too though. The .284 Win case is a "short" case and will work in a "short" action. An '06 won't. Of course the Mauser '98 action and it's variants WILL handle an '06 case length, so that case would have been fine for this wildcat. Secondly, the .284 Win case is "short and fat". While that's all the rage these days, it also makes sense for a case in which you will be using a heavy bullet. A short, fat case (short length but "magnum" diameter) let's you get more powder into a shorter package.

    Actually, the original case I planned for this cartridge was the 7.5x55 Swiss. It is almost (but not quite), identical to the .284 Win case except it doesn't have a rebated rim. In fact I found this out when I first tried to get cases for the K-31s I wanted to reload for. I found out that I could use .284 Win case as a "suitable substitute" for the GP-11. In fact, my daughter shot a nice caribou bull with a K-31 using handloads made from .284 Win cases. (I owe Brithunter that story.)

    Of the four rifles I have made so far, I have yet to "finish" any of the them despite the fact that I have blooded two of them. I like "walnut and blue steel". I am trying to get the time and wherewithal to get the stocks I want The Legacy Continues... (look for the Freischutz Classic or the British Stalker models), get the metal polished and blued, and get the sights (express probably) mounted. I get pulled off onto other projects, and ... well, we all know how that goes. Nonetheless, I am refocused on this rifle because I want it shooting straight. That is likely going to require a better stock than the Hogue.

    I could read this sort of thing all day as it really appeals to me.
    I'm glad to hear that. I'll post some more articles about some of the other wildcats I have already built, and more that I have in mind.

    Last edited by gitano; 14-12-2010 at 01:16.

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