8mm wildcat cartridge ..

[craig_hinshaw]

Looking for a wildcat cartridge that is 8mm and use a 300 rum case that is cut down to about 57mm to 62mm in length.then sized to 8mm..hoping to use cast boolits 200grs+ and powder is h1000, to start with .Would like to hear for everyone about this and get ideas of will work and will not..
I have the gun and a lot of 8mm bullets and casting equiptment, what I have is ideal but I don't want to get people hurt.
Thanks Craig ..

[waksupi]

Sounds like the case will most likely be over bore. The plain ol' 8X57 is awful hard to beat for a CB round.

[bgmkithaca]

A case called the .325 Win. short magnum is a little shorter than you want but is available without the work of roll-your-own for the Ultra mag case. I cant say that using a case that large is real great idea for cast bullets-as stated above the 8 x 57 is great for cast- jacketed is another story in a case that large.

[craig_hinshaw]

ok thanks

[UBER7MM]

Craig,
.
Welcome to the forum.
.
US 8mm wildcats tend to be rifle specific pertaining to the K98 Mauser captures after WWII. The most popular is/was 8mm'06. K98 barrels and 30'06 brass. 8mm Rem Magnum was created to complete with the 338 Win Mag. The 338 WM has the advantage because it will chamber in a standard length action (brass = 2.5") The 8RM is huge and needs a longer action. I don't have my manual available for the details. There is also the 325 WSM. It's a short wide magnum in 8mm as mentioned above. There are some other European 8mm cartridges, 8x64 and others.

I hope this helps,

[FrankG]

8mm -06 is a simple to do round , plentiful 30-06 cases as the parent case, standard dies can be had , plus it is a real good shooter .

[Ben]

Ditto on the 8 mm - 06.

It would take a smart elk to know if it had been hit with an 8 mm -06 or a 338 - 06.

Both are GREAT cartridges.

[bruce drake]

100% on the recommendation on 8mm-06. Great cartridge and the brass is a lot easier to replace when the Range Gods picks up one of your pieces of brass and hides it in the tall grass...

[UBER7MM]

Craig,
You were asking about Magnum cartridges in the 57-62mm range in length. Nils Kvale developed the 8mm Kvale cartridge in 1949. Its a rebated rimmed belted magnum! He was an Engineer at Norma and was one of the fathers of the 358 and 308 Norma Magnums.

http://www.cartridgecollector.net/8-...le-magnum-8x61
http://www.gunsmagazine.com/1957issues/G0157.pdf

Interesting reading,

[littlejack]

Hey Craig:
Welcome to the CastBoolits.
The 8mm/338, was/is the "original" Poor Mans Magnum. The Mauser rifles sold cheap back in the day. So, if a person wanted a
magnum cartridge/rifle at a modest price, re-chambering the original 8mm rifles (.323) was the way to go.
All that was needed to be done after re-chambering was, the bolt face enlarged, and the ways opened up to accept the larger
case size. The 338 Win. magnum case length is short enough to be used without to much alteration to the magazine.
I have an Egyptian Mauser, that I had re-chambered to 8mm-06 AI. One of my favorite rifles. But, I shoot jacketed in it.
Regards
Jack

[craig_hinshaw]

I have an 8mm-06 and was wondering about something odd..
like the old saying goes..A small block is good but a big block is better,if I has 1 engine why not 2 or 3???

[archeratlrg]

Hello everybody, I know this is an older thread but I wanted to weigh in here on what Craig is looking for. I have the round and it is awesome. Right after the 300 RUM was unveiled I started playing with the case. In Feb. 23, 2001 the IMM (Intermediate Mauser Magnum) cartridge line was born. Case length is 2.280 with a 35 degree shoulder with the diameter at shoulder being .530 and my first one was was in 8mm. The line stretches from 6mm thru .416. The 8mm is a little hotter than the 8mm Rem. Mag. It turned out a lot better than I imagined it would. I have several 8mm's and I think my favorite is the 8x57 AI. I get an honest 3100fps with the 160gr Barnes and right at 3000fps with the 180gr Barnes. Nearly all of the X57 AI cases are designed around the 7 x57 Mauser where the 8x57 has the shoulder farther forward. I made the 8x57 AI in 1970 and was very happy with it. Having known Ackley thru my fathers gunstocking business I contacted him and asked why he never used the 8mm case as the basis for any of his wildcats and he said he just hadn't really thought about it but encouraged me. I started playing with the round and again have a complete line from 6mm through .375. I called this line the x57 ASI or Ackley Super Improved. My favorites are the 270, 8mm, and 338 and .35 ASI. The .338 and .35 will do everything the 338-06 and 35 Whelen will do and do it in the shorter action. If anyone would like info on them drop me a line. Happy hunting and shooting!

[357Mag]

Craig -

Howdy !

While not knowing your wildcat's planned shoulder diameter or angle, or neck lg; hear's a few thoughts....

Were you to trial form some cases, you might be able to use a .338 Lapua Mag die for case forming your 8mm wildcat.
The .338 Lapua has major case diameters greater than those for the .300 RUM.

Case forming would provide a shoulder shove downward on the parent .300 Rum brass. This would thicken the case necks.
To arrive @ final desired 8mm calibre and neck wall thickness, you'd inside neck ream. Outside neck turning would be performed to provide neck wall uniformity, as needed.

Your formed shoudler diam might be closer to .530" m than .522", but forming sample cases might help give an idea of a practical reamer configuration that might prove usefull.


With regards,

357Mag

[357Mag]

Craig -

Howdy, again !

Wanted to add.... if one did not want to cut the form die shorter to fit the wildcat's length & other specs; then a "perch" could be used. Make a perch out of a shellholder , a 1/4-20 flat head machine screw; and a 1/4-20 jam nut.
Screw head diameter held to less than that of the lower diameter opening of the form die.

Shell holder snaps in-place in th epress ( such as a ROCKCHUCKER ). Brass to be formed is sat atop th eperch, and press ram operated to advance case up-into the form die.

With regards,
357Mag

[Good Cheer]

In the early eighties I shot a 7-08 with the neck lengthened for cast.
Always wanted to try the same thing in 8x57, to just use 30-06 cases.

[archeratlrg]

Looking for a wildcat cartridge that is 8mm and use a 300 rum case that is cut down to about 57mm to 62mm in length.then sized to 8mm..hoping to use cast boolits 200grs+ and powder is h1000, to start with .Would like to hear for everyone about this and get ideas of will work and will not..
I have the gun and a lot of 8mm bullets and casting equiptment, what I have is ideal but I don't want to get people hurt.
Thanks Craig ..

Good afternoon Craig, I developed a line of cartridges about the same time Remington did their RUMs. Parent is 404 Jeffrey but you could use the RUM or one of the new Nosler cases. Cartridge was designed to be used in the intermediate length Mausers. My first was in 8mm and then had a body shoulder reamer made so I could use removable pilots for different calibers. Cartridge line is called the IMM series for Intermediate Mauser Magnum and holds about 8-10 more grains of powder than a 300 Win mag case. I can send you a print of the cartridge if you want to PM me. I'm building them in 257 up through .416.

[Andy_P]

The 8mm ARP

I did this work in 2005, but have just now posted about it. I still have the gun, brass, etc. but have not shot it for about 10 years. Maybe this year..........

My motivations for this were:

- I like the 8mm bore size – no explanation, no apologies. Some might ask "Why?", or say "An existing round is better.", or "Bullet selection is poor.", etc. I did it because I wanted to, and I have learned a great deal.
- an interest in making use of commonly available and cheap 8mm milsurps
- I have grown a bit weary of my research on the 8x63mm Swedish
- I wanted to design a magnum wildcat that would match or exceed the capacity and performance of the 8mm Rem Mag, but in a standard (30/06 length) action
- it had to use readily available and inexpensive brass (I use 300 RUM or 338 RUM)
- the forming and resizing process had to be as simple as possible and inexpensive.
- the case would have a 35 degree shoulder (same as the new 325 WSM), a bit less diameter at the shoulder than the 325 WSM (so I could use those dies as part of the process), and a calibre length neck. Final specs would take into consideration some interesting Bench Rest cartridge theories for efficient gas flow
- the case dimensions and throat length would allow bullet weights from 180-250gr to be seated close to the lands, but still be fully gripped by the neck at a max OAL of 3.420". Throat length is set at a moderate 0.250", but could be lengthened with a throater for heavy bullets if OAL restrictions are ignored (and I am willing to accept the gun as a single-shot). Given that case capacity is about 105.0 gr of water (96.0 gr loaded with a 220 Sierra), heavy bullets impinging on powder capacity is not a big concern.
- I would make use of the "Ackley" principles of minimum taper and 35+ degree shoulder, to (allegedly) reduce bolt thrust, and to increase brass life.
- The design would prevent the 8mm ARP cartridge from inadvertently being placed in the chamber of either the 300 or 338 RUM (given that the headstamp will show one of those two chamberings). This was accomplished by reducing the taper thereby increasing the cartridge diameter from casehead forward to a size greater than that of either the 300 or 338 RUM. They could not even be forced in.
- I have an alternate design for the same cartridge at 2.54" vice 2.62" long so as to fit in Mauser actions designed for the 8x57 and its 3.25" OAL. I would use the same reamer with a shorter go-gauge (which I have) to chamber, and the same case forming tools and process



The combination of 35 degree shoulder and minimal taper do not pose feeding problems with the Mauser controlled feed claw, but ejection is a bit weak and needs some work.

I want to keep pressure under 60K. I have some experience developing loads for the 8x63mm Swedish, and of course a chrony. If I am, for example, seeing much more than 3100 fps with 220 gr bullets, then that should be a clear sign that pressure is at or close to max. After fireforming, I measure the diameter of the casehead to establish a "Pressure Ring" diameter. I will not use loads that cause that diameter to increase by more than 0.001" - there is no better pressure indicator aside from an instrument (like the Oehler Model 43 - I wish I had one!), to indicate dangerously high pressure.

I bought a reamer and go gauge from Pacific Tool. The test gun is based on a military K98K Mauser action with a military 28" barrel (with 1:9.25" twist, fast enough for even the 250 gr Woodleigh). The bolthead was opened, a properly bent handle was installed, the mag box opened to the max (3.420”), feed rails and ramp tuned, and scope mounts added (it was already bubba'd). Jason Spencer at Gunco in Ottawa did the work, and I am completely satisfied.




Here's how I form the brass:

1. Anneal the top 0.75" of the 338 RUM or 1.0" of the 300 RUM brass
2. Run it through a Lee 8x50R Lebel F/L die, set so that the neck/shoulder juncture is close to its final distance from the base (2.300" in this case). The 8x50R die has a nice gentle slope and the correct 8mm neck. I use the excellent Redding Imperial Sizing Die Wax, which can be bought from Wholesale Sports.
3. Trim to 2.620" (I use a Lee 300 Win Mag trim die)
4. Fireform using 20.0gr of Unique under Cream of Wheat packed under a bit of tissue
5. Deprime
6. Neck size using a Redding 325 WSM F/L die (big enough that it only works the neck and has the correct 35 degree angle)
7. Body size just below the neck back to 0.5320" (when necessary) using a Lee 338 RUM F/L die shortened 0.500” and with the decapper removed
8. Seat the bullet using the 325 WSM seating die.
9. Repeat steps 5-8 for each subsequent firing. Inside neck ream after the first firing only

All I needed was the Lee 8x50R Lebel F/L die (which I already had), the Redding 325 WSM die set and a Lee 338 RUM F/L sizer - total cost less than $100. A set of Custom Dies would be a "Nice to have", but the "MacGyver Set" I use works well.



L to R: 300 RUM, annealed and sized using 8x50R Lebel, trimmed to 2.620", fireformed



L to R: Throat Length (0.250"), 220 gr Sierra seated to 3.420" (0.040" off the lands) showing how little powder space is consumed by the bullet

Loads:

The 8mm ARP holds 105.0 gr of water full to the top. The 8mm Rem Mag holds about 98.5 gr, and the 340 Wby Mag, about 102.0 gr. Logic and experience indicates that my max loads could fall between the two, i.e. greater than max loads for the 8mm Rem Mag, but less than max loads for the 340 Wby for all bullet weights and powders. In fact, given the practice of Wby loads being on the high side of safe pressure, their usual use of a long throat, and the greater bore size of course, I would be wise to stay well below 340 Wby max loads.

My starting loads used 8mm Rem Mag max loads plus about 3% (i.e. about 2 grs) and I stayed at least 4% below 340 Weatherby max loads (i.e. about 3 grs). I can't trust the classic high pressure "signs" (primer flattening, stiff bolt lift, etc.), and will work up an accurate load anyways, but as with any wildcat, am left to my own devices to determine max loads. That having been said, I intend to determine max loads (and hence explore its potential), but then back down to modest pressure, accurate loads. I am mindful of the high amount of bolt thrust this large diameter cartridge will deliver, and want to see relative long life out of the bolt, receiver and barrel. Accurate, below max 8mm Rem Mag #'s are just fine.

Here’s my first round of results (velocity only) and my analysis of them:

8mm ARP
Cartridge OAL 3.420” (0.040-0.080” off the lands for the 200 and 220gr bullets)
28” barrel (might add ~125 fps over a 24" barrel)
Chrony 20’ from the muzzle (farther than typical, but there's lots of muzzle blast!, might deduct ~15 fps over 10' from the muzzle)
Temp 15 deg C (I must be careful when I shoot and it's 30 C)
CCI Large Rifle Magnum primers

125 gr Speer – OAL 3.275” – 89.0 gr RL19 – 3210 fps – powder too slow
125 gr Speer – OAL 3.275” – 86.0 gr H4350 – 3440 fps – powder a bit slow
125 gr Speer – OAL 3.275” – 85.0 gr H414 – 3650 fps – powder about right

150 gr Speer – OAL 3.350” – 84.0gr H4350 – 3370 fps – powder a bit fast
150 gr Speer – OAL 3.350” – 89.0gr RL19 – 3400 fps – powder a bit fast
150 gr Speer – OAL 3.350” – 93.0gr RL22 – 3530 fps – powder about right

170 gr Speer – OAL 3.350” – 91.0 gr RL22 – 3450 fps – powder about right

180 gr Nosler – OAL 3.420” – 90.0 gr RL22 – 3450 fps– powder about right

200 gr Nosler – OAL 3.420” – 91.0 gr RL25 – 3170 fps – powder too slow
200 gr Nosler – OAL 3.420” – 87.0 gr H4831 – 3180 fps – powder a bit slow
200 gr Nosler – OAL 3.420” – 88.0 gr H1000 – 3120 fps – powder too slow
200 gr Nosler – OAL 3.420” – 86.0 gr RL22 – 3230 fps – powder about right

220 gr Sierra – OAL 3.420” – 89.0 gr RL25 – 3070 fps – powder about right
220 gr Sierra – OAL 3.420” – 85.0 gr H4831 – 3010 fps – powder a bit fast
220 gr Sierra – OAL 3.420” – 85.0 gr RL22 – 3100 fps– powder a bit fast
220 gr Sierra – OAL 3.420” – 87.0 gr H1000 – 3010 fps – powder a bit fast
220 gr Sierra – OAL 3.420” – 90.0 gr Retumbo – 3050 fps – powder about right
220 gr Sierra – OAL 3.420” – 104.0 gr US869 (c) – 3170 fps – powder about right


The 170, 180, 200 and 220 gr loads are max loads (as determined by some "signs" and common sense), and will be backed down by 3.0 or more grains as I settle on an accurate load. I would like to try Re33 and IMR8133, as well as more US869,

I did not achieve velocities I have heard that others have achieved with the 8mm Rem Mag and shorter barrels, but have exceeded anything I have seen published for the 8mm Rem Mag. This is about the best I can get from my gun with what I am willing to load for it.