.30 XCB wildcat, from scratch.

[geargnasher]

Somebody had to start this, so I'm jumping in. The .30 XCB is a joint project among several CB members, particularly Larry Gibson, Runfiverun, Btroj, and myself; Goodsteel (Tim) of MBT is the builder.

What we wanted to create is a versatile wildcat with potential for extreme accuracy, high velocity, and low expense to be used primarily, but not necessarily exclusively, with cast boolits. Part of the economy is being able to use several different and abundant parent cases for brass, and to end up with something that will feed easily in most rifle actions, especially large-ring Mausers. We accomplished this by essentially short-chambering a tight-necked .30-'06 to 57mm which enables the use of modified factory '06 dies for reloading, and following the SAAMI-spec throat design allows for the use of a variety of .30-caliber cast boolit designs.

Other advantages of the case include the natural taper of the '06 which tends to extend the pressure curve of any given powder slightly vs. more "straight" designs, a capacity which should enable up to 2600 fps with reasonable pressure and projectiles in the 150-180-grain arena, and being able to eliminate the off-center head bulges of typical once-fired brass through resizing in a cut-down factory die. The straight neck has its own advantages.

Tim just finished his work on my barreled action and returned it to me, I have to say I'm duly impressed. He de-marred and refinished my factory barrel nut, machined a thicker and perfectly flat recoil lug from scratch, chased the threads out on my barrel tenon, cut off and re-chambered to .30 XCB with his custom-made, TRUE floating reamer support, refaced the action, and put it all together for me exactly per my requests. No extra fluff on this one, it is a plain Savage 110. I'm planning to put this in a custom-built, laminate benchrest stock but for the time being the flimsy factory one will do.

This is a fresh start for me, so I'll chronicle my experiences and hope the others will chime in as their rifles are completed.

Gear

[MBTcustom]

I sure hope it works for you Ian. I did my best.

[geargnasher]

It shot pretty well as a .308 with the chamber .0035" off center, the neck about .004" larger than the thickest brass I could make or find, and the face of the receiver .004" outta whack. It can only be improved by your work.

I look forward to some intense high-velocity lube testing now that some of the built-in accuracy handicaps are removed.

Gear

[felix]

Ian, what is the case capacity? Tim, did you cut the barrel to 21.75 per warehouse suggestions? Ian, is 2600 that important to override possible vibe containment? ... felix

[HARRYMPOPE]

Factory Savage 308 Barrel? How far did you set it back to get rid of the 308's shoulder in the 30-06 body before rechambering?

[MBTcustom]

IIRC, I cut 1/2" off the barrel tenon or thereabouts. After I was sure the barrel was running true and stress free, I drilled the shoulder back, then cleaned the surfaces up with a boring bar. Then slipped the reamer into the barrel and pushed it deeper till the old chamber was gone. Of course, at that point the headspace gauge would slip into the chamber about 3/8" LOL! so then, I started trimming off the tenon till I got on the gauge with the bolt face. Just fiddle fiddle fiddle, tweak tweak tweak, keep dinking with it till it's right.
Building a rifle is like raising a child. It comes in the door a spoiled brat, but after a long time and many corrections, it will be obedient, honest, disciplined, and handsome.

[41 mag fan]

Building a rifle is like raising a child. It comes in the door a spoiled brat, but after a long time and many corrections, it will be obedient, honest, disciplined, and handsome.

And you end up with a lot less hair!!!

Good job on the build Tim. I'll be interested in seeing what Gear and the others come up with on accuracy with this wildcat.

[Love Life]

Do you have any pictures of the brass? I keep picturing a long neck 308 in my mind.

[Pat I.]

I did something similar years back but used a spare 03-A3 barrel I had and fit it to a Ruger action I had laying around. I used a 35 Rem as the parent case and cut a 06 die off until the body length looked good and used that as a head space gauge. I then cut off the chamber until it head spaced. Once I found out it would shoot alright I chambered up a Shilen barrel for my bench gun and used it for a season. It shot alright but no better than a 30 BR so I rechambered the barrel to BR and never looked back. It was good experience though. Below is a picture of the finished case next to an 06. If I remember right I was calling it a 30/35

[Hamish]

OK, just to be clear gear, are you saying that you have moved the shoulder back 5mm, so that the neck is now 5mm longer?

Recently Jim and I were discussing lengthening the neck on 7.92x57 to 8mm-06 length, (63mm) as a cure for below the neck seating of heavyweight boolits, specifically the Lee 8mm Maximum.

[MBTcustom]

The shoulder was moved back .254 inches.

[geargnasher]

Ian, what is the case capacity? Tim, did you cut the barrel to 21.75 per warehouse suggestions? Ian, is 2600 that important to override possible vibe containment? ... felix

I haven't made a pound cast yet, but capacity should be close to 7mm Mauser with commercial '06 brass. The barrel is a bit long, but there are so many viable options for boolit weight, powder type, primers, and even buffer/filler if necessary that I'm not too worried about tuning it and synching longitudinal/radial nodes. 2600 is a raw number I came up with for a practical upper limit, likely when things come together on the upper end with the alloy I plan to use I will be in the 2350-2400 range with 175-grain boolits and some flavor of 4350, or a combination of things to achieve the same effective burn rate but with a slower start. My first loads will probably be about 12.5 grains of Unique with a full workup to feel the nodes.

Harry, the barrel is a pre-fit Eabco .308 Palma match barrel, 1-in-12", six-groove, with a .3076 groove x.3000 bore. It was a shame to cut it down, as it would have made a fantastic jacketed shooter, but I bought it with this in mind and played with it some while Tim was acquiring equipment.

Gear

[geargnasher]

OK, just to be clear gear, are you saying that you have moved the shoulder back 5mm, so that the neck is now 5mm longer?

Recently Jim and I were discussing lengthening the neck on 7.92x57 to 8mm-06 length, (63mm) as a cure for below the neck seating of heavyweight boolits, specifically the Lee 8mm Maximum.

It's a normal .30-'06 with a .337", straight neck short-chambered by .254", which should be about 56.55 mm. Imagine a .30-'06 with the case head moved forward a quarter inch.

Gear

[Larry Gibson]

The cartridge should look very close to the one on the left which is the 30x57 (my name for it is all. What it's called doesn't matter.) of which I sent sample cases to goodsteel. The standard 8x57 is in the middle and the '06 on the right. Shortened RCBS '06 die is also shown which was used to form the case.

My plan is to have goodsteel barrel a M98 with a 26" barrel having a 14 or possibly a 16" twist barrel for use with 150 - 180 gr cast at 2600 - 2700 fps for hunting.

Larry Gibson

Attachment 82902

[btroj]

Come on Gear, get some cases made and shoot the darn thing!

[357maximum]

Larry----love the twist path you are taking...attaboy.

Enough H-hybrid100V, H414, H4350 to get a BadgerEdd copper enhanced alloyed 311041 up to 2600 or so should easily be just about like baby bears porridge me thinks.......just keep em of the edible parts of the deer.

[Doughty]

Isn't this getting close to a rimless .30-40 Krag case?

[357maximum]

Vic.......There truly is nothing new under the sun and many versions of this idea have been wrung to completion very successfully(.308 long neck, 30X57, 30 CB, etc are just a few of the names of basically the same) .....Larry's twist/barrel length will make his job so easy it will almost be like cheating His RPM's will be super low and the barrel length will make muzzle pressure easy to control and powder choice will be damn near a no brainer = walla' one very agreeable rifle coming soon.....just add powder and an applicable alloy= TADAAA

Shouldn't everyone own at least one "easy" rifle he can grab for hunting purposes?

[HARRYMPOPE]

why not the 30 BR? its has proven track record for accuracy and quality cases are easy to come by.For a 30 cal accuracy wildcat it holds more records than any and is capable of 1/4 MOA in Nesika, Halls,Panda's ETC.....My 40x in 30 BR isn't quite this good but its .5 MOA sometimes.No matter the case design you wont be wringing out to the n'th degree in the rifles you are chambering it in.Heck just a good dimensioned chamber and throat 308 or 30-06 in a 98 or Savage would be fine.

jmho

[geargnasher]

Vic.......There truly is nothing new under the sun and many versions of this idea have been wrung to completion very successfully(.308 long neck, 30X57, 30 CB, etc are just a few of the names of basically the same) .....Larry's twist/barrel length will make his job so easy it will almost be like cheating His RPM's will be super low and the barrel length will make muzzle pressure easy to control and powder choice will be damn near a no brainer = walla' one very agreeable rifle coming soon.....just add powder and an applicable alloy= TADAAA

Shouldn't everyone own at least one "easy" rifle he can grab for hunting purposes?

Mike, you may be disappointed to learn that ".30 XCB" won out over ".308 Amigo" in a long discussion thread elsewhere

I wanted to call it the .30 Cast Boolit Special" but too many complained about the liberal network acronym. .30x57 is old news indeed, but nobody did it quite right as far as I know. We aim to fix that. You know, sometimes all a person wants is to open a can and start eating.

Gear