Testing the 30XCB

[btroj]

And while rpm is A factor I think it is far more beneficial to discuss the things we can easily change as casters and reloaders. I am far more interested in the powders, alloys, and loads used than I am the twist rate of the barrel. The knowledge gained by testing powders, alloys, and bullets will translate shooting other rifles. Discussing twist is relevant for most only if they are looking to rebarrel.

[Nrut]

Larry,
What is your 30X60 XCB?
Sounds like it is almost a 30-06..
Does it have a tapered or straight neck?

[Larry Gibson]

Nrut

The 30 XCB and 30x60 are both the finalized concept of the 30x57 I proposed about 8 years ago on this forum. Basically the 30x57 (30 XCB) is a match dimensioned 30-06 chamber with a tight neck. The 30x57 gives the basic case capacity of the .308W but it has the '06 length neck. The same reamer can be used to chamber to any length from the 30x57 to the full length 30-06. The case taper also allows for simplified rebarreling of Mauser actions w/o any necessity of bolt face or feed rail modifications. Lastly standard '06 dies (FL, NS and seaters) can easily be shortened for case forming and loading which negates the high cost of dies for a true custom wildcat. Goodsteel took the initiative and had the custom reamer made. We then conflabbed on the design of the XCB bullet to fit the case neck and throat of the reamer.

After I extensively velocity, accuracy and pressure tested the 30 XCB bullet in the .308W cartridge using 10, 12 and 14" twists it was apparent that the 30 XCB cartridge, even with the 14" twist barrel, did not have quite enough case capacity for full potential of the cartridge concept or the 30 XCB bullet. Not to say the 30 XCB cartridge with a 14" twist barrel of 26" length or more is a slouch in accuracy or velocity......not by a long shot. I just want to see what the full potential was. Thus I ordered a Broughton Palma contour (nothing magic about that contour except I wanted long but yet still fairly portable) 3 groove barrel with a 16" twist. The barrel was delivered to goodsteel who did his magic to it installing the barrel on a very nice BRNO VZ24 M98 Mauser action I had. I sent 3 cases along with the action for goodsteel to headspace the chamber to. I had formed these out new Winchester cases to give 5 more gr case capacity with AA4350 than the 30 XCB cartridge has. The case falls just about half way between the .308W and the 30-06 in capacity. After forming it turned out to be basically a 30x60 case. So I had goodsteel stamp the barrel "30x60 XCB". That's the basic history of the cartridge.

Cases are easily formed out of 30-06 cases. I prefer new Winchester 30-06 cases. The necks are turned to .335 OD with a .3105 XCB bullet seated for the straight .337 diameter XCB chamber neck.

Photo shows 5 cartridges loaded with the 30 XCB bullet. Left to right; the .308 CBC , the .308W, the 30 XCB, the 30x60 XCB and the 30-06.

Larry Gibson

Attachment 130296

[Larry Gibson]

I have also tested different sizing of the XCB bullet for use in Dawn. Obviously which size she's partial to. The 1st group is with #2 WQ'd 30 XCB bullets basically as cast at .3105. Second group is with the bullets sized at .309 and the third group with them sized at .308. The velocity of the 1st group was 2932 fps. The second group was 2930 and the third was 2928 fps. The internal ballistics (velocity and psi SDs and ESs) also showed a marked increase the more the bullet was sized. The diamond target measures .75 on a side.

Larry Gibson

Attachment 130302Attachment 130304Attachment 130305

[Bjornb]

That's a crazy group at almost 3K Larry. I may just have to up the ante to a smoothbore.

[Nrut]

Thanks for your reply Larry..
And congrats on your shooting and I expect your groups will only get better with more experimentation..

Now I'll ask again about the neck on your 30X60 XCB..
Is the chamber neck tapered or straight sided?

I would like to get a .35 Whelen chambered using a custom tight necked reamer and I would like a straight sided neck for neck turning...
Neck turning a tapered neck doesn't make sense to me..

[btroj]

Tim, I won't be commenting here more as I want to discuss shooting a rifle, not building a rifle. I understand that as a gunsmith you always see gun work as a means to an end.

The inability of some to discuss how to make a 10 or 12 twist shoot rather than how to rebarrel with the "right" barrel grows tiresome.

I will continue to learn by doing. The knowledge I gain will help me get better HV results from my fathers 30-06, a rifle that won't be re barreled at his request.

Dont ever forget those words you wrote last year Tim. Something about taking the easy way out is what keeps the secrets secret.

[detox]

Have you guys tried water quenched magnum birdshot. I first size and seat gas check, next I heat bullets in oven @480 degrees for 1 hour then dump bullets in water to harden. Birdshot has more arsenic than wheel weights and makes bullets very hard @30-35bhn.

I smelted one 25lb bag of graphite coated birdshot with 1-2 percent tin added. Perfect amount for my high velocity 223 testing.

Veral cut this non tapered bullet (long snug free bore) and recommends Water quenched WW or magnum bird shot for high velocity. First test went well in the 1-12 Twist factory Remington VS..

[dragon813gt]

Isn't a tool a means to an end? Why wouldn't you want the best tool for the job? I've been following all of this and will eventually wade into the waters. But I'm equating the rifles used to tools in my tool bag. Specialized tools make it easier to accomplish your objective in every case. Sure you could use an adjustable wrench almost everywhere but why? Or am I looking at this completely wrong?

[MBTcustom]

Isn't a tool a means to an end? Why wouldn't you want the best tool for the job? I've been following all of this and will eventually wade into the waters. But I'm equating the rifles used to tools in my tool bag. Specialized tools make it easier to accomplish your objective in every case. Sure you could use an adjustable wrench almost everywhere but why? Or am I looking at this completely wrong?

That's true Steve, but you have to admire someone who uses the tools they have to accomplish amazing feats.
One guy builds a kitchen table with an entire woodshop at his back. You see that all the time.
Another guy takes a year to whittle a kitchen table out of a tree stump with his Swiss army knife. Which is more impressive? Doesn't really matter when all you want is a place to set your plate when you're carving up your T bone steak, but it matters a ton to the guy with the Swiss army knife.

[MBTcustom]

Have you guys tried water quenched magnum birdshot. I first size and seat gas check, next I heat bullets in oven @480 degrees for 1 hour then dump bullets in water to harden. Birdshot has more arsenic than wheel weights and makes bullets very hard @30-35bhn.

I smelted one 25lb bag of graphite coated birdshot with 1-2 percent tin added. Perfect amount for my high velocity 223 testing.

Veral cut this non tapered bullet (long snug free bore) and recommends Water quenched WW or magnum bird shot for high velocity. First test went well in the 1-12 Twist factory Remington VS..

Detox,
Nice! Interesting concept HTing with the GC on, what's your reasoning behind that?
No, I never tried it.

[dragon813gt]

I understand that line of thinking. But I'm the guy that spent $7k on work tools last year. I've been in the same line of work for 15 years so I had tools that would work. I guess I'm looking at this as a specialized project that requires specialized tools. I wouldn't expect good results w/ any rifle that I currently own.

[btroj]

To eliminate the bickering we need to eliminate the ONE topic that causes it.

I want nothing to do with any discussing pertaining to rpm. Period.

Help to make this all a reality? What do you think I have been doing? I'm dong the work to see what I can make work and what doesn't work, for me. That takes shooting, lots of shooting.

Unsecreting secrets takes lots of time at the casting, loading, and shooting benches. I plan to do that work. If it burns out a barrel, so be it. If it costs money, so be it.

Everythime me I mention planning to shoot 1500 to 2000 rounds I get told it is easier to screw on a new barrel. Cheaper too. Problem is that if everyone takes the easy way out then who is left to do the unsecreting?

I don't want to bicker at all. I want to shoot and discuss that shooting. I want to discuss how to make my 12 twist barrel shoot to its best. It really is that simple.

[tomme boy]

So can we discuss rotational force instead of RPM?

[Shooternz]

Photo shows 5 cartridges loaded with the 30 XCB bullet. Left to right; the .308 CBC , the .308W, the 30 XCB, the 30x60 XCB and the 30-06.

Larry Gibson

Attachment 130296[/QUOTE]

Hi Larry, I am interested in the .308 CBC cartridge were can I get some information on it? It looks like what I have been thinking about as a subsonic cartridge instead of the .300 Blackout, A shortened .308 with a long neck, I have a 235 grain Boolit that is proving to be quite accurate in the Blackout and fast twist .308's, looking at your picture I would guess that it is made by running a reamer 30/06 in short, Regards Robert.

[Larry Gibson]

Nrut

Sorry about rambling instead of directly answering; yes the chamber neck is straight and measures .337.

Larry Gibson

[Larry Gibson]

Shooternz

The 308 CBC is my own creation. Back in '80, before I understood about the adverse affect of RPM and the RPM Threshold, I wanted a cast bullet cartridge for a new 2 groove '03A3 barrel I had and a M1916 Mauser that had already been sporterized and had shot out it's original 7mm barrel and two .308W barrels. I had read and believed the 311284 was the greatest thing since peanut butter for use with 2 groove '03A3 barrels. I wanted to use the new '03A3 barrel on the Mauser and get 2200 fps with the 31284 to basically duplicate the 30-40 Krag ballistics using 7.62 NATO cases with the shoulder bumped back while retaining an '06 or 30-40 length neck. 4895 was the powder of choice. Using the Powley computer (slide rule) I computed the amount of case capacity required and set the shoulder back using shortened .308W dies. The necks were then turned to a max '06 length giving the case OAL right at 2.0". Had a gunsmith fit the barrel and rent a .308W match reamer with a tight neck. Then finish reamed the neck with a Clymer match '06 reamer I had.

I formed 300 cartridges, cast a lot of bullets and promptly found I could not get any accuracy any better at any higher velocity than with standard 2 groove '06s. I had a chronograph back then too and couldn't understand why I got better accuracy at 2200 - 2400 fps with my M94 30-30 rifle and my M70 .308W with the same cast bullets using the same powders than I could get with my '06s and a rebarreled Mauser in .308W. After all the .308 CBC was in a 2 groove barrel that was supposed to be the cat's meow for cast bullets. It was a short case with minimal taper loaded to 100% density. The necks were turned and concentric with minimal chamber neck clearance. Everything was there so it was a great disappointment that best accuracy was in the 1850 - 1950 fps range and I could squeeze barely usable accuracy out of it to maybe 2150 - 2200 fps. Was a few years until I discovered the reasons it failed to achieve my goals. The case capacity limited the use of slow burning powders to achieve the velocity desired and the 2 groove barrel had a 10" twist. My M94 and M70 both had 12" twists. I still have the rifle and occasionally shoot it. Were I to rebarrel this rifle with the same .308 CBC chambering I would put a 26" barrel with a 13.5 or 14" twist on it. However, the 30 CBC (30x57) would be the much better choice of cartridge for the M1916 Mauser action and it probably would feed a lot more reliably with the tapered case.

However, if you are interested the .308 CBC chambering is easy to do with available .308W and '06 reamers. The dies are easily made by shortening .308W dies. It does make a balanced cartridge and may well be the "cat's meow" for your 235 gr cast bullet.

Larry Gibson

[MBTcustom]

Shooternz

The 308 CBC is my own creation. Back in '80, before I understood about the adverse affect of RPM and the RPM Threshold, I wanted a cast bullet cartridge for a new 2 groove '03A3 barrel I had and a M1916 Mauser that had already been sporterized and had shot out it's original 7mm barrel and two .308W barrels. I had read and believed the 311284 was the greatest thing since peanut butter for use with 2 groove '03A3 barrels. I wanted to use the new '03A3 barrel on the Mauser and get 2200 fps with the 31284 to basically duplicate the 30-40 Krag ballistics using 7.62 NATO cases with the shoulder bumped back while retaining an '06 or 30-40 length neck. 4895 was the powder of choice. Using the Powley computer (slide rule) I computed the amount of case capacity required and set the shoulder back using shortened .308W dies. The necks were then turned to a max '06 length giving the case OAL right at 2.0". Had a gunsmith fit the barrel and rent a .308W match reamer with a tight neck. Then finish reamed the neck with a Clymer match '06 reamer I had.

I formed 300 cartridges, cast a lot of bullets and promptly found I could not get any accuracy any better at any higher velocity than with standard 2 groove '06s. I had a chronograph back then too and couldn't understand why I got better accuracy at 2200 - 2400 fps with my M94 30-30 rifle and my M70 .308W with the same cast bullets using the same powders than I could get with my '06s and a rebarreled Mauser in .308W. After all the .308 CBC was in a 2 groove barrel that was supposed to be the cat's meow for cast bullets. It was a short case with minimal taper loaded to 100% density. The necks were turned and concentric with minimal chamber neck clearance. Everything was there so it was a great disappointment that best accuracy was in the 1850 - 1950 fps range and I could squeeze barely usable accuracy out of it to maybe 2150 - 2200 fps. Was a few years until I discovered the reasons it failed to achieve my goals. The case capacity limited the use of slow burning powders to achieve the velocity desired and the 2 groove barrel had a 10" twist. My M94 and M70 both had 12" twists. I still have the rifle and occasionally shoot it. Were I to rebarrel this rifle with the same .308 CBC chambering I would put a 26" barrel with a 13.5 or 14" twist on it. However, the 30 CBC (30x57) would be the much better choice of cartridge for the M1916 Mauser action and it probably would feed a lot more reliably with the tapered case.

However, if you are interested the .308 CBC chambering is easy to do with available .308W and '06 reamers. The dies are easily made by shortening .308W dies. It does make a balanced cartridge and may well be the "cat's meow" for your 235 gr cast bullet.

Larry Gibson

Sounds awfully familiar Larry. Thank you for taking the time to give us the benefit of your experience and equipment!

[Shooternz]

Shooternz

The 308 CBC is my own creation. Back in '80, before I understood about the adverse affect of RPM and the RPM Threshold, I wanted a cast bullet cartridge for a new 2 groove '03A3 barrel I had and a M1916 Mauser that had already been sporterized and had shot out it's original 7mm barrel and two .308W barrels. I had read and believed the 311284 was the greatest thing since peanut butter for use with 2 groove '03A3 barrels. I wanted to use the new '03A3 barrel on the Mauser and get 2200 fps with the 31284 to basically duplicate the 30-40 Krag ballistics using 7.62 NATO cases with the shoulder bumped back while retaining an '06 or 30-40 length neck. 4895 was the powder of choice. Using the Powley computer (slide rule) I computed the amount of case capacity required and set the shoulder back using shortened .308W dies. The necks were then turned to a max '06 length giving the case OAL right at 2.0". Had a gunsmith fit the barrel and rent a .308W match reamer with a tight neck. Then finish reamed the neck with a Clymer match '06 reamer I had.

I formed 300 cartridges, cast a lot of bullets and promptly found I could not get any accuracy any better at any higher velocity than with standard 2 groove '06s. I had a chronograph back then too and couldn't understand why I got better accuracy at 2200 - 2400 fps with my M94 30-30 rifle and my M70 .308W with the same cast bullets using the same powders than I could get with my '06s and a rebarreled Mauser in .308W. After all the .308 CBC was in a 2 groove barrel that was supposed to be the cat's meow for cast bullets. It was a short case with minimal taper loaded to 100% density. The necks were turned and concentric with minimal chamber neck clearance. Everything was there so it was a great disappointment that best accuracy was in the 1850 - 1950 fps range and I could squeeze barely usable accuracy out of it to maybe 2150 - 2200 fps. Was a few years until I discovered the reasons it failed to achieve my goals. The case capacity limited the use of slow burning powders to achieve the velocity desired and the 2 groove barrel had a 10" twist. My M94 and M70 both had 12" twists. I still have the rifle and occasionally shoot it. Were I to rebarrel this rifle with the same .308 CBC chambering I would put a 26" barrel with a 13.5 or 14" twist on it. However, the 30 CBC (30x57) would be the much better choice of cartridge for the M1916 Mauser action and it probably would feed a lot more reliably with the tapered case.

However, if you are interested the .308 CBC chambering is easy to do with available .308W and '06 reamers. The dies are easily made by shortening .308W dies. It does make a balanced cartridge and may well be the "cat's meow" for your 235 gr cast bullet.

Larry Gibson

Thanks Larry,
That is very interesting, My original idea was to push the .308 shoulder back to get the long neck I want and give the case a 30 degree shoulder sort of a stretched 30BR, I supply the local Custom reloading company with the 235 grain boolit for their subsonic loads in 300 Blackout and .308 8" barrels they are very happy with them, I don't have a rifle I can test the boolits in myself so I though why not come up with something deferent I have a sleeved 700 action I could use,
I also have the 30XCB mould though I haven't done much with it so far I am more interested in it as a hunting boolit than high velocity, I have already gathered a lot of useful information from your work on this thread thanks very much to all the people posting their result here you have been helpful, Robert.

[HARRYMPOPE]

What does this do that the 30 br will not do?from what I've seen nobody has put this cartridge in a benchrest grade action to truly test it.not trying to poo poo it but this reminds me of 20 years ago when everybody was playing with many 30 caliber Wildcats until really good brass for the 6mm BR came in and those Wildcats kind of went to the wayside.