8MM Gibbs

[No_1]

Anybody have any info on this one? Is it a blown-out 8mm-06? Where would one get a reamer?

Robert

[Phil]

Blown out, short neck, sharp shoulder, all on the 30-06 case. There was an entire series of them at one time. I had a 30 Gibbs in the late fifties or early sixties, long before home chronographs were common so I don't know what the actual velocities were. Eventually sold it. I built what was essentially a 7mm Gibbs for a long range match cartridge one time and did lots of chronographing with it. It would do about what my 7mm Rem Mag would do, not quite as the mag case held more powder, but the Gibbs was way more efficient when looked at from the standpoint of feet per second per grains of powder. The big thing with the Gibbs (and lots of other blown out wildcats) is to put a good solid shoulder on the case you are forming so it makes a good crush fit when you shut the bolt. Otherwise you will lose a lot of cases when forming due to separations.

Cheers,

Phil

[No_1]

So what are your thoughts on re-chambering to this vs. re-chambering to 8mm-06? I understand it will be more work case forming but would the outcome be worth it?

Robert

[felix]

Robert, if you are looking for a sharper shoulder, and for shooting cast boolits, I'd stay with the same length of neck, and blow the case out to an ackley configuration, which is 40 degrees. Personally, I would go with the standard 06 necked up. Plenty of power there for boolits. Of course, that depends on the weight of the boolit you intend to shoot 90 percent of the time. ... felix

[No_1]

Felix,

You know me, just looking for something that is different. I found a set of dies and before I commit to them (which means build a gun) I wanted to test the waters for info.

Robert


Robert, if you are looking for a sharper shoulder, and for shooting cast boolits, I'd stay with the same length of neck, and blow the case out to an ackley configuration, which is 40 degrees. Personally, I would go with the standard 06 necked up. Plenty of power there for boolits. Of course, that depends on the weight of the boolit you intend to shoot 90 percent of the time. ... felix

[NVcurmudgeon]

Robert, 45 years ago (good grief) I shot at the Richmond (CA) Rod and Gun Club. That was where Rocky Gibbs had done much of his early experimental work. I never met Mr. Gibbs, as he had moved away, but there were quite a few of his rechambered and rebarreled rifles around. Case forming procedure was to use a fairly heavy load for the standard cartridge, with the bullet seated into the lands. In this more trepid age, most shooters would use a secondary shoulder for forming. One thing for sure is that the Gibbs cartridges were the absolute maximum capacity possible on the .30/06 case. They looked like 5,000 fps was no problem, but nobody had a chronograph then, so who knows? IIRC, there was somebody who wrote a few magazine atricles about Gibbs and his cartridges, and there may even be a book.

[oneshotman]

I've got some dies if you want them....60.00. I was going to do a K98 but I've heard there isn't enough meat in the barrel to ream it that far forward....I still question that one but....

Couldn't find a reamer.

I'm told the brass will live forever after you succesfully fire form them. It doesn't stretch with the gibbs. I believe the ballistics are similiar to a 300 win mag with the kick of an 30-06. Pressure is about 10k less.

[Phil]

Hi NVcurmudgeon,

When I originally built mine (Rocky did indeed chamber the barrel) the recommended procedure was to just jam a heavy bullet into the lands and propel it with a heavy powder charge. However (there is always a however isn't there?) even with lightly oiling the cases I used to get partial and complete head separations. Not the thing a fellow wants to have too many of when shooting a M1903 Springfield. So I started necking the cases up to 8mm and then back down to 30 caliber until they were a real tight crush fit in the chamber. Never lost a case after that. I can't remember what the case life was in that one but in the 7mm Gibbs clone I built I never full length sized a case once I had them formed. Matter of fact I never owned a full length sizer for the rifle.

If I were to go to the 8mm on a 30-06 case today, for shooting cast bullets or j-word bullets, I'd simplify matters and just build a standard 8mm-06. Then again, if I had 8mm Gibbs dies.............................................. .......

(:>)

Phil