My question is,
How do the Gibbs improved cases head space for fire forming.
Shoulder datum, overall case length, or seating at the lands.

Anytime you build a wildcat with the shoulder moved forward you have a requirement for a way to head space.

You can seat the bullet in the lands I've even loaded bullets backwards to allow me to use a shorter cheaper bullet if my rifle had a long throat.

Simply neck the case up to expand the neck then use your die to form a false shoulder.

When I had yet to have custom dies cut I've used other dies to form the shoulder.

I even tried using the extractor on a 98 to hold the case. Worked but appeared to me the expansion was in the rear and cases failed quickly. So that is no a do over.

Does the Gibbs design start as a ghost shouldered case?

Reading his story it talks about him using surplus 06 brass. Except for the 30, 8mm and 338 everything would be a neck down. He designed and patented a hydraulic system to form his cases. Basically a die with a ram and fluid filed. Whack it with a hammer.

Reading the book it stated he originally offered fireformed brass. He could not keep up so he offered the hydraulic.

Looking at the write up on the 270 it references necking down trimed 06 brass then fireforming. To lazy to read the rest.

I have two different 270 Gibbs rifles both based on Pre 64 Model 70 actions.

I use new 30/06 brass and neck them down in the 270 Gibbs die so that it is a tight fit when chambering. I use a SP primer, Bullseye powder and corn meal to fireform the case. This works the best for me. If you use fired cases be sure to anneal before fireforming or you will have a large failure rate. You end up with a fully formed Gibbs case with a slightly rounded shoulder but that does not seem to affect accuracy or change the loading data from fully formed Gibbs cases.

From what I have read the Gibbs hydraulic forming method was very messy and did not do a very good job of forming the case.

quote:

From what I have read the Gibbs hydraulic forming method was very messy

That is an understatement.

I have a tapered spud that I thread into my decapping pin in 35 cal. I then resize to 30 cal. that gives it a dbl. wrinkle in the case neck,then fire form in the chamber. This is for the 30 Gibbs BTW.

I had a 30 Gibbs anda a6.5 Gibbs some many years ago..Its a pain to work with but once done it fine...

One of my favorite stories is I purchased some hydraulic case forming dies from ole Rocky, used with 30wt oil as I recall but oil at any rate..stick the case in, pour the oil in as I recall, and hit the plunger with a big hammer, and get drenched with oil and a half formed gibbs case!!

Right away I decided on a wildcat on a 30-06 std. case or a Ackley at least!! Besides my chronograph showed less velocity increase than I expected by a good deal..

I ended up with a poorly headspaced Remington 721 in 30.06. It would ruin cases in about 2 firings. The kicker is that someone had twisted a nearly new 26" barrel on the rifle. A borescope exam confirmed it and a range session proved the accuracy of the barrel.

After some research, I settled on re-chambering to .30 Gibbs. I use .270 Win cases, anneal, size to .338" in a Lyman M die, then into the .30 Gibbs die. The resultant case is about .008" short, but that means no early trimming. I fireform with cast bullet loads.

After re-chambering and some fiddling with loads, it is a great shooter, and I ended up with a tightly headspaced.30 caliber target rifle.

A friend of mine several years ago went hunting for Kodiak bear with a .30 Gibbs.He says that when that dear reared up,I knew in my memory that the Gibbs was enough,but in my heart I wished I had a 300 Win. Mag. When that animal gets up on 2 hind legs I had fear emanating out of every pore on my body. I can understand that;but as always,shot placement is paramount.

Depends on your confidences. If you feel 100-150fps will make a huge difference you are going to have doubts.

A poor shot with a WMag will result in the same problem as a Gibbs or 06. Good shots give the same results.

I totally agree.As I said,shot placement is paramount,but confidence in your piece speaks volumes.