I have a friend (old timer) who has a nearly new 8mm Gibbs built on a FN mauser action. Bloody gorgeous piece, and I would like some info. I believe its is a blown out -06 case with shorter neck and venturi shoulder, but that is the extent of my knowledge.

Yep the Gibbs were based on an 06 case. In the 8mm the shoulder was moved forward to 2.204" blown out to .455 with a 35deg neck.
Rl15, H414 make good powders. PM me if you want with your email and I'll send you a scan of the write up on the 6.5,7 & 8 gibbs.
200 grs at 2900FPS

A.F. - here's some visual based information for you:

Cartridge Dwg of .30 Gibbs. 8mm is just necked up. Shoulder angle should be listed and drawn at 35 deg.



Picture of .30-06, .30 Gibbs and 300 Win side-by-side:



A drawing I made in AutoCAD and converted to an image. Has your parent case with most of the improveded versions overlaid:



I agree with Ramrod's 200 gr at 2,900 fps figure. I have a .30 Gibbs and I push 180's at 2950 fps pretty easily.

The only "problem" would be with bullets. Most 8mm's are for the 8x57, while you can find a few designed for the 8mm Rem Mag. The Rem 185gr PSP, Speer 200gr HotCore and the Nosler 200gr partition would be excellent choices.

MM

Muskegman,

Ditto on the 30Gibbs. My 30Gibbs has the shoulder held back .050" so I can shoot factory 06 ammo and it still gets 2950fps with 180XLC's/RL22 in a 24" barrel. Some say MRP might net me 3000fps, but I can't find the stuff in Colorado. The 8mm has looked interesting. Who knows if the 8mm bullet selection gets better with the new 325WSM and I shoot out my barrel (unlikely I will kill that many with it) or I get bored, I might rebore/upsize.

Deke.

I have an 8mm. Gibbs. Mine has a 35degree shoulder and a .25" neck. It is a rechambered WWII mauser with the barrel cut to 25". I have several rifles in Gibbs chamberings. I think it's a big improvement on the 8mm mauser and comes close to duplicating the 338 in performance. 200gr.@ 2900 should be right.I have got over 3000 but backed off. I do not have the venturi shoulder on any of mine. Mark

quote:

My 30Gibbs has the shoulder held back .050"

Curious how setting the shoulder back .05" would allow you to fire factory. The gibbs shoulder is moved forward about .145"

If you can fire factory safely then you don't have a Gibbs but a AI with a 35deg shoulder.

If I'm missing something please let me know. I'm only on my first cup of coffee.

You would not be able to safely fire '06 in a .30 Gibbs that has been set back only 0.05" The drawing I did to scale in AutoCAD measures 0.14" of req'd setback. 0.15" Would give a crush fit. You would have a .30 Imp - 35 deg at this point.



MM

quote:

You would not be able to safely fire '06 in a .30 Gibbs that has been set back only 0.05"

Thanks that is what my own drawing were telling me.

BTW, to whom it is concerned, the Christmas colors are great.

My shoulder (and beginning of neck) being held back .050" still puts the start of the neck further out than std 06 and AI. The shoulder is steeper so there is no crush fit involved. The 06 ammo fires fine in my Gibbs because I have done it and if you look at the Ackley specs you will see that my shoulder to head measurement is between a Gibbs and an Ackley. If you look on pg 322 of Ackley Vol 1 you will see that Rocky Gibbs fired 254rds of 06GI ammo through a full blown Gibbs on an Enfield action without any problems.

Perhaps we are using different specs since I have seen Gibbs specs vary between purported experts. I am on AutoCadV14 so feel free to send me a PM and we can exchange drawings.

Deke.

Most of the differences I've seen on the gibbs was a different shoulder angle and the first work done on the 270 used the 270 case. He then standardized on the 06 case.

If your neck is moved forward .05 then your factory 06 will not headspace on the shoulder. If your rifle is a CRF my quess would be your are headspacing on the rim. It is the extractor that keeps the case from moving forward not the shoulder.

quote:

Originally posted by A. Fleming:
I have a friend (old timer) who has a nearly new 8mm Gibbs built on a FN mauser action. Bloody gorgeous piece, and I would like some info. I believe its is a blown out -06 case with shorter neck and venturi shoulder, but that is the extent of my knowledge.

ALL Gibbs cartridges are blown-out .30/'06 cases, but none has a venturi (Roy Weatherby style) shoulder. They have 0.25" necks, and a regular shoulder of 35 degrees. So-called Gibbs cartridges with necks longer or shorter than 0.25" are something ELSE!!, NOT Gibbs' designs.

THIS is the .30 Gibbs cartridge. Note it has a 0.250" neck, a 35-degree shoulder, and the shoulder is blown out to .455".



The best/easiest way to make 8mm Gibbs cases is to run .35 Whelen or .338/'06 cases thru an 8mm Gibbs FL die adjusted to set the headspace to fit your chamber, then fireform them before loading up the service load.

All Gibbs rounds are capable of coming within 100 FPS of the standard-length magnum rounds in their respective calibers.

There is a good little booklet called GIBBS CARTRIDGES AND FRONT IGNITION LOADING TECHNIQUE published by Wolfe Publishing Company in 1991 which is a compilation of articles written by Roger Stowers in Handloader Magazine.

Gibbs received a lot of critizism for using "excessively high pressures" to get the reported ballistics for his cartridges, and he was also accused of lying about the velocities he got from his cartridges. What a lot of his critics did not know was that his cartridges were chronographed for him at the Speer plant. He also had a pressure gun that he'd built himself, and all of his published loading data was within standard pressure limits.

In a 26" barrel, the 8mm Gibbs will produce very close to 2900 FPS with a 200-grain bullet, and almost 2800 with a 220. This is within .300 Win. Mag. parameters.

A bout the only negative feature associated with these rounds is that they are a pain in the posterior to form and load!

quote:

accused of lying about the velocities he got from his cartridges

The other key thing that most people also missed was that he also measured his barrel length from the front of the bullet. So when he claimed a 26" barrel it would be about 29" by normal standards.

Last I checked "GIBBS CARTRIDGES AND FRONT IGNITION LOADING TECHNIQUE" was out of print.

I designed my own case using a 280 and 40 deg shoulder moving the shoulder forward so a 280 had a neck length of .28". That was before I had heard of Gibbs. My case has just a touch more powder capacity. I have loaded it using a pressure guage. My data is very close to Gibbs when adjusted for barrel length.

quote:

Originally posted by ramrod340:

quote:

accused of lying about the velocities he got from his cartridges

The other key thing that most people also missed was that he also measured his barrel length from the front of the bullet. So when he claimed a 26" barrel it would be about 29" by normal standards.

Last I checked "GIBBS CARTRIDGES AND FRONT IGNITION LOADING TECHNIQUE" was out of print.

I designed my own case using a 280 and 40 deg shoulder moving the shoulder forward so a 280 had a neck length of .28". That was before I had heard of Gibbs. My case has just a touch more powder capacity. I have loaded it using a pressure guage. My data is very close to Gibbs when adjusted for barrel length.

That's interesting. But I think the 26" barrels used by Stowers to attain the results he reported in his articles were "regular" 26" barrels (made by McGowen), and not the "fudging" variety. However,I am not sure of this!

quote:

Perhaps we are using different specs since I have seen Gibbs specs vary between purported experts.

Right! This is because Rocky never published his cartridge's specs, nor would he tell anyone what they were-it was a "secret". So the only way to find out for sure was to have Rocky make you a rifle, then measure the fireformed brass.

A lot of "custom gunsmiths" just guessed at the neck length, shoulder diameter, shoulder angle, etc., when they ground reamers for use in chambering rifles for their customers who had requested an "XXX Gibbs" chamber. For example, I had one rechambered from 6.5X57 to 6.5 Gibbs by a gunsmith in Albuquerque, NM back around 1958. It came back with the correct neck length and shoulder diameter, but fireformed cases had 40-degree shoulders. So the world is full of "Gibbs" rifles which really aren't Gibbs rifles!

quote:

That's interesting. But I think the 26" barrels used by Stowers to attain the results he reported in his articles were "regular" 26" barrels (made by McGowen), and not the "fudging" variety. However,I am not sure of this!

I believe you are correct. The Stower article referenced Gibbs using the longer barrel. The way I read the Stower articles he used a normal 26" that was also what I gathered from McGowen whe I talked to them years ago when they did my chambering. Rocky would load to 53,500 CUP. He found that at 53,000 the pocket would start to expand. Considered 53,500 as max. Then go to Speer to use their Chrony. He would also report the highest velocity not the average.

When he died of leukemia in 1973 he instructed his wife to burn all his records.

They say his cartidges were 30year ahead of there time. I'm currently in the process of finishing my 7mm Gibbs. I should have it finished by next years deer season.

John

323 This has got me anxious! I'm going to rebarrel my 30gibbs to a 6.5gibbs and call it a very necessary as I haven't had a new barrel in a couple yrs.

Would agree with most at this time. Mine technically is not a full blown Gibbs. My neck is .300" and my gunsmith achieved this by not running the reamer all the way down. I could swear though that the shoulder has a VERY SLIGHT curve to it, but might need to verify with a magnifying glass. Nonetheless, factory 300WM velocities w/a Barnes XLC which has a very high BC & deep penetration, will fire 06 ammo, and at least one more in the mag than most other magnum configurations, and it is very hard to beat today, not to mention 40yrs ago.

Deke.

quote:

Originally posted by Deke:
Would agree with most at this time. Mine technically is not a full blown Gibbs. My neck is .300" and my gunsmith achieved this by not running the reamer all the way down. I could swear though that the shoulder has a VERY SLIGHT curve to it, but might need to verify with a magnifying glass. Nonetheless, factory 300WM velocities w/a Barnes XLC which has a very high BC & deep penetration, will fire 06 ammo, and at least one more in the mag than most other magnum configurations, and it is very hard to beat today, not to mention 40yrs ago.

Deke.

Where did your gunsmith get his "Gibbs" reamer??

quote:

will fire 06 ammo

Still concerned as to what you are headspacing on.

ramrod340,
This is a commercial mauser action and Rocky fired his through an Enfield. In particular, what is your concern with headspacing?

El D,
Not sure where he got his reamer..... If you are interested send me a PM and I will try to put you in touch with him.

Deke.

quote:

In particular, what is your concern with headspacing?

My concern is you say your smith held the Gibbs reamer back so you could fire factory 06. If a factory chambered barrel is not set back before it is reamed with a Ackley reamer it will not headspace properly on the shoulder. In your case you gained nothing by holding the reamer back. Once it squared up the factory shoulder factory ammo would not headspace correctly.

Since you have a Mauser when you fire factory ammo the shell moves forward. It is the extractor that stops the case not the shoulder.
It appears that you have done it and have had no problem. I simply would not choose to rely on the extractor to provide my headspace.

quote:

I simply would not choose to rely on the extractor to provide my headspace.

Nor would I. At one time, there were people who seated their bullets long so that the bullet contacted the rifling and supposedly held the case head against the bolt face for fire forming. I consider this a hazardous practice also, despite the fact that a lot of people got away with it.

ramrod and ElD,
You are correct that my extractor is holding the cartridge, but incorrect that I gained nothing. With less distance for the shoulder to move forward there is less chance of head separation, hence Rocky did it with an Enfield, I do it with a Mauser, but I do it with less chance of head separation. The gain is that I have a more powerful cartridge than the AI, but still enjoy the benefits of being able to fire 06 ammo if I have to. You can choose to "not rely" on the extractor, and I don't normally since I use ammo sized for my chamber, but what harm/hazard is there in me doing so in my 'Mauser' if I ever lose or shoot up my ammo and the only thing the gas station or my hunting buddy out in the middle of nowhere carries is 06 ammo?

Deke.

quote:

Originally posted by El Deguello:
[QUOTE]I simply would not choose to rely on the extractor to provide my headspace.

Nor would I. At one time, there were people who seated their bullets long so that the bullet contacted the rifling and supposedly held the case head against the bolt face for fire forming. I consider this a hazardous practice also, despite the fact that a lot of people got away with it.[/QUOTE]

Pretty much exactly what P.O. Ackley stated in his Handbook for Shooters and Reloaders. I've ALWAYS gone for creating a "false shoulder" to headspace on for fireforming.

Those who forget Murphy's Law succumb to Darwin's Law eventually.

MM