This one from my archives is a bit wordy, but it will explain the story of the GP11 for Towerofpower.
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Shortly after I got out of the hospital, I saw a post about reverse engineering of the GP 11 cartridge. I couldn't address that then, but I will now.
We'll dispose of the projectile itself in short order. If you look at the diagram, you are going to have to have extremely deep pockets and access to manufacturing equipment to duplicate this projectile. I don't need to get into detail on this as you can see for yourself from the specification and the variables in this projectile, you're not going to duplicate it, so we go to the next best thing. The Berger 175gr VLD (Preferred) and the Hornady ELD. And for performance, the Berger is virtually a dead match for the GP 11 projectile performance wise, assuming that your cartridge prep has been correct.
The Hornady ELD comes in a very close second. You will find the boat tail is approximately 1/64 inch shorter.
For precision and long-range shooting the case prep process is (for us) considered 90% of the entire successful load.
Now for the case. The GP11 case is considered by most, including the Swiss to be a national match caliber case. Unfortunately it is Berdan primed. The next best thing is, if you happen to be in possession of the Swiss national match boxer primed cases, which are going to find, both rare and expensive. Beyond the first 5000 that I brought into this country from RUAG, the balance were brought in by Graf & Sons when I passed the torch to them.
After no more than two months, RUAG stopped the export of this brass because the Board of Directors determined that all of this boxer brass in the hands of American reloaders was going to slow the sales of the remaining GP11 still in Switzerland. It was an economical decision for them and unfortunate for us. From there, that brass went into production in Switzerland and RUAG turned into a number of different hunting loads with different projectiles all sold in Europe. The Brass was the same National Match boxer brass that I brought in some time in 2002.
I find it highly unlikely that (at present) any American manufacturer will duplicate that brass. In all aspects it shakes out more true than Lapua, Norma or anyone else's brass made in our caliber not to mention the wall thickness and weight.
PRVI partisan has proven to be a decent brass for reloading, and if you can find Norma brass, it too is very good for reloading, however remember that Norma brass is very soft and will only stand being annealed so many times before you get a case mouth split.
Crimping. This is also something that you're not going to match, but is not necessary for Swiss bolt action rifles, and unless they are high-power Magnum, the rifles won't require it. The factory crimping involved three points closing in on the case mouth not with a die, but with a machine that did a 360° crimp from three heavy horizontal segments coming in simultaneously around the case mouth.
Suffice it to say that particular feature involves the all-important "neck tension". You're not going to duplicate that, at least not by that process. The closest you are going to come is if you use Redding competition dies and the correct sized collet. When we are introducing a new case to our own system, we order in three collet's. One that we think it is, one slightly larger and one smaller. We let the performance tell us which one were going to settle on.
All of that being said, your chances of actually reverse engineering for production of this this cartridge is as close to zero as it can be. For those of you who don't already know, the .284 brass works really well in the G11 rifles. With the K 31 however, you may get one in 10 cases that do not extract and eject first time because the case rim is a fair bit thinner than GP11 brass.
One last thought about this........... the ladder sight on the K31 does not go to 1500 m just for fun. It's not like a car speedometer that might show 140mph when the engine is in fact only capable of going to 110 or a bit better.
