Tuning Brocock Grand Prix

I'd be interested to see a schematic as well. I've tried to disassemble mine but stopped. Looks like I'd need some heat, and don't have seals on hand to replace any. 

Well, if it helps any, I believe they are almost identical to some of the contour guns, just shorter and with a different trigger. I still couldn't find much on those, though. 

Ah, I havn't had the pleasure of checking out any of the clubs. I recon that might be the closest to me. I've been quite occupied with family matters as well, so I do very little shooting anymore. I actually have my grand prix, which is a very old one, likely close to some of the first produced... I have it in the latest contour s6 stock. I plan to re-work and refinish the pistol grip as the perch isn't right, and overall just looks a bit bulky/funky. I'm very reserved in re-working wood, so I'm not concerned about butchering or ruining it. This will follow the pattern of all my other pistols also having parts that can configure them into carbines. Options are always good, and variety makes things more fun.

But I would really like to know what's going on inside this thing. Best I can tell, I would need some heat, some thick leather, a vice, and channel lock pliers

Simplyhooked asked me to see if I could reseal his leaking Brocock Grand Prix S6 pistol. I came up empty searching online for Brocock GP S6 parts lists or schematics. The S6 was leaking air from behind the barrel band and also from the Foster fill port. The Foster check valve leak was repaired by stacking a pair of 004 90 durometer size o-rings on the valve stem. This forms a seal inside the Foster male fill intake hole. A spring behind the check valve stem seals it. 

This Youtube video showed me how the unusual 2 piece Brocock Grand Prix S6 end cap is configured.

https://youtu.be/nbkj3J3irRY

Without this video I couldn't see how air could be leaking from behind a barrel band since I had no parts schematic to use as a reference. Not only is there an o-ring in the inner half of the end cap, there is second o-ring seal for the outer half of the end cap that encases the barrel band. There is an 012 size o-ring over the male threads leaking in addition to the Foster valve stem leak..

Long_Gun_Dallas is correct that this pistol requires delicate use of pliers and cushioning material to remove the outer half of the two piece end cap without scarring the pistol. I used a strip of inner tube to protect the outer half of the end cap. I unscrewed the outer half of the fill cap to find the failed o-ring without chewing up the cap. Notice the wrench marks on the end cap in the Youtube video. A 90 durometer 012 o-ring stopped the leak behind the barrel band. The Brocock is now holding air. 

I don't like the Brocock's 2 piece end cap. It creates another potential leak point merely to encase the barrel band. The two stacked o-ring fill valve stem is another design that I've never seen in any other Foster fitting. A 2 o-ring wide stem design is unnecessarily troublesome. Brocock designers must be engineering school dropouts. Brocock doesn't provide schematics, parts lists, etc.

AoA quoted $275 to reseal this S6 which sold for $500 new. Buyer beware.