Tuning Brocock Grand Prix

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Simplyhooked

Simplyhooked

Member
Feb 10, 2018
319
11
North Carolina, United States
I've got a couple of questions for those of you that may own this pistol. When was this pistol first introduced and where might find the schematics for this pistol? I've owned mine for just a little over 3 1/2 years and it's developed a leak and I'm looking to fix it, if possible. After charging the pistol, shutting the the valve from the tank and bleeding the hose, air is coming out of the fill valve and hose as best as I can explain it, could the check valve be stuck open?

Thanks,



Fleming
 
Thanks Long_Gun_Dalla for your reply because it's an excellent shooting pistol (even though I'm not into pistols) but I also have the Brocock Concept Lite in .177 and the Bantam Sniper in .22. I must say that I've had problems with the fill system on both of these rifles that I've never had with my Daystates, Air Arms, CZs, Falcons or my FXs. My Brococks are lasers for sure but I've always been able to fix them, this one seems to be a tad bit different.



PS....I was a member of the Tarhill Airgunners Club in Mount Pleasant, North Carolina a short while ago but family matters are always first as a care giver for me.
 
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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


 
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A friend of mine is/was trying to figure out where the leak/leaks are coming from and found more than one but it's not as simple as one may think when trying to repair. It's a p-ss poor design when it comes to the air cylinder and from the way that it looks, it wasn't designed to last. For me, it was a complete waste of money that I could have spent on something else.
 
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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.
 
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Two thumbs up for Humdinger because I've never met anyone that cares more about the sport than him. He's the kind of person that I truly trust because of this knowledge and tenacity concerning our hobby, whether it has to do with compressors (my Air Venturi which is history) or my troublesome Brocock Grand Prix S6. I have to give him his props because of the love that he has for this hobby and I've never owned an air rifle or pistol that's been this complicated. I've owned my Grand Prix for just short of four years and it's not something that I've played with on a regular bases, it was more of a "wall hanger" than a shooter that I looked forward to shooting.



Thanks once again for all that he's done for the airgun community.
 
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