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TM FN Five-seveN GBB

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On 8/18/2014 at 11:30 PM, bankz5152 said:

My 5.7 was fine, did not like Propane on a hot day though so switched to Abbey Ultra which worked better.


Same issue as above the rails came away from the BBU causing cycling issues. I would suggest reinforcing the rail mounts ASAP.


Personally never had the issue of a cracked slide, 70% of the time was run off Propane, rest was Abbey Ultra. Probably 6k - 7k through when I owned it. I did however have the outer barrel detach from the hop unit and a friend of mine damaged to hop unit from use with a steel outer barrel.  


Our answer to this was to epoxy the outer barrel to one half of the hop unit to prevent this.


Apart from those issues it has been the second best performing pistol I've ever owned, and I have owned 100s or all different makes.

Necropost, but can someone elaborate what is a "slide rail" coming away from the BBU?  


I bought an old broken 5-7,  and I had already taken apart the blowback unit out of the slide, and aside from the blowback nozzle not moving in the BBU smoothly which I fixed, everything seems to be working ok.


I am looking to do preventative mods to it to keep it going for the foreseeable future as it is a fantastic gun out of so many pistols I have already owned.


I have even lathed down the hop unit, and added a rubber buffer there to prevent the inner slide from fractures.

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Nevermind, figured it out now.  Slide rails are two piece of metal thats screwed and pinned onto the pot metal BBU.  Normally these slide rails are casted onto a slide but in the case of the FN 5-7 it is a part of the BBU.


One of the slide rails had already snapped the pin thats on the BBU.  So I proceeded to glue the rails onto the BBU with Liquid Nails construction adhesive.  

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