Figured Id post that I recently bought the 7.8" HBI hand guard and Im having the same typical problems that Ive read about on forums.
1. If I torque it more then 30 in/lb the receiver pinches the bolt carrier.
2. The bolts keep coming loose while shooting despite application of blue loctite.
Ive got some new OEM lock washers on the way and will see if it resolves the problem of them coming loose. I still wonder what the factory is torqueing these things to since Ive read 60-80 inches pounds from different sources but all of the above is too much torque for my rifle.
side note: Someone posted on Amazon that these other lock washers work so I ordered some of these as well: https://www.amazon.com/gp/product/B007VAW0M8/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1
Yep. Problems. CZ should have continued with the original “military” extended receiver of the Bren 2S, which is much more useful and trouble free than the “commercial” “hand guard” they contrived for the 2Ms, which is less useful, problematic and forces customers to spend $$$ to try to correct the problem and / or comply with 922r if converted to a rifle.
According to CZ USA Customer Service (way back when they were still answering their phones), the correct torque spec is 64 in.lbs. for the hand guard screws.
There’s been a lot of discussion on here RE: the wisdom (or not) of drastically reducing the number of mounting screws and either drastically reducing or drastically increasing the torque values on the remaining screws from spec to hold the aftermarket hand guard on. Consider the whole structure is integral with holding the barrel / receiver / “hand guard” together…probably not such a great add on to the (often badly overgassed) Bren 2, at least IMO.
Yes, Nordlock washers of the correct size are used, available at Fastenal.
