What you need to do is take out the buffer from the existing endcap and use an Ar folding stock adapter There are many on the market.
And then you use the buffer from Buffer Tech for the HK
That's what I did with mine and it works great. Then Install what ever brace you like.
( suggestion Buy 2 buffers because Buffer Tech is out of business I beleive )
^does that buffer-tech buffer feel better than the standard metal spring buffers? I have a heavy duty metal spring buffer and curious what the difference in felt recoil/impulse would be with the buffer-tech.
I don't have an answer for a side folder brace that will work. However, I do not recommend using the buffer tech HK buffer. I tried one in a PTR91 once and there was significantly more recoil. I have also seen others post photos of roller marks using this buffer. The compound is too hard and does not adequately buffer the action. I highly suggest finding an option that will allow using a proper HK buffer.
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