Stronger body.

I like this crossbow, but body breaks all the time, so I made it a bit stronger. Also I made it to work with M3x5mm brass inserts.
Like this ones https://www.aliexpress.com/item/100Pcs-M3x5mm-L-5mm-OD-Metric-Threaded-Brass-Knurl-Round-Insert-Nuts-LXM/32693221350.html?spm=a2g0s.9042311.0.0.dBV13o