replace the front sight post with one of these (or similar): https://www.ebay.co.uk/itm/Vltor-Style-M4-Dummy-Gas-block-Airsoft-/122749704208
Loads lighter than the FSP and will hold the handguard end cap in place nicely.
replace the front sight post with one of these (or similar): https://www.ebay.co.uk/itm/Vltor-Style-M4-Dummy-Gas-block-Airsoft-/122749704208
Loads lighter than the FSP and will hold the handguard end cap in place nicely.