Andy_d said:
hitting it with the palm of your hand is meant to help push the bolt that last bit forward into proper position for an initial shot.
On the M16A2/M4/C7 hitting may be the wrong word, more like ' pushing with thumb', as hitting or striking with the palm of your hand may cause a bigger problem.
That M16A1 'mod' Kevin mentioned first appeared in 1968 on all rifles less the ones used by the USAF. Theirs too, were modified in time, and in the early 1980s when the A2 appeared the design was changed from 'tear drop' shaped to round.
Other mods to the A1 from the original c.1965 M16 were the replacement of a chrome bolt and carrier, a new 'bird cage' flash suppressor, chrome bore, modified lower reciever which a raised 'guard' around the mag release was brought in, an improved bolt stop (hold open), and improved butt (butt trap and butt plate, and a different sling swivel). Also early M16s had a 1/14" twist, and this later was changed to 1/12" (5.56 x 45mm M193).
Out of the approx 5000 M16A1 rifles still in service here, all are pre-1970 purchase/lend lease Viet Nam issue ( I have seen some with notches cut into the pistol grip and stock :warstory
, and many are actually pre 1968s, some marked XM16E1 by Colt with 5 digit serial numbers, others are post 1968 Colts (marked AR-15, M16A1, or a specific model number, and US Govt Property). Others are made by GM (General Motors). All now have the A1 uppers, and all the A1 mods, but as of last year the odd one was still old style, less the fwd assist. Many were tagged back in the 1970s, and had been in storage since then.
There are M4s on A2 lowers, and since the late 90s, Colt M4s (1/7") and Bushmaster (1/9") similar type wpns. These are all strictly for SF use.
The F88 Austeyr still incorperates a forward assist right on the cocking handle, but I have never used it, nor is it in the trg pam either.
Euro AUG rifles with the folding cocking handle have done away with the forward asssist. Australia trialed this folding thing, but it failed to pass trials, as the rifle was difficult to **** (cockk) when certain optics were used on the Picatinny rail.