i just put together a 4.5in 45acp ar15. i also have a 9mm 5.5 in ar15. i was test firing the 45 for the first time and had my 9 out too. wife came out in the back yard to see whats up. i was kind of amazed how gentle the 45 was so i had her shoot both and she did it 3 times and i didnt tell here which was which and all 3 times she said the 45 kicked less. no doubt because the 9mm kind of cracks when its shot due to breaking the sound barrier vs the dull boom of the 45. ive always said that sound makes up at least 50% of perceived recoil. i said no more ars but my dealer is quitting selling guns so i picked up 2 more bare lowers. they were suppose to go in the safe but sales drew me in and ones going to be an 8in 40sw and the other a 10.5 50 beowulf. all the parts are on the way here. i did sell one of my blackouts to the brother in law to help fund this. now if you dont like recoil your not going to like that 10.5 beo. my 16in rile feels about like a 12 guage shooting 3 inch shells and this one will be a GOOD lb lighter