punching through mild steel with ball ammo running hard and hot - and more importantly straight on - is one thing... thats linear push on a very small point as the entire weight/energy of the bullet dumps. lots of concentrated pressure on a very small point.
if you look at these super slow-mo hits.. you can clearly see where the bullet pushes a slug of metal thru the plate and out the back.
https://youtu.be/QfFoMyMoiX4?t=181shearing off a carriage bolt with spall is an entirely different discussion. we're talking about lead and copper thats already in
fragments from splashing on the plate shearing a bolt head off. MUCH of its energy is already spent from the impact. and the fragments are not moving with enough mass at that point to carry the kind of energy a direct hit in a linear impact has. those fragments will stick in - but not pierce thru - schd 40 pvc (early plate rack test, no bueno with a buncha shards in it after a couple range sessions
), if you cant cut PVC -how is it going to cut thru something SIGNIFICANTLY harder
while i've had it carve thru stuff like nylon webbing before (plate straps).... a bolt head? the only time ive had those come off are direct hits that punch them thru the hole - even when using grossly undersized hardware because its all i had on hand to repair a damaged piece. i think ive managed to punch a dozen or so thru over the last 8 years or so - but after THOUSANDS of rounds on steel i've yet to have any evidence of sheering one with spall, from any caliber. every one i've had to replace has shown a direct, or mostly direct hit from a bullet - ie: linear impact force, not lateral.
the only possible way i can see it happening - or APPEARING to happen as described - is that the bolt head was already damaged, like a crack. either from a prior direct hit with a smaller caliber round, or impact shock from close hits tugging the plate on the chain causing a stress fracture at the bolt head. so if it was already partly fractured, getting repeated stress hits from the 450 (which really whaps a plate hard!) could have pulled the head off the bolt.
but a lateral sheer with already fragmented lead and copper particles... not so much.