Kain McDogal said:
I've also asked myself how a bolter round knows that it hits the armor and has to be primed to explode inside the target. It needs this information otherwise it would penatrate some cover and would just explode before reaching the target.
The ammunition is built with the delay built in. The round strikes and after the delay period, it detonates. Against soft targets, ammunition with less/no delay would be used. There are several occurances in novels where comments are made by Astartes that againest unexpectedly soft targets the rounds overpenetrate and don't explode inside the target.
Deuterium, eh? Nobody at GW did any chemistry, I can see. They should have stuck to made up elements. Handwavium and Uberonium, all the way.
Actually, you need more velocity than to simply plonk the round out of the barrel. In the case of non-PA equipped troops it needs to go a sufficient distance to not burn the user when the rocket kicks in, and it needs to retain enough velocity not to drop trajectory prior to the rocket kicking in in order to preserve accuracy. And it needs to be travelling fast enough to penetrate and set the explosive warhead off at point blank range for CQB. In the case of Astartes weapons (who fight ANYWHERE) the round also needs to be able to perform these functions in far denser atmosphere's than ours, and even in a liquid medium. And-as you say- there is no stock to help further absorb recoil. Bolters kick like a mule, even using generous back-of-***-packet working out of the recoil impulse.
Also: Shotgun ammunition has one hell of a lot of recoil. Autoshotguns are an impractical weapon at the best of times, made barely practical by the naturally short range of engagement and dispersed ammunition (because nobody is strong enough to hold an automatic weapon on target at 100m, even with a stock). And of course, a 12 gauge frag round is relatively light and doesn't include a propulsion mechanism or armour-penetrating warhead. Even if a bolter somehow 'only' had the recoil of a 12 gauge, unenhanced troops could not fire them automatically or rapidly with any real chance of successfully engaging at the theoretical accurate range of the weapon. Doubly so without a stock.
Mwah ha ha haaa.....