How much force does a 12 gauge exert on your shoulder when firing a deer slug?

Mass of gun = 3.5kg

Mass of slug = 0.22kg

System: Gun + Slug

Surroundings: Nothing

$\vec{F}_{net} = \dfrac{\Delta\vec{p}}{\Delta t}$

$\vec{p}_{sys,f} = \vec{p}_{sys,i}$

$\vec{p}_{1,f} + \vec{p}_{2,f} = \vec{p}_{1,i} + \vec{p}_{2,i}$

$m_1\vec{v}_{1,f} + m_2\vec{v}_{2,f} = m_1\vec{v}_{1,i} + m_2\vec{v}_{2,i}$