I know it's not easy with a surname like Jones but I think you are making too many assumptions.
Studying the census records, etc. the Samuel, gun finisher, in 1861 and 'your' Samuel, brass founder, are 2 different people. According to 1841/1851 census the gun finisher Samuel was married to an Ann but in 1861 wife is Mary Ann. Don't know if Ann and Mary Ann are the same person, or whether Samuel remarried between 1851 and 1861. This Samuel is shown bc.1801.
'Your' Samuel - brass finisher - is shown on 1841 census as bc.1806 - remember that ages were rounded down in 1841 so this means he was born 1802 to 1806 so doesn't mean that he was the son of David Jones and Mary - there are at least 3 other possible baptisms (2 in 1804 and 1 in 1805).
Although when daughters Sarah and Emma married (1842 and 1860) they both state father as Samuel Jones, Brass Founder and although Emma doesn't state he was deceased it doesn't mean he wasn't.
A Samuel Jones aged 41 (from GRO own index) death reg'd Mar.1945 Birmingham may possibly have been him which would explain why he isn't to be found after 1841.
I know I'm not helping, but a) Samuel, gun finisher, bc.1801 and Samuel, brass founder, bc.1802-1806 are 2 different people and b) I personally don't think Samuel, brass founder, was the son of David and Mary and that he was actually one of the 3 other possible Samuel's born in 1804 or 1805.
Annette