I know little of civil war arms but, as I recall the Irish Brigade,I'm Irish,along with many others were issued .69 not .60 remodeled Springfield muskets.Converted from Flintlock to percussion. Perhaps by colt.My GGGrandfather was issued one 36IL.Inf.Sept of 1861 at the St.Luois Arsenal.From what I understand they had superior knock down at close range. The drawback at least as discovered at Stones River standardized amunition .577 had its advantages as with the capture of the regiments train it took several hours to locate the needed ,69 cal cartridges.Thus rendering this veteran regiment inoperable. Jan. of 1863 only a handful still existed in the regiment.