According to a lexicanum thread
http://wh40k.lexicanum.com/wiki/Lasgun#M35_M-Galaxy_Short_pattern
And even Codex
IG itself
What are the differences between the M35 lasgun and Cadian ones? one source said that M35 is 2nd edition lasgun (but it is still remain in wide use in updated official sources). one source said that it is actually catachan lasgun with longer barrels, another said Astartes scouts use one as sniper rifle. (as seen in DoW2 and new plastic scout marine set) . yet another said that it is the same as cadian lasgun (though late official source said Cadian uses either Kantrael pattern or ones manufactured in Cadia (the latter might be possible because Cadia is fortress world where everyone is born to become either soldiers or armory workers) though in reality, the 3.5 edition cadian (released shortly before the 13rd crusade) rifle appears to have monocoque seamless housings (and it appears to have a lengh of a 3-band fusil) and different butt end.
From Lexicanum (again!)
^ This is exactly 2nd edition lasgun, once (or maybe still) called M35 'M-Galaxy' lasgun and was a standard issue rifle of the Imperial Guard, older artworks since 2nd edition shown every guradsmen of every regiments found wielding this pattern of lasgun. (Catachans, Cadian, Mordian, Pretorians, Tallarns, and more!) in 2000 the 'updated' versions are abit bulkier but have magazines plugged in the same fashion as any modern assault rifle. (also different pattern of lasguns first appear (since the 2nd edition, the 1st edition lasgun might have been called Ryza pattern by now)
^ A rifle seen above might actually be an M-Galaxy that every joes once used. I wonder where powercell should be plugged into??
^ 'updated' M-35 'standard' lasgun. an exploding view where the same weapon can be switched between normal service rifle and sniper one. possibly a different part swap converts
IG rifle

into Scout marine weapon.
the reciever housing has a lenght of iron tube sight/fiber optics sight. barrel is exposed (held together with underslung rod with only a metal band
^ Kantrael lasgun, sometimes (officially) called Cadian patterns. seen in every Cadian shock troops boxsets. the weapon has a full lengh reciever housing. i guess that full lenght housing might be inspired by many Scifi movies (Aliens) and computer games
^ Mordian Iron Guard, introduced in 1992 along with other regiments, never have new miniatures released. only new artwork updated along when
GW updated the 'M35 Lasgun' . appearances are otherwise akin to Imperial Japanese line infantry from 'The Last Samurai' movie
^ Same Iron Guard, different lasgun. did they begin using Kantrael patterns?
^ Mordian Iron Guard disembarking from Chimera APC. the unit appears to use what's now called Lascarbine due to the unit's formation as mech infantry.
^ Catachans, now and then. upgraded in 2000 with new lasguns
^ Catachan Mk4 Lascarbine. compare this picture with the late picture of 'M35 lasgun'
so. do you think Catachan lasgun is a perfect representations of standard M35 M-Galaxy pattern lasgun? or Cadian is a better interpretation?
L.