Well the MG 34 and Lewis gun are the tip of the iceberg really. The e-11 standard stormtrooper blaster is based on a british sterling SMG, Han Solos DL-44 is based on a Mauser 96, and Princess Leia's blaster on the Tantive IV is based on a Margolin .22 MTs target pistol. One of the Sandtroopers in A New Hope is even carrying an MG15 used in WWII german aircraft as air to air machine guns among other things.
Others that have been used include StG44s used by rebel troops on Hoth and Endor, Jyn Erso's balster is based on a PO8 Luger, and modified M4s can also be seen in Rogue one. The Jawas ion blaster and Zuckus blaster are based off of heavily cut down lee Enfield rifles, Bobba Fett has a blaster based on a grenade launcher that I can't remember the details for as I believe does Bossk also, and Dengar has an MG42 in The Empire Strikes back.
Some are heavily modified others just have a couple of pieces glued on and in the case of Dengars MG42 I think they just removed the stock.
There is a theme in Star Wars that most blasters are based off of real firearms. My understanding is that Lucas wanted the weapons to look real and used like everything else in the Star Wars galaxy, and the quickest and easiest way to achieve the worn look and heft of a space age weapon was to use real weapons and dress them up as "Blasters".
A lot of the weapons used in the original film were hired from Bapti's, a Theatrical armourers here in the UK and because they were hired any modifications had to be easily removable. I guess that this may also be why they went for guns that looked more exotic to their 1977 eye.
I think too that people were much less familiar with weaponry back in 77/78. Sure if you showed them a tommy gun, or a standard Lee enfield or other bolt action they would have known what it was, and of course veterans would have recognised them, but in general, I don't think most would have identified other types easily. It took a lot less to transport a 1977 audience to a galaxy far far away than it would today. We always have to remember too that Star Wars was basically a kids film when released and to kids those were blasters!!! at least they were blasters to an 8 year old me
So there is a lot of scope to either copy a weapon from Star Wars as most of these are available in 1/6 for conversion if not already available in a blaster version, or just make up your own Blaster from a 1/6 real steel of your choice which would be a very Star Wars thing to do
. There is really no right or wrong to it.
Paul