Okay, here goes. All example material will be for the Militech M-20 Ronin. In CP2020, each gun has a stat block that looks like this:

RIF +1 N C 5D6 (5.56) 35 3/30 VR 400M 450eb

Let's break this down. The first thing, RIF, means that it's a rifle, and therefore uses the Rifle skill. This should be ignored, as the breakdown of gun skills is different in SR5. Instead, we need to look at the gun's role, in this case an assault rifle, and use that to determine its classification, and thus its skill, concealability and range. We've already decided it's an assault rifle, so that's what it'll be in game terms.

Second is +1, the gun's accuracy. In Cyberpunk, guns are given an accuracy somewhere between -3 and +3. This functions as a modifier to rolled attacks. However, generally guns fall somewhere between -1 and +1, and guns at the far side of either spectrum are few and far between. A simple solution is just to add 5 to the number for the gun's Shadowrun accuracy. This puts a Militech Ronin at 6. However, it also puts the least accurate guns at 2, so I'm going to say the minimum is 3, barring muskets and things of that nature. Which don't exist in Cyberpunk, so that's a moot point.

Next is concealability, in this case N. This was covered above.

Then there's availability, in this case Common. There are four grades of availability in Cyberpunk. Here is each, with the descriptions given in the book.

Excellent: Can be found almost anywhere.
Common: Can be found in most sports or gun stores and on the Street.
Poor: Specialty weapons, black market, stolen military.
Rare: Stolen, one of a kind, special military issue, may be highly illegal.

Note that legality is not noted per weapon. AS a simple conversion, I'll say Poor and Rare availability weapons are illegal, and Common and Excellent weapons are Restricted.. To determine the availability number, roll a d6+1 for each interval of rarity. So E is 1d6+1, C is 2d6+2, et cetera. In this case, it's E, so I'll roll 2d6+2. Gimme a second. I rolled a 6. So this gun is availability 6R.

Next is the ammo load/damage, in this case 5.56, which does 5D6 damage. This is trickier. I'll rule that each weapon does damage equivalent to similar weapons in SR5. In this case, I'll say 9P, AP-2, as it is a Light assault rifle. A medium assault rifle would do 10P, and a Heavy assault rifle would do 11P.

Next is clip size. This stays the same.

Then there's rate of fire. We'll be using standard rates of fire, so Here's the conversion: 1 is SS, 2 is SA, 3 is BF, and anything more is FA. Guns are assumed to be capable of lower fire modes, barring heavy weapons like LMGs.

VR means Very Reliable. Reliability isn't a thing in SR5, so ignore this as well.

400M is the range in meters. It's an assault rifle, so it uses standard ranges.

Then there's cost. Eurodollars are described in universe as being worth twice an American dollar, so I'll say double the 450eb to 900¥.

Now, this doesn't cover accessories or recoil compensation, so read the descriptions to see what comes standard.

So here's the SR5 stats for the M-20:

Militech M-20 Ronin, Assault Rifle
Acc: 6 DV: 9P AP: -2 Mode: SA/BF/FA RC: - Ammo: 35© Avail: 6R Cost: 900¥

Here's some more guns for completeness's sake:

Colt-AMT Model 2000 (Or Model 2055, if you please), Heavy Pistol
Acc: 5 DV: 9P AP: -1 Mode: SS RC: - Ammo: 8© Avail: 4R Cost: 1000¥

Federated Arms Impact, holdout pistol
Acc: 6 DV: 5P AP: - Mode: SA RC: - Ammo: 10© Avail: 3R Cost: 120¥

Constitution Arms Hurricane Assault Weapon, shotgun
Acc: 5 DV: 13P AP: -1 Mode: SA/BF/FA RC: (1)(Shock Pad) Ammo: 40(d) Avail: 15F Cost: 2000¥

Nice Work.

It's okay. It breaks down when you realize the following:

A) In Cyberpunk, most of the cool guns have something "special" about them, handled by special rules. Dual clip feeds, binary liquid propellant, explosive/hollowpoint/other rounds as standard, etc. So, for example, how do I handle the Suranam Machine Pistol? It gains most of its stats for firing a very light, explosive round (.177 Explosive, to be precise) that costs the same as standard rounds for its damage range, and does less damage than most other machine pistols? If I were to say that it fires explosive rounds as standard, then I'd have to add expense, which would be stupid, as its starting stats would counteract the explosive bonus. It'd end up with 6P AP -1, which is inferior to a cheapass machine pistol firing the same rounds. If I didn't say it used explosive rounds, what would make the gun special? It's otherwise pretty unremarkable.

B) Secondly, there's unconventional ammo loads. How do I handle a carbine chambered in 9mm Long? A lever action .357 Magnum repeater? A .300 Winchester Magnum assault rifle? Guns where the bullets themselves are ramjets? These things defy proper conversion.

C) Flechettes. The Shadowrun devs don't seem to understand that flechettes are actually armor piercing. As a real world backgground, flechettes were designed to penetrate spacesuits back in the 50's when the military thought we were going to have a space war against the Soviets. Of course, that never happened, but we got flechettes as part of the R&D. In Cyberpunk, flechettes ares used for two purposes. One is for the space combat purpose originally intended. The other is for Anti-Borg sidearms. Since the latter is more interesting, and more relevant to Shadowrun, it seems like an excellent idea for conversion, until you realize that armor defeating pistol now has +5 AP.

D) Due to Shadowrun's radically different way of handling melee combat, melee conversions are straight up impossible, minus just fabricating stats completely.

But yeah, for conventional firearms this works okay.