The short answer

Judge an IW5105 first copy on dial layout and case proportions first, movement second, finishing third. A replica with the date in the wrong place, a flat crystal or a case that sits a millimetre thin reads as fake from across a table, no matter how good the polishing is. Before you pay, ask for daylight photos and a short video on a plain background: wrist shot, dial macro, case back, and the crown being wound and set. If the seller will not produce them, walk away.

One honest note. A first copy is a replica. It is not an IWC, it carries no brand warranty, and selling it as genuine is fraud in most countries. Buy it as a lookalike, price it as a lookalike, and keep your expectations there.

Where the IW5105 sits in the family

The Big Pilot's Watch is IWC's oversized pilot design: a broad round case, a large onion crown, a matte black dial with high-contrast numerals, and a soft-iron inner case on the classic references for magnetic resistance. The 46 mm generation carries a power reserve indicator at 3 o'clock and a date window at 6. The smaller 43 mm generation drops the power reserve and moves the date. References inside the family differ in dial layout, case metal and strap, so confirm the exact reference you are offered against the brand's own specification page before you compare photos side by side.

What to check, in order

• Case shape and size. Measure diameter and thickness with calipers if you can. A first copy that is more than about 1 mm off in thickness is the most common give-away. Check the crown: it should be large, easy to grip, and sit flush when pushed in.
• Dial print and lume. Numerals should be crisp with no bleed at the edges. Lume should sit evenly inside the frames, not slop over them. Look at the dial in raking light: a cheap dial goes grey and flat, a good one stays deep black.
• Crystal. The genuine watch uses domed sapphire with anti-reflective coating on both faces, which gives a faint blue or purple sheen and soft distortion at the edge. A flat, uncoated crystal is a downgrade you will see every day.
• Power reserve indicator. Ask for video of it moving: the seller winds the watch, then lets it run down over several days. On many replicas this subdial is decorative, or it tracks day and night rather than true reserve.
• Movement. Most first copies run a decorated Asian automatic. Check the beat rate (28,800 vibrations per hour is the norm for a decent unit), listen for a rough rotor, and time the date flip: it should begin near midnight and finish within about twenty minutes.
• Case back and engraving. Reference numbers, lettering depth and the quality of the markings separate tiers. Genuine cases use a soft-iron cage for magnetic resistance, and replicas almost never do.
• Strap and hardware. Leather should be thick, matte and stitched straight. Check the buckle finish and the lug width before you plan a strap swap.

Parameter bands by tier

Entry tier: mineral glass, flat dial printing, a non-working power reserve, rotor noise, case finishing that shows machining marks under a loupe. Mid tier: sapphire crystal with single-side coating, clean dial print, a working power reserve, a reliable 28,800 vph movement, acceptable brushing and polishing. Top tier: double-sided AR sapphire, thickness within a fraction of a millimetre of spec, sharp case bevels, well-finished movement decoration, accurate lume colour and dial texture. The price gap between tiers is often smaller than the gap in how the watch reads on the wrist, so decide which flaws you can live with before you shop.

Pitfalls that cost money

• Buying from studio photos alone. Retouching hides dial print, crystal coating and case finishing.
• Trusting water resistance claims. Replicas are not pressure tested. Keep them out of pools and showers unless a watchmaker has checked the seals.
• Paying for a factory name instead of the actual unit. Tier labels in this market change often, so ask about the watch in front of you.
• Ignoring after-sales. Ask who repairs it, whether spare crystals and straps are available, and what the return window covers.
• Planning to pass it off as genuine. That is counterfeit trade, not a hobby.

FAQ

Is a first copy IW5105 worth buying?

If you want the Big Pilot look at a fraction of the genuine cost, and you accept that it is a replica, a good first copy is a sensible buy. Judge it on proportions and dial accuracy, not on the label attached to it.

How do I tell a first copy from the genuine watch?

Weigh it, open the case back and inspect movement finish, check for the soft-iron cage, and compare dial print under magnification. The genuine also holds a long power reserve and keeps time to a tight spec across it, which a copy will not.

Will anyone notice on the wrist?

At 46 mm the size does the talking. Most people never see the movement or the case back, so dial accuracy and case thickness matter more than internal finishing.

What wrist size suits it?

A 46 mm Big Pilot is a large watch with long lugs. If your wrist measures under about 17 cm (6.7 inches), look at the 43 mm generation instead or accept the overhang.

Bottom line

Buy the dial and the case, then the movement. Get daylight photos, a winding video and honest measurements before money changes hands, and compare the offered watch against the reference specifications for the exact IW5105 variant you want. A watch that matches on layout, thickness and crystal will look right on the wrist for years. One that misses those three will not, whatever the listing claims.