Build a precision laser bore sighter for your PCP or springer for under £45. Includes a free interactive pellet drop calculator.
Wheeler, Sightmark, SiteLite and Bushnell all sell commercial laser bore sighters for £80–£200. The cheap eBay alternatives are too inaccurate for air rifle work. Build a better one yourself for £45, plus get a free interactive pellet drop calculator below that none of the commercial products provide.
Without a bore sighter, getting a new scope onto paper at 30 m typically takes 20–50 pellets of trial-and-error. With a calibrated laser bore sighter you're on paper after the first shot, and zeroed in three to five. For a UK PCP shooter testing multiple pellet brands across the season, that's the cost of a tin or two of pellets saved per zeroing session. The real win is range time, not pellet cost.
A laser bore sighter also lets you confirm scope alignment between sessions (after travel, transport, or any knock to the rifle), without firing a shot — useful at indoor ranges where live firing isn't permitted but you want to verify your zero hasn't shifted.
A bore sighter projects a precisely-aligned laser dot down the bore axis (or parallel to it with a known offset). At a target downrange, the dot shows you where the bore is pointing. You then measure where the pellet will land (accounting for the offset and the gravity drop), and adjust the scope crosshair to that point. Live fire then fine-tunes the last few clicks.
Commercial cartridge-style sighters fit inside the chamber of a centrefire round — useless for air rifles, which have no cartridge. Muzzle-fit commercial sighters use magnets or O-rings to grip the muzzle, which works on solid steel barrels but slips on shrouded PCP barrels and has poor coaxial alignment with the bore. Our DIY approach uses a precision pilot rod that engages the actual bore for 50 mm, giving better alignment than >£150 commercial alternatives.
| Part | Spec | Source | Cost |
|---|---|---|---|
| Precision pilot rod | 4.50 mm Ø × 100 mm, silver steel / drill rod, h7 tolerance | Cromwell, RS Components, eBay | ~£5 |
| Mounting plate | 3D-printed (PETG, 100% infill) or aluminium, 60 × 30 × 6 mm, two parallel bores 4.5 mm + 16.5 mm, 15 mm centre-to-centre | 3D-print shop / DIY mill | ~£3 |
| Locking grub screws | 2 × M3 × 6 mm hex | hardware shop | <£1 |
| Green laser diode module | OSRAM PL520 (520 nm, 30 mW) pre-built in 3.8 mm housing with collimating G-2 lens | OdicForce PL520 + OFL139 housing + OFL3 G-2 lens | ~£26 |
| Adjustable-current laser driver | Constant-current 30–150 mA, soft-start. Run at ~50 mA (~3 mW) for indoor bore-sighting safety | OdicForce driver boards | ~£10 |
| Green-rated safety goggles | OD ≥ 4 @ 520 nm. Mandatory — 30 mW green is class 3B | OdicForce safety | ~£15 |
| Total (one-time build, no consumables) | ~£60 incl. goggles | ||
If you skip the goggles (don't) it's £45. The goggles are a one-time purchase and useful for any future laser work, so amortise across years of use.
The geometry is simple: a precision rod slides into the bore so the laser module sits parallel to the bore axis, with a fixed vertical offset of 15 mm between the two:
Both the rod and the laser module sit in parallel holes on the plate. Geometry guarantees the beam stays parallel to the bore.
Enter your chronographed muzzle velocity and pellet weight to get the exact scope crosshair offset for step 8 of the procedure. The calculator uses a drag-corrected ballistic model tuned for typical .177 diabolo pellets.
Quick reference if you don't have time to chrono. Use the calculator above for accurate numbers from your actual chrono data.
| Pellet | Typical fps (UK sub-12) | Drop @ 25 m | Drop @ 30 m | Drop @ 40 m |
|---|---|---|---|---|
| JSB Exact 8.44 gr | 780 | ~58 mm | ~86 mm | ~160 mm |
| AA Field 8.44 gr | 785 | ~57 mm | ~85 mm | ~158 mm |
| JSB Exact Heavy 10.34 gr | 705 | ~71 mm | ~105 mm | ~196 mm |
| H&N Field Target Trophy 8.64 gr | 775 | ~58 mm | ~87 mm | ~162 mm |
| JSB Hades 10.34 gr (hunting) | 705 | ~71 mm | ~105 mm | ~196 mm |
For FAC air rifles (above 12 ft·lb), drops are typically 30–50% less at the same distances depending on the muzzle velocity boost. Always chrono and use the calculator.
The procedure is identical for springers, with two caveats:
Got your bore sighter sorted? Time to make sure you've got the right scope to zero. Compare real-time UK prices on hundreds of air rifle scopes — Hawke, MTC, Vortex, Athlon and more.
Find Your Air Rifle Scope on Scope Finder →You don't strictly need one, but it saves significant time and pellets. A laser bore sighter gets your scope close to zero before you fire a single shot, so live-fire zeroing only needs a handful of pellets to fine-tune rather than 30–50 to find paper first. For a PCP shooter going through 8–10 pellet types a year, a bore sighter pays for itself in a single zeroing session.
Commercial cartridge-style and muzzle-fit laser bore sighters from Wheeler, Sightmark, SiteLite and Bushnell typically cost between £80 and £200 in the UK. Cheap eBay variants start at £25 but most are too inaccurate for air rifle use (large offset error, poor alignment to the bore axis, no calibration). A DIY build using a precision pilot rod and a quality green laser diode module costs around £45 and is more accurate than most commercial alternatives.
Yes, provided the pilot rod is the correct diameter (4.50 mm for .177, 5.50 mm for .22), is smooth-finished, and is a slip fit rather than forced in. Never use a tight rod that could damage the rifling or the muzzle choke. Always decompress the rifle before inserting the rod, never have it charged with the rod in the bore, and remove any moderator first.
Yes — the procedure is identical for springers. The only difference is that springer barrels can move slightly during firing (so-called barrel droop), so optical bore-sighting is only the starting point and you'll need a few extra fine-tuning shots compared to a fixed-barrel PCP. The bore sighter still saves significant pellets vs. blind paper-shooting.
For a typical UK sub-12 ft·lb PCP shooting 8.4 gr JSB Exact at around 780 fps, the pellet drops approximately 85–90 mm at 30 m relative to a horizontal bore line. Springers vary by model and pellet but are broadly similar. Use the interactive calculator above to compute your specific drop based on your chronographed muzzle velocity and pellet weight.
Yes, with one adjustment: FAC air rifles (above 12 ft·lb) have higher muzzle velocities (often 900–1100 fps) so the pellet drop at any given range is reduced. The calculator above handles FAC velocities correctly — just enter your chronographed FPS. The build is otherwise identical.
With a precision 4.50 mm pilot rod (h7 tolerance), 50 mm of barrel engagement, and a calibrated plate offset, a typical first live-fire group lands within 50 mm of the calculated point of impact at 30 m. Two or three click adjustments on the scope then bring you to true zero. This is significantly better than visual bore-sighting (down the bore by eye), which is typically 100–200 mm off at 30 m.