17-Jul-2026
There are few things more deflating than settling behind a rifle that used to print one ragged hole and watching pellets drop three inches low at 25 yards. Power loss in an air rifle is almost never a mystery, though it's nearly always one of a handful of well-known culprits, and most of them are fixable for less than the price of a tin of premium pellets.
Before we get into the causes, one piece of advice: put your rifle over a chronograph first. Guessing at power loss from group size alone will send you down the wrong rabbit hole. Most clubs have a chrono, many gun shops will check a rifle for the price of a cup of tea, and a basic unit of your own costs £30–£50. Know your numbers, then diagnose.
A quick legal note while we're at it: a sub-12 ft·lb air rifle must stay sub-12 ft·lb. If you're rebuilding a springer or adjusting a regulator, always chrono the result. Creeping over the limit without an FAC is a serious criminal offence, not a paperwork slip.
Right, here's what's actually wrong with your rifle, in rough order of likelihood.
1. A tired or broken mainspring (Springers)
The mainspring is a consumable. Every shot compresses it violently, and over thousands of cycles it loses length and force, or snaps outright. The telltale signs: a gradual drop in velocity over months, a "dead" feel on firing, or in the case of a broken spring, a sudden drop combined with a crunchy cocking stroke.
The fix: a replacement mainspring, typically £15–£30. It's a straightforward job if you have a spring compressor, and genuinely dangerous if you don't. A compressed mainspring stores enough energy to break fingers or worse. If you're not tooled up, this is a gunsmith job, and it's a cheap one.
2. A failed piston seal (Springers)
If the mainspring is the engine, the piston seal is the head gasket. Modern synthetic seals harden, chip, or wear at the edges; the leather seals on older Webleys, BSAs and Dianas dry out and shrink if they're not kept lightly oiled. A failing piston seal usually shows as inconsistent velocity, 40–50 fps of spread shot-to-shot, before power collapses altogether. A harsh metallic clank on firing (piston slamming home with no air cushion) is the classic giveaway.
The fix: a new piston seal, usually under a tenner. Since the rifle is already apart, it's standard practice to replace the mainspring and guides at the same time, a full "spring kit" service that transforms most tired springers.
3. A perished breech seal
The little O-ring where the barrel meets the action is the cheapest part on the entire rifle and one of the most common causes of power loss. It hardens, flattens and cracks with age. The classic test: cock the rifle, lay a strip of tissue paper over the breech joint, and fire. If the paper jumps, you're venting air.
The fix: a new breech seal costs pennies and takes two minutes with a small screwdriver. Always the first thing to check on a break-barrel.
4. Dieseling and over-lubrication
If your rifle gained power for a while, perhaps with smoke and a crack like a rimfire, and then lost it, you're looking at dieseling. Excess oil in the compression chamber ignites under pressure, which feels exciting and destroys piston seals in short order. It's usually self-inflicted: oil down the transfer port is almost never the answer.
The fix: stop adding oil, replace the seal it has burned (see cause 2), and lubricate sparingly with the correct grease during a proper strip-down.
5. Regulator or valve trouble (PCPs)
Pre-charged pneumatics lose power differently. If your shot curve has gone erratic, a wandering point of impact through the fill, or velocity climbing then crashing, suspect the regulator. If the rifle is simply slow across the board, the hammer spring may have relaxed or the valve may not be opening fully. Firing valve seats also wear, bleeding pressure where it shouldn't go.
The fix: regulator service kits and valve parts exist for most popular models, Air Arms, Daystate, BSA, FX and the rest. Regulator work is fiddly but doable at home on many rifles; valve work on a pressurised system is best left to someone who does it weekly. And again: chrono after any adjustment.
6. Leaking seals: The slow death
If your PCP won't hold a fill overnight, or your CO2 pistol hisses its capsule empty in an hour, an O-ring has given up. The usual suspects are the fill port seal, gauge seals, and on CO2 guns the piercing seal at the top of the capsule. Submerging a (pressurised, safe) action in water or brushing joints with soapy water finds the leak fast.
The fix: O-rings cost pennies; the trick is finding the right one, since sizes and materials are model-specific. Specialist supplier Gun Parts lists seal kits and individual O-rings here on RightGun, broken down by make and model, including for guns whose manufacturers vanished decades ago, which beats guessing from a generic assortment box.
7. The barrel and the pellets
Not every power loss lives inside the action. A leaded-up barrel robs velocity and accuracy together, and it builds so slowly you won't notice until it's bad. Equally, a new tin of pellets that are a whisker under-sized for your bore will chrono noticeably slower and group worse. And check your silencer, a pellet clipping a baffle steals energy and throws fliers.
The fix: pull some patches through, try a known-good tin of your rifle's favourite pellets, and re-chrono before you strip anything down. This is the free fix, so do it first.
Repair it, or replace it?
Here's the honest maths. A full springer rebuild, spring, seals, guides, and lubricants, comes in around £30–£50 in parts, or £80–£120 with a gunsmith's labour. For a quality rifle like a Weihrauch HW80 or an Air Arms TX200, that's money well spent: these actions run for decades when serviced.
Parts availability matters more than people think, especially for older British guns. The good news is that the UK still has specialists holding deep stock for marques like Webley & Scott and vintage BSA, specialist supplier Gun Parts has listed thousands of spares right here on RightGun, including discontinued components you won't get from an importer.
But if you're staring at a budget break-barrel needing a full rebuild plus a new barrel, the sums can tip the other way; sometimes, a clean second-hand rifle is the smarter buy, and occasionally the cheapest source of parts is a donor gun. You can see what's on the market right now in the air rifle listings on Rightgun.
Either way, don't put up with a rifle that's lost its edge. Diagnose it properly, fix the actual fault, and chrono the result, your groups will thank you.
Whether you're repairing, upgrading, or maintaining your firearm, Gun-Parts.co.uk is now live on Rightgun.uk. Browse a wide range of gun parts and accessories today.
Have a diagnosis story or a fix we've missed? Get in touch, we're planning more workshop guides, and reader problems make the best articles.
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