This entry was posted on 11/11/2021.
By Chris Parkin
This may seem like a straightforward concept, but a lot of shooters aren’t always sure of this one, so I have put together a simple list of general differences.
A rimfire cartridge, as the name suggests fires when the rim of the case is struck. The soft brass case is made with a liquid priming compound spread around the internal rim of the case before it solidifies and further filled with powder and a bullet. A Centrefire cartridge has a more complex arrangement with either Boxer or Berdan primed cases using a sperate Primer inserted into a pocket at the centre of the case’s base. This is struck centrally by the firing pin and the flash goes through the flash hole (or holes if Berdan primed), initiating the powder, creating pressure as it burns (very rapidly) and driving the bullet out of the case neck into the lead (where the rifling begins) and barrel.
Maximum operating pressures for rimfires are around 24-26,000 P.S.I. whereas something like a 308 Winchester centrefire will be more than double at around 60,000 P.S.I. and this has several following factors. The cartridge case itself on a rimfire has a lesser pressure to assist in restraining so softer brass can be used allowing the firing pin to physically deform the case to initiate the priming compound, which is itself buried within the propellant powder inside the case. The harder brass of a centrefire case is not physically damaged by the firing pin, just the small primer itself and although the physical gas pressure of firing will deform all cases to fill the slightly oversized chamber, the centrefires can be more easily returned to required size and re-primed with a new primer, hence “Reloading”. The rimfire cannot in general, liquid priming compound on vast industrial scale is a far different factor consider which almost exclusively precludes home loading of all but bullets themselves.
All this pressure leads to significant physical factors in the design of the firearm’s action, no.1 the firing pin has to vary from a central location to a position on the rim but the biggest is that the action length is usually far longer for centuries and generally has locking lugs at the front, not the rear. There are some exceptions, Enfield’s and some Steyr’s spring to mind but most Centrefires have two, three or even four locking lugs that interlock with abutments inside the front of the action just behind the barrel’s chamber (Remington 700), or within the barrel itself (Sauer 404 for example). The latter has increased in popularity as machining capabilities have evolved, especially with multi barrel rifles as it means only bolt and barrel are pressure bearing, the action is just there to hold the barrel in place. If the locking lugs are locked into the action and not the barrel, the barrel is threaded into the action to offer pressure bearing capability. This thread is usually additionally clamped to prevent any rotation on actions where the bolt locks into the action lugs, An Accuracy International AT for example.
Rimfires will often use a smaller, single lug but at the rear of the action, near the bolt handle which itself is often the lug itself. It’s not uncommon for a single lug to restrain firing pressures and forms part of the generally smaller, more compact action that is unlikely to hold more than a 22LR (1”/25.4mm Cartridge Overall Length “C.O.L.”) or 17 HMR case (1.349£/34.3mm C.O.L.). Rifles like the CZ457 have interchangeable barrels that are clamped, rather than screwed into the action as this can handle the maximum 26,000 P.S.I. that either cartridge is ever likely to produce. Now think of a common 223 Remington rifle, 2.26”/57mm long cartridge developing 62,000 P.S.I. to restrain, and that is one of the physically smaller commonly encountered centrefires. You begin to appreciate the differences. A 308 Stalking rifle in comparison is 2.800”/71.1mm long with similar operating pressures and there are endless other centrefire options with bullets both larger or smaller, faster and slower, but the general trend is far broader than the generally limited rimfire market usually restricted to 22LR, 17 HMR and 22 WMR cartridges.
Certainly, in the UK, Rimfires are considered for target use, indoors or outdoors in many formats as well as pest control of smaller species depending on variations from your Police Force. Centrefires, being larger with more pressure, equal more muzzle energy, more range and more controlled terminal ballistics. The higher pressures allow harder bullets to be used, copper jacketed lead or even monolithic copper, whereas the rimfire world is predominantly lead only for 22LR, occasionally with a copper wash. 17 HMR and 22 WMR then start to use copper jackets as velocity increases beyond 1000 to 2000/2500 fps as this minimises lead stripped from the bullet by the rifling and minimises cleaning. Centrefires can also be used for pest control, especially handy for wily corvids at range but Fox control is where they really begin to gather pace, before deer stalking comes into the equation for the UK hunter with larger calibres like 243, 308 and beyond. Target shooting is also a huge factor and whereas rimfire competition has regularly been restricted to 100 yards or less (longer range rimfire is gaining popularity), centrefires have been used for decades well past 1000 yards on targets.
This is by far from an exhaustive article but gives you some general factors to consider and look out for when looking for your next rifle both in terms of size, muzzle energy, range and relative rifle differences.
- A common rimfire action like this Steyr Zephyr is designed around smaller rimfire cartridges with rear locking bolt
- This Steyr CLII has a multi lug forward locking bolt designed to restrain higher centrefire pressures and longer cartridge length
- Long range rimfires like this CZ457 LRP are becoming far more common
- Here you can see the firing pin holes and front locking lugs on rimfire v centrefire
- Exposed firing pins
- Corresponding firing pin deformation to initiate the primer
- 22LR, 17HMR, 22 WMR Rimfire cartridges
- 22LR, 17HMR, 22 WMR Rimfire, 223, 308, 300 Win Mag Centrefire cartridges
- Comparable bolt size and action length, 22LR versus 300 Win mag