Installing a magazine extension on a Remington 870

Installing a magazine extension on a pump-action Remington 870 can increase the number of 12- or 20-gauge shells carried under the barrel. Most compatible kits add capacity with an extended magazine tube and related retaining hardware. The work is compact, yet a poor fit can interfere with feeding, the barrel band or the pump.

The goal is a secure extension that clears the barrel and forearm, feeds shells consistently and preserves the action’s locking geometry. Work from the exact model, gauge and chamber information rather than relying on the broad “870” label. A 870 family member with a detachable box magazine needs a completely different procedure from a tubular-magazine pump.

Australian shooters also need to check local law before changing capacity. Licensing is administered by each state or territory, and an extension may affect magazine-capacity limits, Category A or B classifications or modification endorsements. A firearm that is legal in one jurisdiction may need different approval in another, so a licensed dealer or the relevant firearms licensing authority should confirm the proposed configuration.

Check fitment before ordering

Compare the shotgun’s model stamp, gauge, chamber length, barrel length and action type with the extension chart. Australian 12-gauge shotguns commonly use 70 mm or 76 mm shells, while 20-gauge examples use a smaller tube and different followers. A matching calibre alone does not guarantee that the cap, tube diameter, spring or barrel band will fit.

Choose a kit intended for a Remington 870 tubular magazine, and read its instructions before ordering. Many designs clamp or screw onto the existing tube and use a longer barrel band or cap; others replace more parts. Keep the supplied retaining ring, screws and washers together, and check whether the package includes a new follower spring or a barrel-band spacer.

Do not use a general firearm part as a dimensional guide. The retailer’s semi-automatic handgun options belong to a different magazine system, for example, and provide no reliable fitment reference for an 870. Likewise, a tactical pump with a detachable magazine will not necessarily suit the factory tubular gun.

Prepare the firearm and work area

Work on a clear bench with the muzzle pointed in a safe direction. Read the firearm manual and extension instructions first, identify every component and fit the correct tools before touching the shotgun. Eye protection, stable support and good light are worthwhile; small set screws and spring components are easily lost.

Remove all ammunition before installation. Open the action if the model allows it, eject every shell, then inspect the chamber, bore and magazine tube carefully. Do not rely on a chamber indicator or the position of the action alone. Keep the ammunition in a separate location and confirm the gun is unloaded again before proceeding.

A trigger component should not be altered to make the extension fit. If the gun also needs trigger work, the site’s trigger assembly guide demonstrates a related Remington 700 procedure, but the 870 manual and a qualified technician should govern the actual work. Never place a finger inside the trigger guard during assembly.

Fit the extended magazine tube

On many 870 tube-extension kits, installation is made at the front of the gun. Remove the magazine cap and loosen or remove the barrel band while supporting the tube so it does not drop. Mark the original orientation, retain the barrel lug correctly and move only the components identified in the kit instructions; some models place extra covers or heat shields in the way.

Join the extension to the magazine tube in the specified manner. It may slide over the tube and lock with a clamp screw, engage by thread or form part of a replacement tube. Seat the shoulder fully, start screws by hand and tighten them only to the maker’s specification. Resistance, thread damage or a gap at the joint means the parts should be inspected rather than forced together.

Return the tube to the barrel and restore the barrel band, retaining hardware and magazine cap. Keep the cap aligned so it does not rub the extension, and confirm that the extension clears the barrel, fore-end and any heat shield. Overtightening the cap or band can distort a component, while an undersized band may allow the extended tube to move.

If the stock, forearm or action cover had to be removed, reinstall them in the manual’s order. On a functioning 870, the action bars must be seated correctly so the bolt can lock. Move the fore-end through its full travel and check that nothing contacts the extension. Stop if the action binds, the follower catches or the operating parts will not return normally.

Verify operation before carrying the shotgun

With the gun unloaded, cycle the action several times and watch the follower through the tube opening if accessible. The extension should sit firm, the cap should remain secure and the shell path should be clear. Operate the trigger only as directed in the manual after positively confirming that the chamber and tube are empty.

A bench check is not a firing test. Take the shotgun to a licensed range, use established ammunition for its gauge and chamber, and begin with a normal load while watching for failures to extract, binding or a change in the sound of the action. Stop immediately if any loading or cycling problem appears. A technician should inspect the gun before more rounds are fired.

For the common weekend trip to a rural shooting property in Australia, transport the unloaded shotgun in a locked hard case and keep ammunition separate in secure storage. Local rules vary, including requirements for transport containers and temporary unloading. Record the installation, the parts fitted and the first-use check so a dealer or repairer can understand the gun’s history.

Maintain the extension and complete the order

Check the magazine cap and barrel band after the first range session, then inspect them periodically and before long trips. Keep the extension clean and dry, remove only deposits with products approved for the firearm, and avoid abrasive blasting or paint removal that could weaken a clamp or change a fit. Recheck any fastener specified by the kit maker if vibration or corrosion is present.

The retailer provides customer accounts, order tracking, published shipping, cancellation and refund policies and 24/7 support. It describes firearm fulfilment through a customer’s chosen FFL dealer and direct shipping for eligible ammunition and magazines. For an Australian buyer, that US terminology does not replace state or territory approval; confirm eligibility with a locally authorised dealer before checkout. Discounts advertised for cryptocurrency or military service should also be checked against the order terms.

Before ordering, record the 870’s model and gauge, obtain the supplier’s fitment chart and ask a local dealer or repairer to confirm the result. For shoppers in Sydney, Melbourne, Brisbane, Perth and Adelaide, a licensed dealer can compare the part with the receiver details; regional buyers can use their usual authorised dealer. Review the current Remington Firearms Store catalogue, choose the exact-match extension rather than a general tube, and arrange any required inspection before the part arrives. Keep the paperwork with the firearm and follow the installation manual without skipping the unloaded safety checks.