An old .30-06 barrel removed from an action and milled to expose the chamber and bore. It was modified as a visual training aid to demonstrate how a cartridge sits within the chamber.
The work was carried out by Simon at Precision Rifle Shooting, whose careful machining and attention to detail produced an effective educational display piece.
Some words from Simon,
Looking inside the chamber helps us understand how case sizing works and the relationship between OAL (overall length), bullet seating depth, and the rifling. With handloads in particular, bullets are often seated close to the lands (rifling) to find the optimum level of precision.
The view inside the chamber shows the bullet seated within the leade area, where the rifling begins. Rifle chambers have different neck IDs (internal diameters), with some deliberately cut smaller to reduce case neck expansion during firing. This can improve brass life and may also enhance precision.
Some chambers even require case necks to be turned down to reduce neck thickness and maintain a safe minimum clearance, although this is generally limited to benchrest-style applications.
After firing, cases are resized to closely match the chamber dimensions. Ideally, chamber clearance should be around 0.001–0.003 inches, although the exact amount is often a matter of personal preference. The goal is to avoid excessive resizing, which can overwork the brass and increase stretching during firing. Excessive brass stretch can eventually lead to case head separation, where the brass fails near the base of the case.
By looking inside the chamber, we can better visualise the relationship between these dimensions and how they influence cartridge fit, brass life, and accuracy.
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How do I look after the chamber ?
Failing to maintain the chamber and barrel of any firearm will ultimately lead to problems and a loss of accuracy.
Every time you fire a rifle or shotgun, hot gases and corrosive residues are deposited in the chamber and barrel. Over time, if these are not removed, they can lead to corrosion and premature wear.
The cure is simple: a little oil and some regular care will help extend the useful life of your firearm.
Personally, I never allow a barrel to become excessively dirty, so a light clean after each use is usually all that is required.
The build-up of lead and/or copper fouling can eventually affect accuracy. At this point, a thorough cleaning followed by a few fouling shots to recondition the bore should restore normal performance. If accuracy problems persist, there may be other underlying issues that need to be investigated.
Simon’s milled chamber section provides a fascinating insight into the anatomy of a rifle chamber and the importance of keeping these critical areas clean and properly maintained.
