''BACK-BORE'' REAMERS 184030740

Unlock better patterns and true custom choke performance with the “BACK-BORE” Reamers – Clymer 12 Gauge Back-Bore Reamer .740" Diameter, 184030740. Built for professional gunsmiths and serious shotgun enthusiasts, this precision back-bore reamer lets you enlarge and true up 12-gauge bores, fine-tune bore-to-choke constriction, and bring new life to worn or pitted barrels. Brownells+2Brownells+2

Professional 12-Gauge Back-Bore Reamer – .740" Diameter

This model, 184030740, is a .740" diameter Clymer 12-gauge back-bore reamer, part of a series of reamers available in .005" increments from .725" to .740". Brownells Sverige+2Brownells+2

• Gauge: 12 Gauge

• Style: Back-bore reamer

• Diameter: .740" (largest in the Clymer 12ga back-bore range)

• Length: 5" (12.7 cm) Brownells+1

This size is ideal when you want to significantly enlarge the bore for pattern improvement, custom choke work, or to clean up rough barrels while still leaving room for choke constriction near the muzzle.

Enlarge Bore to Tune Bore-to-Choke Constriction

Back-boring is one of the most powerful tools a shotgun smith has for pattern optimization and recoil management. These “BACK-BORE” Reamers are specifically designed to:

• Enlarge the bore to change the bore-to-choke relationship

• Let you fine-tune constriction for competition or custom hunting guns

• Smooth and true uneven or rough bores for more consistent patterns Brownells Sverige+2Brownells Schweiz+2

A properly back-bored barrel can:

• Deliver denser, more even shot patterns

• Reduce felt recoil slightly by increasing bore volume

• Provide performance similar to premium barrels—without replacing the barrel

For competitive clays shooters and custom bird guns, this reamer is an essential pattern-tuning tool.

Perfect for Shortened & Choked Barrels

Clymer’s back-bore design gives you multiple options for both shortened barrels and existing choked barrels: Brownells Sverige+2Brownells Schweiz+2

• Shortened barrels:

  • Back-bore to within 2"–3" of the muzzle to create a built-in degree of constriction (effectively adding choke to what would otherwise be a cylinder-bore tube).

• Existing choked barrels:

  • Back-bore a choked barrel to enlarge the bore, providing “extra” constriction for competitive shooters seeking tighter patterns.

This flexibility makes the 184030740 back-bore reamer invaluable for shops doing:

• Custom barrel work

• Chop-and-tune projects

• Competition gun setup for trap, skeet, sporting clays, and live-bird games

Ideal for Cleaning Up Rough or Pitted Bores

Shotgun barrels that have seen years of use can develop pitting, rust damage, and roughness, which hurt both patterns and resale value. Back-boring with this reamer can: Primary Tactical+2Brownells UK+2

• Remove shallow pits and rough fouling rings

• Smooth out tool marks or imperfections from earlier work

• Improve both the appearance and performance of older barrels

Rather than scrapping a barrel, a skilled gunsmith can often save and upgrade it using a quality back-bore reamer like this one.

Correct Lead Angle to Blend with Existing Chokes

A critical detail: the lead angle of the “BACK-BORE” Reamers is matched to the angle of most shotgun chokes. Brownells Sverige+2Brownells+2

That means:

• The reamer naturally blends into an existing choke cone, minimizing abrupt transitions

• You get a smooth, progressive taper instead of a step or shoulder that could disturb patterns

• It’s easier to maintain structural integrity and pattern quality when doing partial reams or custom choke transitions

This design detail is one of the reasons these Clymer reamers are a staple in professional shotgun shops.

M-7 High Speed Steel for Long Service Life

Clymer builds these back-bore tools from M-7 high-speed steel, hardened and drawn for durability. Brownells+2Brownells+2

• Material: M-7 HSS – tough and wear-resistant under continuous cutting

• Length: 5" (12.7 cm) for adequate guidance and cut stability

• Built for use with proper cutting oil and controlled feeds on appropriate setups

With correct lubrication and technique, a single reamer can serve through many barrels and long shop service.

Many Uses in a Shotgun Gunsmith’s Shop

According to Brownells and Clymer, “BACK-BORE” Reamers are invaluable for any shop that does shotgun work, especially: Brownells+2Brownells Schweiz+2

• Choke and barrel modifications

• Shortening and re-choking jobs

• Pattern tuning for competitive and custom guns

• Refurbishing older or pitted barrels

If your business or hobby involves precision shotgun setup, a .740" 12-gauge back-bore reamer is a must-have tool in your barreling kit.

Key Specs – “BACK-BORE” Reamers 184030740

From Clymer & Brownells: Brownells Österreich+4Brownells+4Brownells+4

• Product Name: “BACK-BORE” Reamers – 12 Gauge Back-Bore Reamer, .740" Dia.

• Manufacturer: Clymer

• Brownells / Vendor SKU: 184030740

• Gauge: 12 Gauge

• Diameter: .740"

• Length: 5" (12.7 cm)

• Material: M-7 high-speed steel, hardened and drawn

• Style: Back-bore / shotgun bore reamer

• Use:

  • Enlarge 12-ga bores

  • Adjust bore-to-choke constriction

  • Back-bore shortened barrels

  • Clean up rough or pitted bores

Why Choose the “BACK-BORE” Reamer 184030740?

• Purpose-built for 12-gauge back-boring with a generous .740" diameter

• Allows you to tune choke performance, tighten patterns, and enhance barrel quality

• Lead angle matches common choke cones for smooth transitions and better patterns

• Made from M-7 high-speed steel for long life and consistent cutting

• Trusted by professional gunsmiths for choke work, barrel refurbishing, and custom shotgun builds

If you’re serious about shotgun performance, choke tuning, and barrel restoration, the “BACK-BORE” Reamers 184030740 – Clymer 12 Gauge Back-Bore Reamer .740" is a professional-grade tool that belongs on your bench.

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