20lb MJR Tumblers Premium 400/600 Grit Aluminum Oxide - Step 3

In this review of the 20lb MJR Tumblers Premium 400/600 Pre-Polish Aluminum Oxide, the bottom line is simple: this bag is aimed at hobbyists and small-scale lapidary workers who need a reliable third-stage shaping grit. The reviewer found it useful as a bulk refill for the shaping stage before final polish, and appreciated that it is a U.S.-based, disabled and veteran owned operation. While polishing results vary by stone type and process, this product stands out for consistent particle grade and broad compatibility with any brand of rock tumbler.

Key Features

• Premium 400/600 Grit Aluminum Oxide: Provides the correct abrasive size for third-stage shaping to prepare stones for final polishing without overgrinding.
• Compatible with any tumbler: Works in rotary and vibratory tumblers from different manufacturers, making it a flexible refill choice.
• 20lb bulk supply: Large quantity reduces the need to reorder frequently for hobbyists and small shops doing multiple batches.
• American owned and operated: Manufactured and sold by a disabled and veteran owned company located in Pecatonica, IL, supporting domestic business.
• Step/stage 3 specific: Formulated specifically for the shaping stage to smooth edges and remove deeper surface marks ahead of final polish.

Who It's For

The 20lb bag is best suited to rock tumbling hobbyists, lapidary students, and small studios that run several batches and need a dependable shaping grit in bulk. Users who prefer American-made supplies or want to support a disabled and veteran owned business will see that as an added benefit.

Those seeking a final polishing compound should look elsewhere, since this product is intended for the third shaping stage; final shine depends on the subsequent polish and the stone type, so expectations should be set accordingly.

Pros & Cons

Pros

• Consistent particle grade that helps achieve predictable shaping results across batches.
• Large 20lb quantity provides value for frequent users and reduces reordering frequency.
• Broad compatibility means it can be used with most tumbler brands and setups.
• Backed by a U.S.-based disabled and veteran owned company, appealing to buyers who prioritize domestic products.

Cons

• Polish and final shine can vary by stone and process, and some users report a matte finish rather than a high gloss when not followed by an appropriate final polish.
• As a stage 3 grit, it is not suitable as a final polishing compound and must be paired with a proper polish for best results.

Specifications

Brand	MJR Tumblers
Grit	400/600 Aluminum Oxide
Quantity	20lb
Intended stage	Step/Stage 3 (pre-polish shaping)
Compatibility	Compatible with any brand of rock tumbler
Ownership	Disabled and veteran owned, located in Pecatonica IL, USA

Our Verdict

The 20lb MJR Tumblers 400/600 grit is a practical, cost-effective choice for hobbyists and small lapidary setups that need a dependable shaping grit in bulk. It performs well as a stage 3 abrasive and is good value if you run multiple batches, but buyers should plan a proper final polish afterwards for high gloss results.

Frequently Asked Questions

Is this grit suitable for all tumblers?
Yes, the product is formulated to be compatible with any brand of rock tumbler, including rotary and vibratory models.

Will this grit provide a final shine?
No, this 400/600 aluminum oxide is intended for the shaping stage; a separate final polishing compound is needed for a high gloss finish.

Where is this product made?
It is offered by a disabled and veteran owned company located in Pecatonica, Illinois, USA.