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Chapter 1: Measurement units

At GMI, precision starts with how we measure. We build and gauge our dies and punches using metric units, where the smallest increment we work with is a micron—

1 micron = 0.001 mm = 0.000039 inches.

Why does this matter?

Most American die makers work in thousandths (0.001”) or ten-thousandths (0.0001”) of an inch. These are respectable units, but they simply don’t offer the granularity or fine resolution that micron-level measurement provides. No one in the imperial system works in “0.039 thousandths of an inch,” even though that’s what 1 micron actually is.

Today I want to tell you the story the way it actually happened. No marketing, no polished corporate BS. Just the truth, because you deserve it.

Back in 2019, we (two engineers with zero shooting experience) had:

·       No track record

·       Never owned an airgun

·       Never fired a single pellet or slug in our lives

·       No idea we would ever end up in tooling

We warmly invite you to share your real-world experiences right here—whether you’re testing slugs made with GMI kits or any other tooling on the market.

•  If the results are excellent → it’s another proud feather in our cap

•  If something doesn’t perform as expected → it’s a valuable lesson that helps us improve fast

•  If you have a suggestion or idea → we’ll seriously evaluate it and implement whatever is practical

•  If you see any way we (or the wider slug-making community) can do things better → you’re in exactly the right place to speak up

At GMI we have a simple principle - Honesty is the best policy - We take criticism like champions, So feel free.

Thank you all for joining the GMI community. We at GMI engineering welcome you all.

Dear members,

We are excited to launch this dedicated forum as a collaborative space for generating, sharing, and archiving valuable insights from the community on all aspects of PCP airguns and related disciplines.

Key focus areas include (but are not limited to):

• PCP’s, tuning, and performance

• Slug development, testing, and ballistics.

Welcome to the group! You can connect with other members, get updates, share videos, share your experiences and more!

This is the general group on the forum.

GMI Engineering Testing Forum

This forum is exclusively created for the GMI Engineering Testing Team — a space where members can share their technical insights, testing results, and hands-on experiences with GMI products.

Our goal is to build a collaborative environment where:

• Team members can document real-world performance and testing feedback.

• Users and engineers can ask questions, exchange ideas, and troubleshoot together.

• Everyone contributes to improving the precision, reliability, and overall performance of GMI products.

All participants are encouraged to post their findings, share observations, and help one another get the best out of GMI Engineering’s precision systems.

Your expertise drives innovation — let’s refine precision together.

GMI Engineering Forum – Precision Through Shared Knowledge

Welcome to the official GMI Engineering Q&A Forum, a dedicated space for machinists, tuners, and enthusiasts to exchange insights about our precision-engineered products — from the Slug Master and SOC Kits to the Freedom Series Dies and Pellet Molds.

Here, you can:

• Ask questions and get expert answers from our team and community.

• Share your machining experiences, setup tips, and optimization results.

• Explore discussions on maintenance, performance, compatibility, and accuracy improvement.

This forum is designed to help users make informed decisions, resolve doubts, and understand the finer details behind our engineering process. Every shared experience contributes to building a stronger, more knowledgeable GMI community.

Join the discussion, share your expertise, and help others achieve true precision.