The TechT MRT(MASS REDUCTION TECHNOLOGY) Invert Mini & Empire Axe Bolts have been engineered with efficiency and consistency as the most crucial design elements. Over the last few months TechT has tested many different crazy looking super light bolt designs and had mixed results. After long months of testing on the field and shooting over the high precision chrono, they found that using the stock type bolt face o-ring as well as having no cuts between the two rear o-rings yielded the best consistency and efficiency. The results found that removing the stock-type face o-ring and replacing it with a standard o-ring reduced the velocity at any pressure and dwell by about 15-30 fps and decreased consistency. TechT thinks it's because the stock type o-ring seals really well. They also found that placing a groove between the two rear o-rings for added weight reduction actually decreased consistency. Instead of a standard deviation of between 3-4 FPS with no groove, TechT got a standard deviation of about 15 fps with the groove. The MRT is the newest bolt that will produce less kick, peak efficiency, and great consistency. The MRT offers deeper cuts for greater weight reduction in Gold. The MRT GOLD is 30% lighter than stock the metal bolt weighs about 3 grams more than the delrin and because it's metal it should have a longer wear life. The MRT Gold is hard anodized and coated for minimal drag and friction.