Mk 262 Cloning - pt 2 - Sierra vs Nosler with AA2520

Published on August 30, 2017
Duration: 34:21

This video details the reloading process for cloning Mk 262 Mod 1 ammunition, focusing on testing Sierra MatchKing and Nosler Custom Competition 77-grain bullets with Accurate 2520 powder. It covers brass preparation, including decapping, tumbling, resizing, trimming, and primer pocket crimp removal, followed by powder charging, bullet seating to a specific overall length (2.246 inches), and light crimping. The instructor also conducts ballistic testing to compare velocities and accuracy between the two bullet types, aiming to replicate the performance of Black Hills factory ammunition.

Quick Summary

To clone Mk 262 Mod 1 ammunition, reloaders should focus on 77-grain bullets like Sierra MatchKing, using powders such as Accurate 2520. Careful brass preparation, including de-crimping Lake City brass, and setting an overall length of approximately 2.246 inches are critical. Achieving velocities around 2750 fps is the target, which can be influenced by bullet seating depth and powder charge.

Chapters

  1. 00:00Introduction: Mk 262 Clone Project
  2. 00:33Bullet Comparison: Sierra vs. Nosler
  3. 02:27Primer and Powder Selection
  4. 03:08Powder: Accurate 2520 Load Development
  5. 03:53Overall Length Considerations
  6. 04:51Brass Preparation: Lake City Brass
  7. 05:29Decapping and Tumbling
  8. 07:21Resizing and Case Prep
  9. 09:01Primer Pocket Crimping and Uniforming
  10. 10:43Priming Process
  11. 11:44Bullet Seating and Powder Charging
  12. 13:05Crimp Application
  13. 15:01Switching to Nosler Bullets
  14. 16:29Range Testing: 100 Yards
  15. 16:50Initial Factory Ammo Group
  16. 18:06Sierra 23.0 Grains Testing
  17. 19:27Nosler 23.0 Grains Testing
  18. 20:27Velocity Comparison
  19. 20:53Sierra 24.0 Grains Testing
  20. 21:34Break and Cooling
  21. 21:42Nosler 24.0 Grains Testing
  22. 22:30Sierra 24.5 Grains Testing
  23. 23:08Nosler 24.5 Grains Testing
  24. 23:39Sierra 25.0 Grains Testing
  25. 24:46Nosler 25.0 Grains Testing
  26. 25:14Brass Inspection Post-Firing
  27. 26:23Pressure Sign Analysis
  28. 26:31Results Summary: Sierra vs. Nosler
  29. 27:26Accuracy Issues with Nosler
  30. 29:09Potential Causes for Nosler Inaccuracy
  31. 30:40Environmental Data Tracking
  32. 31:08Future Load Development Ideas
  33. 32:00Next Powder Choice
  34. 32:27Load Data Caution: 5.56 Data
  35. 33:37Conclusion and Next Steps
  36. 33:57Next Video Preview

Frequently Asked Questions

What are the key components for cloning Mk 262 Mod 1 ammunition?

Cloning Mk 262 Mod 1 ammunition involves using 77-grain bullets, such as Sierra MatchKing or potentially Nosler, with powders like Accurate 2520. Lake City brass is common, and CCI No. 41 or Remington 7.5 primers are suitable. Careful attention to overall length (around 2.246 inches) and powder charge is crucial for achieving desired velocities and accuracy.

What reloading steps are necessary for Lake City brass with crimped primers?

Lake City brass with crimped primers requires initial decapping, followed by wet tumbling for cleaning. After resizing, the military crimp must be removed using a specific tool. Primer pockets should then be uniformized and flash holes deburred. Finally, primers can be installed using a hand priming tool.

How does overall length affect pressure and velocity in 5.56/.223 reloading?

Reducing the overall length of a cartridge, such as by 0.015 inches from published data, effectively decreases the case volume. This reduction in volume leads to higher pressure and velocity for a given powder charge, allowing reloaders to reach target speeds with less powder and potentially avoid exceeding safe pressure limits.

Why did Nosler 77-grain bullets perform poorly in this Mk 262 clone test?

The instructor experienced very poor accuracy with Nosler 77-grain Custom Competition bullets when loaded with Accurate 2520, despite achieving good velocities. The primary suspicion is that the light factory crimp applied to these bullets may be negatively impacting their performance, as they are known to be sensitive to such crimping.

What are the recommended velocities for Mk 262 Mod 1 ammunition?

The goal for cloning Mk 262 Mod 1 ammunition is to achieve velocities around 2750 feet per second. In this test, 25.0 grains of Accurate 2520 with Sierra 77-grain MatchKing bullets produced velocities of 2761 fps, meeting this target.

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