Cloning Mk262 - Winchester 748 & 760

Published on January 24, 2018
Duration: 18:52

This video details an attempt to clone Mk262 ammunition using Winchester 748 and Winchester 760 powders with 77-grain Sierra MatchKing bullets. The instructor, with experience in this series, tests various powder charges, meticulously recording velocity, group sizes, and pressure signs. While Winchester 748 proved ineffective for accuracy, Winchester 760 showed significant promise, particularly at lower charge weights, warranting further investigation.

Quick Summary

Winchester 760 powder shows promise for cloning Mk262 ammunition with 77-grain Sierra Match King bullets, delivering excellent accuracy and good velocity consistency at lower charge weights. In contrast, Winchester 748 performed poorly, exhibiting bad accuracy and high velocity variation, making it unsuitable for this application.

Chapters

  1. 00:00Introduction: Cloning Mk262
  2. 00:49Powder Selection: Winchester 748 & 760
  3. 01:31Bullet & Brass Preparation
  4. 02:00Primer Selection: CCI #41
  5. 02:07Load Data Development
  6. 04:43Bullet Seating & Crimp
  7. 06:19Range Setup & Conditions
  8. 06:42Firearm Platform Details
  9. 07:13Winchester 748 Test: 23.8 Grains
  10. 08:12Winchester 748 Test: 24.1 Grains
  11. 08:47Winchester 748 Test: 24.4 Grains
  12. 09:34Winchester 748 Test: 24.7 Grains
  13. 10:15Winchester 748 Test: 25.0 Grains
  14. 10:57Winchester 760 Test: 24.8 Grains
  15. 11:51Winchester 760 Test: 25.1 Grains
  16. 12:25Winchester 760 Test: 25.4 Grains
  17. 13:13Winchester 760 Test: 25.7 Grains
  18. 13:49Winchester 760 Test: 26.0 Grains
  19. 14:22Brass Inspection Post-Test
  20. 15:20Group Analysis: 748 vs 760
  21. 15:55Conclusion: Winchester 760 Promise
  22. 17:17Surprise at 748 Performance
  23. 17:39Future Exploration with 760
  24. 18:28Next Steps & Series Continuation

Frequently Asked Questions

What are the key components for cloning Mk262 ammunition?

Cloning Mk262 ammunition typically involves using a 77-grain Sierra Match King bullet, specifically one with a cannelure. The goal is to achieve velocities around 2760 ft/s, often requiring careful powder selection and load development beyond published maximums.

How did Winchester 748 perform in Mk262 cloning tests?

Winchester 748 proved to be a poor choice for cloning Mk262 with 77-grain Sierra Match King bullets. The tests showed consistently bad accuracy, high velocity standard deviations, and generally unfavorable results, leading the instructor to discontinue its use in this series.

What are the findings on Winchester 760 for Mk262 cloning?

Winchester 760 (also known as Hodgdon H414) showed significant promise for Mk262 cloning. At lower charge weights, it produced excellent accuracy and good velocity consistency, although it did not reach the target velocity of 2750 ft/s. Further testing is recommended.

What brass and primers were used in the Mk262 cloning tests?

The tests utilized once-fired Lake City brass, though a batch with loose primer pockets was noted. CCI #41 primers were chosen for their consistent performance throughout the series. Careful brass preparation, including sizing and trimming, is essential.

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