| Type | Duplex |
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| Projectile | FMJ, GM, steel core, yellow tip, 1 knurled crimping cannelure |
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| Case | brass, segmented taper crimp |
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| Primer | percussion, flat, brass, ring crimp, red annulus |
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| Headstamp | W C C 8 8 |
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| Notes | Colt/Olin experimental Phase 3 duplex round for Advanced Combat Rifle (ACR) trials. This was the final test round. Front projectile 35.0 graoins, rear projectile 33.0 grains with no cannelure. From box labeled: 5.56MM DUPLEX PHASE III COLT TEST RDS LOADED 12-23-88 FLUOROSCOPED FLUOROSCOPED (fluoroscoped stamped twice on box, once in red and once in blue). |
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