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300 Blackout for 550

Stock Number: 64226
Introducing the new 300 Blackout trim die kit


The GSI 300 AAC Blackout trim die system is made up of two separate dies: 1) the Rough Trim Die and 2) the Trim Die. They are designed to be used with the Dillon RT1200B or RT1500 trimmer motors, and specifically designed to be used progressively with the GSI Trimmer Toolhead.

The Rough Trim Die is an intermediate size/trim step between 5.56x45 NATO or .223 Remington and 300 AAC Blackout. It was our experience during development that if we used a traditional trim die for the conversion process alone, that the brass was not supported properly when it first contacts the trimmer. This caused the case to spin with the trimmer creating a jam. The roughing die is the proper size to grip the case BEFORE it ever contacts the trimmer, allowing for an excellent roughing cut. Being that it is a rough cut, there is no need for fine adjustment. In most cases following the instructions below will result in a properly rough trimmed case.

The Trim Die is a traditional full length sizing die, manufactured to minimum tolerance. It is designed to be used after the Rough Trim Die, or with once fired brass, for final size and trimming.

Both the Rough Trim Die and Trim Die are hardened steel dies that require the use of case lube.

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