What year is headstamped on that brass?
It's doubtful you have any, but in the early 1970s some Twin City 5.56mm brass was not intended for loading.
Seems odd, but it was 5.56 brass made under the experimental Small-Caliber Ammunition Modernization Program, or SCAMP.
The SCAMP produced cases by a method radically different from established practices, at a much higher rate of production.
Cases were produced to test the system, not to be used as ammunition. The 5.56 brass produced by SCAMP was sold as scrap metal, but some found its way into the surplus market.
ALL unfired brass marked TW and dating from the 1970s should be suspect, and should not be loaded.
Reloaders who have created ammunition in cases produced by the SCAMP system report cases splitting lengthwise. Not a good thing.
Remember:
5.56mm caliber?
Unfired?
TW headstamp?
Dates from the 1970s?
BEWARE!
For more detailed information, see the November 1979 (p. 42) and April 1986 (p. 56) issues of the American Rifleman.