Yes, the MWR cars were known for bringing inbound raw materials for glass making. There was a rumor floating around that some cars were equipped with roof hatches for sand loading, but lets not go there. There is no documentation of such.
From the late 1800's through the 20th Century central Indiana was full of glass manufacturing companies. They gathered here because of cheap and plentiful natural gas used in the glass molding process. When the gas ran out in the early 1900's the plants tended to stay. Ball was the largest and intimately took over many smaller competitors.
The 5.6 miles long Muncie & Western RR (MWR) was owned and operated by the Ball Glass Manufacturing Corporation, later known simply as Ball Corp. This small railroad allowed Ball to connect with all railroads serving Muncie, IN: NKP, NYC, C&O, PRR, and the Central Indiana (CI).
The Ball family had profound influence on Muncie and the surrounding communities. There was Ball State Teacher's college later to become Ball Sate University. And there is Ball Memorial Hospital started at the behest of the Ball family. In the 1930's George Ball even gained controlling interest in the NKP after the Van Sweringan's (spelling) ran into financial problems, or both passed away, I'm don't recall which.
I'll quit right there. I'm getting in over my heard. Just be assured the Ball family had a significant influence on my home area. Then there is collecting glass canning jars, a whole different hobby.
From: main@RealSTMFC.groups.io [main@RealSTMFC.groups.io] on behalf of Todd Sullivan via groups.io [sullivant41@...]
Sent: Monday, May 25, 2020 4:36 PM
Subject: Re: [RealSTMFC] MWR 1201-1275 series Mather Patent Boxcar help - more info
And, according to Tony Koester, the cars were often used for back-hauls of sand for the factory.
I spent a few weeks in Marion, IN in the early 2000s rehab'ing a house for Habitat for Missionaries, and found a closed Ball glass plant there. I think it had been served by the NKP.