Evidently several senators, including Sen. Manchin (of Manchin-Toomey fame), have started answering their own phones as their normal staff are not available due to the shutdown.
If you live in West Virginia you might try giving him a call. According to his Senate page, his DC phone number is?202-224-3954. This is a rather direct way of expressing your displeasure with the M-T gun control bill.
(Hat tip to Bitter.)