Screwtop.243
Ouch...that thing kicks
Groundhogs borrow is actually a very complex setup- its not just a hole in the ground. They make different "chambers" underground - including what some would consider a bathroom - defecation chamber.
This time of year groundhogs are not active (hibernating)-depending on where you live. Occasionally if there is a warm spell, groundhogs will come out of there burrow. Here in Garrett Co, we wont see them until Spring.
A trick Ive used -when you hunt them is to use a high pitch whistle. The one I use looks like a dog whistle -but is not silent (or high pitched outside of the human hearing threshold). If you spot them in the field, and they duck into there hole, I usally set up my bipod on my rifle from afar (few hundred yards). When you toot on the whistle -they stand up out of curiosity - and you sock em in the head with a bullet.
Good advice. I've also found that groundhogs who live in fields a fair distance from any water source get their water from licking dew off of grass, so a good time to catch them out is in the early AM in the late spring/early summer months. I'm not sure, but I think they typically breed around late February, and have a 6 to 8 week gestation (with as many babies), so early spring might be a good time to pop 'em for population control purposes.