To me that seems the opposite of smart and wise to kill ground hogs even at a 1000 yards. First where is this happy nesting paradise you speak of where there are so many ground hogs at 1000 yards to shoot at? Myy father in law operating from a wheel chair would often kill 240 or more ground hogs each year. It is hard to get 1000 yards shots in a lot of places and even hard to get enough varmints that are not prarie dogs in one place where 1000 yard shots and endless populations of ground hogs coexist at the same point in time and space routinely enough to build a rifle just for that task! Groundhogs are not particularly hard to kill. Their shy skidish nature and propensity for water and deep ditches and thick grass are what limit shooting from a fixed location not normaly a range limitation. It takes a lot of food to support a large population.
It seems to me that 1/4 bore, 6mm, and 6.5mm would make a lot more sense. Trying to turn a 300WM into a 30BR seems a bit much and sure seems like a bit much seems like a 308 or 30-06 could do the job just fine. It has been a mad minute but I think you can push a 130gr or 140gr. Barnes TTSX out of a 30-06 at something stupid fast like 3400+ from a barrel like 24 inches long. Using something 130-140gr. from Berger or the like would do better down range and not need to burn magnum levels of powder to get the job done.
Doing 30-06AI or 280AI with a light weight bullet would do the deed.
The slow twist makes no sense for a varmint gun. The slow twist in the 30BR is an attempt at reducing dispersion since the 30BR is used for SCORE and AG shooting and the size of the dispersion cone of the bullet and thus rifle can make or break who wins. In varmint hunting that is not a game changer so their is little to be had from under twisting a bullet. Also keep in mind that 30BR is used at 300 yards and less not 1000 yards on game.
Outside of BR the only place people openly talk about dispersion in at Machine Gun school!
For the record if you exclude the early days of some .22 centerfire varmint cartridges exploding their bullets because bullet construction was not up to scratch yet what most people worry about with fast twist rates is an increase in down range dispersion. If your winning and losing on the podium with groups @ or under 1/4 MOA dispersion is real and flat based bullets seem to be more affected than boat tails. The shape of the rifling and crown on the muzzle play into this as well. Forms of rifling like 5R but not limited to just "5R" reduce dispersion or can. 5R can also reduce damage to the base of the bullet.
Sorry for opening up a huge can of worms! I am getting my underware my Mom made me from M60 barrel change mittens. Some guys like underware made from pancho liners but I like those asbestous mittens!
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