I am going to be doing a custom build with custom ammo. My cartridge length will be about 3.125" but require the .223 bolt head. I was originally looking to use a 700 long action for this but others have discussed using a Savage action since the bolt heads are replaceable.
I happen to have a few Savages and I hope I am not going to get sick but I just turned loose of a .243 Model 11 for 250 bucks... I hope that was not my donor that just left!!! I have a .300 RUM 116 that would work great other than I am not sure there is really a market for my barrel, stock, and bolt face and hate to bastardize a good and marketable, all stainless rifle.
I also have a .308 FCP and the actions are certainly different. the mag in the FCP would barely accommodate a 3.00" round. the action could probably be made to work but....
So that leave me wondering if my 243 would have really worked anyway and if not, what other options might I have? Obviously trying to watch the budget. Someone else suggested the Savage Stevens 200 but again, I am not sure what models and what chamberings had what length actions...
My current 300 RUM is not accu trigger but I was going to work this one over and see if I can get to my target of a smooth 1.5# trigger. If not, that would be an added expense.
Like you already said, 3.125" won't work in your 308 action. Your 243 action would have been the same.
It will work easily on a long action. But, you'll run into two potential problems. Both can be solved with some patience.
First, you'll have to find a long action 223 bolt head. They are not very common, but do pop up from time to time. They are best found on savageshooters from a want ad. I have a LH and a RH, but you can't have either.
Second will be the magazine. If you're going to run it single shot, your gtg. A regular 223 magazine isn't long enough, neither are the 308 magazines. You'll have to run a long action magazine. I think a centerfeed magazine with modified (pinched together) might be your best bet.
The 300RUM isn't a good candidate. It is probably CRF and large shank. It also has the largest mag opening of all the Savage rifles. It's more suited to keep it as a big boomer, like a RUM or something off a 375 Ruger case.
My other option on brass is to turn the rims on S&W .50 brass. My largest concern is that brass is straight, without taper, which could mean extraction concerns. Either way, I will likely be turning some brass.