.257 IMP
- Thread starter hooligan1
- Start date
Brian Pfleuger
Moderator Emeritus
I guess I'd have it checked but abbreviation for a standard Roberts should be Rbt, IMP should certainly mean "Improved". The standard abbreviation for Ackley Improved would be AI not IMP.
If you replaced the word "would" with "should" I would totally agree with that. What if the gunsmith didn't know there was Roberts Improved and only thought there was was an Ackley Improved and through the stamping would be sufficient? I am will to bet there are a lot more AI's out there than Imp.
I'd have to agree a chamber cast would be prudent.
It is ordinarily done with Cerro-safe alloy,a metal that will melt at boiling water temperature and has ideal shrinkage properties to take measurements.
While the cerro safe would give a true,measurable result,another pretty good material is Co-Flex dental impression compound.Its a 2 part,quick setting rubber.,That would likely tell you which version you have.
If the chamber was done right,and if you do have a .257 Roberts Ackley Improved,a .257 Roberts factory or handload is chambered and fired.The case blows out to a straighter case with a sharper shoulder.In hotrod terms,it gets bored and stroked.
There are some subtleties of headspace when you do this.You really want the case head to be held against the bolt face when you fireform.I have found long seating the 117 gr round nose ideal,as it will jam into the rifling.You can usually get them cheap if you can find them.They will be in an old,dusty box.
A caution:If you have a rifle,such as a Mauser,with what is called a controlled round feed,with a long,claw extractor,you must push the cartridge down into the magazine so it can feed up under the extractor.Do not just drop a round in and force the bolt closed.You will crush back a fairly delicate headspace feature well before the extractor can be abused over the rim.
You should always feed these rifles up from the magazine anyway,but a friend of mine did not know that and he did it the wrong way.The case separated,as it was overly stretched.
It is ordinarily done with Cerro-safe alloy,a metal that will melt at boiling water temperature and has ideal shrinkage properties to take measurements.
While the cerro safe would give a true,measurable result,another pretty good material is Co-Flex dental impression compound.Its a 2 part,quick setting rubber.,That would likely tell you which version you have.
If the chamber was done right,and if you do have a .257 Roberts Ackley Improved,a .257 Roberts factory or handload is chambered and fired.The case blows out to a straighter case with a sharper shoulder.In hotrod terms,it gets bored and stroked.
There are some subtleties of headspace when you do this.You really want the case head to be held against the bolt face when you fireform.I have found long seating the 117 gr round nose ideal,as it will jam into the rifling.You can usually get them cheap if you can find them.They will be in an old,dusty box.
A caution:If you have a rifle,such as a Mauser,with what is called a controlled round feed,with a long,claw extractor,you must push the cartridge down into the magazine so it can feed up under the extractor.Do not just drop a round in and force the bolt closed.You will crush back a fairly delicate headspace feature well before the extractor can be abused over the rim.
You should always feed these rifles up from the magazine anyway,but a friend of mine did not know that and he did it the wrong way.The case separated,as it was overly stretched.
I would agree it appears to be a Springfield.I really like them.Along with the history,I like the lines.
While they are a good,strong action,there is something to be aware of and check out.About 100 years ago when they started out making them,they had a few problems sorting the heat treating out.So,there are guidelines regarding the serial numbers of actions considered strong and safe,versus actions that had a bad heat treat and may be weak and brittle.These are called"low number Springfields"
I'll try doing a search here to find you a thread where this is discussed.
While they are a good,strong action,there is something to be aware of and check out.About 100 years ago when they started out making them,they had a few problems sorting the heat treating out.So,there are guidelines regarding the serial numbers of actions considered strong and safe,versus actions that had a bad heat treat and may be weak and brittle.These are called"low number Springfields"
I'll try doing a search here to find you a thread where this is discussed.