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223 trimmed case length
- Thread starter Lilswede1
- Start date
cw308,
I have no certain knowledge of what prompted the change. Other cartridges have not. I can speculate that so many cases are manufactured on contract overseas where they may use different numbers, that there may have been cost problems with tooling changes needed to keep the tighter old tolerance. If you look at the CIP drawing for the case, they have tolerances (about -0.008") for the positions of the two ends of the shoulder (junctures with the body and neck¹), but they give no tolerance for case length except in cartridges that headspace on the case mouth (rimless pistol cartridges). So, it may be understood under their standard that the case length given is a maximum, as it is here, and the manufacturers have some leeway on how much shorter it may be. For that reason, some .223 Rem manufactured in CIP countries could be shorter than the old SAAMI standard allowed. If a U.S. maker then goes to one of these manufacturers for a contract purchase, the headstamp die will be changed to the customer's spec, but it is likely cost prohibitive to require changing the cutting and length inspection system for the .223 Rem they already make just to comply with the last 0.010" of length.
RC20 is correct that this is in no way a critical dimension. When the M14/M1A platforms ruled the roost in service rifle matches, it was common knowledge the hard Lake City brass was only good for about 4 reloadings in those weapons before the threat of head separation became serious enough that the brass had to be scrapped. Knowing it grew an average of about 0.010" per loading cycle, many competitors would trim their once-fired brass down 0.040" below maximum trim length so they would only have to fuss with trimming once in the life of each case. Instead of the nominal trim length of 2.005" for that cartridge, they would go for 1.975". Most serious competitors reloading volume back then used the Gracey power trimmer to get the heavy trimming over with. And these were match shooters, so if the extra trimming impacted accuracy very much, they would not have been doing it.
¹ The CIP standard doesn't use a shoulder datum for a basic dimension, as the SAAMI standard does. Rather, they have a basic dimension value, S, from head to shoulder angle origin (apex) that SAAMI does not use.
I have no certain knowledge of what prompted the change. Other cartridges have not. I can speculate that so many cases are manufactured on contract overseas where they may use different numbers, that there may have been cost problems with tooling changes needed to keep the tighter old tolerance. If you look at the CIP drawing for the case, they have tolerances (about -0.008") for the positions of the two ends of the shoulder (junctures with the body and neck¹), but they give no tolerance for case length except in cartridges that headspace on the case mouth (rimless pistol cartridges). So, it may be understood under their standard that the case length given is a maximum, as it is here, and the manufacturers have some leeway on how much shorter it may be. For that reason, some .223 Rem manufactured in CIP countries could be shorter than the old SAAMI standard allowed. If a U.S. maker then goes to one of these manufacturers for a contract purchase, the headstamp die will be changed to the customer's spec, but it is likely cost prohibitive to require changing the cutting and length inspection system for the .223 Rem they already make just to comply with the last 0.010" of length.
RC20 is correct that this is in no way a critical dimension. When the M14/M1A platforms ruled the roost in service rifle matches, it was common knowledge the hard Lake City brass was only good for about 4 reloadings in those weapons before the threat of head separation became serious enough that the brass had to be scrapped. Knowing it grew an average of about 0.010" per loading cycle, many competitors would trim their once-fired brass down 0.040" below maximum trim length so they would only have to fuss with trimming once in the life of each case. Instead of the nominal trim length of 2.005" for that cartridge, they would go for 1.975". Most serious competitors reloading volume back then used the Gracey power trimmer to get the heavy trimming over with. And these were match shooters, so if the extra trimming impacted accuracy very much, they would not have been doing it.
¹ The CIP standard doesn't use a shoulder datum for a basic dimension, as the SAAMI standard does. Rather, they have a basic dimension value, S, from head to shoulder angle origin (apex) that SAAMI does not use.
Mr.G
You sure have a tendency to make me stare aimlessly at a wall.
For the short response "Thank you", and then there is the long response "Thank you very much".
I have forming die, forming dies are also listed as trim dies with the same stock number. My forming dies can be verified, I can measure the length of the forming die and then add .125" to the length of the die from top to bottom to get the correct trim to length of the case.
If I am forming cases for long chambers I can adjust the forming die off of the shell holder with a feeler gage when I want to add to the length of the case from the datum/shoulder to the case head.
After that it gets real complicated when I use a short forming die. I have adjusted my 308 W short forming die ..388"" off the shell holder when forming cases I do not have a forming die for.
F. Guffey
Unclenick
Thank you for answering my question , I trim every firing , its no big deal for me I shoot 30 rounds of 308 each range trip . My trim length is .005 shorter them max. Every little is shaved off each time.
Mr G
I always like reading your posts , Your background in technical stuff is deeper then most , for a middle of the roader like me , its a little over the top , no disrespect. I always like hearing from you..
Thank you for answering my question , I trim every firing , its no big deal for me I shoot 30 rounds of 308 each range trip . My trim length is .005 shorter them max. Every little is shaved off each time.
Mr G
I always like reading your posts , Your background in technical stuff is deeper then most , for a middle of the roader like me , its a little over the top , no disrespect. I always like hearing from you..