Split Casings - Norc 7.62x51 steel cased in M305 Shorty
- Thread starter dflight
- Start date
yes i notice this after the first shot,it's rechambered to 7.62 NATO. headspace , over-sized chamber or .308 ammo problem maybe?
im no expert here but im sure a headspace/chamber guru will chime in!
but I would say an over sized chamber it looks to be pretty consistent all the way through the casing?
RememberTheSomme
CGN Ultra frequent flyer
- Location
- Nova Scotia
Dieseldawg, the chambers are very generous in the forward body and neck. Mine has 700 rounds of Norinco 762 without one split, so I guess mine is small enough to keep the steel together but just barely. The ammo year is 95, the lot number is unknown.
The unfired rounds are well in SAAMI case dimensions but the fired case is over SAAMI "308Win chamber" dimension max by a fair bit in the forward body and neck diameters only, and this after it has already shrunk back some from firing telling me the chamber is actually a little bigger than this. A chamber cast would show the dimensions I have no cerrosafe.
This appears to be as much not a steel case ammo problem as much as it's a generous neck portion diameter cut into the chamber. I can't find the drawings for the 762NATO chamber dimensions criteria, I'm guessing close to 308Win as far as body is concerned. Can someone find the max neck diameter for a NATO chamber as well as the body diameter at the neck, so we can compare it to the diameter of our fired rounds in this location. Remember we need the chamber dimensions not the loaded round max dimensions many people mix these up.
Lufa.ca for your own reference if you do not have a set of calipers, just stick a new Nork round into the end of a fired un-split case and see the clearance. This looseness would never be there in a .308Win spec chamber.
The unfired rounds are well in SAAMI case dimensions but the fired case is over SAAMI "308Win chamber" dimension max by a fair bit in the forward body and neck diameters only, and this after it has already shrunk back some from firing telling me the chamber is actually a little bigger than this. A chamber cast would show the dimensions I have no cerrosafe.
This appears to be as much not a steel case ammo problem as much as it's a generous neck portion diameter cut into the chamber. I can't find the drawings for the 762NATO chamber dimensions criteria, I'm guessing close to 308Win as far as body is concerned. Can someone find the max neck diameter for a NATO chamber as well as the body diameter at the neck, so we can compare it to the diameter of our fired rounds in this location. Remember we need the chamber dimensions not the loaded round max dimensions many people mix these up.
Lufa.ca for your own reference if you do not have a set of calipers, just stick a new Nork round into the end of a fired un-split case and see the clearance. This looseness would never be there in a .308Win spec chamber.
RememberTheSomme
CGN Ultra frequent flyer
- Location
- Nova Scotia
Just threw some numbers together to compare SAAMI .308Winchester cartridge and chamber drawing dimensions against un-fired Norinco 762 and American Ego
147FMJBT ammunition in my possesion,.. and also to fired Norinco 762 steel cases from my M-14S.
I'll have to allow for a .001" error here, I'm using my old calipers and I need readers and a magnifier to see scale
.
Cartridge Body OD" immediately before shoulder................................................. Neck OD" at shoulder:
SAAMI Chamber .4551" .............................................................................................3462"
SAAMI Cartridge .454".................................................................................................3435"
Norinco Cartridge .452".................................................................................................3331"
AE Cartridge .452"................................................................................................339"
Norinco Fired ..460".................................................................................................349-.351"
Both Nork and AE rounds were similar in case length overall. You can see the Nork round starts out a .333" OD neck versus .339"OD neck on the AE, a full .006" smaller. On firing in my chamber, the Nork OD neck is now .460". It grew by .021" . This dimension is .0049" or 4.9thousanths of an inch over SAAMI .308Win max chamber size at this part of the body.
My chamber is at least 4.9thousandths of an inch(.0049") over SAAMI .308Win. This will allow for an easy extraction of dirty cases from a dirty hot chamber.
This 95 year manufacture ammo I've put through at hundreds of rounds from 20 round green boxes,.. is clean, accurate and runs with no hiccups. No splits, ..no primer pierces as in S&B, ..no extra fouling and erratic low-end velocity as in MFS 145FMJ and the list goes on. It chrony's at 2804fps aveage in my 22" M-14. Bang on NATO spec, you'd think LC loaded it.
Guys that have splitting necks regularly would be nice to know the year and lot#s and the cases that are not failed, measured at the two dimensions given here forward body and neck.
To the OP I apologize in rushing through his post and not seeing that the cases were split in three different rifles
. You said one was chambered to 762NATO though.
These cases are very thin at the mouth, I guess partly because they are steel over brass, and just look at the OD on the Nork before firing compared to AE. It's .006" smaller. I guess that cheap case steel can't make the nearly .030" diameter expansion(that's almost .100" in circumference stretch [.030"X3.1416]) and survive. This 10% circumference growth should be survivable if the steel was good quality mild steel like 300W that should be able elongate at least 20-24% or higher IIRC.
762NATO chamber dimensions would be nice here to see if the case growth to .460" is within 762NATO tolerances if in fact they are different from .308Win at all.
,........I said all that to say this........
Rock on Norinco 762 match chamber and ammo,... putting rounds into the wind Gangnam Style while you earn frequent flyer points at a range near you!
147FMJBT ammunition in my possesion,.. and also to fired Norinco 762 steel cases from my M-14S.I'll have to allow for a .001" error here, I'm using my old calipers and I need readers and a magnifier to see scale
.Cartridge Body OD" immediately before shoulder................................................. Neck OD" at shoulder:
SAAMI Chamber .4551" .............................................................................................3462"
SAAMI Cartridge .454".................................................................................................3435"
Norinco Cartridge .452".................................................................................................3331"
AE Cartridge .452"................................................................................................339"
Norinco Fired ..460".................................................................................................349-.351"
Both Nork and AE rounds were similar in case length overall. You can see the Nork round starts out a .333" OD neck versus .339"OD neck on the AE, a full .006" smaller. On firing in my chamber, the Nork OD neck is now .460". It grew by .021" . This dimension is .0049" or 4.9thousanths of an inch over SAAMI .308Win max chamber size at this part of the body.
My chamber is at least 4.9thousandths of an inch(.0049") over SAAMI .308Win. This will allow for an easy extraction of dirty cases from a dirty hot chamber.
This 95 year manufacture ammo I've put through at hundreds of rounds from 20 round green boxes,.. is clean, accurate and runs with no hiccups. No splits, ..no primer pierces as in S&B, ..no extra fouling and erratic low-end velocity as in MFS 145FMJ and the list goes on. It chrony's at 2804fps aveage in my 22" M-14. Bang on NATO spec, you'd think LC loaded it.
Guys that have splitting necks regularly would be nice to know the year and lot#s and the cases that are not failed, measured at the two dimensions given here forward body and neck.
To the OP I apologize in rushing through his post and not seeing that the cases were split in three different rifles
. You said one was chambered to 762NATO though. These cases are very thin at the mouth, I guess partly because they are steel over brass, and just look at the OD on the Nork before firing compared to AE. It's .006" smaller. I guess that cheap case steel can't make the nearly .030" diameter expansion(that's almost .100" in circumference stretch [.030"X3.1416]) and survive. This 10% circumference growth should be survivable if the steel was good quality mild steel like 300W that should be able elongate at least 20-24% or higher IIRC.
762NATO chamber dimensions would be nice here to see if the case growth to .460" is within 762NATO tolerances if in fact they are different from .308Win at all.
,........I said all that to say this........
Rock on Norinco 762 match chamber and ammo
,... putting rounds into the wind Gangnam Style while you earn frequent flyer points at a range near you!
BattleRife
CGN Ultra frequent flyer
- Location
- of No Fixed Address
What a ridiculous assertion. No metal fails by cracking under normal conditions, unless by "a lot of pressure" you mean pressure that exceeds the materials strength, so that you get stress cracks. Otherwise, cracking is the result of metallurgical flaws, environmentally assisted mechanisms or fatigue.
