My latest Garand build is a 7.62mm Tipo2 Italian using a used surplus 23.5 inch Italian Tipo 2 7.62 NATO barrel on a Beretta receiver. This barrel is stamped SIAU 1967 with a PB drawing number over the chamber area. As with all of the other Tipo2 7.62 barrels that I have it is in excellent condition, gauging .301 at the muzzle and .302 in the throat.
After installing the barrel on these I like to set up the headspace by selectively fitting bolts until I find a bolt which will close on a .308 Win no-go gauge (1.634), but will not close on a .308 Win field gauge (1.638). Even though the minimum headspace will be 1.634, which is somewhat shorter than the 7.62 NATO go dimension of 1.6405, I'm satisfied that the rifle can shoot both commercial dimension .308 Win ammo with an adjustable gas plug installed and MILSPEC 7.62 NATO ammo as well as handloads with cases resized to the chamber.
After cleaning and drying the chamber I had to try 25 used or new Garand bolts of various makes until I found one that would close on the .308 Win go gauge (1.630). I next tried a 1.632 headspace gauge with this same bolt and found that it would not close on the gauge. That leaves me with a 1.630 or 1.631 dimension chamber which is quite remarkable considering that the barrel was theoretically chambered to 7.62 NATO go dimensions(1.6355) when it was first installed on a receiver at time of manufacture. After working with a lot of used .30-06 and 7.62 Garand barrels I've always been able to find a bolt that would work to set up the desired headspace with the headspace gauges w/o any need to finish ream the chamber.
Having established that the headspace is 1.630 or 1.631 I thought I'd trial chamber a variety of factory .308 and 7.62 NATO rounds, as well as some of my handloads made up on once fired DA64/66 7.62 brass that had been FL resized, just to see how they would run. This ammo included MILSPEC 7.62 NATO ammo incl Brit RG 82 and 87 ball, Cdn made DA64 and IVI69 ball and US issue LC71 match ammo as well as Rem .308 Win Core-Lokt , Federal 168gr match .308 Win ammo and WRA "white box" 147gr ball stamped 7.62NATO. The result was that the bolt would not fully close w/o resistance on any of this ammo, but it would close freely on my handloads which were made up with FL resized 7.62 brass. I next did a comparison of all of this ammo using a Wilson .308 Win case gauge and really couldn't see much difference between what was stamped .308Win and 7.62.
So what's the big deal and the caution? Most Garands which are fitted with .308 Win commercial barrels have their chambers cut to minimum .308 Win go dimensions (1.630), so they should be OK with commercial/SAAMI dimension .308 Win cartridge cases, right? Maybe yes, maybe no. As I just discovered, a 1.630/1.631 chamber would not freely accept samples of some commercial .308 Win or 7.62 NATO ammo which creates some possibility of an out of battery detonation as a result of the bolt not fully closing on a chambered case. With a semi-auto there may be some unspecified degree of "drive in" which bumps the case shoulder back somewhat on chambering and which could assist the bolt to close behind the chambered round before firing. OTOH, having a dirty chamber works against this as the chamber will become tighter as a result of accumulated powder fouling. This can be aggravated by firing 7.62NATO ammo, which is by specification longer than .308 Win ammo, in a minimum length chamber.
In view of the above I think that it is a good precaution to have a chamber in a .308 Win semi-auto chambered to 1.632 minimum just to handle dimensional variations in .308 Win ammo and to make some allowance for powder fouling in the chamber. If using the Clymer pull thru finishing reamer you can order a custom sized thrust bushing to use in connection with the reamer to achieve this dimension. I also think that it is a prudent precaution to establish just what the chamber dimension actually is before selecting either .308 Win or 7.62 NATO ammo for it. In the absence of headspace gauges a person can trial chamber ammo that they plan to shoot by using the stripped bolt and the rifle itself as a gauge. If the stripped bolt won't close freely behind the ammo using light finger pressure, I'd think twice about shooting it in the rifle. Whether handloading for either a .308 Win or 7.62 rifle, a shooter can FL resize cases to the extent necessary to permit free chambering, again using the rifle and the stripped bolt as a gauge to check resized brass. When I FL resize I set the die to the point where a case will chamber w/o resistance and then turn the die down another 1/4 turn and lock it. Tight fitting ammo isn't an issue in a bolt gun because the powerful camming action of the bolt will get the bolt closed, but a Garand or M14 type lacks this camming action and relies on the force of the op rod spring to get the bolt closed.
As far as getting myself some additional headspace in this rifle I'm going to pillage another .30-06 Garand that I know has a short West German made SuS bolt installed. If that works, I'll use another bolt in the .30-06 and finish ream the chamber to work with the new bolt. Trial fitting bolts in these 7.62s to get the right headspace is my only alternative as I don't have a 7.62 finishing reamer. A .308 Win finishing reamer wouldn't be a help in this case as I'm already at the .308 Win go dimension. I've never needed one with these used military 7.62 or .30-06 barrels before as they always set up fine by trial fitting different bolts in connection with the headspace gauges.
After installing the barrel on these I like to set up the headspace by selectively fitting bolts until I find a bolt which will close on a .308 Win no-go gauge (1.634), but will not close on a .308 Win field gauge (1.638). Even though the minimum headspace will be 1.634, which is somewhat shorter than the 7.62 NATO go dimension of 1.6405, I'm satisfied that the rifle can shoot both commercial dimension .308 Win ammo with an adjustable gas plug installed and MILSPEC 7.62 NATO ammo as well as handloads with cases resized to the chamber.
After cleaning and drying the chamber I had to try 25 used or new Garand bolts of various makes until I found one that would close on the .308 Win go gauge (1.630). I next tried a 1.632 headspace gauge with this same bolt and found that it would not close on the gauge. That leaves me with a 1.630 or 1.631 dimension chamber which is quite remarkable considering that the barrel was theoretically chambered to 7.62 NATO go dimensions(1.6355) when it was first installed on a receiver at time of manufacture. After working with a lot of used .30-06 and 7.62 Garand barrels I've always been able to find a bolt that would work to set up the desired headspace with the headspace gauges w/o any need to finish ream the chamber.
Having established that the headspace is 1.630 or 1.631 I thought I'd trial chamber a variety of factory .308 and 7.62 NATO rounds, as well as some of my handloads made up on once fired DA64/66 7.62 brass that had been FL resized, just to see how they would run. This ammo included MILSPEC 7.62 NATO ammo incl Brit RG 82 and 87 ball, Cdn made DA64 and IVI69 ball and US issue LC71 match ammo as well as Rem .308 Win Core-Lokt , Federal 168gr match .308 Win ammo and WRA "white box" 147gr ball stamped 7.62NATO. The result was that the bolt would not fully close w/o resistance on any of this ammo, but it would close freely on my handloads which were made up with FL resized 7.62 brass. I next did a comparison of all of this ammo using a Wilson .308 Win case gauge and really couldn't see much difference between what was stamped .308Win and 7.62.
So what's the big deal and the caution? Most Garands which are fitted with .308 Win commercial barrels have their chambers cut to minimum .308 Win go dimensions (1.630), so they should be OK with commercial/SAAMI dimension .308 Win cartridge cases, right? Maybe yes, maybe no. As I just discovered, a 1.630/1.631 chamber would not freely accept samples of some commercial .308 Win or 7.62 NATO ammo which creates some possibility of an out of battery detonation as a result of the bolt not fully closing on a chambered case. With a semi-auto there may be some unspecified degree of "drive in" which bumps the case shoulder back somewhat on chambering and which could assist the bolt to close behind the chambered round before firing. OTOH, having a dirty chamber works against this as the chamber will become tighter as a result of accumulated powder fouling. This can be aggravated by firing 7.62NATO ammo, which is by specification longer than .308 Win ammo, in a minimum length chamber.
In view of the above I think that it is a good precaution to have a chamber in a .308 Win semi-auto chambered to 1.632 minimum just to handle dimensional variations in .308 Win ammo and to make some allowance for powder fouling in the chamber. If using the Clymer pull thru finishing reamer you can order a custom sized thrust bushing to use in connection with the reamer to achieve this dimension. I also think that it is a prudent precaution to establish just what the chamber dimension actually is before selecting either .308 Win or 7.62 NATO ammo for it. In the absence of headspace gauges a person can trial chamber ammo that they plan to shoot by using the stripped bolt and the rifle itself as a gauge. If the stripped bolt won't close freely behind the ammo using light finger pressure, I'd think twice about shooting it in the rifle. Whether handloading for either a .308 Win or 7.62 rifle, a shooter can FL resize cases to the extent necessary to permit free chambering, again using the rifle and the stripped bolt as a gauge to check resized brass. When I FL resize I set the die to the point where a case will chamber w/o resistance and then turn the die down another 1/4 turn and lock it. Tight fitting ammo isn't an issue in a bolt gun because the powerful camming action of the bolt will get the bolt closed, but a Garand or M14 type lacks this camming action and relies on the force of the op rod spring to get the bolt closed.
As far as getting myself some additional headspace in this rifle I'm going to pillage another .30-06 Garand that I know has a short West German made SuS bolt installed. If that works, I'll use another bolt in the .30-06 and finish ream the chamber to work with the new bolt. Trial fitting bolts in these 7.62s to get the right headspace is my only alternative as I don't have a 7.62 finishing reamer. A .308 Win finishing reamer wouldn't be a help in this case as I'm already at the .308 Win go dimension. I've never needed one with these used military 7.62 or .30-06 barrels before as they always set up fine by trial fitting different bolts in connection with the headspace gauges.
