Chilean 1912-61 7.62 has a tight chamber ? Advice

K

Keithjohn

CGN frequent flyer
Rating - 100%
117   0   0
Location
Alberta
I have just purchased a Chilean 7.62 converted rifle . It will not chamber commercial 308 Ammo , I tried a few different brands . I made some undersized brass and found it would chamber some and not others . Investigating further I found the necks were shorter on the ones that chambered. SO I made some more and trimmed brass to 2.00 instead of 2.015 and found they fit so I loaded 20 and fired 8 . The cases only grew 2-3 thou fire forming and the gun is accurate.
And 3 or 4 of the 20 were slightly tight when closing the bolt , I can't see what is different in them so far as I can measure . I fired two of them and no pressure signs noticed.

Is there any advice on this out there ? I'm thinking of getting the chamber touched up but will that help with the short neck ? Is there anything else I should be able to check ? Could the chamber be out of round compared to my dies with a short neck ?
 
You also have to remember most of these would have just been rebarreled and thrown in storage. By 1961 bolt actions though still in some usage, were mostly out of service with the vast majority of nations. Rebarreling them to the new standard cartridge was a way to keep rifles you already have serviceable in the event you might have another war (otherwise you would have two or more different cartridges you would have to produce and stockpile). It wouldn't be the most modern weapon, however it would be a weapon (and for the older men something they had already trained on and knew how to use). Many different nations did this, West Germany, Israel, many different South American nations, Spain, and many tried (look up things like the L8 Lee Enfields for example).

People sometimes screw up, and in this case it could have simply been accidentally turned down too much in the manufacturing process (I believe those barrels were originally excess .30-06 Springfield barrels turned down to .308 length). It seems you already have found a makeshift solution, or if you wanted as mentioned above you could get a gunsmith to ream a couple thou off.
 
Leave it alone. I am willing to bet that chamber is very close to or slightly under minimum spec. The one I have is chambered similarly and I like it. I size my brass with Bonanza small base match dies and like you shorten the necks as needed. The brass lasts a long time when it gets reannealed after four or five shots. I use Lapua brass in this rifle because it can utilize the quality. IMHO these rifles with slightly short/tight chambers are diamonds in the rough for those that know what is happening and how to utilize them.

I find the throat on mine to be fairly long which is good because I can seat the bullets out further. Mine prefers 150-165 grain flat base bullets and has an excellent bore. It doesn't seem to shoot heavier bullets as well. It has a strange 1-11 twist rate as well and the bore measures out at .3075.

I like it because the front sight is way out there at 29in and I can make out both sights with my aging eyes. Same goes for the 1912 Chilean 7x57. For us geezers that long sight radius is a god send.

I got mine several years ago when they first came into Canada. Seemed pricey at the time and when I tried loading some surplus Hirtenberger into it I ran into exactly the same issue as the OPs. Thankfully it was an easy fix as far as I'm concerned. I always wondered if mine was a one off, now I know better. I will admit I do wonder how they got out of the FTR depot or shop with such close or under spec tolerances.

Anyway as mentioned it's an easy fix for most smiths with a 308 chamber reamer. You may want to have it done with a Palma Match reamer though.

You should develop a load for it and take it to the milsurp shoots if they will allow the use of handloads. Many clubs will only allow factory or surplus ammo to keep things on a level playing field.
 
Thanks bearhunter, it's nice to know it's not really a one of a kind . The more I shoot this gun the more I like it and I think I will leave it alone. Any comments out there on 2 groove barrels ? I know they were easier to clean and we're supposed to be just as accurate to ranges that are shot with open sights but my question is about the appearance of the rifling , it seems shallow to what I'm used to seeing especially on a barrel that would appear to be unused since it was converted
 
These were rebarreled with surplus M1903A3 Springfield barrels which were shortened at the breech end and then rechambered to 7.62. The majority of 03A3 barrels were made with 2 grooves vs the usual 4 grooves. Military testing determined that there was no practical difference in accuracy between a 2 and 4 groove barrels which lead to 2 groove barrels being adopted for the 03A3 as a manufacturing expedient. The same thought process applied to the No4 Lee-Enfield which lead to 2 groove barrels being adopted in the interests of higher production.

My experiences with 2 groove barrels in both 03A3 Springfields and No4 Lee Enfields is that accuracy is about on par with the standard 4 and 5 groove barrels. You could check on the degree of erosion of the rifling by running a tapered plug gauge in the muzzle end. New 03A3 barrels run at at the nominal .300 bore diameter, but muzzles can be eroded by heavy use and/or by improper use of a cleaning rod when cleaning from the muzzle end. I've seen used 03A3 and M1903 barrels run up to .303 diameter at the muzzle. This is why you sometimes see counterboring in the muzzles of used military rifles. Accuracy in an otherwise serviceable barrel can also be impacted by the condition of the crown as gouges and puckers will result in flyers.
 
Purple is telling it straight.

The rifling on the 03A3 barrels is a bit shallower than on No4 MkI barrels. I have surmised that this has something to do with alleviating pressures. I could be wrong though and it may just be a cost cutting measure. I would think the No4 barrels were done so because of the designers concerns.

The one thing that makes this sort of rifling different is that there is much more bearing surface for the bullet to overcome and it raises pressures. Modern barrel makers use all sorts of rifling designs anywhere from the original Marlin "Micro Groove" style to the very thin Shilen and Hart style with six grooves. They all work and they all have their advantages.

One other thing, I have never seen a "shot out" 2 groove bore. I have seen damaged 2 groove bores as Purple suggests.

You got me going on this so I went back and checked the twist rate in my rifle. It is one in ten. My recording book show one to eleven. Must have been a loose patch???
 
If it's 2 groove it's a 03-a3 surplus barrel. If it's a long rifle with multi-groove rifling, it could also be a chamber insert.
 
Most 2 groove 03A3 barrels are made by Remington and are stamped "RA over month-year" behind the front sight. 2 groove barrels made by Smith-Corona are stamped "SC over month-year" in the same area.
 
If it's a 2 groove barrel it is a M1903A3 Springfield barrel made by either Remington or Smith-Corona. M1903 Springfield barrels have 4 grooves and were made by all of Springfield Armory, Rock island Arsenal, Remington, Avis, Sedgley and High Standard. To complicate the issue a bit more Remington also produced 4 groove 03A3 barrels as did Smith-Corona.

The 03A3 is a simplified version of the M1903 which was adopted to speed up wartime production. The use of 2 groove barrels, stamped vs milled components, and the use of a receiver mounted aperture sight were the major changes from the M1903.
 
So mine is a 2 groove barrel with unusual stamping ? I'm confused about this but I sure like this gun , shot it again today with a load with 180 grain bullets . I'm trying to see if I can make a load that will match the sights calibration. I have only got out to 200 yards so far . I need more practice with this old girl
 
You must log in or register to reply here.
Back
Top Bottom