Early trials in Canada by the DCRA were done by modifying a .303 barrel to chamber the 7.62 with good results.  The following photos are of a January 1961 Canadian Marksman article written by Dave Reynolds of the DCRA that was in my Dad’s files.  Hopefully they are clear enough to read. 

Unfortunately, I’m not smart enough to know how to stitch these together as a single PDF file.  I’ll try to enlist the help of a more technically savvy member to do that for me. 

Thanks for the document! Interesting.

It’s also been shown that .308 bullets will shoot quite good when loaded into the .303 case.  So, not surprising it works quite well when re-chambering a .303 barrel to 7.62.

Agree, a better way is to find a 7.62 barrel for the No. 4, but good luck finding one. 

Yup, agreed. It just does not sit well with me. I'm usually a stickler for tight bores. Starting out with a .302 bore for a .30 cal round is just backwards to me. It may have worked well enough, but I don't like it. Lol!

All of my U.S. Military .30 cal rifles are well under .302, most under .301

Yes it does.  But there was a pretty compelling reason to do this.  The DCRA matches relied on government issue ammunition at the match.  That was to help keep cost to the shooters down and have a level playing field.   The stocks of .303 ammunition were on the decline by 1960 and new 7.62 No. 4 barrels were not yet available.  

Definately not unworkable just really time consuming,  and only ill-advised if you do not have the proper skill set to do it correctly.

 There is alot of fitting up and re-fitting up just to get the barrel indexed correctly which involves removing excess metal from the barrel that contacts the reciever. Once that is accomplished, the next step is to check the headspace using 7.62 headspace gauges and not 308W. This is the time consuming part. You will have to shorten the boltface by stoning it until the correct headspace is achieved and that take alot of patience.  A 2A1 magazine can be modified to fit into the No4 mag well but keep in mind that cartridge extraction is going to be hit or miss.

Moosm14, to add to Goosic's comment, it's actually very easy to re-index the 2A1 barrel if you have access to a lathe. The shoulder needs to be shortened by about 35 thousandths. It's pure pain if you only have hand tools... But trivial if you have a lathe. You may need to file the extractor cut a bit deeper to match the deeper chamber.

The headspacing part is also very easy if you have a chamber reamer. I've never finish-reamed/set headspace on a lathe, but you can readily rent a pull-through reamer (at least in the US) from reamerrentals.com or others. You cut the chamber deeper rather than grinding the bolt face down and re-heat-treating it.

A .308 Win headspace gauge should be fine. It's marginally shorter than a 7.62 NATO gauge. The 7.62 NATO leaves looser tolerances in the chamber to maximize reliability in military applications. Headspacing to .308 Win spec should leave a tighter chamber and improve potential accuracy.

Where you need to be careful is in the throat. The 7.62 NATO has a longer throat, which decreases chamber pressure vs. the .308 Win. If you use a .308 Win reamer, make sure you load very mild loads. If you use the 7.62 NATO reamer, you should be fine, but don't seat your bullets way out, or your throat will effectively be the same as if you'd reamed to .308 Win. specs.

Lawndart

You actually should never use 308 headspace gauges for a rifle chambered in 7.62x51mm.  There are specific reasons as to why this is ill-advised. Another point that needs to be addressed here is that you need to have whatever bolthead you will be using re-proofed to that particular calibers maximum chamber pressures. If not done accordingly, the potential for a catastrophic bolt failure is highly plausible.  When I did my conversions, I followed a very specific set of instructions. This is NOT a "Plug-N-Play" situation lawndart and headspacing is the most critical part of the conversion step. Use the correct NATO gauges ONLY! There is more to just cutting the shoulder back on the 2A1 barrel to get it to index correctly that many a first-timer gunsmith overlooks as well lawndart...

That "first-timer gunsmith" jab rubbed me the wrong way. By all mean, please tell me about those "specific reasons".

I may not know much about the Enfield, but I'm a mechanical engineer and an 07 FFL. I also spent a good amount of time working in my unit's armory while in the Army. I'm always eager to learn, but am certainly not a "first-timer gunsmith". I've headspaced dozens of rifles, and checked hundreds.

The difference in standard Go gauge dimensions between 7.62 NATO and .308 Win is 0.0055", or 5.5 thousandths of an inch. The armorer's Go gauge used for the L42 is actually 2 thousandths shorter than the .308 Win. The one for an FAL is a mere 2.5 thousandths longer. For reference, these variances are roughly what you'd get if you rotated your FL sizing die by 1/32nd of a turn.

The differences relate to fits, tolerances, and reliability, not pressures or safety. Yes, you may have a bit more trouble closing your bolt on a dirty, corroded, de-linked Indonesian 7.62 NATO cartridge if you chambered your rifle using a .308 Win Go gauge... But as long as you don't need the ability to blast bottom-shelf military ammo with 100% reliability, .308 Win headspace spec will give you a tighter chamber and higher accuracy potential. That's why the L42 is chambered to an even shorter headspace spec than .308 Win.

Keep in mind that I'm not talking about the throat. As I mentioned earlier, you need a 7.62 NATO chamber reamer with a properly-dimensioned throat to avoid running into pressure issues caused by the shorter throat/leade of the .308 Win.

Also keep in mind that I'm not talking about No-Go or Field gauges. Essentially, .308 Win No-Go and Field gauges tell you nothing when inserted into a 7.62 NATO chamber. But it's important to note that these gauges are simply QC checks in the context of finish-reaming a chamber. You'd be very hard-pressed to ream past a No-Go gauge if you're working carefully and checking often.

Now back to the subject of Enfields, where I don't know very much...

Were the bolt heads really any different, or were they simply re-proofed as part of the QC process? It would be good to know what proportion of them failed the re-proof, but I'd be very surprised if the vast majority of non-military conversions out there were not re-proofed to military standards. I expect that would only be a factor if you've taken a significant amount of material off your bolt face to set headspace rather than reaming your chamber deeper.

Lawndart

Got it, thanks. Sometimes things come across differently over a screen than over a beer.

I just want to make sure I don't come across as shade tree Bubba with a hack saw and a hand file!

Happy Friday!

Steve

If only my hands were steady enough...

Yes, this one is tricky!  

I checked both my DCRA conversions with .308 Win headspace gages.  The bolt closed on the GO gage and was a fair way off from closing on the NO GO gage. Based on this, and the article written by Dave Reynolds, I’ve come to the conclusion that the DCRA 7.62 conversions were set up to .308 chamber specs rather than 7.62.  Or, perhaps the Long Branch chamber specs for headspace just happened to be within .308 Win specs, I don’t know. 

I don’t see much of a downside to setting up a 7.62 barrel on a No. 4 using .308 Win headspace gages.  The worse that could happen is a 7.62 NATO cartridge made to the long end of tolerances may not chamber.  That cartridge should not be used.  Even with the tight chambers in my DCRA conversions, I’ve not experienced this problem with any of the Canadian surplus ball ammo I have shot. 

Now, the throat leade may be a different issue.  I’m not sure what the NATO specs are for the throat leade. 

Thanks for checking!

The leade is longer in a 7.62 NATO chamber. That's what keeps the pressure lower when using the same load in 7.62 NATO vs. .308 Win rifles.

Which NATO 7.62 headspace gauge are you referring to ?

There are actually 12 different sized NATO 7.62 headspace gauges that serve a variety of functions and different rifles from the L8 to the 'mini-gun' and this is why the (NATO) gauges are marked with the rifle model.

The Ishapore 2A1 (1.633"-1.642") is very close to L1A1 (1.625"-1.643"), which is not quite the same as the L42 (1.628"-1.635").

The other 'problem' is where the datum point is taken from on the 'tapering neck' - one manufacturer could take it from one position and another from another position - same gauge with different measurements, or quoting the same measurment but the guage is very different.

The military STANAG guages all have known datum points, but are the SAAMI gauges using the same datum points ?

All of these issues (differences in .308 vs 7.62) is exactly why I would rather load my own cartridges for my 7.62 Conversions.  That way I have control of the pressures I’m comfortable with.  I have shot a few hundred rounds of 1959/60/52 Canadian 7.62 Ball ammo, but only for some initial testing and to get the cases for reloading.  My loads with military brass are reduced, about 2 grains below minimum .308 Win published data. 

I have no idea about where the datum is (I just put the correct gauge in and it passed or failed).  I know from talking with Peter Laidler that some commercially made gauges that show (say) the same sizes as the STANAG gauges are nowhere near alike - they can only be using a different datum.

STANAG 7.62 gauges very rarely escape into the wild, I guess they are still 'on the books' and need to be accounted for.

The STANAG 7.62 gauges I have came from my dad. He was a Base Armourer between 67' & 69"

There was a trick used to index (align) FN-FAL barrels that might work.

get some Wet 'n Dry "sanding discs" in various grits & punch or cut out a hole that JUST clears the barrel threads.

Slip over the breech end (you decide which face you're sanding, for the FAL its the barrel shoulder) then tighten the barrel on the receiver front just enough top apply some pressure & rotate the disc. Usual recommendation was back & forth a few times about 1/3 turn  then 1/2 a turn & repeat. gently apply tension as the abrasive wears down.

Remove & check frequently.

It might work for a L-E because neither headspace by the standing breech but by the rear of the bolt locking.

My knowledge about NATO gauges pales in comparison to yours. My only point was that using a .308 Win Go gauge isn't going to cause any danger.

Thanks for that tip! I'm planning to have a friend with a lathe set the shoulder back for me. It does seem like a bear of a job to do manually.

Thanks. How hard was it to make a new extractor cut? Were you able to do it with a file?

I think I'll want to go the method of shortening the shoulder, because finish-reaming the chamber deeper should give me a tighter result. Not sure if it would matter if I'm just neck-sizing my brass, but it seems like a tighter chamber is rarely a bad thing for accuracy potential.

Once I have the 2A barrel and the .307 Win case, I will measure the gap between the front of the rim and the rear of the breech face of the barrel. If the  see if the gap is smaller than ~35 thou I'll have to take some 

Damn, that take a lot of skill... 

This is awesome, thanks. This picture also does a great job of showing how much lighter that 2A1 barrel is...

What did you modify with the Dremel and file? Did the extractor slot require modification after indexing the barrel? 

I assume you lathe turned the shoulder of the 7.62 barrel to clock the extractor slot the 180° required for the no4 receiver.

Apologies if this is a dumb question; but I don't get what the "down and drity trick" is!

I had one of those 45 ACP conversions for a while, but it was from the now-defunct Special Interest Arms.

I reached out to Rhineland though, and he told me he'd sell me barrel nuts if I go with a barrel nut rather than a shoulder.

I just reached out to Shaw Custom barrels to see if they'd do a Savage-style tenon but in 1" x 14 tpi Whitworth instead of the 1-1/16" x 20 tpi. If not, I can order it unthreaded and try to get that done locally. it doesn't seem like an overly exotic thread spec.

Lawndart

Could I run a tap through the receiver to convert the threads from Whitworth form to standard 60-degree V form?

Lawndart

Thanks, I'll post on some of the machining forums in the meantime. I bet there's some knowledge out there on thread forms.

The cheaper custom barrel makers I'm talking to aren't used to cutting other forms. I'd prefer to keep the original form if I could get that from a barrel maker that would turn a barrel for a reasonable price. Otherwise, I'm open to chasing the threads if that would work and give me options.

For example, I could do Shaw Custom for a hair under $200, or McGowen for a bit under $300.

Lawndart

Lawndart