L42a1

[tbonesmith]

Once the bulge was there, would barrel removal relieve the problem in the barrel? Ie would the chamber return to its unbulged state?

[broadarrow303]

Thanks Peter.

Really keen to see if anyone else with a L42 can check out the the number of grooves and type of rifling in their barrel. Please also state the date on both barrel (remove top wood to find) and the action. Many thanks in advance!!!.

Head space in my rifle is spot on-gauged it before firing and also the barrel through which a .297 gauge passes smoothly for the full length.
The rifle shot several groups of less than 1inch at 100m and about 2inches through the iron sights.

I also have quite a few questions regarding the upgrading of the No1 MkVI to service specs. I have a 1931 MkVI that has the serial number stamped out and replaced with a new number with an A suffix to indicate the parts are not interchangeable. I have found a No1 MkVI thread so will ask them on it.

Happy Christmas
Graeme

[jmoore]

Ensci will give a more exact scientific answer but we suspected that overtightened breeching up was the problem. Any 'bulge' was caused by the inability of the material to resume its natural state. The MAG (the Maintenance Advisory Groups) who worked with the RSAF took some chamber castings in alloy but even then they were tight to remove! I had/still have somewhere one of the bulged chamber sections that I machined down to make a simple calibration cup for the various 7.62mm CHS gauges

This scenario seems likely to me, for what it's worth. I've seen myself and have also seen in other write ups where overtightening has resulted in elastic and/or plastic deformation that cause localized bore enlargement. Specifically the "non-pinned" Smith and Wesson revolver barrels will bulge the bore at the point where the frame meets the barrel- often these are cured by removing a small amount off the barrel's crush face. So elastic in nature.

Another common bore bulge is caused by overtightening the AR15 flashhider/muzzle brake with the beveled "crush" washer. Unfortunately, these bulges are generally permanent!

Both will severely degrade accuracy more often than not.

It takes no major stretch of the imagination to apply the same notion to the chamber area of the L42a1. What's curious is that the rifles took a while to develop hard extraction. Possibly an instance where the incremental momentary increase in pressure at the moment of firing was enough to cause a small amount of plastic deformation? A tiny annular jackhammer effect that only exceeded the elastic limit at the already stressed barrel/body junction?

That's not really clear, is it?.... Where's the sketch pad function?

[Peter Laidler]

Do you have the CHS gauges for the L42 Broadarrow? 1.628 to 1.635 if I remember correctly..........

You have probably hit the nail on the head JM regarding the hard extraction. I'll look for my bulged chamber section and see if I can't get it photographed internally somehow. But it'd be interesting to hear if anyone else has a rifle that exhibits this hard extraction trait. Although we'd scrap them on site initially, later they were returned to Ordnance for destruction and disposal. Some of those will have been sold off because I know of one L42 that exceeded the CHS limit by almost .012" eventually that was returned to Ord, complete with the ZF marks, that later emerged onto the civilian market. This was a case where the hardened locking shoulders had totally broken down

[broadarrow303]

Hi Peter


The No Go gauge is marked MA L7 1.6380 and the bolt will not even look like closing on it. The Go gauge is marked L154. It measures out at 1.628. The bolt closes on it so that the bolt handle is perpendicular (flat) compared to the up right line of the rifle action and body.

Cheers
Graeme

[nzl1a1collector]

Hi Peter


The No Go gauge is marked MA L7 1.6380 and the bolt will not even look like closing on it. The Go gauge is marked L154. It measures out at 1.628. The bolt closes on it so that the bolt handle is perpendicular (flat) compared to the up right line of the rifle action and body.

Cheers
Graeme

The headspacing gauges you have were made by SAF Lithgow.

I'm curious as to why you think the barrel has "chordal rifling", what is it about the barrel or markings that makes you think this?

[Peter Laidler]

Just a qouple of niggling questions.......... The 1.638 gauge is for the GPMG, to cater for the fact that the barrels get xxxxing hot and expands somewhat in service. How do you know that the gauge marked L154 equates to 1.628" unless you have the calibration kit to measure it? Youi need a special calibration cup to measure rimless CHS gauges

All I can reiterate is that the CHS spec for an L42 rifle is 1.,628 GO and 1.635 NO-GO. Get these gauges and you can go from there. But if the bolt won't close over the supposed 1.628" GO gauge, it means that either the rifle or the gauge is wrong. Of that you can be sure.

You can send it to me to calibrate, but if you have already done it or worse still '....my mate said it was OK ..........................'

[broadarrow303]

Rod W has had a very close look at this rifle and Ian S has seen the photos. It comes out of a well established Invercargill collection. The now deceased owner and Peter L shared information. Peter probably knows this rifle.
None of us ( the 3 previously mentioned )has any information at this point in time indicating that 74 dated barrel and 74 dated action were produced in chordal rifling. The rifling in this rifle is rounded and we are confident it is chordal - refer attached photos. The barrel is also stepped as per the 1980/81 dated chordal barrels mentiond by several other writers. The interesting aspect is that this barrel is 6 not 4 grooved.

Help needed.
Has anyone seen a chordal barrelled L42 and if so what are the dates on the barrel and action and how many grooves does it have?


More importantly- what makes you think it is not chordal rifled? We would be very pleased to find out.

[nzl1a1collector]

I would say your L42 rifle doesn't have Chordal Rifling, and here's why.

A limited number of L1A1 rifle barrels were made c1975 with RSAF designed Chordal Rifling, each barrel was marked to indicate it was one of these special barrels because the rifling is so radically different.

According to SM&MG D119 Misc Instr No. 30, dated Dec 1975;
...The Chordal rifle barrels are identified by the letters 'CB' engraved on the reinforce that provides location for the sling swivel and this marking can be seen without the need to remove the handguard... .

This tells me that if any other weapons were fitted with barrels with Chordal Rifling then they too would be marked in the same way as indicated for L1A1 barrels with 'CB' engraved in a place that would be visible without having to remove anything from the rifle. Does your rifle have 'CB' engraved on a visible place on the barrel?

BUT the biggest give away that your rifle doesn't have Chordal Rifling, is that your rifling doesn't match the diagram below which clearly shows the vast difference between Standard Rifling and Chrodal Rifling.

[/IMG]

[Thunderbox]

I would say your L42 rifle doesn't have Chordal Rifling, and here's why.

A limited number of L1A1 rifle barrels were made c1975 with RSAF designed Chordal Rifling, each barrel was marked to indicate it was one of these special barrels because the rifling is so radically different.

According to SM&MG D119 Misc Instr No. 30, dated Dec 1975;
...The Chordal rifle barrels are identified by the letters 'CB' engraved on the reinforce that provides location for the sling swivel and this marking can be seen without the need to remove the handguard... .

This tells me that if any other weapons were fitted with barrels with Chordal Rifling then they too would be marked in the same way as indicated for L1A1 barrels with 'CB' engraved in a place that would be visible without having to remove anything from the rifle. Does your rifle have 'CB' engraved on a visible place on the barrel?

BUT the biggest give away that your rifle doesn't have Chordal Rifling, is that your rifling doesn't match the diagram below which clearly shows the vast difference between Standard Rifling and Chrodal Rifling.

http://<a href="http://i129.photobuc...ifling.jpg</a>

I think we have to define what we mean by "chordal". On the one hand, it refers to a specific pattern of rifling in your "CB" labelled L1A1 barrels, on the other it is a generic term for rifling that can be drawn/described as a series of arcs or chords.

The smooth-skinned "stepped" Enforcer barrels used on some L42A1s do have a form of "chordal" rifling, in that the rifling consists of curved sections raised from a cylindrical bore - ie the rifling does not have the sharp edges of "standard" rifling. The Enforcer barrels differ from the hammered "snakeskin" Enfield barrels in this respect. As the "grooves" appear to be the cylindrical bore itself, I guess Enforcer barrels could be described as "half Chordal"?

I suppose an example of true chordal rifling would be Metford rifling - ie where the land and grooves are both curved and derived from certain radii.