Ishapore 7.62mm 2A1 CHS

[Peter Laidler]

Don't say I don't try hard for you. The CHS for an Ishapore 2A1 is (They call it LOW) is GO 1.633" and HIGH or NO-GO is 1.642.

Now the observant of you will immediately see that this just about/almost/nearly/neatly inside the 7.62mm L1A1 limits of 1.6325 and 1.643". It's a bit higher that I would have expected from a bolt action rifle BUT, it is still the generally accepted .010" between go and no-go.

I don't know whether these gauges are in the current Armourers gauging sets (any idea Tankie, Son or Skippy.....?) but I'll have a look and see..........

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Thunderbox]

I bet that they just made that up in response to your enquiry.....

[barbarossa]

Peter, do you think the Indians did such a good job on headspacing the 2A barrel and bolt due to tighter manufacturing tolerances, that they managed to fit the same size bolthead to all rifles during series production? As I remember, I once measured the boltheads for about a dozen 2A rifles a dealer friend had in stock and there was not any significant variation in bolthead length in the entire lot. Is that possible?

Tu amigo

Mark Stamps

[Alan de Enfield]

Peter - refering to an old thread of yours - "Fred Blogs takes his datum point from one point and Fred Smith takes his from another datum point" - is this relevant to the figures you have been given ?

Can standard NATO gauges be used with confidence ?

[Peter Laidler]

What makes you say that Thunderbox, you old sceptic? I make an official enquiry via the usual channels and they answer............. On your basis, I could have simply ignored the answer and carried on spouting what I'd said before.

I don't know about Indian production at all. BUT, due to the fact that they made some of the rifles using bog standard old No1 bodies (which defeats the myth that they were made from higher quality steel - they weren't), it stands to reason that they'd use bog standard boltheads and bolts too. If they used different sizebolts and heads for the different calibres, then presumably, like any sensible person, they'd mark them, like we did with the 7.92mm/.303/7.62mm Bren bolts otherwise there would/could be a catastrophic failure.

On that basis, the chamber would be bored to a depth in relation to the breeching up geometry which ensured that when ithe barrel was breeched up, the distance from the datum line in the chamber to the face of the bolthead was between 1.633 and 1.642"

As for exactly which point in the neck that the Indian Engineers take their CHS datum from, well I can't answer due to the fact that I cannot calibrate an RFI set of CHS gauges against our own specification. BUT, at the risk of being wrong - as I was when I ventured to suggest originally that the CHS would be the same as the L39/42/96 etc etc, I'd say that it was the same datum as standard NATO.

I could calibrate your gauges (anyone else got the gauge calibration kit?) until the cows come home but unless we accept those figures, then you're in the dark. Don't get me going about AK47 CHS gauge limits either.................

---------- Post added at 11:56 AM ---------- Previous post was at 11:50 AM ----------

Further............... The GOOD news is that many of you who gauged your 2A1's up using the 1.635 NO-GO gauge and found it over size can now rest in peace because it MIGHT be in specification.

[Brian Dick]

I'll continue to fit bolt heads to 2A/2A1 rifles using the L39/L42 gauges because the tighter the better in my humble opinion. Many want to turn these rifles into their favorite shooters for some reason. Better safe than sorry as many are very tired and we know the 7.62 round is stressing them to the limit.

[GibbsNo7]

I have a 1968 2A1 from RFI that was imported and chopped by Gibbs into the 'Experimental Australian No.7 Jungle Carbine'. CHS concerns led me to get the rifle checked and it was determined that the head space was over a .308 Go by .010+ making my CHS 1.640+

The smith didn't have a set of NATO gauges and I can only hope he meant that + was a ten thousandth increment, however, I don't think he could have judged that by shimming a standard gauge. Am I correct in my skepticism?

However, If the + was indicative of + a few thousandths (instead of ten thousandths), that rifle, already bordering on NO Go for NATO, could easily approach Field dimensions and I'd be pretty concerned about shooting the rifle.

I've only shot about 60 rounds through it and will stick to NATO rounds (My initial concern was brought about by a hard extract on a steel cased .308. I've learned my lesson and will keep .308 and/or Steel away from my rifle) but would like to keep the rifle and enjoy it as much as possible.

So, my main question is should I mic the existing bolt head, order a larger one from Numrich, and have a gunsmith stone the face of the larger bolt face until the required CHS is met...Or, If I just plan on occasional shooting (less than 100 rounds/year) juts keep the CHS as is?

[Bruce_in_Oz]

I would be interested in any information that anyone has on Indian bolt heads for the 2A / 2A1 series.

To the best of my knowledge NOBODY made incremental bolt heads for SMLEs anywhere until Lithgow made a set in the early 1950s, just before the L1A1 came into service.
Viz:

Part Number Body length Size No.
B1/BAA 3425 0.635” 5
B1/BAA 3426 0.636” 6
B1/BAA 3427 0.637” 7
B1/BAA 3428 0.638” 8
B1/BAA 3429 0.639” 9
B1/BAA 3430 0.640” 0

The entire "engineering premise" of the SMLE involved incredibly stringent gauging at every stage of manufacture. Furthermore, and I believe this is critical, the method of arriving at he final chamber form included firing of "special" high pressure cartridges and a certain amount of careful reaming after the barrel was fitted to the receiver and bolt.

From SA 462

Chambered. first. - The chamber will be gauged with gauges smaller in diameter than the finished size, and the extractor way gauged for depth and position from flat; also the position of the key for slot for block, band, foresight, will be gauged.The bore will be examined and the barrel spun.

Sights, fitted. - The barrel will be submitted with the sight bed assembled, and the block, band, foresight, fitted. It will be examined for fit, and gauged for the position of block, band, foresight; bed, back sight; and sight axis pin hole; and size and depth of fixing screw hole, also for height of block, band, foresight, and figure of dovetail. The exterior will be gauged at the muzzle, radius, and breech end, also for the figure of the reinforce.

Proof. - The barrel will be submitted with the action attached for proof. The distance from end of bolt to face of barrel will be tested with a cartridge head gauge .067-inch. The proof will then be carried out with a proof cartridge, the charge being about 33 grains of No. 9 cordite, having a Service bullet of 215 grains, giving a mean pressure not below 24 tons per square inch, after which the action will be examined; and the barrel, body, bolt, and bolt head will be marked with the proof mark.

Browned and finished chambered. - The barrel will be examined for browning and bore (which should be burnished with wire gauze), and to see that the entrance to chamber is rounded, chiefly at bottom, The bore will be tested far straightness by being spun in the testing machine on a rod with two bearing points, one at the breech end and the other at the centre of the bore; the muzzle end will be allowed a total lateral movement of .006-inch. The chamber and bore will again be gauged. The bore must be parallel from end to end, and take a .303-inch or .304-inch plug, and reject a .305-inch plug; the receiving: plug, according to the diameter of the bore to run, The barrel will also be gauged for length.

Barrel with body (breeched up). - The barrel will be submitted for view assembled to the body, the latter being examined for browning and for polishing of the bullet lead. The barrel must be well bedded down into the body. The barrel will then be gripped in a breeching-up vice, and the position of the flat on the barrel gauged from the body. The breeching-up will be tested by means of a hand-operated spring wrench, which, when pulled to completely depress the spring, should not unscrew the body. A pull of about 30-lbs. applied 12-inches from the axis of the movable arm of the wrench being required to move it, and about 55-lbs. to completely compress the spring; the axis of the movable arm being 2,32-inches from the axis of the body. The position of the flat on the barrel will again be gauged, and the barrel and body spun.

What I gather from this is that the firing of the “special” proof cartridge was not just to see if it all held together, but to “pressure forge” the chamber to almost final dimensions: interesting technique indeed.

I don’t have the equivalent document for the No4, but I would hazard a guess that there were a few procedural differences.

[BubbaTheKid]

Posting here so I can refer this to a friend whom is buying an Ishi. Hope all are well.

Best,
BubbaTK

[arado]

I used my NATO head space gauges To set up a tight fit for my FAL target rifles. Never tried it on a turn bolt gun. It worked on the tilting bolt. gary