What to do about headspace after #4 bolthead?

[Sunray]

Rumour has it that the DCRA target rifles had some #4 bol theads made prior to changing to 7.62NATO in the mid to late 50's. A #4 bolt head is not a standard bolt head.
In any case, like John says, if the headspace is ok, don't worry about it. However, if the bolt is closing on a No-Go, but not a Field, the headspace is on the high end of tolerance. Still not going to be an issue, but if it goes bad, the barrel will have to be removed and the threads set back by a smithy.

[Son]

Rumour has it that the DCRA target rifles had some #4 bol theads made prior to changing to 7.62NATO in the mid to late 50's. A #4 bolt head is not a standard bolt head.
In any case, like John says, if the headspace is ok, don't worry about it. However, if the bolt is closing on a No-Go, but not a Field, the headspace is on the high end of tolerance. Still not going to be an issue, but if it goes bad, the barrel will have to be removed and the threads set back by a smithy.

Setting the barrel back won't do anything, I'm afraid. The back of the barrel would still be in the same place. The problem is at the rear of the action. As Peter stated here earlier, and on the old board, it was judged by the MOD that by the time a No4 rifle requires a bolthead in excess of the No3, the hardened contact surfaces of the locking lugs on the bolt and receiver would likely be worn beyond servicability. This sentenced the rifle XX/BR = SCRAP!

Lets face it, do you keep repairing punctures in a tyre with no tread on it?

[louthepou]

Lets face it, do you keep repairing punctures in a tyre with no tread on it?

I really like that analogy.

Thanks for this great thread folks, it's quite an interesting read.

Learnin' Lou

[Edward Horton]

If the existing bolt and a special test bolt head that is 0.640 long fails the .074 gauge a new bolt would be fitted.

When a new bolt and the test bolt head (.640) fails the .074 gauge test the rifle is sent for FTR, FR, overhaul, I do not know if the old receiver could be repaired or if it would be worth the cost of repair.

[Edward Horton]

Headspace FYI





Sometimes the term “headspace” is meaningless

[Jim K]

The 7.62 NATO is larger at the shoulder than the .30 is at the same point, so the shorter cartridge wedges into the chamber. I don't recommend firing any gun with the wrong ammo, but I once fired two clips of 7.62 NATO through a .30 M1 rifle just to show it could be done with no problems. The case is supported, but not the way it should be, on the shoulder.

Because of the shoulder, the 7.62 round is usually difficult to chamber, and nearly impossible in a bolt action rifle, but the M1 operating spring takes care of that nicely.

And all of that proves nothing about headspace so far as wear on the rifle goes. If the case could back up, it would, and could still stretch and still burst if headspace were really excessive. Gen. Hatcher reamed the chamber of a M1917 way out, and fired a .30 round, giving much the same result. He then fell into the same trap (very unusual for that gentleman) of confusing headspace with excess chamber length. Not the same thing.

Jim

[Jim K]

Hi, Mr. Horton,

Exactly, that case was way outside the chamber when it burst, and the rifle had shown no signs of excess headspace. The cartridge was 7.7 SMI, dimensionally identical to the .303, for their heavy machinegun, and worse, had been sitting in the hot sun. I have no idea what the pressure was, but it must have been humongous.

There was no hangfire and the bolt was closed. In fact, the bolt head was broken and the extractor missing; the bolt had to be hammered open. (No anti-matter, either but then I might not have noticed.)

The rifle had been fired many rounds before that with British .303 with no problem, in fact I had fired several magazines from it, but was not shooting it at the time of the incident. Afterward, the rifle was checked and showed slightly excess headspace, but was fired with the British ammo (from a tie-down rest - the front stock was destroyed), again with no problems. That receiver sprung under pressure enough to let the cartridge back out, then sprung back. Yes, it sounds hard to believe, but it did happen, and I have been told that it is not unknown when someone loads the wrong powder or tries to make a .303 Super Magnum.

The owner decided to scrap the rifle because no one knew what damage the receiver had sustained.

Jim

P.S. That SMI ammo was sold as .303 British in a blue box containing 100 rounds. If you encounter any of it, I STRONGLY recommend not shooting it in a No.1 rifle. I eventually fired the other 99 in a P-14 and a Ross M10. Even with those strong rifles, high pressure was obvious, but without the sunshine and heat, not dangerous.

JK

[Son]

Hi, Mr. Horton,

Exactly, that case was way outside the chamber when it burst, and the rifle had shown no signs of excess headspace. The cartridge was 7.7 SMI, dimensionally identical to the .303, for their heavy machinegun, and worse, had been sitting in the hot sun. I have no idea what the pressure was, but it must have been humongous.

There was no hangfire and the bolt was closed. In fact, the bolt head was broken and the extractor missing; the bolt had to be hammered open. (No anti-matter, either but then I might not have noticed.)

The rifle had been fired many rounds before that with British .303 with no problem, in fact I had fired several magazines from it, but was not shooting it at the time of the incident. Afterward, the rifle was checked and showed slightly excess headspace, but was fired with the British ammo (from a tie-down rest - the front stock was destroyed), again with no problems. That receiver sprung under pressure enough to let the cartridge back out, then sprung back. Yes, it sounds hard to believe, but it did happen, and I have been told that it is not unknown when someone loads the wrong powder or tries to make a .303 Super Magnum.

The owner decided to scrap the rifle because no one knew what damage the receiver had sustained.

Jim

P.S. That SMI ammo was sold as .303 British in a blue box containing 100 rounds. If you encounter any of it, I STRONGLY recommend not shooting it in a No.1 rifle. I eventually fired the other 99 in a P-14 and a Ross M10. Even with those strong rifles, high pressure was obvious, but without the sunshine and heat, not dangerous.

JK

Ok, could you please make something a little clearer for me here... If the bolthead was closed, the action sprung back enough to let the case out so it blew the side out, then it closed again, how did that case get back into the chamber? There's no way that would fit- The torn flap around the base doesn't even look like it was forced against the chamber, so the bolt must have been back about half an inch and still locked as you said you needed to hammer it open. Also, how could you check the headspace after the incident and compare it to the measurement from before? You said the bolthead was broken, so to fire it, a different bolthead must have been fitted. Wouldn't that most likely change the headspace?
I just had a closer look at the base of the cartridge. Even from this angle, you can see that the primer still has it's rounded edges- the first sign of overpressure is the flatening out of the primer into the recess left by the radiused edge. No such indicator here. This tells me it definately was outside the chamber before it went off.

Having trouble getting my head around this one...
I'll go with Mr Horton's hangfire theory- you said you were not firing the rifle at the time, maybe the bloke that was needed something else to blame other than his impatience for wrecking a good rifle.

Here's the pic of that case again... save going back to look at it.

[Thunderbox]

SMI made normal .303 ball & tracer with a nitro fill - they didn't make any exotic high pressure loads. I'm not sure there are any military .303/7.7mm loads which are not safe in a No1 - they can withstand standard proof rounds that far exceeds anything any military ever used. You'd have to fill the case with something very silly in order to bust a rifle.

I'm with Son on this one. No rifle action "springs" open by 1/2" without the parts continuing to head in opposite directions.... That case clearly blew outside of a chamber and never went back in again. Thats either a hang-fire thats been opened too soon, or the safety lug is broken off the cocking piece - i.e. the pin was protruding as the bolt closed, and it fired the round before the locking lugs engaged.

Commenting on the rest of this thread: apart from locking lug wear (sometimes exacerbated by over-tight headspace....), there is no other way that Lee Enfield actions "grow" headspace. The action may or may not spring by a microscopic amount, but it does not permanently deform in any way. look at the empirical evidence: there are millions of Enfields out there that have been shot-out, re-barrelled and shot out again - yet they have remained in spec regardless. I have here an Envoy with a "0" bolt head: its last owner logged 9,000+ rounds on this barrel using only 155gn ammo (which the UK NRA dribbles on about being "too powerful for No4 actions"...), and yet the headspace almost too tight to gauge.

[Mk VII]

No one seems to agonise about Mosin boltheads like this .....