Headspacing alternative

[nanewt02]

Probably just wishful thinking, but lets say I want to make a wildcat, the case is rimless and I want the bullet to be flush with the case like a 22 lr is, is there any possible way of headspacing with a ball detent lock that pushes into the groove of the case where the extractor would normally grab on to

[Nathan]

Not sure I understand.

Basically headspacing is the critical fit which allows the case to be held in the chamber within reach of the firing pin and within the stretch limits of the case...

[nanewt02]

Basically a spring loaded ball bearing, one every 60 degrees, will push into the rebated rim of the case

[Scorch]

Using an extractor groove for headspacing sounds kinda iffy. Round detent balls do not hold very tightly. This is just one reason why most straight walled cartridges headspace on the mouth (like 45 ACP). If you used an angular anvil-shaped extractor to hold the cartridge, it would have to be fairly heavy to withstand the force of the discharge.

Bullets straight with the case neck like 22 LR are called heeled bullets. In the late 1800s, many cartridges had heeled bullets. Mostly they either switched them to internally lubricated or they disappeared. Heeled bullets are a terrible way to insert bullets in a case. It deforms the bullets as the crimp is rolled into the case, affecting accuracy. You are stuck with externally lubricated bullets.

[4V50 Gary]

Variable spring compression because of built up dirt or grease will result in varying lockup.

[nanewt02]

So there needs to be more compression then, it will be for a bolt action so there won't be much dirt due to lack of shots, but assuming multiple ball detects could in fact hold the cartridge in place from the force of the firing pin, would it work?

[Nathan]

Yea, I think so, if it could resist the firing pin whack. Not sure why a person would go this way over case rim or shoulder headspacing.

[nanewt02]

I'm on a budget, and the problem is the caliber barrels available will work if the bullet is flushed with the case, but if I have one not flush with the case like on modern day cartridges, the bullets smaller diameter will require a custom barrel caliber

[PetahW]

FWIW, if the case and/or projectile are a (very) slight crush fit in the chamber (fore/aft), there will be no excess headspace.

There does, however, need to be something (a chamber step or neck) to crush against.

Close attention does have to be paid to case length, though - since cases usually lengthen with firing.

If the correct AOL is determined, it's fairly easy to make a try gauge from sheet metal for the cases or loaded rounds.


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[oldgunsmith]

Do you have leather gloves and good safety glasses?

[Gunplummer]

Not sure how potent a round you are using, but I did something like that to check an old pistol round. It was a load one at a time setup. I used an Arisaka action and bolt. I turned the bolt down in the front of the lugs and threaded the area I turned down. I then made a bolt head and tapped the back so I could screw it on the turned/threaded bolt. The face of the bolt head I milled a "C" into with a key cutter I ground to the size of the bullet case rim. The threaded area gave you enough room to function the bolt without the opening to the "C" cut changing position. Basically, this set up is headspaceing on the case groove and working as the extractor. I guess you could really spiffy it up and refine it some what, but I used it just to do quick checks on weird stuff.

[nanewt02]

Sounds pretty ingenious , I'm stil trying to find the right barrel so I can avoid the headache altogether

[Gunplummer]

You could just try your idea, if it is a low pressure round. It may just work for you.

[Jim Watson]

What caliber and load level do you plan?
I can't imagine a very hot load with heel type bullets in a straight case.

Gunplummer describes a "shellholder" action, similar to what is seen on some economy model .50 BMGs. It will work... but not very fast.

You could try headspacing with the bullet against the origin of the rifling. It MIGHT hold against the firing pin fall. But you would still have to furnish a rimless extractor.

Instead of a ball detent, look into a chisel pointed locator spring loaded into the extractor. This is how the extractor on a double express rifle that the customer insists be chambered for a rimless round works.

[Gunplummer]

Now you are getting somewhere. More options than you realize if you really think about it.

[nanewt02]

It will have pressures up to 35000 psi, I wonder if pacnor will do Really shallow rifling

[Clark]

This rifle I built 10 years ago has two spring ball detent things from MSC in it. I drilled and tapped through the bottom of the receiver to push up on the bolt.

I had to grind a ramp on the bottom lug to get it started going over the ball.

[nanewt02]

Nice, does yours serve to purpose of headspacing, I think I'm just goin to use a different caliber

[Clark]

My little springs were so that the bolt would lock up into the same spot and give me better accuracy. That rifle is very accurate, because it has a good clean barrel. My lock up probably has little to do with it.