308 win OAL

[Howland]

With a rimless bottleneck case with its shoulder bumped back a couple thousandths....... or with less headspace than chamber...

Doesn't a 2.5 ounce firing pin pushed 9 fps by a 26 pound spring drive the case shoulder hard into and against the chamber shoulder on those headspacing on their shoulders? Then dent the primer and fire the round so positioned?

It could. It depends on whether the inertia of the cartridge at rest allows ignition first or whether the force of the firing pin overcomes that inertia prior to ignition. You'll have to ask someone with more wisdom than myself to get a definitive answer because I don't know for sure. I'll bet there are some math whizes among this crowd who can answer that with certainty. It sounds like a simple math equasion except for the tricky part about resistance from an extractor and friction against the chamber.

 

[Bart B.]

It does. It'll fall to the chamber limit from it's own 1 ounce weight with the muzzle straight down and the bolt open.

 

[muleman69]

resistance from an extractor and friction against the chamber.

I have always wondered about this?

 

[Howland]

It does. It'll fall to the chamber limit from it's own 1 ounce weight with the muzzle straight down and the bolt open.

OK, I've just got to ask. If you already knew, then why did you ask?

 

[Bart B.]

OK, I've just got to ask. If you already knew, then why did you ask?

To find out if you know what happens when firing pins smack chambered rounds.

 

[Bart B.]

I have always wondered about this?

It's not enough to be concerned about. Push a round full into the chamber to tell how easy they go all the way in stopping at their headspacing point.

Often, firing pins drive 308 cases hard enough to set shoulders back a few thousandths. I've measured up to .006 inch.

 

[Bart B.]

I have always wondered about this?

It's close to zero.

Remove the striker and ejector springs from the bolt, put it back together then chamber a round. Point the rifle straight up then push the firing pin up and down to see how easy it moves a tiny amount. Helps to have the case shoulder set back as far as possible to have maximum case head clearance.

 

[Zero333]

I found this doesn't work with a Savage action, even taped. The Savage bolt just isn't as smooth as a custom. Besides, I can ascertain CBTO to lands on a half dozen bullets in the time it takes to tear down and reassemble the bolt for the Wheeler method. After you've mastered the method, it goes pretty quickly.

I've done the Wheeler method on some of my Savage actions and got within 0.002" of the same reading as with the Hornady OAL tool.

However I do agree that a rough cycling bolt will be a challenge using this method.
Believe it or not, one of my Savage Long Action's is as smooth as many Custom actions. Feels like it's on ball bearings, and I never oil it. It's something you gotta feel for yourself to believe.

 

[Texas10]

With a rimless bottleneck case with its shoulder bumped back a couple thousandths....... or with less headspace than chamber...

Doesn't a 2.5 ounce firing pin pushed 9 fps by a 26 pound spring drive the case shoulder hard into and against the chamber shoulder on those headspacing on their shoulders? Then dent the primer and fire the round so positioned?

This, of course presumes that the bullet is not loaded at jam. Fire forming is best done loaded to jam so cartridge expands forward, instead of rearward. Or so I've read. Been doing it that way and it seems to work.

 

[Bart B.]

This, of course presumes that the bullet is not loaded at jam.

If bullets are soft seated, the case neck will move forward on the bullet before its shoulder stops against the chamber shoulder. Then the case expands. Either way, my case length is a couple thousandths less after firing.

 

[Texas10]

If bullets are soft seated, the case neck will move forward on the bullet before its shoulder stops against the chamber shoulder. Then the case expands. Either way, my case length is a couple thousandths less after firing.

Is that because the case will expand and shrink on the first firing? Then gradually expand further with successive fire forming?

 

[Bart B.]

Is that because the case will expand and shrink on the first firing? Then gradually expand further with successive fire forming?

If only neck sized, possibly.

When I fired, full length resized with a .001" shoulder bump, reloaded then fired again, the case length shortened about .002" then grew about 003" after resizing. Starting at 2.000", I trimmed it back to 2.000" every 9 shots across 47 shots on that single case with a max load.

 

[Texas10]

So you trimmed that one case 5X over 47 firings, with no case head separation? No thin wall inside the case?

You gotta be doing something right! What was the chambering?

 

[Toejoe12]

What brand of barrels do you shoot? They must be made of something other than I shoot. I've never experienced erosion of that magnitude. The barrel I'm currently shooting has 2200 rounds and has only eroded 0.010. Bartlein 5r, heavy varmint, Berger 200 hybrids@ 2650 + or - a few...

I'm with Dean on this one! I believe you left out a 0 somewhere. Maybe you meant to type every 300 to 400 rounds........or .0001?? I have multiple Bartlein and Brux barrels in 308 and none of them have displayed the level of erosion you state.

@Bart B.
308's erode the throat further down the barrel about .001" every 30 to 40 shots.

Can you see accuracy degrade if you don't "chase the lands" seating bullets to keep up?

 

[Bart B.]

So you trimmed that one case 5X over 47 firings, with no case head separation? No thin wall inside the case?

You gotta be doing something right! What was the chambering?

308 Win Federal case and only a tiny bit of wall thinning. A friend got 58 loads on his Federal 308 case.

 

[Bart B.]

Can you see accuracy degrade if you don't "chase the lands" seating bullets to keep up?

Not much through 300 yards in NRA highpower matches with bolt guns with ammo OAL fixed for loading from a box magazine. Accuracy degradation was noticeable with soft seated bullets seated against the lands for 600 yards and further. Barrel lives about 3000 rounds with Hart, Obermeyer and Kreiger barrels.

600 yards with 7.62 Garands. Barrel lives about 4000 rounds before their bore erosion gauge went in about 4/10ths inch from when new and long range accuracy degraded to about a foot or more: hard to tell with service sights and almost 5 pound triggers.