When does the case neck expand?

[mks]

The 2 gr of neck is attached to the rest of the case.

This is a valid point for the part of the neck very close to the shoulder. Here the shoulder adds stiffness and makes it harder to expand the neck. But with a 0.010" neck, once you get 0.010" away from the shoulder, the effect is significantly decreased, and 0.100" beyond the shoulder, the effect is negligible. The bullet is seated about 0.200" above the shoulder.

 

[Wilbur]

Im still trying to figure out why it matters? Its not like youre gonna be able to change it like with a bushing change

It doesn't really matter at all....it's December!

That said, has anyone taken note of a zero clearance neck? If so, what degree of black stuff did the neck have after shooting?

 

[Joe Woosman]

Back when I was heavily experimenting, I was chasing a theory of the neck helping the alignment of the bullet into the throat and reducing in bore yaw as was mentioned earlier. I felt conventional necks just weren't strong enough to have a significant influence. I hardened the necks to a spring temper. I thickened the necks to increase strength. I made dies that had a step at the base of the neck near the shoulder. This step would create an interference fit with the chamber, ("zero clearance"), perfectly centering the rest of the neck and bullet - in theory.

Anyway - As I recall, as the neck became stronger the carbon wave pattern grew with neck strength until the entire outside of the neck was sooted up pretty good. It seems I remember the carbon even making its way into the shoulder area.

 

[alinwa]

Im still trying to figure out why it matters? Its not like youre gonna be able to change it like with a bushing change

Actually, you can change it tremendously. I've tested 5 different neck thicknesses in one barrel by changing the neck.

When I was testing this I used 5 completely different 6BR chambering reamers in a bunch of barrels, all of the reamers have different neck diameters. I also have a couple "uni-throaters" and some neck reamers so's I could (can) try any combination of such. It's a pita but it all CAN be varied The uni-throater setup is extremely handy because you can make the freebore longer in literally minutes, this way you can (I have) TEST whether or not the bullet startup is strongly affected by entry into the lands.

And given time Kiff will build pretty much any configuration of supported or unsupported reamer one could want. I had no lathe when I tested all this stuff.

Or, if you're as well equipped as (and as good as) Joe Woosman you can reach in and single-point these changes.

As Joe, I've tested necks from .005 to .020 thick, of varying hardnesses as well as super-gluing, epoxying, "cold-welding," crimping and even mechanical interference fits.

And I've got many setups even now with ".000" radial clearance, it's one of my pets. I first heard of "scuff-fit" from Allie E, he used it to good effect. (surprise, surprise )



To think about:

To duplicate one of my tests, make up a 20" lever with drivers in 1" increments from the fulcrum, use this driver with weights or using a scale to show that it takes 400-550lb of driving force to swage the typical jacketed bullet into the lands, or 5,000-12,000psi, BUT.......increase your freebore incrementally from .000 to .250 to graph whether or not it matters....


((((As an aside, squish some bullets. Find out for yourself what 6000psi, or 60,000psi does to the skinny liddle buggers!))))


BTW when I drop a bullet to the floor from 20" I set it aside.....it's wrecked!...... LOL

I realize all this flies directly in the face of those of you who prefer to argue, but I, like Joe, found the results to be enlightening.

I guess I'm weird..... I'm the kind of guy that, when my Beloved is dying I ask for the DOCTOR in the room, preferring his opinion over all others'....the opinion of the guy who's actually carved living human tissue ..... successfully ..... outweighs all the opinions of the guys who've spent their lives watching ER


I say again, LISSEN to mks

And Joe

 

[Dusty Stevens]

No Al what i mean is that you cant change which one happens first. Just say if the neck expands first with 60kpsi theres no way to change anything to make it not expand first. I agree of course with all you say about the rest of it. For the experimenters out there you better have some good dies the less clearance you have! I discussed this tight neck thing for hours and hours over the years with one of the houston warehousers and like him i use .001 to .0015 on a ppc. I have done the checks, got the deltronic pins, got the absolute best dies i could dream of, and i still err on the safe side.

 

[alinwa]

No Al what i mean is that you cant change which one happens first. Just say if the neck expands first with 60kpsi theres no way to change anything to make it not expand first. I agree of course with all you say about the rest of it. For the experimenters out there you better have some good dies the less clearance you have! I discussed this tight neck thing for hours and hours over the years with one of the houston warehousers and like him i use .001 to .0015 on a ppc. I have done the checks, got the deltronic pins, got the absolute best dies i could dream of, and i still err on the safe side.

Agreed, but you can vary it. It works just like "seating depth" and "neck tension" and other such apochrypha......

As far as "the safe side" I've found that unless you've interference so bad that you have to physically jam the hannle down there is no safety issue. And even in this case the only real dangerous jam is from a too-short neck where the jamming crimps the casemouth onto the bullet. Radial clearance is not a safety issue IME because you can FEEL it.

Turn/roll/sand some necks so tight you can feel them and try it.

Really, it's easier than measuring, and more accurate.

 

[alinwa]

SAFETY CAVEAT


I'm slipping.



Dusty raises an interesting point, and coupled with Joe"s post I must add this



JUST IN CASE someone is actually led to experiment with this (Please Lord!!) I must add one SAFETY CAVEAT. It is possible to make necks such that they're as thick as the sides of the case. THIS IS OUTSIDE THE DESIGN PARAMETERS OF BRASS CARTRIDGE USAGE AND IS UNSAFE!!!


!!!UNSAFE!!!

Joe mentions case necks blackening clear to the shoulder, I should have cued on this and didn't......


IF when one is messing about with this sort of stuff, varying the ht of the "scalloped line" or moving the black stuff up and down the case neck......IF the line gets down near the shoulder IT'S TIME TO STOP!!!!!!

Or at least to exercise extreme care.


Once that pressurized gas starts creeping into and even past the shoulder there is imminent danger of FAILURE.

It needs be said that the primary design intent of the brass cartridge case is NOT to offer a handy way to carry your powder, it's to act as a GASKET and when this gasket fails things can get ugly.

I've got several sets of photos here somewhere showing caved in, scalloped, and mutilated cases that look like they've been driven over or worse. Problem is, they're old, not digital. But take my word for it, BE CAREFUL when skewing sealant pressures below design parameters!!! More people have been hurt by under-loading than by over-loading. (((And lest I get dumped on.... by "over-loading" I mean running up loads using appropriate powder, not inadvertently using the wrong powder!)))



KEEP THE BLACK LINE ON THE NECK!!!

sorry

rant off

al

 

[Joe Woosman]

Al - I was unaware of that there safety concern. Fortunate for me I didn't learn the hard way.

I've heard of reduced loads causing a secondary pressure spike. Since the thick/strong neck thing probably hasn't been tested to failure, are you sure what the failure would look like? Maybe the strength prevents collapse?

 

[alinwa]

Al - I was unaware of that there safety concern. Fortunate for me I didn't learn the hard way.

I've heard of reduced loads causing a secondary pressure spike. Since the thick/strong neck thing probably hasn't been tested to failure, are you sure what the failure would look like? Maybe the strength prevents collapse?

Not IME. I've had three things cause case collapse, too low a charge of too-slow powder (I had this happen in a 7MM Magnum and know of others), Too thick necks and too-slow powder (this was a 308, cases made from 30-06) and too-light bullets with slow powder (kindofa' combination of the other two effects while fiddling with big cases) 15-18yrs ago when opining here on BRC I'd often yell about how much "I hated messing with slow powders" cuz they scare me!


I've since moved past my "slow powder" phobia, routinely running them up to very high pressures JUST NOT WITH LIGHT BULLETS, EVER!! I use slow powder only with heavy bullets and since I only mess with light and heavy, ignoring all the middle ground, I'm now using all sorts of slow loads, HOT.

I never actually collapsed any 6BR's even though I got creasing and staining down past the shoulder. This was back in the late 80's/early 90's, first time I messed with 105/115 bullets in the BR, nobody had any idea what powders to use...... and then in the later 90's when making cases from 308's, thick-thick necks. I had another experience with subsonic 308's that caused fluting and staining.....and just within the last year I've been messing with a subsonic 50cal based on the 338L case cut back, graphing burn-rates from pistol powder, thru shotgun, clear up to Retumbo. Several times I've walked the staining down as much as 1/2" on the neck but I haven't broken seal on any. I've pretty well got a feel for it now, there are 3-4 other signs of incipient leakage.

I'm hearing of lots of failures recently by people trying to make their hunting rifle into a subsonic....

Basically it has been my experience that when the bullet gets out of the way too soon for the neck to seal, IF GAS GETS BACK PAST THE NECK, the cases will be destroyed and gas will escape.

Back when money was an object there were times I'd try out a bullet/powder combination just because "it was what I had" and before I realized that TOO LITTLE POWDER is more dangerous than TOO MUCH in most instances!

"gas will escape" doesn't really capture the event.... I've never been even singed but I wear safety glasses ALWAYS and have had them discolored more than once.

I've never experienced "detonation" as Keith describes it but I don't doubt him. I've got several articles on the subject, several others that reference it (though some ref Keith)

And I have a small collection of other people's cases, stuff they've brought me that I've been allowed to keep, along with a description of the load........ several of them with "I just started reloading and wanted to be safe SO I STARTED 'WAY BELOW THE MINIMUM IN THE BOOK!"

 

[Al Nyhus]

From my experimenting, the 'scallops' or 'feathered' appearance of the soot on the case neck happens as the pressure falls off and the neck begins to return to a smaller o.d. dimension. -Al

 

[alinwa]

From my experimenting, the 'scallops' or 'feathered' appearance of the soot on the case neck happens as the pressure falls off and the neck begins to return to a smaller o.d. dimension. -Al

And this is from an experimenter who shoots dots using a case with almost NO NECK!

I'm listening......

(I thought about your WildDawg when I posted my WARNINGS!!! but reckoned you're so far outside the box that if anyone got to your stage of experimentation they'd have the sealing thing figgered out )

Can you show us your Wolf Pup please Al?

 

[Al Nyhus]

Can you show us your Wolf Pup please Al?

Parent 30BR case (lt) and 30 WolfPup (rt).


The case on the right had been fired/loaded about 40 times at that point. You can clearly see the lower edge of the powder stain on the neck. The short sealing area of the neck necessitates high pressure loads to seal the neck quickly. Since the base of the bullet is generally around .150 below the neck/shoulder junction, the neck clearance is basically a gauge fit between the neck of a loaded round and the chamber neck area. Stan Ware and I shot this case for 8 seasons and it brought home a good amount of hardware. We also had a heck of a lot of fun creating and working with it.

 

[Wilbur]

From my experimenting, the 'scallops' or 'feathered' appearance of the soot on the case neck happens as the pressure falls off and the neck begins to return to a smaller o.d. dimension. -Al

Al, what are you going on here?

 

[Al Nyhus]

Al, what are you going on here?

Just my own work with neck clearances and powder rates. Almost all was done with .30 cal. stuff with case capacities from the 30BR case to the 45.5 gr. range (30X47-ish) and powders from the 4227's to N135. No laboratory or piezoelectric stuff involved. Pretty basic dirt clod stuff, really. But through enough barrels, there were definite traits that would repeat themselves.

But, like Tim Wilson sang....I could be wrong.

 

[Joe Salt]

alinwa my understanding of gases coming back down the neck, was with a heavy load the shoulder seals first because that part of the case gets pushed forward first. I guess if you are jumping the bullet or jamming also makes a difference. I also have cases with dents below the shoulder from too light a load. Then what about the guys that only size half the neck. Its going to make a difference how they seal also. I've also tried tight necks but I'm back to 3 thou. on clearance, better bolt lift.

Joe Salt

 

[Wilbur]

You're probably not wrong!

 

[alinwa]

alinwa my understanding of gases coming back down the neck, was with a heavy load the shoulder seals first because that part of the case gets pushed forward first. I guess if you are jumping the bullet or jamming also makes a difference. I also have cases with dents below the shoulder from too light a load. Then what about the guys that only size half the neck. Its going to make a difference how they seal also. I've also tried tight necks but I'm back to 3 thou. on clearance, better bolt lift.

Joe Salt

I guess I don't know how to address this as I pretty much disagree with all of it

But I'll try.

#1- No, IMO the 25-30lb of pressure from the firing pin has no effect on the sealing of the chamber. My reasoning, on two points, first new cases seal just fine and dandy when you fire them even though the shoulders are rougher than a cob, certainly not gas-tight. And two, it takes somewhere in the neighborhood of 6,000-10,000psi to pop even a thin neck out. Harold Vaughn built gaged equipment to test all this in slow motion and I've kinda' taken him at his word but it sure seems to be corroborated by my shooting all sorts of necks from .004 thick to over .020 thick. and no, jumping and jamming have no real affect IME.......I shoot thousands of rounds over the chrono during testing (my ape way of monitoring pressure) and rarely see ANY effect

#2-I've used dozens of setups with partially sized necks..... I've even got stepped-neck chambers and dies. Dies which leave the last .200 untouched, longnecked cases with two different thicknesses of brass, Wilson dies backed off a couple hundred thou....in fact I've had difficulty getting my reamer-maker and my die-maker to establish the same radii at the NS junction so I've a bunch of setups which just leave it alone. I happen to like .030 radius, this is not typical.

#3-And while I've heard 3-4 others also talk about neck diameter being tied in with bolt lift I've never experienced it so I can't make the connection. Obviously some HAVE experienced this connection, yourself included but I have not. And I shoot one case in particular where I can feel the drag going in AND coming out and if anything it's looser coming out. I've never experienced clearance on the way in, drag ON THE NECK on the way out. I once thought I did but subsequent resizing with oversized neck bushing proved me wrong.

Again, I'm not trying to argue, I've just not experienced it the same as you...

al

 

[Joe Salt]

Al No argument from me, its all hard to prove. But I feel the shoulder being at a 35 deg. or 40 deg. the blast would push that first to seal the chamber, then the neck would open once the bullet started to move, but the neck is the last part to seal that's why you get carbon down the neck to the point were the shoulder seals. That's with the right load not a reduced one. Hope this is in the ball park.

Joe Salt

 

[gonehunting378]

I've always just figured the neck lets go then the bullet moves. Reading along here, I'm thinking of the few times I've seen sooting on dasher cases. I don't have notes that I can find, but my recollection is that only happened when I played with too light of neck tension. Is it possible that in those cases I was seeing not quite enough start pressure to seal the neck, but yet enough to move the bullet. I don't mess around to much anymore with light grip as my stuff always seems to tune best with more tension. Those pressures weren't light, but possibly the start pressure does have some influence on witch comes first. Just thinking out loud here.

Tom

 

[dk hunt 14]

Like I said in my last post, if the bullet doesn't move first, how comes more tension tunes a gun? What you said Tom makes sense to me. I also see where more tension gives me better long range accuracy. This is with both the 300 WSM and the Dasher. I believe you would get carbon on the neck either way because the neck springs back after release. Matt