SON OF NECK TENSION

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  • Last Post 23 August 2018
joeb33050 posted this 22 August 2018

What happens in that first few milliseconds after the primer is struck? I don't know, but...

When investigating "does case length affect accuracy?"; I was able to produce rings of lead that was extruded into the space between case end and ?throat? start. I could produce these on demand at sorta high pressure/soft alloy.

Something is going on squeezing the dickens out of the bullet before/as it begins to move.

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Shopdog posted this 22 August 2018

Joe,very slight tangent.....

"Although" most handloaders suggest not using a roll crimp on bolt action rifle cartridges..... I've found them almost indispensable.

Most of my shooting is done with hunting in mind.As such,the rounds have to survive a rather,brisk trip up through the magazine.I also like a "jam" fit.

A slight rolling in of the case mouth acts as an abutment to the bullet seating depth.Consider this to be the final bit if seating.

So,we have an EXTREMELY well fitted,swaged bullet with a roll crimp. It,and the case,ain't goin no where at the point of ignition.

This isn't "tension" in my book.Tension is better described as an interference "fit".Very easily changed..... also this isn't based on seating friction.Which is independent of tension because there's a huge difference in how the interior of the neck and the lubed bullet interfaces during the seating process..... not to mention annealing and/or brass hardness.

In my example,crimp & jam.... this is where "hold" enters the picture.Also can be corrosion.... bullet can "weld" itself to case neck.... as in shooting old ammo.To say tension has no bearing on acc is very myoptic... it may not.How's that working for you? To say,never roll crimp is the same thing.Good luck with your project.

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Ross Smith posted this 22 August 2018

Joe: I get they very same phenomena in my 06. I've not produced it on demand though. I always assumed it was from shaving a little lead during the bullet  seating or cartridge seating into  the chamber. ....?????? Any thoughts??????

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Ken Campbell Iowa posted this 23 August 2018

every 22 rf rifle leads just at the neck/bullet junction ....   softish lead at 1100 fps ...  and they shoot pretty well, so maybe it isn't a bad thing ... some say it is a good thing ... it fills in that small void and once built up helps the following shots to make that first 1/2 inch more smoothly.  and these are mostly pretty tight chambers .  there are many theories of how that happens, but i am not sure, they all sound plausible.

it is interesting that usually 22 rimfire bullets have a base dimple ... and that is flattened when shot ... and these " distorted " ( or formed to chamber?? ) things still shoot 0.6 moa .

i once chambered my match chamber 22rf  so close that it nearly engraved the front of the case.. it engraved so much i could not easily extract an unfired round, i had to shoot it ...  ... i still got the same ring of lead !! ....  btw, i rechambered to add a teensy freebore, and it shot just as well .   same ring of lead also .

i was disappointed that we couldn't modify the ammo in our 22 rf. classes .... they even stopped me putting a teensy bit of moly on my bullets ... which didn't help short term accuracy.  the moly didn't stop the lead ring either .

ken, rambling on ...

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Ken Campbell Iowa posted this 23 August 2018

shopdog ::

yes, as johna pointed out, we us group has roiled the clarity of this thread by not noting early that we were separating neck tension at firing from neck tension/crimps which serve to hold the bullet prior to shooting.

both are interesting topics, and i always read everybody's thought and experiences on both.

even today, being a self-appointed expert on all things reloading .... i still don't know how much crimp to put on a new load ...  until i shoot a few and have them come apart or fall into the case while shooting the gun.    ever have to clean 50 grains of powder out of the deepest crevices of a remmy 742 ?? ... dang recoil spring ........   or load up a hunnert 223 coyote loads and have them self-adjust seating depth while pumping them through a remmy 760 ... ?? ...   i am still finding new ways to jam a perfectly good ruger security six revolver ...

i have been using the lee factory crimp dies quite a bit lately ...  they are a bit tedious to set ... your post makes me think about grinding a little more taper on the collet on the rifle dies ....  i really don't want to take that 742 apart again ... ...   so thanks !!

ken

 

 

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joeb33050 posted this 23 August 2018

Joe: I get they very same phenomena in my 06. I've not produced it on demand though. I always assumed it was from shaving a little lead during the bullet  seating or cartridge seating into  the chamber. ....?????? Any thoughts??????

 

Ross:

I did the testing in 2002, and wrote;" At high pressure and velocity I have been able to shoot cast bullets and have a ring of lead left in the chamber. It looks like the bullet expanded into the gap between the case neck and the step at the end of the chamber, and then the resulting ring was sheared off."

Here's a response:

 

Norm Johnson:

 

With cast bullets, it is particularly helpful to keep the trim length within about .010" of your chamber dimension so that when the cartridge is fired, the bullet does not enlarge (obturate) to chamber neck diameter just ahead of the case mouth.

 

Depending on pressure and bullet hardness, the bullet can upset into the chamber neck area just ahead of the case mouth, then the remainder of the bullet will shoot through this ring of lead.  With cast bullets, an indication of this is when a portion of the above mentioned ring of lead sticks to the case mouth and is withdrawn as the case is extracted.  The unwanted obturation damages the bullet's integrity and leaves a varying cylinder condition that, at best, is not conducive to good accuracy.  Under some circumstances, subsequent rounds fired in that chamber could cause increased pressures.

 

The above can happen even to jacketed bullets with short necked cases and/or long cylinder necks. 

 

See the photo of the resulting anomaly where there was a .050" space between the case mouth and the end of the chamber neck.  The jacket expanded, and then sheared as the rest of the bullet passed through it. 

 


God Bless!"

 

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joeb33050 posted this 23 August 2018

Norm Johnson's photo.

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joeb33050 posted this 23 August 2018

It seems to me that the bullet compresses, shortens, just after, microseconds after, the primer starts to go off; and it seems to me that that compression might squash grease grooves unevenly, making the bullet out of balance. Then I started experimenting with no-grease-groove bullets. Never had a NGG mold with  a GC shank-that might be the secret.

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RicinYakima posted this 23 August 2018

Grease is  non-compressible under the pressure we shoot at normally. That is the reason there are case neck and shoulder dents if you over lube when full length resizing. However, it will flow at less pressure and temperature than the lead alloy. So as pressure is applied at the moment of firing, and being driving into the lands, to takes up the space on the leeward side of the lands and flows forward. This lubes the barrel in front of the bullet?

Somewhere in The Fouling Shot back issues is an article about a guy who only lubed half of each grease groove and only on the same side. His groups were slightly larger than with totally filled grooves. His conclusion was that the lack of grease allowed the driving bands to move in irregular ways because there was no grease to support the lead.

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Ken Campbell Iowa posted this 23 August 2018

merrill martin ....   did a lot of interesting stuff  ... i think that article was in PRECISION SHOOTING ...  maybe.

merrill also did some " pushing " of his ideas ...... not an exclusive in the shooting game ...

ken

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Tom Acheson posted this 23 August 2018

Follow-up to Ken's recent observation, this is not a neck tension"subject".

Ken is correct. Merrill Martin did a series of articles in Precision Shooting magazine on the use of 0.060" thick poly wads in straight wall cases. The cast bullet alloy was specific, tied to the needed pressure to allow the bullet's lube grooves to collapse. The goal was improving accuracy.

Merrill theorized that as the bullet was moving down the barrel, it was being compressed, the lube grooves were gradually collapsing and lube was uniformly squished out of the grooves onto the ID of the barrel surface. The use of the wad kept the combustion gases from eroding the base and lower areas of the bullet. If I recall correctly (IIRC?) he specified a certain lube groove design. Was it square corners rather than round because the squared cornered design would collapse more uniformly? Not sure.

This was a smokeless (not black) powder endeavor.

In conjunction with this he emphasized the need to use varying grades of grit to polish the ID of the bore to a certain level of "shinyness". The use of straight wall cases only helped keep the wad in place (at the base of the seated bullet) in the case, avoiding the dreaded loose wad flying down the barrel, looking to ring a barrel.

I might have copies of the MM articles.

Tom

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John Alexander posted this 23 August 2018

Tom's memory is same as mine on Merrill Martin -- only much better.  Martin also believed that bullet lube acted like other lubricants (instead of whatever it really does) and believed lube was pressed onto the bore by the bullet being shortened like the pressure in a grease gun and as described by Tom and others above.

I also have seen the lead rings. They bugged me so much that I wrote a TFS article on them hoping that someone would tell me if I should keep on worrying about them. As usual no replies.  I made 250 223 match cases out of Rem Mag cases and eliminated all but a couple of thousandth of the gap which eliminated the lead rings. Still using the cases and I think they "will see me out".

However,  probably a total waste of time like a lot of the other farting around with other details stuff that I rant about so there is some irony in the tale. I am sometimes guilty of chasing tiny nits just like the rest of you.

BTW -- Norman Johnson's remark about holding the gap to < .010" must refer to using custom chambers or custom made cases since the gap in factory rifles and new cases seems to usually be far larger in the many I have measured. 

John

 

 

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Ross Smith posted this 23 August 2018

Joe: Going back to your question: Is this phenomena eliminated by breach seating? Is this why Harry Pope was able to do so well? at least in part that is.

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joeb33050 posted this 23 August 2018

Ya know, Norm Johnson shot unlubed bullets in revolvers, as a matter of course. He and  his work were thoroughly ignored-I hadn't/haven't seriously shot revolvers since the late 60s, a la Elmer. However, a few others tried no lube without problems. And, I, at the suggestion of others, am able to shoot rifle bullets with lube only above the gas check. Hence my suspicion of lube squeezing from grease grooves. No lube? Anyone? Who'll send me some .360" unlubed soft bullets?

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frnkeore posted this 23 August 2018

Joe: Going back to your question: Is this phenomena eliminated by breach seating? Is this why Harry Pope was able to do so well? at least in part that is.

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If it happens, I haven't heard of it. I suppose that people that don't know how to breech seat, may had it happen but, most competitive shooters, BS with 0 - .030 of the base band, not already in the throat.

Although a bullet contained in the barrel, itself  (assumed all bands are at groove size or larger) can not change it's shape, in the driving band area, nose excluded. In a commercial chamber, there is enough clearance that the bullet can expand to the maximum of the neck to chamber clearance and the case neck thickness, especially in mil chambers, will allow the bullet, lots of clearance to expand and the lube to flow, to any place it can get. With part of the lube gone, soft bullets and high velocity can allow the driving band area to deform also, until the lube becomes compressed again.

In that case, the bullet will be much larger than the throat and can shear lead, as it enters the throat.

Frank

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pat i. posted this 23 August 2018

I don't know if I'm understanding everything being said but are some people saying that the purpose of lube is to do what the name implies and lube? Or are people still saying its a seal. I'm a bullet lube is to lube guy myself. Rounded lube grooves would have to be stronger than square grooves if you compare it to architecture. Being an arch would the bullet accelerating down the bore force the lube out the back of the groove instead of compressing the grooves and squishing it out?

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frnkeore posted this 23 August 2018

Regarding Merrill Martin, I respect him, very much and have one of his NEI GC molds.

In 1985, when I started Schuetzen, he is one of the extremely few shooters, that did well shooting PB, fixed bullet ammo in Schuetzen matches. I can't remember him ever winning a match but, he placed well, most of the time.

I never got to meet him and I believe he has pasted now? But, I would diffidently listen to anything he has to say, especially regard how to get accuracy with PB fixed ammo.

Frank

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joeb33050 posted this 23 August 2018

I don't know if I'm understanding everything being said but are some people saying that the purpose of lube is to do what the name implies and lube? Or are people still saying its a seal. I'm a bullet lube is to lube guy myself. Rounded lube grooves would have to be stronger than square grooves if you compare it to architecture. Being an arch would the bullet accelerating down the bore force the lube out the back of the groove instead of compressing the grooves and squishing it out?
If no-lube cast bullets can be shot without leading or any other difficulty, maybe it is neither a lubricant nor a seal, maybe it's a myth.

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John Alexander posted this 23 August 2018

No lube cast bullets can be shot without leading in SOME situations but maybe not all.  From what I have read just omitting the "lube" in whatever load you happen to be shooting results in a lot of lead removal.  Anyway the reading was convincing enough to me that I have never been tempted.  Others who are braver please speak up.

I too have a lot of respect for Merrill Martin as well as for Pat, but  the work by Mollohan on what bullet "lube" "does" and doesn't do convinced me that is doesn't lubricate as in your crankcase.  Is his articles in your book Joe?

John

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RicinYakima posted this 23 August 2018

Molly convinced me to do  the following test: ten 311291 bullets with just the gas check and no lube, at the bench dipped each one  bullet first into a jar with Hoppe's #9 and immediately load and fire. Powder was 14.5 grains of H2400 for about 1350 f/s. No leading, but group was larger than normal. Ken Mollohan pretty much had "how" bullet lubes work nailed down. Ric

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pat i. posted this 23 August 2018

I mentioned this before but I had a mold that one cavity cast a smooth sided PB bullet and the other the same bullet with a gas check shank. I impact coated the pb bullet with moly which was all the rage in jacketed shooting at the time and filled the space over the check with LBT blue on the other bullet. The moly coated bullet was a disaster. The lubed and checked bullet was alright but nothing stellar. Dick Reese bought the mold and had the same outcome. Maybe having grooves in the pb bullet would have helped by having a place for the displaced lead to go but I'm a little gun shy of running no lube now so will leave that to others to play with.

John thanks for the compliment and right back at you but it'll take one hell of a lot of proof to ever convince me lubes purpose is anything but to lube.

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