Questions using expanding mandrel

[Martin52]

I definitely like this approach with un-turned brass. I do however wonder if the result would be equal, or if it would be inferior, if you simply used an expander ball .002" under bullet diameter in the Forster sizer. If the same result coul be obtaine with one step less, then it only makes sense. I turn necks on match guns, so the only thing I run over an expander is hunting guns, but I've not identified any noticeable accuracy issues from condensing the steps. I can't determine that with my match guns because my necks are turned.

Using a Whidden FLS die with 0.334 bushing and 0.306 expander produced <0.0015 run out on my turned (to ~ 0.014) Lapua case necks. The expander ball lightly touches the inside of the case neck as the ram is lowered. For comparison, I then full length sized a few cases in the same die but without the expander ball and then opened up the necks used my K&M 0.307 expander - this produced ~0.004 run out and is consistent with past experiences.

Body sizing and then using a Lee Collet die gives me a result similar to the Whidden die.

Martin

 

[Bart B.]

Case head is firmly against bolt face, case shoulder ought to be as well against the concentric angled shoulder profile between body & neck; case neck - if left partially unsized - is nicely centered in the neck bore. Any induced run-out should be negated by bullet aligning in throat once chambered, helped by case head being perpendicular to bore's axis with its being in firm contact at bolt face.

That never happens all the time. Think about the parts fit tolerances when the bolt is in battery. And the extractor's pressure pushing the case head sideways until the case body stops against the chamber at its pressure ring.

When neck only sizing was the only way for some wanting best accuracy, any time their bolts started binding the slightest amount, group average got bigger. Then they bumped case shoulders back so bolts would go back into battery the same for every shot. Head clearance to bolt face needs to be at least .001".

I've never seen the unsized part of a case neck be the same diameter as the chamber neck. Measured several, all a thousandth or more smaller.

Read post #53.

 

[ImBIllT]

S

Using a Whidden FLS die with 0.334 bushing and 0.306 expander produced <0.0015 run out on my turned (to ~ 0.014) Lapua case necks. The expander ball lightly touches the inside of the case neck as the ram is lowered. For comparison, I then full length sized a few cases in the same die but without the expander ball and then opened up the necks used my K&M 0.307 expander - this produced ~0.004 run out and is consistent with past experiences.

Body sizing and then using a Lee Collet die gives me a result similar to the Whidden die.

Martin

so if I read this correctly, the pull button gives you less run-out than expanding separately on a mandrel afterword?

 

[ImBIllT]

That never happens all the time. Think about the parts fit tolerances when the bolt is in battery. And the extractor's pressure pushing the case head sideways until the case body stops against the chamber at its pressure ring.

When neck only sizing was the only way for some wanting best accuracy, any time their bolts started binding the slightest amount, group average got bigger. Then they bumped case shoulders back so bolts would go back into battery the same for every shot. Head clearance to bolt face needs to be at least .001".

I've never seen the unsized part of a case neck be the same diameter as the chamber neck. Measured several, all a thousandth or more smaller.

Read post #53.

Not all actions use a spring loaded ejector.

 

[Bart B.]

Not all actions use a spring loaded ejector.

I'm talking about the extractor whose claw lip presses against the bottom of the extractor groove sideways on case heads. Ejectors push cases somewhat straight out of the bolt face

All extractors are spring loaded whether they be coiled springs like post 64 push feed Win 70's have or the Mauser style flat spring ones pre 64 Win 70's use.

 

[ImBIllT]

You

I'm talking about the extractor whose claw lip presses against the bottom of the extractor groove sideways on case heads. Ejectors push cases somewhat straight out of the bolt face

All extractors are spring loaded whether they be coiled springs like post 64 push feed Win 70's have or the Mauser style flat spring ones pre 64 Win 70's use.

You did say extractor didn't you. I misread it.

I wonder if this is yet another reason that short fat cases with limited body taper seem to have such an advantage.

 

[Bart B.]

Short, fat and steep shoulder angle cases have one important advantage; their shoulders set back the least from firing pin impact which means more uniform primer firing and longer case life. I've measured 308 Win case shoulder setback from firing pin impact as little as .002" with military brass and as much as .007" with nickel plated Federal cases. Nickel plated ones are more slippery than brass.

As virtually all rimless bottleneck cases are a thousandth or so smaller in body diameter than chamber bodies, their back end can be anywhere at the back of the chamber. They sometimes skew off center by firing pin impact if not pushed sideways by extractors. But their front end is always dead center in the chamber shoulder. How much body taper doesn't matter.

Some think that back end of the case being off center causes bullet misalignment. Well, they're right. A 308 Win cartridge that's got no bullet nor neck runout being perfectly straight, but its body diameters .001" smaller than that of the chamber body diameters, will have its bullet tip .0005" off bore center opposite where the case head is with its back end against the chamber body wall at its pressure ring. If body diameter's .002" smaller, bullet tip will be .001" off center. No big deal at all, in my opinion. If they're all the same, they'll all be exactly the same for every shot fired. Accuracy and precision of groups down range will not suffer.

 

[Martin52]

S

so if I read this correctly, the pull button gives you less run-out than expanding separately on a mandrel afterword?

Yes, that is my experience provided the pull button is only expanding up 0.001, the button just skims the inside of the neck.

 

[ImBIllT]

Yes, that is my experience provided the pull button is only expanding up 0.001, the button just skims the inside of the neck.

I wonder if only skimming .001" is going beyond the elastic limit and actually changing the neck diameter. Have you measured necks sized with the bushing only and compared them to those that were pulled over the expander button?

 

[Martin52]

I wonder if only skimming .001" is going beyond the elastic limit and actually changing the neck diameter. Have you measured necks sized with the bushing only and compared them to those that were pulled over the expander button?

Good point, bushing only sized case necks measure 0.334 and those sized with the 0.306 expander measure 0.3345.

 

[jsthntn247]

I ran some over an expander last night and used my Hydro press to measure seating force. All case prep was the same, same # of firings, annealed, cleaned, yada yada yada. Using a .335 bushing FL die (not expanded with mandrel) yielded and inside diameter of .3055 and 24-32lbs of seating force. Expanding the neck with a .3075 mandrel after sizing with the .335 bushing made the inside diameter .306 with seating pressure of 36-40lbs. Question, how did seating pressure go up with a larger inside neck diameter? Using the mandrel also made the seating pressure allot more consistent, more than 90% were 38lbs.

 

[Sheldon N]

Seating pressure went up due to work hardening of the brass, even though the diameter was bigger.

 

[jsthntn247]

Seating pressure went up due to work hardening of the brass, even though the diameter was bigger.

Work hardening by expanding .0005 on brass annealed 20 minutes prior?

 

[Dos XX]

Some might call this crazy, but here goes anyway. When you use a bushing and size the neck from the od, the natural reaction of the brass is spring back in the opposite direction of the way it was last forced to move. The bushing sized it in, so spring back makes it want to open up. When you size with a bushing from the ID, the opposite happens?

To test this, you could size with a bushing that gives you the same ID as the mandrel and see what happens on seating pressure.

Also, is it possible the mandrel roughed up the surface finish of the id of you necks, in which case the Hydro Seater wasn't reading tensions but roughnesses? Run a nylon brush in and out of the neck and see if the seating pressure goes down?

I am not a metallurgist, nor did I play one on TV, but I did stay in a Holiday Inn Express Monday night. OK, it was The Doubletree.

 

[Sheldon N]

Work hardening by expanding .0005 on brass annealed 20 minutes prior?

Hmmm, for only 0.0005 it might be something else too. Maybe the mandrel is doing a bit of scraping/cleaning of the inside of the neck and taking off some of the carbon. That could increase friction and make seating pressure a bit higher.

 

[Ned Ludd]

I ran some over an expander last night and used my Hydro press to measure seating force. All case prep was the same, same # of firings, annealed, cleaned, yada yada yada. Using a .335 bushing FL die (not expanded with mandrel) yielded and inside diameter of .3055 and 24-32lbs of seating force. Expanding the neck with a .3075 mandrel after sizing with the .335 bushing made the inside diameter .306 with seating pressure of 36-40lbs. Question, how did seating pressure go up with a larger inside neck diameter? Using the mandrel also made the seating pressure allot more consistent, more than 90% were 38lbs.

What method(s) did you use to make these measurements and how sure are you that they are accurate, or even consistent relative to one another? Your question regarding increased seating force hinges on the actual difference between the two circumstances that you measured as .3055" and .306", respectively. Although their readability often goes down to .0005", calipers are not capable of reproducibly measuring to .0005" accuracy. A precision micrometer would be necessary to reliably distinguish the difference (if any) between the two variables you're trying to differentiate.

 

[Martin52]

I ran some over an expander last night and used my Hydro press to measure seating force. All case prep was the same, same # of firings, annealed, cleaned, yada yada yada. Using a .335 bushing FL die (not expanded with mandrel) yielded and inside diameter of .3055 and 24-32lbs of seating force. Expanding the neck with a .3075 mandrel after sizing with the .335 bushing made the inside diameter .306 with seating pressure of 36-40lbs. .

Did you check run out on the case necks by any chance, mandrel v bushing ?

 

[Martin52]

......1) When you use a bushing and size the neck from the od, the natural reaction of the brass is spring back in the opposite direction of the way it was last forced to move. The bushing sized it in, so spring back makes it want to open up. When you size with a bushing from the ID, the opposite happens?

2) Also, is it possible the mandrel roughed up the surface finish of the id of you necks, in which case the Hydro Seater wasn't reading tensions but roughnesses? Run a nylon brush in and out of the neck and see if the seating pressure goes down?

That's my experience - 1).

Re 2) - I brush inside the case necks using 0000 steel wool on a bronze brush, they do cone up very smooth. Doesn't help the issue with run out though! If I expand up more than 0.001 I progressively get worse run out with each increment in expansion. Still trying to solve that one !

 

[jsthntn247]

Don't have anything to check runout but plan on checking that. I stuck the back blade of my calipers in the neck to a point and opened them up, ran it over the mandrel and repeated. Before reading this I too also thought that it might be scraping the graphite off the inside so I loaded a few tonight like last night and all were at 38lbs. I then mandreled a few, added more graphite then seated bullets and all were at 38, so that's not it. I know the mandrel is opening the necks because it's tight on the necks and you can't push one on it by hand. Here's my theory: When you turn necks, after a few firings the brass has flown into the necks (brass grows .002-4 after each firing and resizing). I have re-turned brass (at same setting) after a few firings before and always it ONLY cuts near the case mouth and near the shoulder. With the bushing only sized brass when seating a bullet I can feel the bullet sliding down the neck and sometimes I feel it skip, then catch, then maybe skip again. I know y'all all have felt that. After running it over the mandrel I don't feel that anymore. So I believe that the mandrel is ironing and straighting the inside diameter of the neck which causes the bullet to encounter more of the case neck when seating. This additional friction (not squeeze) tension causes an increase in seating force. Since the bushing only is pushing the irregularities inside you get and uneven inside diameter and less friction of the bullet in the neck. However, bushing only in this gun shoots lights out so who knows, just more to ponder on.