To bush or mandrel

[fightthenoise]

I've started sizing 1 thou under caliber with a bushing and expanding using a caliber sized (not smaller, not bigger) mandrel to turn the spring-back around so that it's working in the direction of the bullet as per @Mikecr recommendation. I thought the bullet would just fall out but it seems to be in there pretty tight. Neck tension (interference fit, sorry, don't yell at me) seems to be about 1 thou by my before and after measurements. Maybe even less. From what I read, that isn't actually a measurement of neck tension, as the bullet becomes your mandrel if you don't use one and you always end up with a spring-back's worth of grip (0.5-1 thou worth). I've loaded the rounds but haven't yet shot them. I'll report back.

 

[wonderman4]

Mandrel expanding will give 0.001" or less runout.

Caliber Specific Expander Mandrels

21st Century Shooting, Reloading products, Caliber Specific Expander Mandrels

www.xxicsi.com

Expander Die Body

21st Century Shooting, Reloading products, Reload, reloading ammo, 21st century, twenty first century shooting, shooting, expander die body, gun reloading, tools for reloading, front rest, f class, bench rest, short handle, arbor press, powder measure, bullet, bullet comparators, die base, shell...

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These go up to 338 caliber.

 

[Tiny Tim]

Anyone know how much interference fit the brass will "hold" before it yields. Some talk about .004 interference but I wonder if the brass can hold that much before yielding and your bullet becomes the mandrel. I realize it is dependent upon the hardness of the brass and the thickness. I believe standard dies would act this way if the expander button were removed.

 

[SageRatShooter]

Tiny Tim - interesting question, haven't seen any data on this but it seems to reason that as you increase the neck tension you would get diminishing returns in bullet grip. So for example, 2 thou vs 1 thou (doubling tension) might double grip but 4 thou vs 2 thou (again doubling) might only increase grip by 50%, etc. until eventually you hit the yield wall and get no more increases in grip no matter how much the tension increases. I do not have any data thats just my theory. I think the key is it doesn't matter what the grip is so long as it works for your rifle and is proven shooting a ladder with a reasonable range of tensions. The goal to get the grip circumferentially uniform around the bullet and also the same on average from cartridge to cartridge, obviously within reason. I typically hear my bench rest buddies running almost 0 to 1 thou (just enough to hang onto the bullet - these are single fed actions so no rounds in a magazine subjected to multiple recoils) general LR rigs mag fed running 2 thou and some guys recommending 3 to 4 for heavy mags so the bullet stays at the correct CBTO in the rounds in the magazine that will be subjected to several recoils.

 

[MagnumManiac]

I can tell you this with 100% conviction.
None of this matters unless your brass is consistent in grain structure.
If your brass is work hardened even the tiniest bit, it will not be consistent across each and every piece.
The only way to ensure that is to anneal before every sizing.
Another aspect often ignored is how much neck clearance you have in your chamber.
I find .003" tight, but .004" is the sweet spot. Have turned away from tight neck chambers and only turn necks to clean them up, not for clearance, as thinning the necks too much also changes how much tension that brass will have.
All of this boils down to how much spring back your brass has.
If you have ever pulled down Bullets, you will notice that all the neck tension that was present has gone...the same thing happens in the chamber. As soon as the bullet moves, all the grip has gone. It's that initial microsecond of hold that wins or loses in the sweet spot tension game. Unless you figure out what the barrel/load likes, you're just chasing your tail around endlessly.

Cheers.

 

[Rardoin]

^^^^^What MM said^^^^^^

 

[Tiny Tim]

While I did ask the question, its purpose was to get the responses that followed. There are a multitude of variables to be considered, each either adding or detracting a small amount. Thanks for the responses.

 

[BillLarson]

So im stepping up my reloading game for my 375 rum and focusing on getting the neck tension and concetricity spot on I've got a set of type s Redding bushing dies and I'm now wondering weather or not I'm going to see better results with mandrels or the correct bush?

cheers
Lucas

Question:
do you have to crimp for that caliber...???

 

[Mikecr]

Some talk about .004 interference but I wonder if the brass can hold that much before yielding and your bullet becomes the mandrel.

Sizing means yielding.
That is, dimension change beyond springback causes yielding, and yielded only allows partial recovery to a new dimension (i.e. sizing).
When downsizing necks for more than ~1thou interference, seated bullet bearing will just re-expand/size that much of it.

Unless you size necks beyond seated bearing, you have no more than springback energy from cal dimension gripping your bullet (tension).
This is not a 'problem' as that's what you have.
Where you do size necks beyond seated bearing, you add bearing-base binding and bring donut area/shoulder angle into tension, which is a horrible plan for hunting capacity cartridges.

Good minimal sizing brings necks down ~2thou interference (after springback) for no more length than seated bullet bearing. This would be followed by an expander mandrel at cal in a pre-seating operation. That drives any thickness variance into yielding outward, away from seating bullets, to reduce loaded runout. It also sets interference to ~1thou, which is what you'll have anyway, but without using your bullets for expansion sizing. Better to use a mandrel for this, as bullets make terrible mandrels.
If you had left a carbon layer in necks (the perfect lube) then with this sizing plan you reduce seating forces, so you reduce seating depth variance. It get's a lot easier to set exact CBTO.
Less annealing rate is needed. And tension is then tweaked through sizing LENGTH adjustment (with a bushing die).
After all, neck tension is springback force X area applied to seated bearing. It's PSI.

Whatever you do, apply it through load development.

 

[Rflamm250]

Sizing means yielding.
That is, dimension change beyond springback causes yielding, and yielded only allows partial recovery to a new dimension (i.e. sizing).
When downsizing necks for more than ~1thou interference, seated bullet bearing will just re-expand/size that much of it.

Unless you size necks beyond seated bearing, you have no more than springback energy from cal dimension gripping your bullet (tension).
This is not a 'problem' as that's what you have.
Where you do size necks beyond seated bearing, you add bearing-base binding and bring donut area/shoulder angle into tension, which is a horrible plan for hunting capacity cartridges.

Good minimal sizing brings necks down ~2thou interference (after springback) for no more length than seated bullet bearing. This would be followed by an expander mandrel at cal in a pre-seating operation. That drives any thickness variance into yielding outward, away from seating bullets, to reduce loaded runout. It also sets interference to ~1thou, which is what you'll have anyway, but without using your bullets for expansion sizing. Better to use a mandrel for this, as bullets make terrible mandrels.
If you had left a carbon layer in necks (the perfect lube) then with this sizing plan you reduce seating forces, so you reduce seating depth variance. It get's a lot easier to set exact CBTO.
Less annealing rate is needed. And tension is then tweaked through sizing LENGTH adjustment (with a bushing die).
After all, neck tension is springback force X area applied to seated bearing. It's PSI.

Whatever you do, apply it through load development.

I Know you have mentioned it in other post. But if you will enlighten me again. I have run an experiment with FL die vs bushing die. I consistently get better ES and groups with the Bushing die and Mandrel vs a FL size die with the guts out then mandrel. Both ending with the same amount of tension or whatever we are calling it say .002 under loader round. The only difference I can find is that the bushing die is not sizing the last little bit of neck, say where a doughnut may be forming. The bearing surface of my bullet does not enter the doughnut area of brass so one would think that sizing that part with a FL die would not effect it but best I can see is that it does. Am I figuring right?

 

[Mike Matteson]

I use to anneal my brass only once, and use them until the primer pocket got lose up. I would cut all my brass necks no matter what to achieve the same neck thickness, and that was 20 years ago. I generally could achieve groups at about 1/2" @ 100yds. I push the bullets down the tube hard. No ejector marks, but flat primes, and No creator either. I am very careful, because I generally over what the reloading manual call out for if I am not happy with the velocity I am getting or want to see what I can get. I do us a powder dump, but I scale all my powder loads with an Ohaus Powder Scale. Back then and even now I use a Lyman 55 powder measure and finish with my Ohaus scale. I use to weight all my brass by weight then, now I use volume weight. I am changing all my brass to either Peterson or Lapua brass too. All I can say is "THANKS TO ALL THAT WRITE HERE" I have found it to very enlightening. It hard to brake an old dog of bad habits, but you can teach him now tricks. I am learning lots of new tricks.

 

[Mikecr]

The only difference I can find is that the bushing die is not sizing the last little bit of neck, say where a doughnut may be forming. The bearing surface of my bullet does not enter the doughnut area of brass so one would think that sizing that part with a FL die would not effect it but best I can see is that it does. Am I figuring right?

Unless loading for a small underbore, running extreme pressure loads, you won't likely be rewarded for an excess starting pressure that FL neck sizing causes. For most of us by far, partial neck sizing is superior to full neck sizing.
So yeah, you got it right.

 

[Tech4]

Sizing means yielding.
That is, dimension change beyond springback causes yielding, and yielded only allows partial recovery to a new dimension (i.e. sizing).
When downsizing necks for more than ~1thou interference, seated bullet bearing will just re-expand/size that much of it.

Unless you size necks beyond seated bearing, you have no more than springback energy from cal dimension gripping your bullet (tension).
This is not a 'problem' as that's what you have.
Where you do size necks beyond seated bearing, you add bearing-base binding and bring donut area/shoulder angle into tension, which is a horrible plan for hunting capacity cartridges.

Good minimal sizing brings necks down ~2thou interference (after springback) for no more length than seated bullet bearing. This would be followed by an expander mandrel at cal in a pre-seating operation. That drives any thickness variance into yielding outward, away from seating bullets, to reduce loaded runout. It also sets interference to ~1thou, which is what you'll have anyway, but without using your bullets for expansion sizing. Better to use a mandrel for this, as bullets make terrible mandrels.
If you had left a carbon layer in necks (the perfect lube) then with this sizing plan you reduce seating forces, so you reduce seating depth variance. It get's a lot easier to set exact CBTO.
Less annealing rate is needed. And tension is then tweaked through sizing LENGTH adjustment (with a bushing die).
After all, neck tension is springback force X area applied to seated bearing. It's PSI.

Whatever you do, apply it through load development.

Less annealing rate? Are applying heat for less time or are you saying something else?

 

[Mikecr]

That process annealing to manage tension is needed less often.
With reasonable neck clearance (<3thou) you can probably go many cycles without re-annealing. Possibly more than your cases will last anyway.

I anneal initially for fire forming, and then later as needed. I know it's time when I'm fighting to match measured seating forces.
If your annealing is really good (like salt bath good), and chambers are big in clearances, then you might anneal more often than I do.
Makes sense.