Ive been researching ways to lower my ES and SD. One of those ways included running an expander mandrel die. Ive read where i still use my bushing die without an expander before i use the expander mandrel die. I have my bushing set up for a two thou neck tension. I see that Sinclair has an expander that is .263, which is one thou less than the bullets diameter. My question is, if I start running a expander mandrel die, will I need to change my bushing? And Is there any steps that Im missing?
Questions using expanding mandrel
- Thread starter Josh11
- Start date
ImBIllT
Silver $$ Contributor
If you turn your neck properly, the expander will likely not improve anything. If you're shooting unturned brass, I recommend sizing with a die with an expander in it. I'm not convinced that expanding as a separate operation will result any improvement as opposed to pulling the brass over the expander in most threaded dies. The Sinclair neck expander a exist primarily as a step for prepping brass prior to neck turning. Their expander diameter yields a good fit for their neck turning mandrel diameter. Even if you choose to use an expander as a separate operation, I would not adjust your bushing size. The brass will spring back tighter than the expander, just as it springs back looser than the bushing. One thou bullet diameter for an expander will probably yield almost identical neck tension when compared to two thou under bullet diameter for a bushing.
The sinclair expander is .001 less than the bullet diameter to account for brass spring back. So the .001 under from the mandrel plus another .001 under for spring back gives you .002 neck tension. With your current bushing I dont see that it would do a whole lot for you as stated ^^^^ unless your necks arent consistent. The die bushing will push any discrepancies to the inside. The mandrel will push any discrepancies to the outside providing a consistent inner diameter.
If you were already turning necks (which I doubt since youre asking this) you wouldnt have any discrepancies/inconsistencies in your brass thickness from case to case. Personally, if I were doing this in your place I would go for a bushing thats .001 smaller than you already have and then use the expander to bring it back up to size. That would give you a little wiggle room ensuring that everything gets brought back up consistently on the inside diameter regardless of brass thickness.
If you were already turning necks (which I doubt since youre asking this) you wouldnt have any discrepancies/inconsistencies in your brass thickness from case to case. Personally, if I were doing this in your place I would go for a bushing thats .001 smaller than you already have and then use the expander to bring it back up to size. That would give you a little wiggle room ensuring that everything gets brought back up consistently on the inside diameter regardless of brass thickness.
ImBIllT
Silver $$ Contributor
Yeah on second thought, I have to agree. Your current bushing might not give an expander enough to bite to fix anything. Going .001" tighter than current could help that.
On a side note, bushing only dies are ideal for neck turned cases. They will CAUSE terrible accuracy when used with inconsistent necks. Type S dies have a bushing, but they also include the expander. When not using turned necks I use conventional dies to partial size or full length size, or I use type S dies to neck size. Brass with inconsistent necks will shoot surprisingly well when used with dies that expand the neck after sizing the neck.
Alex Wheeler
Site $$ Sponsor
Are you turning your necks? Your going to need to tune your neck tension so you want a set of mandrels. @AlloyTargets is going to be selling them in different sizes. What kind or es are you getting and what do the groups look like? You should be able to achieve 15 or better es pretty easily, under that es has to effect on group size at long range in my experience.
X-Caveman
Gold $$ Contributor
http://forum.accurateshooter.com/threads/seeking-a-good-source-for-expanding-mandrels.3926813/
Lots of good info here^^^
I don't have any first hand data to support my opinion, but I think they make a lot of sense. So much so, that I've ordered almost $2k in high quality 6 & 7mm sets. I'll have them for sale in August (hopefully). I know for a fact that expanding in a separate operation with the Sinclair die is used by some of the top long range BR shooters in the world. And yes, they turn necks and still see the need.
Lots of good info here^^^
I don't have any first hand data to support my opinion, but I think they make a lot of sense. So much so, that I've ordered almost $2k in high quality 6 & 7mm sets. I'll have them for sale in August (hopefully). I know for a fact that expanding in a separate operation with the Sinclair die is used by some of the top long range BR shooters in the world. And yes, they turn necks and still see the need.
Do you want to test ammo prep or do you want to shoot?
If I could consistently claim those numbers I'd be Very Happy Indeed.
I typically call it done when I can shoot 5-shot group tests, see my stats approach those. Mind I don't shoot groups out at 1,000 (sling & irons mostly) so your demands may be tighter.
My opinion? I think practically you've reached what it's possible to achieve unless you're willing to spend more time reading indicators than actually shooting... if then!
Oh and I use an expander mandrel on my bushing-sized, neck-turned brass too, as a last step before cleaning then prime & load.
Alex Wheeler
Site $$ Sponsor
What cartridge and load?
Most folks see about 1/2 to 1/3 the SD and ES numbers when their rifle is shot free recoil versus shouldered at a bench resting on bags. But average muzzle velocity is less with free recoiling rifles resting on bags. Lowest SD and ES numbers happen with fixed (non-recoiling) barreled actions; highest average velocity happens, too.
Us humans don't hold rifles exactly the same from shot to shot. A 50 fps spread in average velocity is common with a given rifle and load across several people shooting it. A 90 fps spread has been observed.
Some rifles with ammo having big spreads in velocity shoot very accurate at longer ranges. Their barrels' muzzle axis whips vertically such that slower bullets leave at a higher angle than faster ones that compensates for their greater drop at target range.
Us humans don't hold rifles exactly the same from shot to shot. A 50 fps spread in average velocity is common with a given rifle and load across several people shooting it. A 90 fps spread has been observed.
Some rifles with ammo having big spreads in velocity shoot very accurate at longer ranges. Their barrels' muzzle axis whips vertically such that slower bullets leave at a higher angle than faster ones that compensates for their greater drop at target range.
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I tried every sizing method known to man to get bottleneck case necks as straight as possible on resized cases. Ended up doing what Sierra Bullets' ballistic tech said; hone full length sizing die necks out to a thousandth or two less than a loaded round neck diameter. Set the die to bump fired case shoulders back 2 thousandths inch.
This is the only way to keep the sized case neck perfectly aligned with the case shoulder (most important) and body axis. All of the case is held in alignment with the die chamber when it's full into the die. No expander ball at all because even the slightest friction it has coming back up through the case neck bends the case neck a tiny amount.
It's the case shoulder centering in the chamber shoulder (from firing pin impact) on bottleneck cases headspacing on their shoulder that centers the case neck in the chamber neck. The rest case body does not touch the chamber body except at the back end at the pressure ring where it's pressed against the chamber wall by the extractor or firing pin impact moving the case head. Nor does the case neck touch the chamber neck when the round's fired; there's always some clearance all the way around the case neck. Even a 243 Win case neck centers perfectly in a 308 Win chamber neck; both their shoulders center perfectly in the chamber shoulder.
If neck wall thickness varies 1 thousandth inch, cases so sized will have their bullets only .0005" off center in the chamber throat when fired; .0010" off center with neck wall thickness spread of .002".
This is the only way to keep the sized case neck perfectly aligned with the case shoulder (most important) and body axis. All of the case is held in alignment with the die chamber when it's full into the die. No expander ball at all because even the slightest friction it has coming back up through the case neck bends the case neck a tiny amount.
It's the case shoulder centering in the chamber shoulder (from firing pin impact) on bottleneck cases headspacing on their shoulder that centers the case neck in the chamber neck. The rest case body does not touch the chamber body except at the back end at the pressure ring where it's pressed against the chamber wall by the extractor or firing pin impact moving the case head. Nor does the case neck touch the chamber neck when the round's fired; there's always some clearance all the way around the case neck. Even a 243 Win case neck centers perfectly in a 308 Win chamber neck; both their shoulders center perfectly in the chamber shoulder.
If neck wall thickness varies 1 thousandth inch, cases so sized will have their bullets only .0005" off center in the chamber throat when fired; .0010" off center with neck wall thickness spread of .002".
ASbobcat
Silver $$ Contributor
I have also personally seen no correlation whatsoever between ES and actual vertical spread at long range. As "Bart B" correctly points out, there are too many other variables at work. For example, I am currently working with a Dasher load registering ES greater than 100 that shoots actual vertical dispersion of 0.1moa at 600yards.
To the original thread, I use the expander mandrel method. .002 tension is fine for hunting ammo and semi-auto, but .001 generally gives much more consistent accuracy in a single shot.
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A 105 Berger vld at 3000 fps gives 11.3 moa and 70.9" of drop to 600 with the jbm trajectory base numbers. Drop that to 2900 and you get 12.2 moa and 76.9" of drop to get to 600. If your slow rounds are leaving on the top of the sine wave and your fast are on the bottom so that the meet back up and coincide perfectly at 600 youre telling me that your .1 moa at 600 rifle would have to be a .9 moa gun (12.2-11.3) at 100 yards? Because thats how the numbers are looking from my end...
I can fall into the slow on the top and fast on the bottom of the wave theory but not when it gets to extremes that far out.
While a dimensional tension (.002" is very popular), that much interference fit between bullet and case mouth diameters does not give the same neck grip force all the time. It'll be less with softer case brass.
The industry standard for how tight bullets are held in case mouths is release force; or sometimes called extraction force. It's the force needed to push the bullet out of the case. 20 pounds has been the arsenal standard for M118 7.62 NATO match ammo. As much as 60 pounds for service ammo.
Measure your own stuff by fitting a shell holder upside down to a bar clamped on a bench, slide a round point down into it, then affix a collet type bullet puller to the bullet with a string holding a bucket on it. Load the bucket with bullets until the bullet in the case pulls out. Weigh the bucket of bullets and the bullet puller to get the pounds number.
A 30 caliber bullet with a 20 pound release force needs 268 pounds of pressure in the case to push it out of the case. Bullet cross sectional area is about .0745 square inches. 268 psi multiplied by .0745 equals 20 pounds of force on the bullet.
The industry standard for how tight bullets are held in case mouths is release force; or sometimes called extraction force. It's the force needed to push the bullet out of the case. 20 pounds has been the arsenal standard for M118 7.62 NATO match ammo. As much as 60 pounds for service ammo.
Measure your own stuff by fitting a shell holder upside down to a bar clamped on a bench, slide a round point down into it, then affix a collet type bullet puller to the bullet with a string holding a bucket on it. Load the bucket with bullets until the bullet in the case pulls out. Weigh the bucket of bullets and the bullet puller to get the pounds number.
A 30 caliber bullet with a 20 pound release force needs 268 pounds of pressure in the case to push it out of the case. Bullet cross sectional area is about .0745 square inches. 268 psi multiplied by .0745 equals 20 pounds of force on the bullet.
As far as i know, Sierra Bullets still uses Redding full bushing dies without expander balls to full length size all their bottleneck cases testing bullets for accuracy; for cartridges they're made for. All other cases use standard Redding full length sizing dies. I doubt anyone gets better accuracy with their bullets shot from cases so sized than they do. All their match bullets have to shoot under half MOA at 200 yards with 10-shot test groups. Good lots of them shoot sub quarter MOA group after group after groups with no case prep at all including inconsistent neck wall thickness.
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ImBIllT
Silver $$ Contributor
My personal experience is the very opposite of what you express. Perhaps their cases are better than you realize, perhaps their dies have expanders in them, or perhaps I'm all washed up.
For my first AI cartridge, I was using standard RCBS dies while I waited for a set of Wilson's to show up. The gun shot from the high .3's to the low .5's. The Wilson dies came in. The gun went to crap. I tried a new scope, lots of cleaning, different bullets etc. Then it dawned on me...could it be the dies? I backed my die way out and dropped the expander ball down low, and ran all my sized cases over the expander. Bingo, the gun shot just as before. That was my first and only experience using bushing dies on un-turned brass without using an expander. Maybe Sierra is using good enough brass to shoot .5 MOA in a machine rest without an expander. And maybe the difference between the .5 MOA lot of bullets and the sub .25 MOA lot of bullets is actually an unusually consistent batch of brass. Whatever the case, .5 MOA ammo through a test gun in a machine rest under what are probably good conditions is NOT the ammo I want to shoot in a match. If the best the ammo can do is .5 MOA, then because I am an imperfect operator shooting in adverse conditions, then I will be shooting larger than .5 MOA groups. If turning necks or running over an expander gives me .25 MOA ammo, then perhaps I can average something under .5 MOA in a match.
ASbobcat
Silver $$ Contributor
Your mathematical model is a good example of why performance at 100yds does not necessarily predict accuracy at 600 or 1000yds. If it did correlate, we wouldn't have 600 and 1,000yd matches. We would all just compete at 100yds.
Internal and external ballistics are too complex to be calculated exactly. That's why we go to the range. One can only find out where the bullets actually end up empirically, by real world experience. Your calculations also neglected to account for variations in bullets.
Nonetheless, it is an interesting mental exercise.
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