Seater stem/s


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More 223 load development today. I put a comment in another thread about seating created run out. With everything DANG close protocol 'y speaking.... I could induce run out on finished rounds by being a little too quick on the press handle.

Which got my curiosity pegged cause of the pride involved with getting DEAD NUTS STRAIGHT loaded ammo..... to the point of testing the accuracy of our Brown $ Sharpe metrology systems.

So,shooting and loading this a.m. paid extra attention during the very beginning of the seating op. What's happening is because of relatively soft CB's.... add in factory seater stems "cut" for JB's...

If I don't slow way down,the stem is grabbing bullet tips and "driving" them cocked. Don't matter if you do the age old,spin it 180 or not. If that bullet doesn't go cleanly up in the stem that little beeatch is gonna have .003" run out. Conversely, feel it ease up into the stem and bam,straight.

Love RCBS dies.... but mr seater stem is headed for surgery. Couple pics may help show how to do hands off,steady inspection. 20180914_102825_resized.jpg


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Or.... "toolroom lathe",... wait that's two,haha.

Been wandering around in the woods getting wet. Came in and chucked the stem cell in above lathe and straightened it out.

The last one was done a little differently. Still chucked up in a lathe but,heat swaged it "out" to a slight tulip shape.

Going to load some more 223's tonight.Up to 18g of IMR4198 and the rig still wants more.


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Forster lets you do that on the press, faster, and with positive case/shoulder/neck/bullet axial and radial alignment. I like lo-buck clever fixes, but some things I can't make as cheap as I can buy and Forster BR seating dies are one of those things.


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Saving lunch money for a Timney.... no new dies on the horizon.

I have a spare Hornady 308 seater with the "sleeve" thingy..... I'll turn a sleeve and stem for it to my 223 specs and see if it works better.

I definitely straightened out the RCBS stem's chamfer.... noticeably so. And will say it's easier to "hit" in the seating process. But still getting a few with run out 'round .003.... right next to dead nut straight ones. So,won't say the stem surgery was a failure because it is cleaner/more centered.... but curiosity didn't get satisfied,yet...

These cases are inside expanded vs bushing dies so any variance in neck walls ain't impacting run out. I still say this batch of cases is kinda soft.... not gonna waste brain cells on it but; you could conceivably test,although it may be "destructive",brass hardness with a std roll crimp die.

Take a cpl cases,these soft new RP examples vs some work hardened,trimmed to exact same length and roll crimp them. I'm saying these soft cases will buckle well before the others. Heck,don't even need to be that old or work hardened.... the weeker/softer case is gonna yield.
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I purchased Forster seating dies for the calibers of rifle that I care about for best
accy. Watched dBay for a couple of years and have all I need at bargain prices.

Ammo it pretty straight if you have straight necks to start with. Some dies pull
the necks crooked when pulling out the expander. Spin them with the expander installed
and used, and without the expander to see if the ball is pulling them crooked. If so,
size without it and then re-install and push expander into neck, will usually stay straight.

All my new dies are Hornady Custom Grade dies with a floating bullet alignment stem like
the Forster dies. They work perfectly for Jbullets....often not too good for fat cast bullets.

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Found the problem..... gotta make a little bigger expander for M die setup. The way these bullets get "sized" is at issue. The noses are a no bump.... so that ain't it. The GC gets sized 225 but,thr body is "as cast".

Now,once again started to weigh some 225-55 last night. Waste of time..... yup,that dang close on weight. What isn't being addressed because the body isn't being sized is,out of roundness. The prognosis being,as good a caster as I "may" be(hitting weights) that ain't or don't always reflect on roundness. We shall see,as the lathe runs at idle,warming up the bearings..... headed for tenths world,.0001's.


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Bill, it isn’t too hard to make a replacement seating sleeve for Hornsby does on the lathe. I had to do that for 44mag as my dies refused to allow a .432+ sized bullet. Tried to open the existing sleeve but discovered they are hardened.


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Googlefoo a cutaway of an L.E.Wilson inline seater die. Compare the fewer moving parts with any of the "typical" micrometer seaters put out by the big 4.


Awhile back Ian suggested an RCBS expander as a..... oh how you say? Alternative to a Lyman M die...... I ordered what I think he was talking about,anyway... I have one RCBS die body with a 1/4-20 threaded hole in the top. Backing up a bit,micrometers have thread pitches of 40tpi. Do the math,it's about convenience not some inherent accuracy WRT 40tpi.

Now we have 20 tpi.... do the math,think about the convenience. The proposal here is a hybrid seater die utilizing the RCBS expander body with 20tpi stem acting on a full case supporting male section that slides up into the die body. It takes the simplicity and accuracy of the inline Wilson and mates it to the press you already have mounted.

Is it perfect? Naw,nothing is but it definitely is easy to make and has a high potential for reducing stacked tolerances.
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Yep, mine too. Same as most of their pistol die seater stems.

If you read the item description it says you need to buy the stem, jam nut, and spuds sepearately. Use all those accumulated extra rn or swc seating stems, borrow jam nuts from other die sets, and all you need is the die body and the spuds....which are hardened tool steel.


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Yup 1/4 -28.... was thinking 40tpi and depth settings 40/2.

Anyway.... took a 2 1/2" stainless socket cap of the 1/4-28 variety, haha. Cut the cap off,turned the smooth part of the shank to a stepped expander. Dimensions split the difference between the one I was using and the "new" O1 steel M spud made after the above for the Lyman die body. Easy peasy.

They're "DANG" straight. Have three different diameters now. Oh,and made a nice,much larger "jam nut" for the RCBS stem top. Round,and larger than the die body,for easier purchase than those little factory versions.


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Going to make the hybrid seater tomorrow. Look up; drill point geometry Joseph Mazoff.

I'd read his papers years ago but going over them again to drill the case holding part of the seater die. Don't have a 223 reamer and don't feel like grinding one or buying. Think I can accomplish this guide with just drilling on the lathe. It's interesting looking at 223 prints..... it's pretty neat. A .375 drill will work for the body because the case will be below the insert.Look at the print....the callout is .376 but that's max @ about deck height of shell holder up from base.

Neck is .250,my unturned necks with loaded .227 bullets installed are @ .249. The only other drill needed is .359... A 23/64" is .3594. It's this last drill that needs the point ground at a certain angle.

I'll leave both ends long.... final OP is trim to length.... but only the bttm is critical. Top length is not. Seating stem O.D. is a sliding fit within the insert. Easy peasy.

Got the material chucked up. 5/8" mild steel,take 10-20 thous off and it's as slick of a fit into die body as you want it.Part stays chucked,die body is the gage... cut/try to requirements.


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This really sounds like an interesting project however I'm so lost in trying to understand the information. I'm still going to be following the thread!
Thought I was mechanically adept but just not sure what I'm seeing or what is happening.:rolleyes:


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He's making a Forster-style seating die out of the RCBS cast bullet expanding die body. The 5/8" stock will become a sleeve that holds the cartridge case still and is drilled through the top for a seating stem he made that's a close fit in the top of the sleeve. The stem and sleeve will bring the bullet and case together in perfect goes in the sleeve all the way, then sleeve/case are moved together against the stem that holds the bullet point-on-center relative to case body/shoulder and stuffs it straight into the neck. A .223 chamber reamer would be the would be turning the sleeve from the chamber of a junk .223 barrel, but sometimes ya run what ya brung and drills (and a boring bar) can accomplish the same thing well enough.


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Done.... took a cpl hrs. But that included grinding 3 drills....having to go snag a she'll holder from loading room.... and taking time out to blast a cpl 223 groups downrange.

Pretty uneventful really..... hit ALL my specs,only one that I snuck up on was the shoulder datum.... which is why the shell holder was needed.

It's almost foolproof,well I guess you could try to put the case in upside down? but barring that.... put the bullet on top and run it up in there.

The issue with using a reamer is on banana cases.IOW's this guide only needs to interface at/near the base and then around shoulder..... and obviously the neck stem. Any other contact is unwarranted.