guys, I need to know about sizing .38 bullets down to 9mm

[caffe]

I've got a pair of 6 cavity Lee molds, tumble lube and so far, just their hand sizer. I've only got a Lee 1000 press. Both the 125 gr 9mm 356 bullet and the .358" 150 gr bullet are pretty hard to mallet drive the bullet thru the .356 die. They shipped the press to me without the attachment for the handle. I"m working on getting the proper part. Lee seems inclined to do so for free. Also, a LOT of lead is displaced onto the base of the 150 gr .38 bullet after I size it with a mallet. Is there a way to mitigate that effect?

Does anyone know if the Lee press has enough leverage to hand size bullets thru the Lee hand sizer die? I detest using 2 cavity molds and Lyman's prices are sky high, anyway. Right now, end of May 2020, everything is out of stock/hard to get. I want to use the 125 gr bullet for wussy loads in my Sig pocket 9mm, like 800 fps,and the 150 gr in the Commander 9mm, 850 fps, to avoid fouling and keyholing. Any help is very much appreciated.

[MT Gianni]

What size do your bullets measure with a micrometer, not a caliper?
What is your alloy?
What do your bbls slug out to?
How big are your cylinder throats?
It looks to me that you may be sizing a too hard alloy to an assumed size that may or not fit when you are done. I doubt you can size down more than 1 or 2 thousandths with a hand press unless you're a professional arm wrestler.

[murf205]

I have sized .458 405 gr Remington's (jacketed!) down to .452 with a bit of gun oil on them BUT...I use a RCBS Rockchucker. I have no experience with a Lee press like yours but it DID take some serious pushing on the Rchucker handle. If you are talking about the Lee push through die, I would use a tight patch coated with Semi chrome or Flitz paste to polish the inside of the die. It helps and the oil helps as well. Like MT Gianni said, the proper measurements will help to get a starting point. Unless the boolits you have are super hard, you should be able to size down .002. Welcome to the site, by the way. You will love this place and find the people here have a wealth of knowledge and are more than willing to help.

[toallmy]

Have you tried ' plunk testing ' your boolits in a case as they are .
You might find them to chamber as is , try loading a dummy round , without powder and prime , to test function .

[caffe]

haven't tried loading them as Is. I can see the .356 bullets working that way, but not the .358"? any way, the bullets are very hard and the 125 gr lrn might be able to handle being driven 1000 fps, for decent recoil-effect in training. I cast them out of wheelweights and suspect zinc contamination to a certain amount. Any recommended lubes? I currently have only the lee alox tumble lube. I would have thought that a sizing die would be already highly polished? Is the polishing not going to increase the OD of the bullet? .001" overall Diameter is just 1/2 of a thouandth of polishing the entire perimeter of the dies ID. I have no mike. I doubt that the bore or throat ID makes much diff in an autoloader? I mean I had to BEAT on the .358" 150 gr bullets with the mallet to get them thru the die. What do I do about the displaced lead around the base of the bullet's edge? doens't that hurt accuracy? it's not very consistent as to its addition to the OAL of the bullet. It might be that I can add the pure lead of the adhesive wheel weights to soften the alloy. That would be a good deal. I've got about 80 lbs of the hard stuff and 10 or so lbs of the soft lead.

[la5676]

I've got a pair of 6 cavity Lee molds, tumble lube and so far, just their hand sizer. I've only got a Lee 1000 press. Both the 125 gr 9mm 356 bullet and the .358" 150 gr bullet are pretty hard to mallet drive the bullet thru the .356 die. They shipped the press to me without the attachment for the handle. I"m working on getting the proper part. Lee seems inclined to do so for free. Also, a LOT of lead is displaced onto the base of the 150 gr .38 bullet after I size it with a mallet. Is there a way to mitigate that effect?

Does anyone know if the Lee press has enough leverage to hand size bullets thru the Lee hand sizer die? I detest using 2 cavity molds and Lyman's prices are sky high, anyway. Right now, end of May 2020, everything is out of stock/hard to get. I want to use the 125 gr bullet for wussy loads in my Sig pocket 9mm, like 800 fps,and the 150 gr in the Commander 9mm, 850 fps, to avoid fouling and keyholing. Any help is very much appreciated.
Is this the press you are referring to as the hand sizer?
262894

I think you could certainly build up your wrists doing very many boolits on this. I'm guessing you are prolly "upsetting" or basically obturating the boolit when you hit it with the mallet, causing it to swell in diameter just a bit, enough to cause shear like you are seeing. You need the right tools for the right job for sure. You need to find an old used LEE basic single stage cheap press for your sizing if ya wanna keep your investment down for now, ya can't do this job on a LEE 1000.

[la5676]

haven't tried loading them as Is. I can see the .356 bullets working that way, but not the .358"? any way, the bullets are very hard and the 125 gr lrn might be able to handle being driven 1000 fps, for decent recoil-effect in training. I cast them out of wheelweights and suspect zinc contamination to a certain amount. Any recommended lubes? I currently have only the lee alox tumble lube. I would have thought that a sizing die would be already highly polished? Is the polishing not going to increase the OD of the bullet? .001" overall Diameter is just 1/2 of a thouandth of polishing the entire perimeter of the dies ID. I have no mike. I doubt that the bore or throat ID makes much diff in an autoloader? I mean I had to BEAT on the .358" 150 gr bullets with the mallet to get them thru the die. What do I do about the displaced lead around the base of the bullet's edge? doens't that hurt accuracy?
I hate to say this, but I'm not sure you should be reloading on your own yet. You need a few more tools, a micrometer is an important one, believe it or not. And read a few more books on ballistics.

[megasupermagnum]

You do not need a micrometer to reload ammo.

The Lee hand press works great for sizing bullets, many people even use them for dedicated sizing presses. Using a mallet is upsetting the bullet, and expanding it. Once you get the handle figured out, they size like butter. .002" is nothing, you will barely feel it. Lube helps, although I have sized many bullets dry.

Tumble lube works great. Add a thin coat before sizing, then a second coat after sizing. By thin, I mean you should hardly be able to see it. A pea size drop of alox tumble lube should do 300-500 bullets.

[marek313]

Your skipping couple steps if you ask me. First of all you need to find out what size bullets will chamber in your guns because standard 9mm sizes to .355 which is actually to small for most 9mm cast projectiles. You need to make ammo for the gun and not just to the standard specs and all guns are different. There are 9mm guns that will only shoot .355 because they have tight chambers and ones that have no problem handling .359. I feed my two 9s with .3575 but my Taurus will only run .355 and thats fine I dont shoot it much.
I dont know if you have .357 sizer but I would try to size couple to .357 and see if they chamber. I think you'll have better luck with better accuracy and no barrel leading with larger bullets.

Second thing I'll tell you is that 9mm in general is hard to get and takes long time to get right. Honestly i dont recommend it as a first caliber to learn on. Larger slower calibers like 45acp are much better to learn on. The only analogy i can think of is like walking the rope. 45acp is like walking on a sidewalk curb while 9mm is walking on a rope.

Third of all. Heavy 150gr - 160gr+ in 9mm are a whole another step up from standard 115-125gr projectiles. Very little room for error you have to get seating depth just right and work up a small enough charge no to cause pressure spikes. Now your on a rope hanging between two tall building and you dropped your balancing pole.

Not trying to scare you or maybe I am a little bit because it only takes one bad round to leave you standing in a cloud of smoke wondering why your gun just blew up. I've seen it happen and it was with reloaded 9mm too right next to me. What I'm trying to say is learn how to walk before you run. Start with 125gr, get sizing correct, powder coat and shoot. Or maybe even start with some fmjs to get the hang of things. There is a lot of tricks and knowledge here on this board. Once you learn the basics then move to more complex things like heavy 9s.

[toallmy]

There is a lot of very helpful information in the archives , that can be found in the Google search box at the top right side of the screen . I suggest taking your time researching your new found adventure , even though - I'm shore your excited to begin stuffing your cast boolits in a case . It can be very dangerous a lot can go wrong with the pressure inside a 9 mm case .
If you don't mind start from the beginning with things like
I'm a new caster , but long time reloader , or I'm sorta new to reloading but eager to get started . SAFELY
I choose this mold to start with because ?
Lube choice lee tumble lube .
Will this sizing die get me the right diameter Boolit ?
Loading cast boolits over size , safe over all length .
How can I load safe , dependable , accurate ammunition with cast boolits ?
This will help members try to get you started working out the details .

[tomme boy]

try lubing the bullets before you size them. Also most 9mm guns will take a 0.357" or 0.358" bullets.
load a few dummies and see if they chamber..

[caffe]

I hate to say this, but I'm not sure you should be reloading on your own yet. You need a few more tools, a micrometer is an important one, believe it or not. And read a few more books on ballistics.

I've loaded well over 100,000 rds, almost all of it .45 ACP and 90% of it on a star progressive. A little bit on a dillon 550. About 10,000 on a Rockchucker, but all of it over 30 years ago. I've loaded a few rifle rds 308, 223, 30-30, 44 mag, 45 l Colt, 38, 357, 380. I know that a mike means nothing for practice 9mm lrn rds. :-) I've never had to mike a thing other than when gunsmithing.

[caffe]

try lubing the bullets before you size them. Also most 9mm guns will take a 0.357" or 0.358" bullets.
load a few dummies and see if they chamber..

of course I lubed them first and I"ll lube them again before loading. This alloy is hard and I've always just dropped the slugs into the water bucket with the sprue and quenched the molds there when they got too hot and ran frosted bullets, too, but that was with multiple 4 cavity H&G molds in .45.

[caffe]

using heavier bullets doesn't mean anything special, as long as you bring the powder charge and velocities down in a commensurate manner. I know that 850 fps with a 150 gr lrn is nothing. Lyman used to recommend a charge of 4.5 grs of UE with a 158 gr lrn in 9mm, for 1050 fps in a 5" barrel. The only thing that's complicating things right now is the "out of stock' bs because of the virus. Everybody got a 3 month head start on me. I think that the issue is that the alloy is so damned hard. I might leave it that hard for casting the 125 gr lrn , in the interest of not stripping the bullet in the rifling. I dont intend to cast many of the lighter bullets, cause they are intended for the pocket model. If I can use up some of the softer lead and thus, make the 150 gr .358" bullets easier to size, that will let me use up this soft lead that I thought I had no real use for. Given the softer alloy, that might well mean less displacement of lead to the base with sizing of the bullet, and it should certainly mean that sizing them will be easier. While setting up my Lee 1000, I discovered that the connector between the ram and the handle is missing. lee is supposedly making good on that in the next few days. So we'll see.

[caffe]

have you guys ever used or even seen a lee handsizer for bullets? there's a pushrod sort of deal, so the mallet impacts are on the head of the pushrod. There is no chance for the bullet to obture.

[caffe]

Is this the press you are referring to as the hand sizer?
262894

I think you could certainly build up your wrists doing very many boolits on this. I'm guessing you are prolly "upsetting" or basically obturating the boolit when you hit it with the mallet, causing it to swell in diameter just a bit, enough to cause shear like you are seeing. You need the right tools for the right job for sure. You need to find an old used LEE basic single stage cheap press for your sizing if ya wanna keep your investment down for now, ya can't do this job on a LEE 1000.

no, the only press I currently have is the lee 1000 progressive and at this point, it still lacks the connecting piece for the handle. The lee hand sizer is normally used in a single station loading press, but I just held it in my hand and hit the pushrod with a mallet, forcing the bullets thru the sizer die.

[caffe]

I thought I said that I chose the 125 gr lrn for wussy loads in the Sig P938, cause I dont consider any of the pocket 9mms to be all that durable. Which is why I practice with the alloy commander 9mm. For the latter, I want a heavier bullet, so that I can match the recoil of ball ammo, without the fouling and keyholing problems that come with 1100 fps and most lead alloys. By upping the bullet weight to 150 grs, I can hold the velocity to 850 fps and still qualify to shoot IPSC and IDPA minor class. When IPSC was set up, minor caliber required the same recoil/momentum as regular pressure .38 special 158 gr lrn, at 800 fps. and I doubt that it's been made any more difficult to handle. I know Bill Wilson pretty well. I shot with him back in the 70's.

[la5676]

have you guys ever used or even seen a lee handsizer for bullets? there's a pushrod sort of deal, so the mallet impacts are on the head of the pushrod. There is no chance for the bullet to obture.

Just never heard it called a Lee hand sizing die. What I think you have is a Lee push thru die, which mounts in any press, but ain't gonna mount in your 1000. There is no place to put the push pin, the 1000 uses a plate.

Is this what you have?
262904

And you are hitting the head of the push rod, but it transmits the smack inertia to the body of the boolit. Law of physics and all ya know.

[Jniedbalski]

You can size your bullets like your doing but it will be hard to do. Some guns can take a .358 boolet. My star and Beretta will take a .358 the high point will only take a .357. To bad about the missing part. Hope you get it soon. I also have been waiting on parts. It will help putting your sizer in any of lee’s single stage press. I have the lee hand held single stage press and it’s not that hard to size your bullets. I have the same mold you have.

[Bazoo]

I've used the lee hand size die. Whack a mole sizing is much harder than press sizing with the lee push through dies. If you've water dropped your bullets that's half your problem. If you lube the bullets with something like Hornady one shot, or maybe remoil it'll ease sizing. I've done it in small quantities and I don't remember if I tumble lubed or if I had any issues with lube sticking. This you'll have to experiment out yourself. Water will lube some though and it will dry and not affect the tumble lube.

Long story short the lee dies are often in need of polishing. You don't lap them 10 minutes. Use a piece of 800/1000 grit paper on a dowel with a fine kerf in it's end, powered by a drill, to smooth some and then use some green polishing compound on a mop.

[la5676]

I've used the lee hand size die.

I've looked all over LEE's site. What is this Lee hand size die? Pics please. Do they even make it anymore, not that I want one.

[caffe]

Just never heard it called a Lee hand sizing die. What I think you have is a Lee push thru die, which mounts in any press, but ain't gonna mount in your 1000. There is no place to put the push pin, the 1000 uses a plate.

Is this what you have?
262904

And you are hitting the head of the push rod, but it transmits the smack inertia to the body of the boolit. Law of physics and all ya know.

yeah, but since the bullet's in the die, there's no place for it to obture. obture means "swellling" and in bullet nomenclature, it means swelling as to diameter, which is impossible when it's inside of the die.

[la5676]

yeah, but since the bullet's in the die, there's no place for it to obture. obture means "swellling" and in bullet nomenclature, it means swelling as to diameter, which is impossible when it's inside of the die.

It's not completely in the die before you whack it, or you wouldn't have to whack it. If it is completely in the die, there is no need to size. It's in the throat of the die.

[caffe]

I"ve still not heard anything about the lead that's displaced into a ring around the edge of the .358" OD bullet's base? Has that happened to you guys? is it an accuracy problem? If water quenching helps THIS much, as to hardness, I dunno why anyone would ever add any antimony or tin to a lead casting alloy. WOW.

[la5676]

a subsequent post to yours has a picture of the lee bullet sizer die.

That is the LEE push through die everyone is referring to in this thread. Never heard it called a hand sizer die. It has threads on it, intended to be mounted in a press, either mounted or the hand press I also posted above.

[caffe]

It's not completely in the die before you whack it, or you wouldn't have to whack it. If it is completely in the die, there is no need to size. It's in the throat of the die.

I see what you mean, cause there's gotta be clearance to let the pushrod move. That makes sense. Thanks.

[caffe]

I might wind up having to buy a single stage press. Does anyone know if the lee 1000 progressive can size 223 brass? I've heard it both ways. They sell it "set up" for 223.

[la5676]

I"ve still not heard anything about the lead that's displaced into a ring around the edge of the .358" OD bullet's base? Has that happened to you guys? is it an accuracy problem? If water quenching helps THIS much, as to hardness, I dunno why anyone would ever add any antimony or tin to a lead casting alloy. WOW.

No, never had your issue of the ring you are getting, but I don't use a hammer. I have pushed .362 cast boolits through my .358 "hand sizer die" as you will, and still don't get a ring. I think you need to wait on a press and try that.

And, you are using way too hard an alloy of lead for 9mm, IMHO. Holy gawd, that is hard, man. Straight COWW is all I have ever used for 45 years. I've only recently started to PC, but haven't changed the alloy.

[la5676]

I might wind up having to buy a single stage press. Does anyone know if the lee 1000 progressive can size 223 brass? I've heard it both ways. They sell it "set up" for 223.

.223 is about the limit of the 1000. Just lube them well. I use the 1000 on for all my pistol loading, love it.

[caffe]

if the 1000 will size 223 cases, I'm elated. I didn't do anything to harden the ww alloy, other than if the water drop did so. i agree that it's way too hard and that might be causing the ring of displaced lead, and so might the mallet process. It appears that I'll either have to buy a sizer luber or the single station press for sizing the bullets. Crud!

[megasupermagnum]

Ok, it looks like we need a clarification.

So you ONLY have a Pro1000 press and nothing else? Lee also makes a hand press, shown in post #6 that works great for sizing bullets. Lee just came out with a new press called the APP, and can be seen here. https://leeprecision.com/deluxe-app-press.html This is a fantastic tool for processing both bullets and brass.

The next thing is your nomenclature for the sizing dies is off. Lee makes two styles of sizing dies, and while I have done it too, neither is designed to be used with a mallet. They are designed to be used in a press, and the press needs to be able to accept shell holders for the push rod to mount in. The Pro1000 can not be used to size bullets. I'm going to guess that you are using the older style bullet sizing kit, seen here. https://leeprecision.com/bullet-casting/bullet-sizing-kit/

Lee also makes a new style called the Breech Lock sizing kit. The difference here is that instead of buying a $25 die for every size, you buy the breech lock body, and change the size with $12 bushings. Prices are lower from most other sources. This kit can bee seen here. https://leeprecision.com/breech-lock-bullet-sizing-kit/

The next thing I would like to address is that you seem reluctant to load normally because you are afraid of leading. First of all, I can promise you lead fouling is not that bad. It comes out easy with a couple tricks. Secondly, there is no magical limit that causes leading. You can load 9mm to it's limits and have a load that shoots clean. Provided your barrel is not rougher than a cob, all you need is a decent lube (Lee Alox works well), reasonable alloy (anything from 20:1 to linotype should be no problem for 9mm), and third and most important is the bullet needs to seal the barrel. There are many different ways to go about this, the most common is to size .002" over groove diameter of the barrel. Some size to the throat. Some use a softer bullet and hope it bumps up with pressure. A hard bullet like you are using is ok if it starts large enough, but is the worst possible scenario if it is too small. Along with sizing the bullets correctly, you need to make sure your brass is not sizing them down. Most of the time you can get away fine, but sometimes you need to use an oversized expander plug to flare the brass.

Hopefully we are on the same page now. Getting back you your sizing die. The die is tapered most of the way, which is why they work so well. The part that actually sizes the bullet is very short on a Lee die. When you use a mallet, you are smashing the bullet to fit the tapered section, and by continuing to force it, eventually getting it through the die. These dies really do need to be used in a press. If you had an arbor press, that could work, even a bench vice could work, although slowly. I would recommend buying the Lee APP press.

You also mentioned the sizing die finning the base. This is to be expected, as the push rod is smaller than the die. Normally the bullet pushes through with minimal force, and this is no problem. When you are forcing it through, the lead has nowhere else to go. This will greatly effect accuracy, and unless you really needed them, would be best re melted.

[megasupermagnum]

I"ve still not heard anything about the lead that's displaced into a ring around the edge of the .358" OD bullet's base? Has that happened to you guys? is it an accuracy problem? If water quenching helps THIS much, as to hardness, I dunno why anyone would ever add any antimony or tin to a lead casting alloy. WOW.

Water quenching only effects certain alloys. In your typical clip on wheel weight metal, there are four main types of metals that make up the alloy. Lead, tin, antimony, and very slight amount of arsenic. It has been said the arsenic is the key to quench hardening, although I've heard that a antimony alone can do it too. This would be a question for a metallurgist. Your classic Lead/Tin only, or pure lead will NOT quench harden in the slightest. Further, Tin does wonderous things to an alloy. If equaled with antimony, the two will bond together, and produces a much more ductile alloy. An alloy that is only lead and antimony is terribly brittle. OK for target work, but not the best for hunting.

[caffe]

thanks. SOMETHING has made my bullets harder than the hubs of hell. The ingots also wont mark with a thumb nail. So I'll see about adding some of the soft lead when I cast in quantity.

[megasupermagnum]

thanks. SOMETHING has made my bullets harder than the hubs of hell. The ingots also wont mark with a thumb nail. So I'll see about adding some of the soft lead when I cast in quantity.

You water quenched them, which is why they are hard. This is not the end of the world. In fact this makes them less prone to damage during handling. All that you need to do is make sure that you are sizing them, such that they are larger than the barrel, yet still function. Some guys don't even measure, and size the largest that will still fit in the chamber. Many calibers you can get away with a standard sizing if you will, for example .311" for 30 calibers. The problem with 9mm in particular is that the barrels have been made all over the map. I've seen guys sizing from .355" all the way to .359". If I had to start somewhere, I would size .357", which should work in the majority of the pistols out there.

[Bazoo]

http://castboolits.gunloads.com/showthread.php?130146-pan-lubing-kit

The sizer has a rod and die body like the current production and is made for mallet use. No longer in production. No threads.

Dumb question, are you using the die body upside down? The one I've used the bullet dropped in the body flush with the top and then you whacked it through.

[la5676]

There are many different ways to go about this, the most common is to size .002" over groove diameter of the barrel. Some size to the throat. Some use a softer bullet and hope it bumps up with pressure. A hard bullet like you are using is ok if it starts large enough, but is the worst possible scenario if it is too small. Along with sizing the bullets correctly, you need to make sure your brass is not sizing them down. Most of the time you can get away fine, but sometimes you need to use an oversized expander plug to flare the brass.


Can a guy do this without a micrometer? Asking for a friend of course.:kidding:

[Rattlesnake Charlie]

My 9mm's all function with bullets sized to .358.

[RU shooter]

You maybe getting that finning on the bottom of the 150 bullet because it's being sized down a lot more than you think , what size is it dropping out of the mould? And what are you sizing it down to ? Just because it's a .358 mould don't mean it's .358 dia as cast. And as has been said you don't need hard alloy for 9mm add that soft lead in

[tomme boy]

I have gone from 0.361" down to 0.356" in one pass and never got any flashing. Use the proper tools in the way they are designed and you will not have any problem.

Reading the instructions is going to be the first thing you need to do. Then ask if you have any questions. You have already set yourself up for failure the way you are proceeding. And get the right tools, that would help.

[la5676]

if the 1000 will size 223 cases, I'm elated. I didn't do anything to harden the ww alloy, other than if the water drop did so. i agree that it's way too hard and that might be causing the ring of displaced lead, and so might the mallet process. It appears that I'll either have to buy a sizer luber or the single station press for sizing the bullets. Crud!

I've got a couple Lyman 450's that I'd love to make someone a deal on, don't use them much anymore, mostly went to PC, but that isn't gonna do you much good on TL boolits.

[charlie b]

First, I would stop water quenching. Air cooled wheel weights are hard enough for 1000fps loads. Since you have tumble lube bullets then I would use Lee Liquid Alox and tumble them (or a variant like Bens LLA or 45-45-10).

Second, stop pounding on that thing. Put the sizing die in your press and size them that way. The hammering is causing you the problems you are seeing. Whacking enlarges the bullet a bit before it goes through the small part of the die and then it expands a bit around the punch before getting sized.

(yes, Lee is a good company for making good on their products. I haven't paid for a replacement part on any of my Lee presses in several decades).

If you have an arbor press you can use it with the push through sizing die. MUCH better than a mallet.

Third, if you don't know what your bore and groove dia are, then why are you sizing the .358 bullets? You can take one of those (not water quenched) and 'pound' it through the barrel (once it is removed from the pistol). Then see how much lead is 'moved'. Do the same with the 9mm bullet for a comparison. Better is to measure the resulting bullet (especially the bore dia). You can use a vernier caliper to do so, even one of the cheap Harbor Freight ones.

Yes, you can do a lot of reloading and casting without a precise measuring tool, but, I would not be without my vernier caliper. Most of the time it is used to measure overall length of bullets so I can set my seating dies correctly.

[megasupermagnum]

Can a guy do this without a micrometer? Asking for a friend of course.:kidding:

Of course. A calipers is accurate to .001" if you know how to use one. I know many of us like to take things right down to the thenths, but that level of measurement simply isn't needed to get ammo that shoots well.

[la5676]

Of course. A calipers is accurate to .001" if you know how to use one. I know many of us like to take things right down to the thenths, but that level of measurement simply isn't needed to get ammo that shoots well.

I know that, hence the chain pulling meme thingy there. I use my calipers far more than the micrometer for sure, so dang much easier to use. But, I do check it with the micrometer from time to time. I have seen calipers go out of accuracy at times.

[TDB9901]

As stated in an earlier post.. I don't think the old Lee mallet sizer I started with in the early 70's is in production any longer.
The chamber was tapered on them so the boolit was completely in before it hit the sizing area.

I do recall having a "flange" of sorts form on the base occasionally if I was sizing down too far.

[MT Chambers]

keep poundin' on 'em.