Thormold Pellet Swaging Die (early impressions)

Executive summary: this is an expensive and time consuming way to make a pellet and buying this swaging die kit does not guarantee top notch results. The cost per pellet in lead material is very good ($.01/pellet for 13.5gr) but it would take a lifetime to swage enough pellets to cover the initial equipment cost. I believe this tooling makes it possible to make superior pellets with minimal rejects if you have appropriate attention to detail and the right supporting tools. After developing my process over the course of a few hundred pellets of varying quality and efficiency, I can produce 80-100 really good pellets in 1 to 1.5 hours. My hope is that I can spend about this amount of time to produce enough very consistent for a field target or benchrest match. The cost is still fairly high but at least I don't have stacks of tins of pellets that don't shoot very well or to sort through (if you're a sorter). The swaged pellets look really good and come out free of visible flaws and they can shoot really well in the right conditions. And I'm enjoying this right now - there's something satisfying about making your own and seeing them out-shoot anything you can buy.
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My personal interest in airguns centers around accuracy. One thing that most seasoned accuracy shooters agree on is that having consistent and uniform pellets is a huge element. I got quite interested when I first saw the HM Hen dies but they were already unavailable. So when Thor announced split swaging dies I decided to jump in and be an early adopter. At about $1000 it was no small chance.

Big thanks go to my friend Rod (@bearbar) for his help and involvement all along the way. Anything good that came from this is a team effort.

I am using the terminology swaging and die because that's technically what this is: cold forming the lead in a die (as opposed to casting molten material in a mold).

Figuring out how to make perfect pellets took work. It takes the right lead wire, consistent pressing force, a very good swaging die that is perfectly clean, very careful handling of the pellets, and a consistent process. And after all that, some batches don't come out as well as others so you need to inspect your pellets. I use a digital microscope for that. The idea of inspecting handmade pellets might sound like a step backward but it's not bad since most of them are acceptable or easily fixed by brushing away flashing.

I'm using a 20 cavity, Gen 1 .177 / 13.5 grain model die. I chose this because I have two accurate rifles tuned for JSB Monster 13.4's. But I still struggle with flyer shots and so there is room for improvement. Also, sorting and inspecting tiny .177 pellets for debatable improvement just sucks and I wanted to get away from that entirely. The 13.5gr die is based on the JSB Monster and while it's not an identical copy it's pretty close. I get 13.6x or 13.8 grain pellets depending on how much press force is applied.

The Thormold die arrives in a compact foam-lined plastic carrying case which is adequate. The punches each have their own cases. The die has information printed all over it and logos on one end that serve as match marks. Always assemble the die parts with the logos facing the same end.
The die is listed as 440C stainless with 55 Rockwell C hardness. I haven't tested it using the inspection gear we have at my work but I have every reason to believe that is the spec. The die surfaces are all fairly shiny and well finished.
The dowel pin fits were very snug at the beginning. They've loosened up quite a bit since I've made about 500 pellets with it. Now I'm considering whether I need to monitor the pins for wear and periodically replace them.
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Safety moment: this process involves extensive handling of soft lead and it creates shavings and pieces lead along the way. Take precautions, perform this work in a place where lead will not harm anyone, and sweep up your scraps. Rubber gloves make a lot of sense. I'm already in the habit of getting my lead levels tested with my annual physical and this gives me additional reason to continue that.

The die has three socket head cap screws and two 8mm dowel pins joining across the split halves. It has ten cavities per long side. There is a base plate and a guide plate - place the die on the base plate with the working cavities facing up. Then once those 10 pellets are pressed and scraped you can flip the die over on the base plate and do the second ten. In my current testing I have found the cavities to be fairly consistent to each other. Within a batch of pellets I am seeing the final pellet weight vary based on the pressing method I used. Using heavier press force results in 0.2gr lighter pellets, and I believe that is because the guide plate flexes a bit more and that allows the finishing punch to push a bit deeper into the cavity and displaces more lead. I've tried using the quill of a milling machine as a press, a K&M bullet seating arbor press, and a bench vise. For 177 caliber I think you don't need a huge press, and in fact too much press force can separate the die faces and cause flashing. So it seems like the right amount of pressing force will fully form the pellet and will not form flashing.
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The flashing is an issue that must be resolved. If you ignore it, it ruins the aerodynamics. If you roll the flashing over onto the pellet with your fingertips it will imbalance the pellet and still affect aerodynamics. So far my best solution is to brush off the flashing with a tiny stiff bristled brush and use a good magnifier so I can see what I'm doing.

I've tried a few types of lead wire. The ideal wire for this pellet is just under the 4.1mm waist diameter, so that the core drops fully into the cavity and simply expands to fill the head form and skirt. 5/32 and 4mm wire is ideal. I bought some 5/32 wire on eBay that was listed as 'lead' but in fact it was half lead and half something else (probably tin or antimony). I managed to make some nice shiny pellets with it but the pellets came out 2gr light and shot very poorly. That metal was also hard to form and cut. I'm now testing with .166 dia (4.2mm) Nielsen wire and 1/8" wire from rotometals.com. They are both nearly pure lead and form well. I'm using a Corbin wire cutter to make the cores at 14.5-15.0 grains. I suggest you source some pure lead wire based on the waist diameter of the pellet type you choose.

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The actual swaging process works like this:
1) Cut the lead wire into cores. I cut a hundred or two at a time and collect them into a large pellet tin with the foam liners. I spray a little WD-40 on each batch of cores and roll them around. So far I think the WD-40 helps but Rod's .177 BM-500 shot better with unlubed pellets.
2) Clean the die split faces with a lint-free rag and assemble and torque using a torque wrench. No torque specs were supplied but the bolts are M8 fine thread / Class A2-70 so you have to be careful. I'm using 144 in-lb torque based on my calculations for reasonable torque with anti-seize on the threads.
3) place the splits on the base plate, place the 10-hole guide plate on top. Drop a core into each cavity on the top side.
4) Take the flat 'seating' punch and press each core down fully. Then take the pointed 'finish' punch and press each core fully. Remove the top guide plate and using a very sharp razor scraper, scrape off the extruded lead.
5) Repeat the finish punch press operation and scrape excess lead two more times. (I've seen others do the finishing press step twice, I'm doing it three times, and I may end up changing). With each finish press operation the donut of lead that gets scrapes off is much smaller. On the last pass I use a nonabrasive scotchbrite pad to scuff the exposed skirts and a dry paintbrush to clean out any lead shavings from the skirt pockets.
6) Flip the die and swap the base and guide plates. Repeat steps 3-5.
7) Untorque the screws. I like to loosen them partway and not fully remove them. Remove the guide and base plate.
8) Set the mold on a clean surface with the protruding screw head down. Tap the assembly on the screw head just hard enough for the lower die half to pop free and slide down. I like to go down the line one-by-one and use my fingertip on the skirt to pop each pellet loose and tip it out of the die in a controlled manner. But you can just open the split and you'll end up with some pellets popping loose and the rest will be sticking to one or the other die half. Given the work involved I don't like having multiple pellets rolling around in random directions.
At this point I've got 20 pellets. I inspect them for flashing in my magnifier and I brush off any that I see using a very fine brush. It takes me about 15 minutes to press 20 pellets and another 5 to inspect and de-flash them.

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The die itself has a major design error. The three bolts that clamp the split are too small, too short, and too far away from the pellet cavities to hold compression on the cavity split lines. The pellets either had flashing when enough press force was applied to fully form the pellet or the pellets weren't fully formed if the press force was reduced to avoid flashing. If you're familiar with the pressure cone theory of bolted joints or have experience with FEA you'll know what I mean. So I designed a pair of pressure plates and changed to longer threaded rods with flanged nuts to put the clamping force over the split faces. This is much better overall and the design needs to be corrected.

I'm still evaluating the flatness of the faces, perhaps a tiny improvement in the flatness will finally eliminate the flashing. There are local injection molding shops and I may visit one to get their opinion on this and the dowel pins.

I still get some flashing. I suspect it's from having any contamination on the die split face. I'm brushing the flashing off of those pellets and using them anyway. I do know that if you leave it on they will shoot poorly and fouled the barrel quickly. My friend did try tumbling them in walnut shell media and that is worth further testing. I'm nervous about anything that takes these carefully crafted pellets and bangs them around. The outer edge of the skirts is shaped sharply and I'd like to keep those edges uniform and crisp.
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I have weighed the pellets I'm making and found that cavity-to-cavity variations are small (.05 grain total). Changing the lead wire or the pressing force shifts the weight of all pellets by up to 0.2 gr. I know pellet weight isn't the be-all-end-all of accuracy but I may improve my pressing process to improve consistency.

Based on what I've learned with this tool and information elsewhere, I can't rule out having swaging dies made myself using a domestic supplier. I don't know what it will cost but just like powder-burning shooters who reload or cast bullets, pellet swaging is sort of becoming a hobby in itself. It's hands-on, technical, and it's something I can do in bad weather or when I can't just be shooting.
 

The Young's modulus of steel usually falls between 190 and 215 GPa. This value represents the material's stiffness or ability to resist deformation when subjected to tensile or compressive forces. It is a measure of the material's elasticity, indicating how much it will stretch or compress under stress.

So if you have cheap hot rolled steel vs heat treated tool steel the stiffness doesn't significantly change. The tensile strength does, but no decent design should ever get close to the yield strength. The type of steel used isn't important as long as you don't exceed is yield strength.

For forming pellets you want to minimize the deflection under load to keep everything in "perfect" alignment. To do that better you have either change to a material with greater stiffness, or increase the cross sectional dimensions. The best approach is larger cross section, since the stiffness with increase by (cross section) squared. As we can clearly see the Precision Press has a much greater cross section than the Thor press. Beefier pivot points as well lower the strength requirements.

So the Precision press should be much stiffer and have smaller loads on the pivot points. Whether that matters for making pellets, I don't know. Since the smaller Thor press maybe stiff enough so the greater deflection doesn't matter, and the pivot points may be stronger than the forces it encounters.
 
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None of the presses that have hijacked this thread will press a split pellet swaging die. They are slug presses and 100% irrelevant
@dgeesaman I am replying to this post and not the original post because its well written and detailed.

I saw the problems you face with the halves not closing and lead flashing in the cavity. A hydraulic vice with electric motor pump (power pack) to close the two halves evenly ,
I've attached the image of a manual bottle jack application. I think you can mount the two haves on the vice jaws, The guide pillars of the die can work without a problem. And if you add another plunger type hydraulic press, With 10 punches you can swage all the cavities simultaneously in one stroke. Awesome productivity.


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None of the presses that have hijacked this thread will press a split pellet swaging die. They are slug presses and 100% irrelevant.
@dgeesaman My apologies. I didn’t mean to detract from your pellet swaging thread with my response to the press post. The amount of detail you’ve put into swaging pellets with this mold is nuts!! Thank you.

Can you show us an open-die photo of the facing and pins (that have loosened up) causing the flashing? If you drew arrows pointing to the problematic area(s), it may make it a little easier to envision for some. Is it the way the pins are affixed to one side of the mold that is problematic or has friction worn away parts of the pins creating play in the fit between the two halves? Because you felt the need to create your own pressure plates, to me, rules this out as a consumer-ready product. The process you’ve detailed to make 20 slugs seems lengthy with the current design. Having to use brushes and a magnifier to clean up the pellets seems time consuming. Are the weight variances acceptable to you? Were they mentioned in the literature that came with the die? Of all of the presses you’ve used with this die, which seems most compatible?
 
@Engg.Ken: that kind of setup has crossed my mind many times. I haven’t researched it seriously because 1) the 3 M8 studs are producing over ten tons of clamping pressure and I don’t think there is a lack of face compression. For reference pure lead yields at about one ton of pressure. 2) Bolting/unbolting a pressure plate is a minor operation in this grand scheme and a low priority until I resolve other things. And to your point I’d need ten punches to go significantly faster. So I might just start by clamping in the mill vise on the mill drill you see in the pictures and using the horizontal movement to advance from one cavity to the next.

@Ezana4CE: I think the flashing issue may be face flatness. The flashing cleans up pretty easily with a compact toothbrush and that gives me to chance to inspect them in detail. Weights have been pretty uniform, under 0.1gr total spread.

There was no literature. Their website had a video tutorial and that’s no longer available. Doesn’t matter much though.

I am planning to take this to a local tool and die shop and discuss upgrading the dowel pins and refacing the faces or at least confirming their flatness. Maybe see if they can make more punches. Then if that goes well I may investigate making my own design and doing this whole thing more properly.

I suspect that I need to control the punch pressure to stop the flashing. Probably going to start with a hydraulic pressure-to-force gauge. Ideally there will be a punch force that will form the lead thoroughly but not separate the faces and allow flashing. I might also experiment with heat - the yield and creep behavior of lead is varies strongly with temperature and just getting it to 200F could help drastically (provided I don’t burn myself).

I haven’t attempted to see if the flashing comes from a few specific cavities more than others but I should investigate that.

Fun fact: using off the shelf pellets of the same caliber but heavier size works well. I have a tin of JSB 16.2 gr .177s that my guns don’t shoot well but they make great cores for this.
 
@dgeesaman What can you do to ensure repeatability of the pressure applied to the punch? I’m assuming that you’re moving the punch from cavity to cavity in order to press each pellet individually. That sounds promising to take a crappy shooting or deformed pellet and swaging it into something usable. Didn’t realize that the flashing is removed so easily. For some reason I was thinking of a wire brush.
 
A fine brass bristled brush takes the flashing off very quickly but it leaves fine scratches in the lead. The finish all over is very smooth so I immediately searched for alternatives. Right now I’m taking it off with a few back and forth scrubs of a nylon brush. I can deflash 40 pellets in about five minutes and I get a visual inspection as a bonus.

Since the mill quill has a hand wheel I’d be applying force manually while reading the p2f gauge. I considered adapting a torque wrench to it but that’s more work and not as direct of a measurement.

Using my bench vise or the mill quill a person can be somewhat consistent in the force they consciously apply but it’s completely blind.
 
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When you mentioned putting it in a milling vise. If you have a CNC mill you can index to each pellet position and use the quill to push the punch down to a repeatable Z depth.
Indeed. I think there are a number of solutions if I had a permanent workshop. Right now I live in a rental condominium with a small garage so all of the fun solutions are out. I do have access to that manual mill drill and using its powered traverse works well if I don’t rush.
 
Thanks for stopping in to discuss pellet swaging everyone :rolleyes:
Thankyou for the excellent write up . i very much enjoyed the read over AM coffee . i just do not have the drive to do what your doing and i have found two pellets brands that shoot very very consistently in most all my rifles and pistols .
 
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Thankyou for the excellent write up . i very much enjoyed the read over AM coffee . i just do not have the drive to do what your doing and i have found two pellets brands that shoot very very consistently in most all my rifles and pistols .
Spotty consistency (or maybe unusually high expectations for consistency) is what led me to try this. I’m enjoying it more than I expected I would.

Relief from detailed sorting and the so-so improvements of that sorting were a major motivator for me.

David
 
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