Tips for Using Lee Collet Dies for Neck-Sizing Brass

Editor’s NOTE: We generally recommend full-length sizing your cases. But there may be some situations where you may want to body-size your brass in one operation, and then neck-size the case as a final operation for reduced run-out. Or, perhaps you have a non-bushing FL sizing die and you want to modify the neck sizing. This article explains how to use a Lee Collet Die to size case-necks.

For those who prefer to neck-size their brass (rather than full-length-size), the LEE Collet Die is a popular, inexpensive option. It works by having collet tangs or “fingers” press the neck against a central mandrel. A collet squeezes the case neck against a precision mandrel for a perfect fit with minimum run-out. The benefit is that you get a very straight neck, which is sized consistently from top to bottom. Canadian shooter Jerry Teo explains: “LEE Collet Dies produce sized cases with very low runout (measured runout is under .001″ using a Sinclair concentricity gauge). You also don’t get the build-up of brass at the base of the neck, as can happen with bushing neck dies. The neck-shoulder junction stays nice and crisp.”

Here’s a good video that explains how to use a Lee Collet Die to Neck-Size .243 Win brass:

UPDATE to LEE Collet Dies — Neck Protrusion Change
The Lee Precision website notes a small design change: “If you’re a long-time user of Lee Collet Neck Sizing Die you may notice we have modified the Collet so a small portion of the neck protrudes through the end of the Collet-sizing portion. This often-requested modification was implemented in 2019. This change allows the portion of the neck that protrudes above the Collet to remain in its fire-formed condition. This provides a natural flare to the case neck allowing easy and concentric seating of bullets. This is especially important when seating cast bullets or low-drag coated bullets.”

TIP ONE — Adjusting Tension
LEE Collet dies don’t have a specific mechanical adjustment for neck tension. But you CAN easily modify the die to provide more or less tension. If you want to adjust the neck tension using a Lee Collet die, you can simply chuck the mandrel in a drill and reduce the diameter with some sand-paper (to increase neck tension) or you can order a mandrel the next caliber larger and turn it to whatever diameter you want (the larger the mandrel diameter, the less the neck tension). You can also order custom mandrels from Lee sized to any diameter you want.

Regarding neck tension, Boyd Allen makes an important point: “The only way to properly get more neck tension with collet dies is to either reduce the diameter of the mandrel, or order a smaller-diameter mandrel from Lee. I remind folks that adjusting the die position to have more toggle at the top of the ram stroke (not the factory recommended method), or leaning on the press handle with more force than recommended will NOT increase neck tension.”

No Custom Lee Collet Dies For Now
In years past, Lee also offered Custom Collet Dies, made from two fired cases. Hopefully these will be available in the future. However, earlier this year, Lee announced it had suspended sale of most custom dies including Collet Dies: “March 17, 2021: Due to unprecedented order volume, we have suspended custom services for Collet Necksizing Dies, Full-Length Sizing Die Sets, Quick Trim Dies, Case Length Gauges, Factory Crimp Dies, and Bullet Molds until we are able to meet the required volume of our standard products.”

TIP TWO — Polish and Tune for Easy Case Removal
Some users have complained that their Collet Dies grab the case-neck too firmly, making the case hard to remove. There are solutions to this problem. First inspect the collet fingers and smooth the inner surface up a bit with polishing compound or an extra-fine sanding pad. Second, you can open up the fingers a little bit. LEE recommends that if your Collet Die is sticking, take a steel punch and tap the fingers apart a little bit so that the natural “unloaded” position is wider. Lastly, you should lightly lubricate the outside of the collet fingers (see arrows) before you re-assemble the die. This will ensure they slide smoothly. Also, to prevent the collet fingers from closing too tight, never load up the die with your press without putting a case in place first. Without a case neck between the collet fingers and the mandrel, the collet can clamp itself too tight as you raise the ram.

TIP THREE — Always Have a Case Inside When Operating Collet Die
Our friend Boyd Allen tells us that you need to follow directions and NEVER operate the die without a case inside. Boyd explains: “This is because doing so will spring the quadrents of the collet inward so that they interfere with the insertion of a case, and the user will have to figure out how to undo the damage if the die is to operate properly. This advice would not be needed if everyone read the instructions before using the die…. but many times, they don’t. Another thing that I tell new users is to take the die apart so that they will have a better chance of understanding how it works.”

TIP FOUR — Size Twice and Spin Your Case 1/8th Turn
After reaching fully “down” on your press handle, withdraw the case about an inch and manually rotate it about 1/8th (NOT 1/4 or 1/2) turn while still in the shell-holder, then size again. This will place the die’s collet petals on the four “high spots” of the case neck and will result in a rounder, more evenly-sized neck with slightly more bullet tension. This takes only about one second more per case and is well worth the slight extra effort. (We thank reader Stonecreek for this smart tip).