Use Collet Dies for “Ultra” Accuracy
When striving for precision accuracy in your hand loads, attention to every detail, large or small, is of the utmost importance. This includes sizing die selection. There’s no real argument when I say that fire-formed brass can produce some of the most accurate ammo. That’s not to say that extremely accurate ammo can’t be made with a Full Length Sizing die, because it absolutely can be, but the theory behind fire-formed brass speaks for itself and real-world results confirm it. I load ammo for various purposes. My main reason for loading my own ammo is for precision accuracy and anyone who knows me will vouch for that.
The one thing that all my precision loads have in common is the sizing die I use. It’s the Lee Collet Neck Sizer. This die has what I’d call an acquired taste. Most sizing dies are designed so that once you get them adjusted to the correct position in the press frame, then all you do is lube (if applicable and necessary) and give the ram handle a full stroke down and then back up. Then you’re done with that case. Pretty simple, even if that die is a full length sizing die, a bushing style neck sizer or a fixed neck sizer. The Lee Collet Neck Sizing die is a little bit different.
If you disassemble the die, you’ll see a collet (the longer piece) with a tapered end split into four equal segments, a collet sleeve, a mandrel/decapping pin, and a threaded cap and body to hold it all in. The key to the operation of this die is the collet with the four equal segments. Those splits allow the metal to flex and give way under pressure. So with a die in place in the press, the shell holder will actually contact the collet before it reaches it highest position. With a case in the shell holder, it’s raised into this die, not contacting the die at all except for the neck as it enters the tapered portion of the collet. The ram is then forced into the collet. The upward movement of the collet into the receptive sleeve forces the tapered portion to collapse inward against the neck of the case. This will force the neck to be squeezed tightly against the mandrel. Once that final forced motion is complete, the case is finished with the sizing process. This is where this die differs from all the others. Just the simple motion of raising and lowering the ram is basically all there is to sizing with the other dies, but with the collet die, it takes a certain touch to get precise. The instructions that come with the die tell you to apply a certain amount of force against the handle of the press to achieve complete neck sizing, but that’s still awfully vague since none of us have any way of knowing how much force 20 pounds really is. With any repetitive motion, we develop a certain amount of muscle memory and this is really no different.
It took me a while to get the hang of it but I didn’t have anyone to explain it to me. I just pushed the handle down what I thought was enough, but when it came time to seat the bullets, they’d just fall right thru the neck. I kept practicing and once I actually felt what it was doing, it became perfectly obvious. The key, at least as I learned, is to slow down. Raise the case up into the die until your shell holder reaches the collet. Right before that, the pin should remove the spent primer. The distance the ram moves from the moment the primer is removed to the point where the neck fully compresses is the entire effective part of the stroke. It’s literally all done within maybe 1 ½ inches. Much less if you don’t count the decapping part.
To practice, put the Lee Collet Die in your press and adjust according to the instructions. When it’s in place, the shell holder should contact the bottom of the collet well before it reaches its highest position. To make it sound easier to understand, set the die so that the shell holder contacts the collet before the handle cams over. That’s where you want the die, so thread the locking nut down and lock it in place. Now that it’s locked down, make a few empty strokes on the press. Don’t apply so much pressure that things start creaking. You don’t have to be that aggressive. When the shell holder reaches the collet, apply gentle force to the ram handle downward. Watch the die where the collet protrudes and notice the movement. As you raise the ram, that collet is forced upward into the sleeve. The tapered part of the collet then begins to force inward toward the mandrel. You’ll reach a point when it stops moving and reaches a solid stop. Stop forcing it once that happens. What you just simulated is the whole effective stroke of the collet die. Now put an empty case in the shell holder. You can use good brass if you want because you can’t destroy a case with a collet die. If you do it wrong, then the neck just won’t hold a bullet. With the mandrel in place, you simply cannot size the neck too small. So with the case in place, raise it up until the collet and shell holder make contact. Just as you did without the case, force the handle downward and watch the collet in the die. Apply enough pressure to the handle to make the collet rise up into the die body while you pay close attention to what you feel in the handle. It’s going to feel different from the dry run you did before. You’ll feel the collet first engage the sleeve that forces it inward. Just as the collet begins to collapse, it makes contact with the brass neck. You’re going to feel that, too. Once you feel that, give the handle some pressure and feel for that neck to collapse. It should offer some resistance and then suddenly that resistance will decrease. That feel is the neck being sized. Lower the case from the die and measure the inside diameter of the neck. Depending on the diameter of the mandrel and the health of the brass, the diameter should be around .004” to .006” under bullet diameter.
Now that we know how it works, how does it help with accuracy? When a round is fired in a rifle chamber, the brass is stretched under the tremendous pressure until it perfectly matches the inside dimensions of that chamber, hence the term fire-forming. I only recommend using this neck sizing die in bolt action and single shot rifles. With fire-formed cases, fitting in the chamber can be tight. That’s not suitable for semi-automatic rifles. They rely solely on spring pressure to chamber each round and if that case is tight in that chamber, then you could potentially end up with rounds that won’t chamber into full battery. Not only is it inconvenient to have to assist a round to chamber fully, it could potentially create a out-of-battery firing situation if all things happened just right. We won’t go into all that, though. In bolt actions and single shot rifles, you, the shooter, manually lock each round into battery so if they’re tight, you can still lock them by adding pressure to the bolt handle.
Ok, now we have brass that have been fired in a particular firearm and will be reloaded for that rifle, only. After the case has been formed to that chamber, you can put the empty case back in and it will have a perfect fit. Remember this: A case can’t grow larger than the chamber it’s being fired in. Physics won’t allow it. I’ve had discussions with some people on this subject and I’ve heard the arguments that when it’s fired, the case will stretch to fit the chamber and retain some potential energy while it’s still in that chamber, meaning that when the bolt is opened and the case is removed from that chamber, it would actually spring out slightly, making the case larger than the chamber. I disagree. The reason I disagree is because I’ve gotten over 21 firings on a certain batch of brass using the Lee Collet Die exclusively in the reloading process. It was an on-going experiment I conducted over a period of time just to see how long that batch of brass would last. Once cases started failing, I ended the experiment with some cases still in working order. That batch of brass never got harder to chamber as the experiment went on. It offered a slight resistance when closing the bolt but it was very manageable. The brass simply did not grow larger than my chamber, period.
Now, how can the Lee Collet Die add case life expectancy longer than other neck sizing dies? The difference is the mandrel versus the expanding ball. On dies with expander balls, the necks are sized below a specified diameter and, in turn, enlarged as the case is pulled out of the die. The Collet Die’s mandrel is the same diameter all the way to the end, so when the collet squeezes the neck down against it, that’s it! The brass is no longer manipulated by the die or any part of it. You don’t feel the resistance when lowering the case from the collet die like you will from a die with an expander. So the brass in the neck area is only being worked in one direction. We all know that brass becomes hardened by repeated sizing and stretching. Basically, the design of the collet die removes one step from the process, which translates into slightly longer case life, provided the cases are annealed regularly.
Another advantage that provides is there’s nothing pulling on the brass as you lower it from the die. In the die with the expander, the resistance generated by the expander ball can literally stretch the case ever so slightly as you remove it. As you pull the case over the expander, you feel that resistance. That can undo the fire-forming you did when you fired that round. Some people complain that they neck sized their brass and loaded a batch and now they won’t chamber, or they’re very tight to chamber. That’s why. The case was a perfect fit after fire-forming; therefore there was already very little tolerance to begin with. If you stretch the case any at all on the way out of the die, you just made that case too big for that chamber. Most people won’t catch it until they try to chamber that round at the range. My advice, if you use an expander, is to chamber the empty cases after sizing to make sure that’s not happening to you. Once you’re certain they’ll chamber, then you can proceed with the reloading process.
If you shoot as much as I do, and reload ammo as much as I do, at some point along the way you’ll come up with ‘favorites’ as far as components and equipment goes. The Lee Collet Neck Die is a perfect example of that for me. Is it the only die available to load precision ammo? Absolutely not! You can load precision ammo with practically any dies available as long as you have a complete understanding for what it takes to be classified as such. I’ve shot some mind-boggling groups with ammo loaded with dies from various manufacturers. RCBS, Hornady, Redding, just to name a few, have produced very accurate and consistent ammo for me and millions of people like me, and you!
I’ll branch out slightly into an advanced reloading secret. Sometimes, a load just won’t come together like you’d hoped. When you think you’re out of ideas, consider adjusting neck tension. I mentioned earlier that some dies have removable bushings that size the necks. Those bushings come in different sizes that allow some fine tuning on neck tension, but what if you don’t have those dies? I do it with the Lee Collet die. I remove the mandrel and chuck it in a drill and spin it in sandpaper until I get to a specific diameter. Then I put the die back together and load some to test. It’s tedious and time consuming, but it can often seal the final deal on a very accurate load!
Jason Ray, Nachogdoches, Texas