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Nocturnal Specialties
7,323 Posts
Discussion Starter #1
Was reading earlier and come across this..
In case some of you guys use them.

"I started using Lee collet dies when they first came on the market and have found that they are very good for the purposes for which they were designed. I have found that there is a lack of understanding of how to use the die properly and as a result people fail to see the advantages that the die can deliver over standard neck sizing dies. This is not the fault of the product , it is just a lack of understanding of how the die works and what it will feel like when you operate the press correctly.

Standard dies use a neck expanding ball on the decapping rod and size by extruding the neck through a hole and then drag the expander ball back through the inside neck. The collet die achieves neck sizing by using a split collet to squeeze the outside of the case neck onto a central mandrel which has the decapping pin in it’s base. One advantage is that there is no stretching or drawing action on the brass. The inside neck diameter is controlled by the diameter of the mandrel and to some extent by the amount of adjustment of the die and the pressure applied to the press.

This results in less misalignment than can occur in standard dies because of any uneven neck wall thickness in the cases.Cases will last longer in the neck area and require less trimming. If cases have very uneven neck wall thickness then this can cause problems for the collet die they definitely work smoother and more accurately with neck turned cases but it is not essential.

When you first receive the die unscrew the top cap and pull it apart check that everything is there also that the splits in the collet have nothing stuck in them then inspect the tapered surface on the top end of the collet and the internal taper of the insert to make sure there are no metal burs that might cause it to jamb. Next get some good quality high pressure grease and put a smear onto the tapered surface of the collet. Put it back together and screw it into the press just a few threads for now. The best type of press for this die is a press of moderate compound leverage that travels over centre.

Over centre means that when the ram reaches its full travel up it will stop and come back down a tiny amount even though the movement on the handle is continued through to the stop. eg. is an RCBS Rockchucker. This arrangement gives the best feel for a collet die sizing operation. Place the shell holder in the ram and bring the ram up to full height then screw the die down until the collet skirt just touches on the shell holder, then lower the ram. Take a case to be sized that has a clean neck inside and out and the mouth chamfered and place it in the shell holder. Raise the ram gently feeling for resistance if none, lower the ram. Screw the die down a bit at a time. If you get lock up (ram stops before going over centre) before the correct position is found then back it off and make sure the collet is loose and not jammed up in the die before continuing then raise the ram feeling for any resistance, keep repeating this until you feel the press handle resist against the case neck just at the top of the stroke as the press goes over centre and the handle kinder locks in place.

This takes much less force than a standard die and most people don’t believe any sizing has taken place. Take the case out and try a projectile of the correct caliber to see how much sizing has taken place.
If it’s still too loose adjust the die down one eighth of a turn lock it finger tight only and try again .
Once the die is near the correct sizing position it takes very little movement of the die to achieve changes in neck seating tension. This is where most people come undone , they move the die up and down too much and it either locks up or doesn’t size at all.

It will still size a case locking it up but you have no control over how much pressure is applied and some people lean on the press handle to the point of damaging the die. A press like the RCBS Rockchucker, that goes over centre each time gives you a definite stopping point for the ram and the pressure that you apply.

There is a small sweet spot for correct collet die adjustment and you must find it , once found , how sweet it is ! Advantages : With a press that travels over centre it is possible to adjust the neck seating tension within a very limited zone. No lubricant is normally required on the case necks during sizing.

If you still cant get enough neck tension to hold the bullet properly for a particular purpose then you will have to polish down the mandrel. Be careful polishing the mandrel down and only do it a bit at a time as a few thou can be removed pretty quickly if you overdo it.

You can't get extra neck tension by just applying more force. The amount of adjustment around the sweet spot is very limited and almost not noticeable without carrying out tests. For example, to go from a .001 neck tension to a .002 or .003 neck tension you would be talking about polishing down the mandrel.

There are some other advantages but I will leave you the pleasure of discovering them. One disadvantage that I have found with the collet die is that it needs good vertical alignment of the case as it enters the die or case damage may result so go slowly.

Also some cases with a very thick internal base can cause problems with the mandrel coming in contact with the internal base before the sizing stroke is finished. If pressure is continued the mandrel can push up against the top cap and cause damage . If you are getting lock up and cant get the right sizing sweet spot, then check that the mandrel is not too long for the case you can place a washer over the case and onto the shell holder and size down on that. It will reduce the length of neck sized and give the mandrel more clearance. If it sizes Ok after adding the washer then the mandrel could be hitting the base. This is not a usually problem once you learn how to use them.

The harder the brass is the more spring back it will have so very hard brass will exhibit less sizing than soft brass because it will spring away from the mandrel more. If this is happening to excess then use new cases or anneal the necks. Freshly annealed brass can drag on the mandrel a bit in certain cases because it will spring back less and result in a tighter size diameter. I have experienced it. I always use some dry lube on the inside and outside if I get any dragging effect. Normally you don't need lube.

I make up a special batch 1/3 Fine Moly powder. 1/3 Pure graphite. 1/3 Aluminiumised lock graphite. Rub your fingers around the neck and It sticks very well to the necks by just dipping it in and out and tapping it to clear the inside neck. After a few cases it coats up the mandrel. Other dry lubricants would work also. Use the same process for normal neck sizing also.

I noticed a definite improvement in the accuracy of my 22-250Rem. as soon as I started using a Lee collet die instead of my original standard neck die."
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