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General primer system discussion
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Much has been written about the Load Master primer system. Some claim to have little trouble with it and some have nothing but trouble with it to the point where they give up and sell the press out of pure frustration. This is a sad thing. From what I have read and heard over the last couple of years, it appears that the original system was the least troublesome. I personally never owned an early system so I cannot claim to have any experience with it one way or the other. All I can go on is what I have heard or seen others say. My understanding is that the slider in the early system captured the primer in a much more robust manner than the new slider does. In doing this the slider was put in harms way if for any reason the press was short stroked. The primer pin would pinch the slider and mangle it beyond use. Lee, being the benevolent folks they are, would send anyone a new slider who contacted them and reported that their slider had met with an untimely death. OK, what to do about that say the folks at Lee? Hum, lets redesign the slider so that if the press gets short cycled the primer pin can't pinch the slider and we won't have to be handing out free sliders and whatever else got destroyed in the mishap. While we're at it lets change the color of some of the trough parts and add some mysterious letters, holes and such so everyone has something to talk about and life will be good. And so it was written and so it was done and now here we are with a new and improved slider that doesn't get pinched by the primer pin anymore. Unfortunately for some we still have priming problems. No pinched sliders, but problems none-the-less.

OK, what exactly the hell is going on here? In my view there are a few things either alone or in concert with the others that will bring hurt to your fox hole. Some have an effect on a sucessfully installed primer and others prevent the sucsessful installation of the primer. Listed below are the things I have discovered over the last two years that have caused me the most grief with the LM priming system. Some are direct self inflicted screw ups and some are directly attributable to the machine's design or operator setup.
Self Inflicted Screw Ups
1. Crimped primer pockets. There is nothing to say about this other than shame on you! You must inspect every piece of brass you are going to reload, period! If you don't, you are just an accident waiting to happen. There is absolutely nothing else to say about this!

2. Mixed primer pocket size. See #1. Enough said!

3. Running out of primers. Duh! Pay attention, focus on what you are doing and if you become distracted stop and do not resume until the distraction has been eliminated. Check everything first and then resume.

4. Verify your setup. Take a minute to cycle the press a few times without any cases in it. See if the primers are being delivered properly to the priming pin. So what if you have to put a few primers back into the tray the next time you add primers. It's better than smashing them or loosing them down the press ram.

5. Housekeeping. Keep your press clean! If you decap and size on your press you know how quickly it can get dirty. Debris from spent primers and spilled powder will find its way into the primer system of your press and if not cleaned on a regular basis it will cause you grief. Better yet, do all your case prep off the LM and avoid the dirt alltogether.
Mechanical problems
1. Burrs, flashing etc. Check the entire primer system for any burrs or small pieces of plastic flashing left over from the molding process that would inhibit the smooth flow of the primers through the trough assembly. Also inspect the slider, slider arm and trough cover and take whatever steps necessary to put them in good working order.

2. Check to see if the primer trough fits snugly into the socket in the carrier. If the trough flops around in the socket it can be tightened up with the addition of a small piece of tape affixed to the back side of the portion of the trough that fits into the carrier socket. This will also help to keep the trough from leaning away from the press when the primer tray is full of primers.

3. Check the clearance between the slider arm and the case retainer. The slider arm should pass over the case retainer without contacting it. If it does contact the case retainer it can be raised by the addition of a small cut washer between it and the body of the primer trough. Also lube the o-ring and adjust the attachment screw to prevent any binding inhibiting the free movement of the arm.

4. Primer pin spring. I have found that the primer pin spring is about 1/4" longer than it needs to be and because of this it is easily bent and will cause problems. Personally I don't use a spring on the primer pin. I use a magnet to secure it.

5. Primer pin rocker arm. The primer pin rocker arm is a die cut part and as such does not have smooth, square surfaces for the primer pin or the primer depth setting bolt to contact. If you have the tools at your disposal to be able to smooth and square up these surfaces it surely can't hurt anything. Be advised that the rocker arm is hardened and a file won't get the job done. You will need a Dremel with a stone or some sort of sander to get it done.

6. Primer depth adjustment bolt. Remove the grade markings from the top of the 1/4-20 depth adjustment bolt to aid in obtaining smooth and precise primer depth adjustments.

7. Primer pin resting height. This is a tough one. In my humble opinion, I think the primer pin resting height is the biggest contributor to flipped and missing primers. In my tests, I have discovered that it is IMPERATIVE that the end of the primer pin be ABSOLUTELY LEVEL with the floor of the primer trough. If the pin is even a few thousandths above the floor of the primer trough the primer will on occasion flip up sideways and sometimes even flip completely over depending on the speed with which the press is being operated. We all know what happens next. Also, if the pin is sticking up too high it is possible that the primer will not get deposited onto the end of the primer pin at all. In this case what happens is that the primer pin blocks the primer and as the ram raises the primer slider actuating arm contacts the tapered wedge bar mounted in the press frame and instead of the arm moving the slider it simply flexes and no primer is inserted into the case. The pin being SLIGHTLY lower than the floor of the trough doesn't seem to be as bad as I have not been able to cause many problems because of it. I am sure that if the pin were to be too low that the primer would tip far enough to cause a problem.
OK, what if the pin is too high, how do you fix it? Well it depends on what is causing it to be too high. I submit the following:

A. Dirt/debris on the ledge that the short leg of the pin rests on in the carrier and/or dirt/debris on the press frame under the long leg of the pin keeping it from resting on the ledge in the carrier socket. Either way, clean your press.

B. If the above mentioned conditions don't apply and the primer pin is in fact sticking up above the trough floor the only remedy I see is to either grind the top of the pin down until it is level with the trough floor or grind the short and long legs of the pin down to get the desired result. Keep in mind that if you grind the top of the pin you must keep it flat and at 90 degrees to the C/L of the pin. As long as the long leg of the primer pin is not contacting the frame of the press I personally would choose to grind the top of the pin.
Smiley Faces
Smiley faces are caused because the primer pin is not centered on the primer pocket in the case. I can think of two things that would cause this. One would be that the case retainer is not properly adjusted. Another would be that the primer trough is loose in the carrier socket and therefore is leaning away from the center of the press, pulling the primer pin out of alignment.
Conclusions
Well that's about all I know about the Lee Load Master priming system that might be of some use to those of you who might be having some problems with it. I don't claim to have all the answers but I have spent a ton of time studying this thing and I believe that what I have outlined above will definitely be of help. Good luck and if you have a question drop me an email and I will try to help you out.

Mike