By Damon Cali
Posted on May 15, 2013 at 01:21 PM
One of the first and necessary pieces of gear that a new reloader will buy is a reloading press. I was given an old RCBS Rock Chucker twenty years ago. It was old then - I don't know how old, but it works and works well to this day. But that press lives on another bench in another state far away.
So when it came time to add a new press to my new reloading bench I went back to familiar territory (after looking at everything out there). These days, they call it the RCBS Rock Chucker Supreme (also available as a reloading kit for beginners). I'm not sure what's so supreme about it - it looks very much like the decades-old version I once had. The finish is a little shinier, I suppose.
OK, so maybe a few things have changed - there are some subtle and welcome improvements. But before I get into that, lets back up a bit and take a look at what the purpose of a press is and what is important to consider when buying one.
Put simply, a press's main job is to push the cases straight into the dies - emphasis on straight. For precision rifle shooters, there are two main operations to be concerned about - sizing (neck or full-length) and seating. Both of these operations must be done squarely and evenly to maintain the symmetry and alignment of the finished ammunition. Ammunition that is not square and centered is more likely to result in a bullet that is tipped, either in the bore or immediately outside of it. This is bad for accuracy. A press that isn't square will not give you square ammunition.
But what does "square" mean?
It takes considerable force to full length size a rifle case. That force has to be reacted by the press in some way. With the Rock Chucker, the force of the ram is countered by the thick O-shaped frame. There is a reason the frame is an O shape and not a C shape, which would be more convenient. If you removed one of the frame pillars, you would still have a press that had more than enough strength to react the loads of sizing. But you'd also have a press that was unbalanced, and the force of the ram pushing the case into the die would tend to bend the frame pillar during the sizing operation. Not very much, but it's better to be balanced. The Rock Chucker is well balanced in this manner, and this O-frame design is common in the industry for this reason.
There are a few presses that are not balanced, like the Sinclair Benchrest Press and the Redding Ultramag reloading press. But one thing in common they all have is considerable heft. In order to counter the bending force inherent in a C-frame, you must use a very stiff, heavy press. There is no other way - you can't eliminate the bending force, but you can minimize it's impact with lots of metal. That metal has cost, and as a result, C frame presses tend to be more expensive than O-frame presses. This is why the slender, inexpensive RCBS Partner press can load perfectly good ammunition - it is a balanced design despite its light weight.
Apart from a balanced design, a good press will be precisely machined. There are a few areas we care specifically about:
1) The axis of the die threads should be parallel to the axis of the ram. It's not critical that they are perfectly concentric because the shell holder allows the case to float laterally, but it is important that the angle between the the two pieces be as close to zero as possible. There is also some play that allows a case to rotate slightly in the shell holder, but we do not want to rely on that. If the case is tipped in the shell holder, the ram will exert a force on the edge of the case, which isn't what we want. Unfortunately, this alignment difficult to measure, and I'm not equipped to do so.
2) The face of the die thread bushing (the part at the top of the press where you screw in the die) should be parallel to the top face of the ram when the ram is at the top of it's throw. If the threads are true as described above, the face that the die bears upon should also be true to provide a repeatable, consistent die adjustment. This is not as hard to measure. I measured the distance from the top of the bushing to the top of the ram at several places around the circumference of the bushing and was pleased to find that my press was square within .001". There was literally no detectable angle between the two that I could see with the equipment I had available. That's a good thing, and a sign that RCBS makes some effort to keep the important tolerances in check. This measurement was not as precise as I'd like it to be, but it inspires confidence nonetheless.
So as best I can tell, the new RCBS Rock Chucker Supreme in my possession is as square as one might expect to be possible. I wish I could measure the thread axis angle, and if I figure out a good way to do it I will update this article. But given the way the bushing is manufactured, I'm reasonably confident that the threads are inline with the ram. It's important to reiterate this: All I care about in a press is how squarely it is constructed so that it has the best chance of producing straight ammunition. The rest is just details and convenience and of considerably less importance. The RCBS Rock Chucker Supreme meets these needs as best as I can tell with my measurement tools.
The Rock Chucker Supreme, like it's earlier incarnations, comes with a priming arm designed to be used on the press. I will never use it. I don't know why they bother with these things, but they do. Do yourself a favor and get a dedicated priming tool. There are several good ones on the market. I'm partial to the 21st Century hand priming tool.
I've heard the Rock Chucker called a "Primer Chucker" for it's tendency to drop spent primers in places other than the receptacle designed to catch them. I wish I could say that won't happen any more, but the new design is not much better than the old. The plastic bit also made an appearance for the pictures, but like its friend the priming arm, it gets in the way without adding a lot of value. Thankfully it's easily removed. Looks like I will be sweeping up the spent primers that do not fall into the small trash can I have strategically placed under my press.
But enough with the flaws. How about the good parts? I've already discussed the most important part - the precision. The press is also very strongly built. Maybe it's just the engineer in me, but I appreciate that they took the effort to put the linkage links in double shear (that is, the pins are supported on both sides of the link), unlike some of it's competitors. Supporting the linkage in double shear makes for a stiffer, stronger joint, and it is this kind of detail that elevates the Rock Chucker to a level slightly higher than its peers.
Left handers can also rejoice. Sort of. Although the O-frame is offset to the benefit of right-handed reloaders (and to the detriment of lefties), the handle can be switched between two angled holes, making the press at least usable with your left hand. It would be nice if they would make a fully left handed press, but I'm not holding my breath. If I were left handed, I would be very curious about the new RCBS Summit press that was announced at the 2013 SHOT show or consider one of the more symmetrically designed presses like the Forster Co-Ax (which has an excellent reputation, although I have never used one).
Compared to my trusty RCBS Partner press, the Rock Chucker looks pretty big. I've loaded plenty of very good rounds with the Partner, but you can see the difference - the O-frame is much thinner in cross section, and the linkage pins are cantilevered out in single shear. If you've got the budget and room, the Rock Chucker is just better. But the Partner will do the job and can be helpful to apartment dwellers or as a portable press for use at the range.
Not being particularly brand loyal, I shopped around when I needed a new press. I looked at them all, and came back to the one I was most familiar with. RCBS has a winner and it's really hard to come up with a reason to go with someone else for a single stage press at this point. I can heartily endorse the newest iteration on the venerable Rock Chucker as a basic press for most any reloader's needs. If you are just getting started with reloading, I would recommend picking up the RCBS Rock Chucker Supreme Master Reloading Kit to save a little money.
Damon Cali is the creator of the Bison Ballistics website and a high power rifle shooter currently living in Nebraska.
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