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RELOADERS CORNER: Press Tricks, Linkage

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Reloading press designs vary, and some offer advantages, if they’re needed. Read more about which, what, and why HERE

rcbs summit
RCBS Summit

Glen Zediker

This is the last (for now) look at reloading press designs and features, and it’s all about power — leverage and linkage.

The more leverage a press can generate the less input effort from us is required in performing an operation, especially a more challenging operation like reforming cartridge cases, but that’s got another side to it. A longer stroke, and a heavier mass to move, also means more exertion on each stroke, and more time spent case to case.

Since we don’t always know the ultimately most demanding operation we’ll call on a press to perform, my advice is to err on the “stronger” side, and also on the “longer” side. I prefer a press with a shorter handle stroke (and a shorter ram stroke) because it’s less tedious to operate — but that’s true only when the press ops are not taxing. Yes, I’ll explain more: when the duties are sizing small to medium sized commercial brass cases (like .223 Rem. up to .308 Win.), seating bullets, decapping, seating primers then excess press isn’t needed. But when it’s more taxing, like in the case reforming already mentioned, and also sizing once-fired military cases, or loading for a honker like .338 Lapua, a longer ram stroke and more leverage is most welcome.

reloading press design
Forster offers a shorter handle option for its CoAx because there are many who want to increase feel on some ops. The shorter handle reduces leverage.

I’ve been doing all this long enough to have collected more than one press, at more than one “size,” and I’ve used them all over a good many years. The one I use the most is on the smaller, shorter end of the press spectrum, and that is only because the most of the loading I do now is decidedly not taxing. But give me a Kroger sack full of Lake City 7.62 and my Forster CoAx or Harrell’s Sportsman is getting mounted up on the bench.

Speaking of effort, case lube is decidedly important in smoothing out taxing sizing ops. I prefer a petroleum-based lube, but that’s not meant to start an argument!

There are a few different takes on the best way to design linkage (the levering mechanism that powers the ram), including those that operate more or less upside down. I’ve not used them all but have, generally, found that handle length has the biggest influence on leverage.

reloading press design
A press that’s set up to “cam-over” really means it’s set up to flex. Any press with enough leverage can warp over on itself. This is a Harrells Sportsman: huge leverage.

Cam Over
Speaking of linkage… Some reloading presses are designed with eccentric linkage such that it’s possible to “cam” the ram. The concept involves circular motion and linear motion, meaning that when the ram traveling in a linear path reaches full extension, the linkage which is traveling in a circular path, can move through the 0-degree mark and go to a negative degree — like a crankshaft in an engine. To get a picture of this: As the handle is moved downward to elevate the ram, the ram reaches its maximum height just short of the very limit of its travel upward, and, at the last little bit, lowers. So when the handle is all the way through its arc, the press ram is sitting a little lower. This action, called “cam over,” has essentially increased “ummph” in the linkage, and it’s done that by making contact (plus) with the die.

I’m not a fan.

Now, any substantial press, whether it has eccentric linkage or not, can produce the effect of camming-over. A Forster Co-Ax, for instance, can just about crush a chrome car bumper and doesn’t have eccentric linkage. To set up that press, any press, to cam-over, turn the die a little (1/8 turn or so) downward beyond what provides full and flush contact with the shellholder when the ram is at its full height. Then, when the press handle is fully down, the additional pressure in the last bit of the handle stroke goes toward flexing the press. Simple as that, and that is what camming-over does: flex the press. And, again, that’s true whether it has eccentric linkage or not.

Don’t do it. Just don’t.

There’s no need to cam-over a press for a case-sizing operation. It creates unnecessary stress. Dies can get deformed and bent, carbide dies can break, and the press hisself can suffer, and even break. Some defend this practice by saying presses are designed to “take it,” but eventually there’s a penalty for taking any machine to its limits, continually.

The real deal is that it’s just not necessary! Using a cartridge case headspace gage to determine sizing die positioning to get the correct amount of case shoulder setback, it’s clear that sure should occur at a point short of full contact between the die bottom and the shellholder surfaces. But, and this is important, if it’s not then trying to push a case farther up into the die by crushing the shellholder against the die isn’t going to do much. Done is done. The flexing might, maybe (maybe), increase setback 0.001.

If your sizing die doesn’t adequately set back a case shoulder, then that die has to be modified by having material ground off its bottom.

Camming-over a press is a “feel-good” measure for some folks: there’s this satisfying “ka-thunk” at the limit of press handle stroke, and that lets a loader know that they gave it all it could get. I’ve also had some claim that the stress and flex brings “everything into perfect alignment.” No it doesn’t. Alignment in a press was determined by the maker, not pressure. If your press hain’t straight, bending it more won’t help.

Cam-over has its application in some bullet making operations, but those are not on-topic here.

reloading press design
Here’s eccentric linkage at work. On left is the maximum height attained by the ram; on right is the ram position at the full-limit stop on the press handle. It’s 0.020 inches on this press, a Harrells Turret.

More, And Some Is Good!
To find out if you have a “cammer” run the press ram fully up (press handle fully down) and thread a die in until it touches the shellholder. Try to move the handle back down. If it won’t budge, it’s got eccentric linkage. It won’t move because the ram is trying raise again. Back out the die until the handle moves and pulls the ram away. It’s at this point where “flush” contact with a die bottom will be. As long as the shellholder is not being contacted, presses with this sort of linkage have a smooth feel to them and do a little more positive job of sizing. In effect, the case gets sized twice (the ram elevates again just as the press handle is lowered). Linkage, either way, has zero effect on setting up a die because you measure what you get anyhow, and adjust the die accordingly, after you see what it is that you got.

The preceding is a adapted from information contained in from Glen’s books Top-Grade Ammo and Handloading For Competition. Available HERE at Midsouth Shooters Supply. Visit ZedikerPublishing.com for more information on the book itself, and also free article downloads.

 

RELOADERS CORNER: Barrel Throat Erosion

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How long does a barrel last? About 5 seconds. KEEP READING

throat erosion
Well, it’s hotter than this, but it’s flame cutting over time and distance, and hotter for longer is the issue.

Glen Zediker

As is by now common enough in this column I write, ideas for topics very often come from questions that are emailed to me. As always, I figure that if someone has a question they want answered, then others might also like to know the answer. This question was about barrel life and, specifically, this fellow had been reading some materials on the interweb posted by some misinformed folks on the topic of bullet bearing area and its influence on barrel life: “Is it true that using 110 gr. vs. a 150 gr. .308 bullet will extend barrel life because of its reduced bore contact?”

NO. Not because of that.

However! The answer is also YES, but here’s why…

Wear in a barrel is virtually all due to throat erosion. The throat is the area in a barrel that extends from the case neck area in the chamber to maybe 4 inches farther forward. Erosion is the result of flame-cutting, which is hot gas from propellant consumption eating into the surface of the barrel steel. Same as a torch. There is very little wear caused from passage of the bullet through the bore, from the “sides” of the bullet, from friction or abrasion. The eroding flame cutting is at or near the base of the bullet.

When the propellant is consumed and creates the flame, the burn is most intense closer to the cartridge case neck. There are a few influences respecting more or less effect from this flame cutting. Primarily, it’s bullet weight. Time is now the main factor in the effect of the flame cutting. Slower acceleration means a longer time for the more intense flame to do its damage.

The slower the bullet starts, and the slower it moves, the more flame cuts in a smaller area for a longer time.

Bullet bearing area, therefore, has an influence on erosion, but that’s because it relates to acceleration — greater area, more drag, slower to move.

The amount of propellant, and the propellant nature, do also influence rate of erosion. Some assume that since there’s more propellant behind a lighter bullet that would create more erosion, and that’s true, but that is also not as great a factor as bullet weight. Other things equal, clearly, more propellant is going to cut steel more than less propellant. A “lighter” load will have a decidedly good effect on barrel life.

throat erosion
It’s heavier bullets that have the most influence on shortening barrel life.

Heavier bullets, without a doubt, are a greater influence than any other single factor. “We” (NRA High Power Rifle shooters) always supposed that it was the number of rapid-fire strings we ran that ate up barrels the most, but that was until we started using heavier bullets and found out in short order that our barrels weren’t lasting as long. That was moving from a 70gr. to an 80gr. bullet.

The “nature” of propellant is a loose reference to the individual flame temperatures associated with different ones. There have been some claims of greater barrel life from various propellants, but, generally, a double-base will produce higher flame temperature.

Even barrel twist rate plays a role, and, again, it’s related to resistance to movement — slower start in acceleration. Same goes for coated bullets: they have less resistance and move farther sooner, reducing the flame effect just a little. And, folks, it’s always “just a little.” It adds up though.

There are bullet design factors that influence erosion. A steady diet of flat-base bullets will extend barrel life. There’s been a belief for years and years that boat-tail bullets increase the rate of erosion because of the way the angled area deflects-directs the flame. And that is true! However, it’s not a reason not to use boat-tails, just a statement. We use boat-tails because they fly better on down the pike, and, ultimately that’s a welcome trade for a few less rounds. An odd and uncommon, but available, design, the “rebated boat-tail” sort of splits the difference and will, indeed, shoot better longer (they also tend to shoot better after a barrel throat is near the end of its life).

The effects or influences of barrel throat erosion are numerous, but the one that hurts accuracy the most is the steel surface damage. It gets rough, and that abrades the bullet jacket. The throat area also gets longer, and that’s why it’s referred to as “pushing” the throat.

The roughness can’t much be done about. There are abrasive treatments out there and I’ve had good luck with them. Abrasive coated bullets run through after each few hundred rounds can help to smooth the roughness, but then these also contribute their share to accelerated wear. I guess then it’s not so much a long life issue, but a quality of life issue. I do use these on my competition rifles.

lnl gage
Use the Hornady LNL O.A.L. gage to record and then track barrel throat wear. This isn’t technically a “throat erosion gage,” which do exist, but I’ve found it an easy and reliable way to keep up with an advancing throat. As the seating depth gets longer, it’s indicating how far the throat is advancing. Get one HERE 

Keeping in mind that the throat lengthens as erosion continues, using something like the Hornady LNL tool shown often in these pages can let bullet seating depth that touches the lands serve as a pretty good gage to determine the progress of erosion. On my race guns, I’ll pull the barrel when it’s +0.150 greater than it was new. Some say that’s excessively soon, and a commonly given figure from others in my circle is +0.250. One reason I pull sooner is that I notice a fall-off in accuracy sooner than that since I’m bound by a box magazine length for my overall cartridge length for magazine-fed rounds with shorter bullets, and I’m already starting with a fairly long throat (“Wylde” chamber cut). And another is because gas port erosion is having some effect on the bullet also by that number of rounds. Which now leads into the “big” question.

So, then, how long does a barrel last? Get out a calculator and multiply how many rounds you get before pulling a barrel by how long each bullet is in the barrel and barrels don’t really last very long at all! At full burn, maybe 4-6 seconds, some less, or a little more.

Another misgiven “fact” I see running rampant is associated with comparing stainless steel to chromemoly steel barrels for longevity. Stainless steel barrels will, yes, shoot their best for more rounds, but, chromemoly will shoot better for an overall longer time. Lemmeesplain: the difference is in the nature of the flame cutting effect on these two steels. Stainless tends to form cracks, looking like a dried up lakebed, while chromemoly tends to just get rough, like sandpaper. The cracks provide a little smoother surface for the bullet to run on (until they turn into something tantamount to a cheese grater). The thing is that when stainless stops shooting well it stops just like that. So, stainless will go another 10 to 15 percent more x-ring rounds, but chromemoly is liable to stay in the 10-ring at least that much longer than stainless steel.

throat erosion
Stainless steel barrels keep their “gilt-edge” accuracy for about 15% more rounds, but hit the wall head-on and in a big way when they reach their limit. Chromemoly steel tends to open up groups sooner, but also maintains “decent” accuracy for a longer time, by my experience — the groups open more slowly.

Do barrel coatings have an effect? Some. A little. I’ve yet to see one that made a significant difference, or at least commensurate with its extra expense. Chrome-lined barrels do, yes, tend to last longer (harder surface), but they also tend not to shoot as well, ever. Steel hardness factors, but most match barrels are made from pretty much the same stuff.

The preceding is a specially-adapted excerpt from Glen’s book Top-Grade Ammo. Available HERE at Midsouth Shooters Supply. Visit ZedikerPublishing.com for more information on the book itself, and also free article downloads.