Taper And Springback Issues
by Ed Wosika

Introduction

I can think of no sport other than that of cast bullet shooting in which there is such a strong need for congenial coordination between the competing manufacturers of products used in that sport. One shooter’s bullet is cast in a SAECO mold, sized in a Lyman (H&I) sizer die sitting in an RCBS lubrisizer press, and fitted with a Hornady or Lyman gas check. Meanwhile, the shooter to her left, at the firing line, is shooting bullets cast from an RCBS mould, fitted with Paco Kelly’s lovely invention — the aluminum FreeChec — and sized in a SAECO lubrisizer and die.

This extreme mix-and-match approach is standard in our lovely sport. Any product aberration which causes one-or-more of the other supporting products to work poorly causes a great and unnecessary disturbance. In this piece, I will discuss two such problems, and will suggest a solution for each. I’m sending a copy of this letter to each of the manufacturers mentioned. It is my intention that the several manufacturers will view my observations as helpful input, rather than useless carping, and that they will fix these problems.

Springback or Fall On Yo Face: These are Options?

“Gascheck springback” is a term I use to refer to the tendency for a gas check’s skirt, upon emerging from the sizer die, to spring back up to a diameter that is considerably more than that of the sized portion of the bullet. Any time a gas check gives you more than five tenthousandths (0.0005”) of springback, the check will not be solidly attached to the bullet’s shank and the check’s large diameter may cause troubles. For example, it could make chambering a round difficult in a tight-chambered piece, through over-swelling the case neck; or, the check’s large diameter could prevent consistent, smooth entry into the chamber throat, upon firing.

First, let’s look at that Paragon of excellence in gas checks: the .30 caliber Hornady check. This little lovely has no check springback, under the above definition. If you use good micrometers to measure the check’s sized diameter, you’ll find that it is only around 0.0005” larger than the diameter of the sized CB itself — a lovely, tight fit. Moreover, when the CB is fired, the check will not be absurdly oversize, with respect to the internal diameter of the throating.

In my opinion, the reason that the .30 caliber Hornady check does so well, in this regard, is that the check’s skirt has both a reasonable thickness (0.0017”) and considerable internal height (0.060”). There is nothing magical about these dimensions, except that they work.

Let’s look at what makes this check special. The check’s as-manufactured diameter, across the lip of the skirt, is 0.319” (= 0.285” shank diameter + twice the 0.017” skirt thickness). This check’s skirt thickness (0.017”) is the first key to its stellar performance. Thus, upon being sized-down to, say, 0.309”, the check will go through a 0.010” reduction in diameter. This is enough to exceed the thick guilding metal skirt’s slight elasticity. The base and skirt go into the “yield” mode and then spring back only around 0.0005” upon exiting the sizing die. The second key is less important, but still worthy of consideration: this check has a reasonable internal height (0.060”). Any skirt having less height than this will tend to have more springback; and a thinner short skirt would be even worse.

Now lets look at a check which, in my opinion, is a bad actor: the Hornady .35 caliber gas check. This is only any example. Please give this test to all of your Lyman and Hornady checks…. you’ll find that many will fail the test. I encourage you to report troublesome checks in these pages, listing both brand and caliber. In spite of being made for a larger caliber (than our reference check), this check has a skirt thickness of only 0.012”! Likewise, it has a skirt height of only 0.053”. According to my measurements, its as-manufactured diameter, across the lip of the skirt, is 0.367” (= 0.343” shank diameter + twice the 0.012” skirt thickness). For a CB sized to, say, 0.360”, this represents only a 0.007” size-down. The check’s thinner skirting is springier and makes for less size-down. This, in combination with its short skirt height (0.053”), makes for a bad case of check springback, as follows.

In my SAECO lubrisizer, when put through a 0.361” sizer die on the shank of a Lyman #358315, the check emerges with a 0.363” diameter (0.002” springback). If I use a 0.357” die instead, the check emerges with a 0.3585” diameter (0.0015” springback). Therefore, with this thinner, shorter skirt, even the 0.010” size-down that works so well with the .30-caliber check still results in springback in the .35 caliber check.

Suggestion — I am hoping that both check makers will run springback tests on all of their checks and will solve the problem in all check calibers in which it occurs. One option, at least for the larger calibers, is for the checks to be redesigned to provide: 1) a skirt thickness at least equal to, if not greater than, that of the excellent .30 caliber Hornady check (0.017”); and 2) an internal height of at least equal to that of the .30 caliber check (0.060”). Alternately, it may be possible for the current designs to work if the checks were annealed as part of the manufacturing process. Whatever works is fine. The typical springback should be on a par with that exhibited by the Hornady .30 caliber check. In the mean time, about the best we check users can do with the current line of large-caliber checks is to anneal them, prior to use, to minimize their inherent springiness.

Are We Having Funnel Yet?

Lately, I’ve been measuring a good variety of sizer die mouths, in many diameters, from SAECO, RCBS, and Lyman. Why? Because one of my dies gave very rough entry of the check into the die mouth. I wanted to know the cause of this problem and to determine how common it is.

This trouble occurred: 1) when seating conventional gas checks base-first, in the conventional manner; 2) when using the Dave Scovill’s savvy invention, the Noze-First top punch (available from The Hanned Line, P.O. Box 2387, Cupertino, CA 95015-2387), to achieve coaxial sizing and flush check seating; and 3) when sizing on FreeChecs (soon again to be available from The Hanned Line) in the usual base-first manner. The factory-made check would enter the die only with difficulty, requiring considerable force, with sudden and loud entry; this die ruined my carefully-made FreeChecs.

I decided to analyze the problem die’s entry taper (funnel). This does not include the 45-degree bevel at the die mouth. Rather, it is the gradual downward-tightening cone each die is supposed to have in its upper 0.3” or so, which “funnels down” to the die’s nominal diameter. I’ll describe what I did so that you can do it on yours too; none of us needs badly made sizer dies!
On this problematic sizer die, I removed the die’s push rod and cleaned off all lube, then carefully inserted the pointed internal diameter probes of my dial calipers around .3” into the die mouth. The internal diameter reading agreed with the “0.308” nominal diameter stamped on the die top. I then moved the probes up to just below the base of the 45-degree entry bevel and made another measurement. Based upon dies that work well, I expected to get a reading of 0.330” or more. Instead, it was only around 0.311”! No self-respecting check is going to enter such a tight-mouth die, except with difficulty. [Note: for dies under .30 caliber, the hole is too small for accurate I.D. measurement of the funnel bottom, using common dial calipers. Therefore, measure only the funnel mouth diameter.]

This die is an obvious cull that escaped quality control checks during manufacture. However, in checking through my collection of dies, I found another of the same brand that had the same problem. Such dies can cause all manner of evil results to your group size and can increase the frequency of fliers. May God help the first-time cast bullet shooter that purchases such a die!
Having measured all three main makes of sizer dies, I’d like to describe what the good sizer dies share in common. A properly functioning sizer die will have an entry funnel that:

- tapers down gradually, reaching the die’s nominal diameter at a point between 0.22” and 0.35” below the top of the die;

- has an entry diameter (at the base of any 45-degree entry bevel) of between 0.022” and 0.032” larger than the caliber’s nominal groove diameter (e.g., in 0.30 caliber, a funnel mouth diameter of between 0.330” and 0.340”).

Although I discovered this problem first in a SAECO die, I have since found a similar problem in the other makes as well. Using properly funnel-mouthed dies from any of these makers (dies that meet the above standard), your CBs and checks, including FreeChecs, will go down like socks on a rooster. That’s what we pay for in our sizing dies, with all due respect to the roosters.

Suggestion — For the sake of our sport, I hope that sizer die makers will include the entry-funnel dimensional standard described above (which I derived from well-working samples of their existing dies) as part of their quality control parameters, so that cull sizer dies no longer get out the door. In the mean time, I suggest returning for replacement all sizer dies that either lack a funnel or that have a dysfunctional minimalist funnel.

I know that RCBS (605 Oro Dam Blvd., Oroville, CA 95965 // 1-800-533-5000), for one, is very good about responding to actual problems related to their products. I suspect that Lyman (475 Smith St., Middletown, CT 06457 // 1-800-22-LYMAN) and SAECO (Redding Reloading Equipment, 1089 Starr Road, Cortland, NY 13045 // 607-753-3331, 756-8445 FAX) will, likewise, be willing to respond to this very real problem. Be sure to include a polite, succinct description of the problem you have with any die(s) you return. Remember, we are lucky to have several fine companies producing the tools and dies we all need for our sport.

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