Fryxell data on Vulcan aluminum checks

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Fryxell data on Vulcan aluminum checks

Post by mtngun » Wed Mar 04, 2015 7:56 pm

Glen Fryxell provides some good dimensional data on Vulcan aluminum checks.
6.5 mm GC Dimensions (ID measurements are only approximate):
Hornady (crimp-on copper GCs) .010” thick .061” deep .273” OD .250” ID
Vulcan Check .013” .013” thick .105” deep .273” OD .249” ID
Vulcan Check .0145” .0145” thick .118” deep .272” OD .249” ID

(Just for reference, the GC shank on bullets cast from my Lyman 266469 is .250”).
Point being, the Vulcan checks were thick enough to crimp on tightly, unlike the Sage's 7mm checks that I tested.

Here's the full article, but unfortunately my copy does not show the photos. :(

Vulcan Check: Aluminum Gas Checks

by Glen E. Fryxell

Historically, dating back to 1906, gas checks (GCs) have been made out of copper or brass. The reasons behind this include that copper and brass have suitable properties (hardness, melting point, etc.) to protect a bullet’s base, they are widely available and affordable, and they are soft enough to make mass production of GCs easy (by stamping). Other metals have also been used, for example zinc, with the Harvey bullet designs of the 1950s. More recently, handtools have been made to allow handloaders to make their own GCs out of aluminum cans. I have used these, and they work just fine, but the handloader has no control over the thickness of cans, and one might get stuck with substandard results if there is too much can-to-can variation, or if the manufacturer chooses to change the thickness for reasons entirely unrelated to the shooting of cast bullets. The bottom-line is the metal that a GC is made out of needs to be harder than lead, softer than barrel steel, easily worked and formed, and reasonably affordable. Many different metals could conceivably serve in this role.

Aluminum used to be a very expensive metal. Recall that the apex of the Washington monument is made of pure aluminum metal – chosen because in 1884 (when the apex was put in place), aluminum was the most exotic metal they could obtain, and they felt that this was a suitable way to honor George Washington. This expense was due to the extreme difficulty encountered in the 1880s to electrochemically reduce aluminum ore (bauxite) to aluminum metal. Today, aluminum is much cheaper due to abundant electrical power and active recycling programs, and we use aluminum metal for everything from packaging cheap beer, to wrapping our baked potatoes.

So, does aluminum make good gas checks? Well, I’ve shot a few handmade aluminum GCs that I made using the aforementioned handtools and empty aluminum cans, and they worked just fine. With that specific set of tools and the bullets I was using, the fit of the GC on the bullet’s shank was a little loose and sloppy, but I made a point of keeping the GC within the neck of the loaded round so that throat tension would hold it in place and everything worked just fine. Accuracy was good, the bore was clean, the GC went out the barrel with the bullet, and everybody was happy. My ability to exert quality control was somewhat restricted because I was limited to whatever thickness aluminum I could get in empty aluminum cans (e.g. .006” on a Diet Pepsi can of recent manufacture), and obviously the manufacturer of those put zero thought into making those cans a specific thickness to satisfy my needs as a cast bullet shooter. Aluminum, as a material to make GCs out of, is a perfectly adequate material for the job, it’s just a question of whether or not aluminum cans are a suitable (i.e. thick enough) feedstock to make quality GCs with. The answer to that question depends on which cans one is using (they do vary somewhat in thickness), and the size of the GC shank on the particular bullet mould(s) in question. Generally speaking, copper-based GCs have been made in the range of .009-.016” thick (depending on caliber; thinner for smaller calibers, thicker for larger calibers), so a .006” aluminum can would, at first glance, appear to make a GC that would be too thin. However, as any experienced bullet caster can tell you, there are quite a few bullet moulds out there that produce bullets with oversized GC shanks, in which case these thinner aluminum can derived GCs work beautifully. In addition, copper-based GCs are made that thick so that they will be slightly oversized and deliver the desired diameter when run through the sizing die, even if the bullet’s shank is slightly undersized. The thinner aluminum can derived GC may (or may not) have the dimensional flexibility to serve in such a case.

What if aluminum GCs were made out of thicker stock? That’s a very good question, but one that I didn’t have a ready way to address until just recently. The good folks at Vulcan Checks ( ; 191 Whitney Road, Penfield, NY, 14526) make a wide variety of GCs for the cast bullet shooter, and they make them out of both copper and aluminum. Their prices are better than I have seen anywhere else recently (i.e. online, retail outlets, or gunshows), and their aluminum GCs are cheaper than their copper GCs. Recently, they put out a request for people to field test some of their new products, and one of the bore sizes they were interested in was 6.5mm, which is one of my favorites, so I volunteered to test them. A little while later, in the mail I got samples of their 6.5mm aluminum GCs, in two different thicknesses, .013” and .0145” (about 25 of each). These are good looking GCs, and at first glance it was obvious that they covered more of the GC shank than do the traditional copper GC, so I broke out the dial calipers and took a few measurements.

Picture of GCs and letter

6.5 mm GC Dimensions (ID measurements are only approximate):
Hornady (crimp-on copper GCs) .010” thick .061” deep .273” OD .250” ID
Vulcan Check .013” .013” thick .105” deep .273” OD .249” ID
Vulcan Check .0145” .0145” thick .118” deep .272” OD .249” ID

(Just for reference, the GC shank on bullets cast from my Lyman 266469 is .250”).

The dimensions of the Vulcan Check aluminum GCs result in a GC that snaps snugly onto the GC shank. These taller aluminum GCs essentially cover the entire shank of the 266469 (see photo). Sizing them down to .266” required a little more effort than usual since essentially the entire GC shank of the bullet was being swaged down inside the taller aluminum GC, but this resulted in a very tight fit on the GC shank. Once sized, it was not possible to pull these GCs off with my bare fingers (even without a crimp-on lip, like the Hornady GC has).

Picture of GC-ed bullets with all 3 GCs
l-r: Lyman 266469 as-cast; sized with copper Hornady crimp-on GC; sized with Vulcan Check .013” aluminum GC; sized with Vulcan Check .0145” aluminum GC.

I wanted to test these loads in a rifle with a known performance record with cast bullets. In this case, the choice was an easy one. Many years ago, my wife made me a Christmas gift of a 1906 vintage Swedish Mauser 96, chambered in 6.5x55 (of course), that had been converted to a target rifle at some unknown date (probably in the 1920s) and fitted with good, target grade peep sights. This rifle is not only very special to me, it is also accurate and very fun with cast bullets. The fast twist barrel (1 in 7 ¾”) means that there are limitations, and cast bullets cannot be driven at full throttle (e.g. 140 grain bullets at 2500 fps) with any hope of accuracy, due to stripping of the soft bullet from the fast twist. Nonetheless, at more moderate velocities, it is a good cast bullet shooter and routinely produces groups of 1 ¼” to 1 ½” at 50 yards (with iron sights). Not surprisingly, being a military rifle, it has an oversized throat, so I size all cast bullets .266” to better fit that throat. I have had a lot of fun over the years with this rifle loaded with the Lyman 266469 over 16.0 grains of 4198 (1650 fps).

Picture of rifle
1906 Swedish Mauser 6.5x55 target rifle.

With the rifle chosen, I sat down and cast up a batch of Lyman 266469s using an alloy of 3 parts recovered range scrap (BHN of about 8) and 1 part linotype, for an overall BHN of about 12. All bullets were sized .266” and lubed with 50/50 beeswax and moly grease. All GCs were installed concurrent with lube-sizing. I wanted to see how these Vulcan Check aluminum GCs performed over a range of velocities, so I used 3 different test loads: 9.2 grains of Red Dot (1400 fps), 15.5 grains of 4227 (1600 fps), and 26.5 grains of 4895 (1900 fps). CCI 200 primers were used throughout. 5-shot test groups were shot at 50 yards, from a sandbag rest. The gun was not cleaned during testing.

5-shot groups for both of the Vulcan Check aluminum GCs averaged right around 1 ½” and compared favorably with those groups using the Hornady GCs. Average velocities were also very similar to one another. In all cases, strings for each powder charge varied less than 20 fps from one another, and in most cases were only a few fps apart. In each case the Vulcan Check loaded ammo came out ever so slightly faster, but this is from a very limited number of shots (i.e. of highly dubious statistical significance), and could easily come out in reverse order with the next test.

picture of rifle with representative groups
Representative groups fired with the Vulcan Check aluminum GCs.

In this particular case, with this particular rifle and bullet mould, I see no advantage to using the thicker (i.e. .0145”) aluminum GCs as the extra thickness was not needed to fit either the bullet’s GC shank, or to fit the rifle’s throat. It is, however, nice to have that option for those recalcitrant cases (either mould or rifle) where that thickness IS needed (and there were some wide dimensional variations in some of these World War I vintage military rifles).

Based on this very limited test, it seems that these aluminum GCs work as well as traditional copper GCs, both in terms of sealing the gases behind the bullet’s base to avoid leading and get the most velocity out of the powder charge, and in terms of cleanly delivering the bullet from the barrel into stable free flight for good accuracy. They are easy to install, well made, and affordable. They are sufficiently thick to insure that they provide a full diameter bullet base after installation and sizing, and once they are swaged onto the bullet’s shank they steadfastly stay in place. All in all, the Vulcan Checks aluminum GCs do a good job of getting a cast bullet down the barrel and accurately on its way. What happens beyond that point depends on the shooter, their ability to estimate range, and read the wind.