300 Win mag resizing die update

As I reported the other day:

I have lots of one fired brass but I knew that brass wouldn’t chamber in any some other rifles even though I was using a full length resizing die. I got my hands on a .300 Win Mag rifle that had problems chambering it. Then with a few rounds of empty, once-fired, brass, my micrometer, and the specs for the brass I sorted out the problem. I found the case just forward of the belt was one to two thousands of an inch larger in diameter than spec. I think the die is the problem so I ordered a new resizing die from a different manufacture and which I expect will fix the problem.

The new die arrived yesterday. It does fix the problem, but just barely. The specification for the case dimension in question is 0.513 inches. The once fired cases were 0.514” –> 0.515”. After going through the new die they are about 0.5135. The brass chambers, but it is tight. I ordering still another die.

Update: I looked up the SAAMI specs on the cartridge and chamber rather than what the reloading manuals tell me.

The portion in question of the case is specified as 0.5126”. The chamber is specified as 0.5136”. I suspect the rifle in question is at exactly the minimum specification while the dies, combined with the “spring-back” of the brass being used results in something oversized. I ordered an RCBS undersized die which should solve the problem.

Update 2: Thanks to an email from Bob B. I ordered what looks like a better solution. The Belted Magnum Collet Resizing Die. I canceled the order for the RCBS undersized die.

16 thoughts on “300 Win mag resizing die update

  1. Yeesh! I had the same problem with 5.56/223. One of my ARs has a tighter chamber than the others. NASTY stuck cartridge (wouldn’t lock, wouldn’t extract). Same cartridge chambered in the Colt and others just fine. Got the RCBS black box, FL die for autoloaders, and still had some stuck carts. Talked to some others, one of whom went as far as shortening his die so it would size farther. Didn’t want to do that. Headspace and all.

    Then I discovered that a bit more case lube (the Hornady aerosol lube in this instance) would allow the brass to slip circumferentially in the die more easily, and size down a bit more with the same die. Problem solved, with naught but lube.

    So enough lube to reliably prevent stuck cases is not necessarily enough lube, or the right lube, to allow complete sizing. You might want to “spearmint” with that.

    All but the most “dead-soft” brass will have some “spring-back” to it, and depending on the state of the brass (number of times fired, for example) some cases will size smaller than others with the same die. Enough, or better, lube will sometimes help. In the extreme instance I’ve had a 9mm pistol case, reloaded too many times I guess, “bounce” right out of the fairing die, tossing the press handle as the case comes down off the expander. “Spring Brass”. And on that note; I’ve made actual flat springs out of brass, as replacements for ancient musical instruments which originally used the same. All you have to do is work it (hammer and anvil) until it reaches near brittle hardness.

    Brass formulation and state-of-hardness are a part of the recipe for the particular cartridge, so I would never go so far as to suggest annealing the brass in the web area (safety issue there), but the lube idea might help if the new die doesn’t.

    • I’m using the Hornady aerosol lube. I’ll try a bit more and then a different lube just for the knowledge. I have an RCBS undersized die on order.

  2. Reloading is a controlled cluster f@^k.

    I once spent a great deal of time finding a nice load for 30 Carbine SP, then needed to order more bullets so I could start in with the mass production. The new bullets, having the identical description from the manufacturer, and even the same stock number, were so different in the nose profile that they wouldn’t even chamber when loaded exactly to that same manufacturer’s loading manual COAL spec.

    Atlas Shrugged. I haven’t loaded a single round for 30 Carbine since, and I have a pile of those new bullets and pounds of powder for it. If I were to write the manufacturere, I expect they’d reply with an “I don’t know what you mean. We haven’t changed a thing. Surely you must be doing something wroing…” and yet anyone can see the difference in nose profile from several feet away. It’s not as though you need some special measuring equipment. Sierra, FYI.

    I’ve found that different lots of Hornady XTP 10mm bullets (again, same stock number they’ve had for years) nearly always seat to a different OAL, so anytime I open a new box I know that the seating die will need to be adjusted if I want OAL to be consistent. Obvious visual differences there too. A custom seating stem, formed perfectly to the nose profile, will be “perfect” only for that lot. So now when I buy bullets off the shelf I look at the lot numbers so I can get as many of the same lot as possible.

    All the testing and time required to settle on a nice load makes it rather intimidating to switch to some other bullet, which may end up, after two years or whatever, having the same kind of variations. Maybe the trick is to call the manufacturer and order an entire lot of like 100,000 bullets or so.

    Maybe I’m too picky. Maybe I should just close my eyes and keep pulling the lever, hoping for the best…but I don’t expect that would work out well.

    Reloading is a controlled cluster f@^k.

    • Well, in all seriousness, that is why some of us buy ourselves a “life time supply” of a component once we settle onto a load we are not fiddling with anymore.

      Its not a big help if you are still experimenting, I grant.

  3. Please keep us advised on the results with the belted magnum collet resizing die – I’ve run into the same problem – although only rarely, fortunately – with 7MM Rem Mag cases.

  4. Joe,
    If the chamber is at minimum spec, have you thought about renting a finish reamer and just open it up a tiny bit? Get a piloted reamer and hand turn it, likely a couple of well-lubed (with appropriate cutting oil) turns of the reamer would eliminate your issue entirely. Having to fiddle with undersized sizing dies seems like a workaround for a problem best solved at the source, perhaps?

    • I did think about that.

      It’s not my gun. And I would rather the ammo be in spec than modify a gun within spec.

      Thanks for the suggestion.

  5. I had a similar issue with my M-14 clone. The chamber is so tight that I had to purchase a small base resizing die before my handloads would fit. On my .300 Mag I had trouble EXTRACTING rounds, and had to have the chamber polished. The joys of reloading!

  6. Most of my reloading experience is with straight-walled pistol rounds, so I won’t comment on the sizing issues with tapered case cartridges, for fear of saying something stupid.

    Having said that, a fellow Australian shooter has come up with a way to bring cases back to specified dimensions by roll-sizing, rather than relying on the more common coaxial “insert case in tube” resizing die method.

    Having checked his website (www.rollsizer.com), it appears that he has versions of his product already available for .223/5.56.

    Perhaps this might be a viable alternative solution.

    • It looks like it still uses regular resizing dies. Interesting albeit pricey approach to the case bulge issue.

      • I’m not sure what you are referring to here.

        Yes, the reloading process continues to use standard reloading dies.

        The roll-sizer itself addresses the “base-of-case bulge” issue; re-sizing of other areas of the brass is, as normal, done with the standard tools.

        In my particular circumstances, I don’t find a need for roll-sizing. All my competition guns have fully-supported chambers that eliminate (or at least greatly reduce) the bulging problem, and I only reload my own brass.

    • Check out the Belted Magnum Collet Resizing Die suggested by Bob B. It’s a little different and looks quite promising to me. Mine should arrive tomorrow and I think I will have time to try it out before I get sucked into a whirlwind of activities (a wedding, among other things) for a week.

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