So, I recently decided I wanted to add a gascheck to a .311 bullet that I had designed some years ago for the 7.62x25, which I now want to use in a rifle in that caliber at higher velocity. Intended velocity is between 1600-1800fps. I looked on Sage's website and found they do in fact sell plain base checks for the .30cal. So I ordered 500 of these to try out with this boolit. However, after some experimentation I have found a few issues with it. And I'm hoping someone has some advice for me.
So first off, I was left a little underwhelmed by the plain base checks. They all appear to have tears in the skirt, as well as being slightly uneven in skirt height. I haven't shot any yet, so I'm not certain how much if any this affects accuracy. I just figured these would be a little more uniform, having used their standard gaschecks in the past. I could just be making a fuss about nothing here, it's just an observation. Now to some general measurements. Where it comes to the outer dimensions of the check itself the flat portion of the base measures approximately .3090" of an inch, followed by what I would consider to be a fairly large radius which widest part is approximately .3205", with the top of the skirt measuring about .3315". As to the inner dimensions, the best I can tell is the base is approximately .2960" tapering up to approximately .3150".
As for the bullet, this is a custom design I had make about 14 years ago by Mountain Molds - an older picture of the bullet below for reference. It's pretty similar to Accurate's 31-085G, though the dimensions are not exactly the same. This boolit drops at about .3115, and is powder coated using Smoke's powder. This brings the diameter to approximately .3125-3135" depending on how thick the powdercoat is. Picture for a reference:
Now for the issue I am having, seating these things squarely... So I have tried seating these things in both a Lyman 4500 with a (RCBS) .311 sizer (my bore on the rifle is .310"). As well as a Lee .311 bushing mounted in a breach lock press with the adapter. The problem is that I have a high rate of unsquare checks, or deformed boolits. In the Lyman press, due to the nature of the gascheck being about .320", the check doesn't center itself in the seat of the sizer - this is an older sizer without much of a taper at the top. This can be centered slowly, and manually, but often results in the nose of the boolit being slightly canted due to the radius on the inside of the check not allowing the bullet to seat very squarely. In many cases this leads to boolit deformation. Which as you guessed, is undesirable. When using the lee push through bushing, the real problem seems to be an issue of getting the tiny bullet square while entering the sizer upside down. Which causes the check to cant to one side or the other - i.e., the boolit is longer on one side than the other due to an imperfect seat on the check. If sizing nose first this seems to be little less of an issue, but creates an uneven rim on the base of the check - due to the punch being a smaller diameter than the bore of the sizer. Again, not desired for accuracy in a rifle I would think. But as a note, this also isn't entirely square, as I can see a small but noticeable difference in how high up the skirt sits on the boolit.
Now, I do not have a proper top punch for this bullet, I don't think Dan offered them back when I ordered this, or if he did I didn't receive one with the mold. So I have always used a flat top punch when sizing in the Lyman 4500. This hasn't ever been an issue when sizing the bullet on it's own. But when trying to square the nose with the base when seating an oversized check this is what I feel is causing deformation when using the Lyman sizer. As for the Lee bushing, I feel it really comes down to the bullet being tiny, my fingers being fat, and trying to balance the bullet on it's .184" nose when using the punch that has a certain amount of play.
Now, I did read the instructions for the gaschecks. I've also seen where it is suggested to chamfer the base of the bullet so they see more uniformly, something a little difficult to do with a bullet only being .510" long. If I'm super careful, I can get about a 75-80% rate of usable boolits when using the Lee bushing and sizing base first. But that is still a lot of wasted checks and bullets. Not to mention pretty slow going. Does anyone have any advice?