I was supposed to fly to Dallas yesterday for a training conference, but Mother Nature decided otherwise. To console myself, I ventured into the reloading room to work on my 9.3x62mm loads. I had done a bit of research and talked to some folks who do quite a bit of reloading in this caliber (in addition to some good advice from people reading here), and it made me confident of some of the dimensions I would need. So, off to the loading bench I went.
As commenter "BS" mentioned after my earlier reloading post, I started with a lower charge and worked up. I loaded a few rounds in each charge weight, going up one grain at a time. So now I've got 18 rounds theoretically (see below) ready to test-fire, hopefully next weekend if the weather cooperates (and it's Phoenix in March, so it usually does).
I did find some unusual results. All of my cases are once-fired Prvi Partizan brass. I miked four or five out of the batch to see if I needed to trim, and they were all within a few thousandths of each other, and well within acceptable length. When I loaded them, I got a fairly wide range of COL. Minimum was about 3.295, and max was 3.307. That seemed like a large discrepancy, so I used my bullet puller to tap the projos slightly forward, and reseated them, thinking my seating die might have come loose. They all reseated... to the same COL they were before being pulled. The 3.295 cartridge reseated to 3.295, and the 3.307 cartridge reseated to 3.307. All of them fed and chambered in my rifle with no issues, but it's troubling. There seemed no rhyme or reason to why they were different lengths. I had rounds with the same powder charge near each of the extremes. None of the charges got up into the neck of the case, so I'm not yet dealing with compressed loads. I'm going to start with the lightly-loaded rounds and see if there is any variation in point of impact, recoil, or any signs of pressure. If not, then I'll gradually work up. I didn't load up to the max yet, I can always come back and load them if I see no pressure signs. The next batch I load, I'll mike every case to ensure uniform length, and the projos as well.
The second thing I wish to accomplish before the weekend is to construct a basic set of shooting sticks. I'll shoot groups off sandbags on the bench, of course, but I would also like to shoot some factory ammo from the sticks to refine my technique before the match at the end of the month.
All in all, a day of both frustration and satisfaction. The weekend will determine how it all ends up.
Nice to hear you're making progress. When reloading for a rifle, the seating die registers off of the ogive on the bullet (I.e. approximately where it would start engaging the rifling), as such when measuring rifle cartridges, this is the dimension to measure. This does lead to some variation in the overall length, if there is any variation in the bullets themselves. I would recommend getting a bullet comparator (basically a jig the goes on your calipers to measure from the ogive) to see what level of variation you have there.
ReplyDeleteAlso, regarding case length, for true precision loads, it is generally best to trim to a common length after sizing, even if they are within spec. This ensures consistent neck tension which will help make your velocity and POI more consistent.
Good luck!
That ogive difference makes sense. My 'dummy' or 'gauge' round initially came out 3.303", but when I chambered it, the rifling pushed it back to 3.301", so I reset my die for 3.297" and figured that would be my new gold image. So imagine my surprise when the next (live) round came out to 3.305", and chambered without getting any setback at all! In fact, all of the loads chambered without contacting the rifling as far as I could tell. At least, none of the projos had any setback. That would make sense, as the cartridges would all have the same length from rim to ogive, and that's what both the seating stem and rifling contact.
ReplyDeleteThank you again for the information!
It used to be called a "Stoney Point" gauge but I think Hornady bought it out. It's basically a hole at caliber diameter which you attach to your calipers to measure the length from the base to the point where the bullet is at groove diameter, i.e. the bit that touches the rifling first.
ReplyDeleteMake a dummy cartridge as you have done, touching the lands. Then work from that. -4 thou is a bit on the small side, I'd aim for 20 thou for starters.
As data points, my 30-30 likes the bullet to be 27 thou off the lands. Not 25, not 30, 27. Prima Donna.
On my 300 Win Mag I'm struggling to get close. With the round at max COL the ogive is something like 80 thou from the lands. Fortunately the magazine takes longer bullets, because the rifle seems to like 30 or 35 thou most.