TLDR: I've been screwing around with a new rifle. Seriously, if you don't like reading the ramblings about someone experimenting with a bit of a wildcat - might want to save yourself the time here.
I've started down the path to putting together my own hobby-level ELR/long range hunting/just messing around rifle. Why? Because I got a small case of "the envys" when I got to do load development for my buddy's 300NM. However, I'll admit it right off the bat that I wanted a tad less recoil and was willing to trade 20% less barrel life for 20% less recoil with similar ballistic performance. There, you can have my man card.
I chose the 7-300 because quality 300 PRC brass is plentiful. There is some difference between it and the 28 Nosler, but not a whole lot...and I wanted access to more brass offerings. And I didn't want the length of the RUM case or to open my bolt face up for the Norma Mag.
(7-300 / 195 Berger Vs. 7RM /150 ABLR)
I went with the Manson 7-300 PRC M2 reamer because it has a generous .225 freebore, allowing me to load long, and a .319 neck, negating my having to neck turn (.313 loaded). Perhaps other reamers are similar here, to be honest I didn't really look much further after stumbling across the Manson.
My minimum goal was 3K FPS and 2/3 MOA accuracy. Of course, I'll always settle for better than that. I know that some guys claim to hit 3K FPS with the 7RM and PRC and a 190+ bullet. I don't doubt that it might be possible, but I didn't want to live at 70K PSI pressure either.
Barrel is a Bartlein, 1:8, heavy palma, that I had cut to 27". Any longer wouldn't fit in any of my safes with the Area 419 Hellfire attached.
** Here is where I handicapped myself a bit **
-Rifle is built on an older 1086 Surgeon that was originally in .300WM. That thing feeds and shoots beautifully in its WM version. I'm going to have to mess with it in 7-300 configuration, as right now it is a single-feed rifle. The 195gr Berger at .035 off is measuring 2.945 CBTO or right at 3.700 OAL.
-I bought 500, 195gr Berger EOLs on a flash sale for about .47 cents per. I was extremely fortunate to find that sale. However I'm forcing myself to a single bullet and hoping that the barrel likes them well enough (it does).
-Same with powder. Found an unopened keg of N568 for about $270 and just went with it. N568 is not going to give me the same velocities as N570 or perhaps one of the Reloader powders, but I'm not a velocity hound. I have read about guys hitting >3,150 FPS with 190+ bullets, but that isn't going to be me here.
So with only one bullet, and one powder to do load development... what could go wrong?
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This is an extremely easy cartridge to form. I just neck down in a Redding bushing die (.315? I'll have to look later) and then mandrel back to .282. I already had the .282 mandrel from my 7mm RM, so I just added the step... it probably isn't necessary, but if I am remembering the .315 correctly it is taking it down a bit too far. One of the other forum members here gave me good advice when I asked: "make sure you give it a good chamfer and lube". No issues so far, and I've prepped 150 pieces of brass. I will probably look at getting a .316 and .317 bushing to try once I go to once fired brass.
That's it. Prime, charge, and seat afterwards.
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So, not having a clue about actual data, I started breaking in the barrel at 76.0gr N568 and trying a few seating depths. Velocity was everything that I'd expect out of a 7 PRC (about 2,820), so after the first 20 rounds and a general idea of where I'd want to start my seating depth at I started increasing charge weights.
Oh, accuracy was about a half-minute for (3) shots. I don't trust three-shot groups though. I'm a "do three, five-shot groups and aggregate" kind of guy. Not that it makes my data all that more valid, but I can at least eliminate chasing the lucky group.
I did five-shot groups from 76gr up to 80gr in half-grain increments. by 79gr I was getting some decent flattening of the primers with a bit of cratering. 79.5 the crater was definitely THERE, and I started seeing a hint of ejector mark. And by 80gr I had a very noticeable ejector mark. Granted, this is on virgin brass, so I might get away with trying a bit higher in subsequent loadings. 80gr gave me 3,012 FPS. I had hit that goal, but also hit pressure. From the data I had read on VV's website, I was expecting to be able to compress the load before I hit noticeable pressure signs. Not the case here.
However, from 76.0 - 79.0 across three full grains of powder the groups stayed consistently around the 3/4 MOA mark for five shots at 100 yards. Even more surprising, the POI didn't shift half a tenth in all of it. On top of that, I think 5 of the 9 groups had single digit SDs. By this point, I had 65 rounds on the barrel. I loaded tried a single five-shot group at 79.0gr at 300 yards and it came out to 2-5/8". Velocity for that (79.0) during testing was about 2,955 FPS with a SD of 9.
On another day, I then tried seating in and out again in .010 increments, going from .015 - .065 (@ 79.0gr), but did all of that at 300 yards this time on steel (five round groups still). Across that .050 range, every group measured between 2-1/16" and 2-5/8". I did have one group with an uncalled "flier", but it was still only 3" on the nose. I doubt that I could shoot much more consistently if they had been the same length. This barrel/bullet/powder combo might not be lights out, but it has the widest window of consistent accuracy that I've got. I'm surprised. That test took me up to 100 rounds even. I just went with .035 off as it is going to give me at least .030 erosion before I have to (or don't have to) worry about it.
I then gave 25 rounds of 180gr ELD-M a try. I didn't have much luck at all and gave up on them. I will verify that this barrel will indeed - shoot greater than 1 MOA.
At 125 rounds, I chronographed 79.0 and 79.5gr again, and shot them at 300 again. The barrel sped up about 45 FPS. 79.0 gave me 3,001 FPS with an ES of 26 and SD of 11, and 79.5gr gave me 3,018...but I didn't like the primers and faint ejector mark.
I shot the 79.0gr load again at 650 to verify/true velocity (I use an old chronograph, but it works). It was spot on at 3.3 mils. Accuracy was ~.6 MOA. That is right in line with the 2-1/16 and 2-1/4" @ 300 yards groups I've shot with it.
So, bottom line: I've hit my minimum goals, and don't completely feel like I wasted money (even though I did). I'm probably the limiting factor in the accuracy. And I probably need a different powder if I am going to jump velocity anymore and run with the fast guys. For now though I'm content.
I've only got 135 rounds through her.
I'll probably leave it by the back door during hunting season so I can completely overkill a 170lb whitetail at 250 yards, or maybe see how the 195gr Berger does on a coyote or two. Why? Because 'Merica.
If you made it this long...thanks.
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