"Puts on flame-proof suit and sets his shoulders"
I just bought one of the last Remington 700 PCR's in .260. I have all of the tooling for truing a 700, and I have never owned a .260, it was on sale for $655, and I have almost a full 55 gallon drum of once-fired .308 FedGMM. I plunked a 5-25x56 Strike Eagle on it and I am curious what it will do. Enough said.
Since I have no background with the .260 I will do my own load test - which follows no conventional path.
I start by looking at the books and deciding what powder\primer\brass\bullet combo I am going with. I may also scour the internet to confirm or disprove my theory, but lately availability and in-stock have been determining a lot of the recipe. So I have a lot of H4350 and R16. I use H4350 on 3 other rifles and RL16 on one... RL16 it is. I have more CCI-BR2's than anything else, so they get the nod. I have 500+ .308 once-fired GMM, brass selected. I will be using the Berger 140 Hybrid, got a few hundred of those. Load parameters selected.
Now I begin by working on brass. I select 100 cases and start trying to reduce variables. They are all tumbled for a couple of hours and re-sized. Then I toss them in the sonic cleaner for 15 minutes. Scrub the primer pockets and measure length. I trim to ensure they are all plus\minus 0.002. I skim the necks to clean them up and try for plus\minus 0.001 neck diameter (settles in on 0.292"). I will micro-manage necks later, I just want them close now.
Looking at loads for .260 Remington in books I have:
- Hornady 38.1-45.1
- Nosler nothing
- Lyman nothing again
- Sierra 34.4-40.4
- Berger more nothing
- Alliant Website 38-42
- Internet says 42gr from looking at other people's load development
I also know that I will be seating long. I OAL check the barrel with a Berger 140 and get an overall length of 2.932 (typical Remington and their long throat). I am shooting from the magazine so I will load to 2.870, this gives me 0.015 forward to tune and possibly chase the lands later.
So I settle on a ladder of 38.0 38.3 38.6 38.9 40.2 40.5 40.8 41.1 41.4 41.7 42 42.3 42.5 twelve rounds to load. I will load two of these "ladders". Off to the range...
At the range I will set up a target for something to aim at; but, that isn't the goal. I hook on the Magnetospeed and shoot the ladder recording velocity. In this case I recorded:
2311 2316
2323 2330
2368 2372
2440 2442
2445 2444
2450 2448
2488 2492
2552 2549
2601 2597
2608 2611
2622 2608
2648 2657
2699 2705
Light pressure signs at 42.5. It is 20 degrees outside and I am at 6550 feet with an altitude\density of 6250. I graph this out on paper and find that 38.9 - 40.5 and 41.4 - 42 appear relatively insensitive. These are what I refer to as "velocity nodes". (Checks for gaps in the flame suit...) So far I am in 24 rounds. I go back to the loading room and start setting up an OCW test for the higher velocity (of course!).
I resize all 24 and load up 5 rounds each at 41.6 41.7 41.8 41.9 and 42. Back to the range! Shooting all 5 OCW groups I get this:
MOA = .455 (circular) .421 (slightly oval vertical) .333 (straight line horizontal) .339 (circular slightly horizontal) and .422 (slightly oval vertical). Not a bad first outing for OCW!!! Back to the loading bench!
I check the seating depth again and find that the lands are the same. Doing some simple subtraction I find that CBTO (jammed) to CBTO (2.870) is .062. I resize and load all 25 at 41.8gr and seat them to 2.870". I clean thoroughly with BoreTech C4 and Boretech Cu+. I load up 3 fouler rounds, (42gr R16, some loose Barnes 130's), I grab the seater die and my Lee Hand Press and go back to the range.
After shooting the foulers I shoot 4 at 2.870" (2.237" CBTO) and get a .299MOA group. I use the hand press to seat to 2.230" CBTO and send 4 more to get .247MOA. I seat 4 more at 2.225" CBTO and get .252MOA. Just to confirm I seat 4 more at 2.220" CBTO and I see .311MOA.
Looks like 2.230" CBTO (or 2.863" OAL) and 41.8 grains of RL16 over a CCI-BR2 using Federal GMM Brass set back 0.002" with a neck diameter of 0.292" is the load. I send the remaining 9 out with the Magnetospeed hung and get an overall .417MOA group at a half inch to the right and slightly higher. 9 rounds averaged velocity is 2655fps, it looks like the barrel is speeding up a little.
So there it is. From here I may tweak neck diameter or seating, but this load is as done as I need it to be. Shooting from a FACTORY (including the BS trigger) Remington using a mid-line Vortex I am pretty happy with this. All told it took me 74 rounds (plus 3 foulers and 10 barrel break-in rounds) to find a recipe using these components.
If H4350 ever gets back on the shelf I can do a more focused OCW\Seating to find an alternate recipe by using velocity as my base. I may also try 4831SC, which I have a bunch of.
Time to buy a trigger, bed the scope, and find a muzzle brake.