At least for the Remington 700. I’m still working on the Encore.
If you’ve been following the saga, I’ve been trying loads using both the Sierra 175 grain MatchKing bullet that the 700 5R was designed around, and the Lapua 155 grain Scenar bullet that is almost identical in length to the Sierra. I’ve gotten some good groups, but I haven’t really had a chance to sit down and work on an accuracy load until the last couple of weeks. The first thing that I determined was that I could safely push the 155’s a lot faster than the 175’s, and with ballistic coefficients of 0.508 and 0.505 respectively, faster is better – especially since I’ll be shooting at targets 700 yards away.
I’m also a subscriber to Handloader magazine, which just paid for itself. The December, 2008 issue contained an article by one Gary D. Sciunchetti, an apparent obsessive-compulsive who wanted to develop “the most accurate .308 load.”
He went overboard.
Based on his belief that the single most accurate commercial load available (defined as giving the smallest groups in the largest variety of rifles) was the 168 grain MatchKing in the Federal Gold Medal Match loading, he set out to test every possible combination of cartridge case, powder, primer, and bullet in the 165-168 grain range. Very quickly he settled on Varget as the powder of choice. Where it got interesting (for me) was when he came to primers:
There is a rule of thumb that magnum primers are good if you need them, but if you don’t need them, don’t use them. Needing them is generally viewed as using a large volume of slow-burning, deterred ball powder, or extreme cold weather shooting. The .308 Winchester does not meet this requirement, but this research was to include all primers that might be suitable.
What he discovered was that the CCI 250 Large Rifle Magnum primer provided better results with Varget than any of the other eleven primers tested – all else being held the same.
If I hadn’t read the article, I wouldn’t have even considered a magnum primer.
Anyway, my testing started out with similar magazine-length loadings of 155 Scenar and 175 grain SMKs fired at 300 yards, which I reported on back in January. That was when I decided to concentrate on the 155’s. For my next test, I loaded the bullets out just shy of the lands, which made them much too long to fit the magazine, but that’s OK for Boomershoot. I don’t mind single-loading. I loaded twenty rounds each of loads ranging from 45.5 to 47.5 grains, in half-grain increments, ten each with CCI BR2 and ten each with CCI 250 primers, and fired them over my chronograph, getting two five-shot groups at 300 yards for each load. (Use this and any web-based data at your own risk. The Hodgdon web site lists 47.0 grains as a max load for the Sierra 155, but I am seating the Scenar way out there, yielding more space in the case.)
The load that gave the best performance (FOR ME, remember!) was 46.5 grains over the CCI 250. So last week I loaded up another hundred rounds, twenty each at 46.3, 46.4, 46.5, 46.6, and 46.7 grains – ten using BR2’s and ten using 250’s.
Here’s the data for the 46.4 grain load using the BR2 primer:
| Shot | Velocity |
|---|---|
| 1 | 2903 |
| 2 | 2883 |
| 3 | 2901 |
| 4 | 2822 |
| 5 | 2837 |
| 6 | 2840 |
| 7 | 2883 |
| 8 | 2897 |
| 9 | 2897 |
| 10 | 2868 |
| Avg | 2876 |
| ES | 81.92 |
| Sd | 28.96 |
The two groups ran just over 2″ at 200 yards (I’m shooting at a different place, and 200 yards is more convenient there.) Now, here’s the same load using CCI 250 primers:
| Shot | Velocity |
|---|---|
| 1 | 2929 |
| 2 | 2895 |
| 3 | 2905 |
| 4 | 2914 |
| 5 | 2911 |
| 6 | 2903 |
| 7 | 2900 |
| 8 | 2910 |
| 9 | 2899 |
| 10 | 2913 |
| Avg | 2908 |
| ES | 33.64 |
| Sd | 9.74 |
Both groups ran just over 1″ (except for a called flyer). The magnum load picked up 30 fps, and the standard deviation dropped into the single-digits! My shooting partner brought his 7 Mag rifle to practice with. His 168 grain commercial load wasn’t significantly faster than 2900 fps! There’s quite a bark when I touch off this load, but there were no pressure signs of any kind.
This week I’ll assemble 100 rounds of this load and see what I can do with it at 200 and further out. I’ve got powder now, 500 more bullets coming, and about 800 primers left.