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Posted: 8/8/2015 3:38:52 PM EDT
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.308 Win Savage 10T with a PST 2.5-10x32mm scope. I plan to shoot for groups at 300yds and closer and steel silhouettes beyond that. I don't compete.
168gr Hornady BTHP over IMR 4064 in virgin Lapua brass (zero case prep!). Everything was loaded to ~2.795in OAL. Fired prone off bipod and rear bag. 5 each of test charges 41.0 to 43.0gr in 0.5gr intervals. Shot in ascending order to watch for pressure. All at 100yds. Dots are 1in diameter. 
No signs of pressure all the way up to 43.0gr. 42.5gr has the least vertical spread. 43.0gr looks the tightest of today's group. Which is better for future load development? Lowest vertical spread or tightest extreme spread? Is it worth it (in terms of components, time, and gasoline) to fine-tune the powder charge using 0.2 or 0.3gr intervals? What about testing OAL versus loading everything to mag-length? ETA: Those sighters were South African R1M1 in case you were wondering. It was frustrating trying to (roughly) zero the scope using that ammo. |
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I would not bitch about any of those groups. I'd go with the tightest group possible.
Also, when sighting in a scope, did you know that you should tap the scope between adjustments? Apparently,with some scopes at least, it helps move the reticle into place. I read this on a Arfcom thread some years ago. |
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Those are very good groups. The fact that it stays good over your range loads should be a very welcome sight to you.This means changes in atmospheric conditions including temperature change should not effect you accuracy much.
Shooting good groups off of a bipod is not an easy accomplishment rear bag or not. I think maybe your vertical strings could be traced back to the bipod rest. Using a chronograph would be the best way to tell just how hot your loads are but back in the day before the affordable Chrony if I was getting results like that and still had no pressure signs I would go up more if I wasn't already at book max. I would do this mostly to see where the group starts to open back up. Knowing both ends of the accuracy nod will help you decide what load to go with. I do think a solid front rest would make those groups more cemetrical. This is of course assuming your letting it cool between shots. Motor |
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Given the trend line, your rifle appears to be happier with the 42 and 43 grain loads.
The problem is that it's impossible to tell much from single five shot groups. Once you get a total of 3 or 4 five shot groups you'll start to be able to determine if there are any significant differences between the two. I'll generally shoo two 5 shot groups in the initial ladder, then work up a second round of testing base on the first round results, with either two or three finalists that shot well, or a further ladder at .5 or .3 gr intervals between two promising loads like your 42 and 43 grain loads. After another two 5 shot groups there, I'll load another batch of 10 rounds in the intended load to confirm it still shoots as well as it looks initially. That's normally followed by about 50 more rounds before I adopt is as a standard load that I'll produce in quantity. |
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Congrats on the rifle. Bought mine last month. One thing I do before shooting reloads is figure what grain bullet I will want to stay with, buy a box of commericial ammo, usually hornady 168 match or amax, and use that to zero at 100 yards. I know you cannot match commercial ammo but I try to mimic anyways. Plus, the commercial ammo is usually tighter. Then I start on my reloads working up and see which one does a close to the commercial ammo. When I am close, but not as tight, then I figure its my brass prep. One thing I notice when I am seating the bullet is the difference in resistance while seating the bullet. I don't crimp for the bolt like I do on my AR 10's. I purchased this.. https://www.kmshooting.com/catalog/case-neck-expanding-tools/expand-iron_complete.html . Since using this, all of my bullets seem to press in about the same pressure. Of course there are other things to consider but this has helped me.
Am curious on your measurement to the lands with 168's. For mine the Hornady 168 match is 2.814 and 168 A-Max is 2.813 measured 3 times. Been seating mine at 2.800. |
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First off,... good shooting!
IMR4064 is my favorite powder for 308. It's so good, I've never bothered with any other. I use 42.0 gr for all SMK bullets in the 155 to 190 gr range. It's a stout load for the 190 and a light load for the 155. What you have not told us is whether the lateral dispersion was caused by, influenced by, the wind. Even at 100 yards, wind is important once you start shooting small groups (<1-2 MOA). Another thing, did you call every single shot? Did they impact on call? With small groups, even tiny variations in point of aim at let-off have to be called in order to separate the shooter's aiming errors from the dispersion of the load. A thought, the groups keep getting better. Is 43.0 the max load for that bullet? If not, go a little higher in charge weight and see if the groups stay small. Don't go above published max. Don't go higher if pressure signs appear. Don't go higher if groups start to open up. I hope some of that helps in some way. |
| Hodgdon's web site list 41.5 to start and 45.9 C for max. I4064 is a great powder but have found Varget to be real good also. But Varget seems to be hard to find and I4064 is usually around to get. When I did a series last time out, I was popping primers at 43.5. But am thinking it was the brass (SSA) so will try with a different brass. I won't buy SSA again as 3 out of 100 had to big primer holes on 1st load, lost 5 more after 1st shooting. |
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