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6.8mm ... Mikein
sandwarrior
Member Posts: 5,453 ✭✭✭
Mikein,
I clearly had to have gotten the bullet weight wrong then. That or the barrel, but I don't think the possible 2" would make that much difference. At least not in that short of a cartridge.
Anyhow, as you develop loads I'd be interested to know what goes on with them.
I clearly had to have gotten the bullet weight wrong then. That or the barrel, but I don't think the possible 2" would make that much difference. At least not in that short of a cartridge.
Anyhow, as you develop loads I'd be interested to know what goes on with them.
Comments
I'm heading out this morning for a varmint hunt and then some serious work with 4 new loads for the 6.8. I'll let you know what I discover. The new news on this round of load development is that I'm going to try a 130 grain Hornady over 20 grains of 4198. Be interesting to see what I get. My s/w tells me it will be thundering out of the muzzle at a very slow rate of speed. . . But I'll be more interested in terminal velocity and performance than MV.
M
Just returned from the range. The most interesting of the new loads I tried was the 130 grain Hornady SST over 20.0 grains of H 4198. M V is not too impressive, clocking in at 2177. My chrono read 1989fps over 5 rounds at 100 yards; a loss of 188 fps. My s/w program estimates muzzle energy for this load at 1240 ft. lbs, and terminal energy at 1043 ft lbs; a loss of 197 ft lbs. The Taylor Index is calculated at 9.78. The BC on this particular bullet is .46. My best 5 shot group was 5/8ths inch. I have a sneaking suspicion that this load, or one quite close to it, is going to become my hunting load in this rifle, since most of my shots at game in the Central Texas area are less than 150 yards. I'll nudge this load up a tenth at a time and also move the seating depth out just a tad to see if I can tighten the groups up a bit.
M
Cool! Thanks for the update. It sure seems to lose velocity pretty quickly as you go up in bullet weight. How does recoil feel when you get up in bullet weight? Noticeable? The Rem700 I shot had a little kick with 115's but hardly a disraction. The AR I shot of course had a lot less. But the arc to get that thing to 300 was a lot. 22" from a 100 yd. zero. It had a 16" barrel I believe. The guy was happy with it. It would get him out to as far as he was going to shoot deer in MN.
The felt recoil is not noticeably higher with the 130 grain bullets. Still less than my .243 Win shooting 95 grain Nosler BTST's.
If I zero this load to be 1.8 inches high at 100 yards, it will be 1/2 inch high at 140 yards, 4.45 inches low at 200, and 10 inches low at 240 yards. I figure I can probably estimate a 10 inch holdover, but trying to dope out and scope out a 22 incher required for a 300 yard shot is way beyond my capability! If I can safely goose up the MV, I should be able to improve on those numbers. But I want to keep that level of accuracy, so it's the eternal tradeoff we make! It looks like I have room to safely move the MV up to around 2400fps, so I'll be creeping up on that number over the next week or two. I'll keep you posted.
M
I have creeped up the MV scale and continue to push the bullet seating depth out (the reloading manuals and my s/w package give a 2.260 COL), and I am now at 2420 MV and a COL of 2.37. I wish I could report that I've seen noticeable changes in accuracy, but I really haven't. The only consistent trend has been that the hotter the load, the less accurate it is. I've noticed this same trend many times in other calibers. Last night I built up 20 more rounds with a COL of 2.40 that I'll be trying at the next weather break we get. Even at 2.40, the rounds chamber smoothly and I see no indication of contact with the rifling. These rounds are predicted to produce an MV of 2420; I'll graph them and see what they really run. I'll keep you up to date on what I discover.
Thanks again for the update. I know what you mean about getting the max accuracy below max velocity. Anytime I work up loads I usually expect to hit peak accuracy about 1-2 grs. below max.(of a normal pressure load). a lot of times I continue upward with the thought of attaining a given velocity with 'acceptable' accuracy. The only case that has really been the reverse of that for me has been the .223 Rem. I load them right to the top for best accuracy. In some data I'm listed as over the top. But I was loading these before there was data.
My one outstanding incident of higher velocity giving me tighter groups was with the 204 Ruger. When it first came out, I got a Ruger #1 chambered for it and really pushed the limits to see if I could achieve the MV's Hornady had published for it. (There were no published loads for it when it first arrived on the scene, so I was using 222 Magnum data and working up very slowly and carefully.) I easily attained their velocities, plus some, and my groups didn't fall apart as I pushed higher and higher; they were a bit tighter at 100 yards, and at 200 yards they were noticealby better than the lower velocity rounds. My conclusion on that was that the elements had less time to work on that little 32 grain bullet as it whistled down range!