Tks for the support Dan. I'd like to add something to the bench technique post.
I use this postion, holding the rifle in my left and right hands the same as if I'm shooting offhand, with all my hunting rifles - no matter the period. All of them shoot identically off the bench to shooting from postitions, as I use the same holds in all postions, whether I'm then resting the back of my had on the bags for further support, or my elblows on my knees - the hands are at the wrist and forend.
Left to bounce, all will shoot to different points of impact from different postions. Th is was struck home to me with a little M94 with 16" bl. in .45 Colt. I was running 300gr. bullets at 1,740fps from that gun, and the difference shooting with bags under the forend to holding was a good 12" to 13" at 100 meters. The difference with my .375 was only 3 1/4' but would still promote a miss or wound at 200 yards on a deer. The .69 REALLY throws the shots high if left to bounce off the bags, however shoots perfectly held as noted. Hold as above noted double handed holding, the poi off the bags was identical to shooting offhand no matter what the calibre. Since then, I've done it this way with every hunting rifle & have been rewarded with identical poi.
Light recoiling guns will shoot very close off bags to what they do offhand, however there will usually be some difference.
Note also, that holding the gun in both hands will not provide the tightest groups, not as tight as a good bench-rest technique, however the centre of the group is what we're after in sighting in, not exactly how tight that group might be. A tight group that misses in the field is now where near as good a group that hits.
Where to rest a gun, as Dan noted is very important. In chunk, it is normal to rest the gun near the muzzle. Taylor and I both started resting the forend at the first pipe and found accuracy wasn't as good as we wanted. We then tried the next pipe back and immediately were granted tight grouping. Different guns are different. I usually rest the back of my hand, that hand holding the stock at the entry pipe, but was satisfied with the 1" 5 shot group over the log prone - not as tight as the gun does off the bench, but close enough that day. The difference in that particular gun as-rested over the chunk (left her bounce), compared to offhand, was approximately 1 1/2" of elevation at 50 yards. Of course, a .40 doesn't bounce up off the bags, not like the .69. I'm looking for someone who wants to shoot THAT one, prone, off a chunk.
Even Taylor's little (heavy) .50 made a purple spot on his arm from about 60 or 70 shots prone, altogether.
When I shoot the smoothbore of bags to check sighting and load grouping capability, I hold it as if shooting offhand, that way I don't find my shots going high or low, or to one side, unexpectedly - it shoots the same offhand as off the bags. That's another gun I wouldn't want to shoot chunk with, even though 3 drams and a 310gr. ball don't kick much----offhand.
