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I reloaded 40 rounds of 243 shells keeping everything very uniform. I started with 38.5 gr. of IMR 4350 and going up to 42 gr. 5 bullets each at 1/2 gr. increments. Shooting all 100gr sierra game kings.

What just doesn't make any sense to me is the accuracy that I got. It was pretty bad at first but every load I put through it the group went up about an inch at 100 yards. I was getting like 3-5 inch groups and then at 40 gr. it dropped to about 1", stayed the same for 40-41 then 41.5 I got a about a 1/2" 5 shot group. I was hoping that the group would tighten up more with the 42.0 gr. which is the hottest load I made, but they spread out to about a 4 inch group again.

Everything I've heard or read says that the differences would be very subtle.

Does this make any sense to anyone?

Should I just work up another 10-15 at 41.5 and see if I get the same results?
 

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john, if your not confident that's an accurate representation I might load up 5 more but I'd hate to load up 10-15 and find out after 4 or 5 it's just a bad load for that rifle. But you got better results than I did today the best group I shot was a 2.146 with a 58gr. Hornady V-Max loaded with 43gr of IMR4064. I am going to start over however because I wasn't happy with with setup as far as shooting position and target selection today. I need to take some targets with something other than a black 1" bulls-eye.
 

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Does this make any sense to anyone?

Should I just work up another 10-15 at 41.5 and see if I get the same results?
Makes perfect sense. You have learned one of the advantages of reloading - being able to tailor the load to YOUR rifle. If you were shooting factory loads, if 3" was the best it would do, you'd be stuck with that load. I'd load up another 5 to 10 and make sure the results are the same. If so, load up a good supply while your measure is set and everything is still set up. IMR4350 is agreat powder for the 100 grain .243 bullets.

You'll see the same thing with bullets at times. One bullet weight or one brand will shoot 4" groups, change to a different witght or brand and it's under an inch. I have found that my AR10 shoots 165 grain Ballistic Tips like a champ, the cheap 150 grain Rem Cor-Lokt bullets shoot about 3" at 100 yards. In other rifles, the 150 grain Rem's shoot just fine. That's my luck... :smack:
 

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My old Ruger 30/06 will stack 150 flat base bullets with about mid-ranged loadings, go to hotter with the loads and it opens up the groups fast, put a boattailed bullet in it and it throws them all over the paper. My Tikka 25/06 groups tighter the hotter the loads, right up to max loads. Every guns different.
 

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Sounds like you found your 'sweet spot'. With different powder loads you change the harmonics of the barrel. When working up a load you'll usually have 2 loads in the bunch that will shoot well. While you're working your way up to higher charges the groups should shrink - not always, but most of the time. Then you'll usually have a group that's pretty tight. The next load or two might be the worst of the bunch, then the next load should be pretty close to "as good as you're gonna get". Remember that .223 target I showed you? My first 4-5 loads sucked, then I got a good group. The next one sucked and the one after that was TIGHT. That 2nd 'good' group is your sweet spot - the happy place where your load matches your barrel's harmonics.

There's another load work method (called the ladder method) that works off the change in POI you mentioned between loads. You fire 1 round each from min to max charge at the same point of aim. Each load will be a little higher than the last. When you're done, look over your target and measure (or just eyeball) the distance between shots. There will be 2 places where they get closer together, and the higher one is real close to your sweet spot. Then you head back to the house and load up a mess, starting at the bottom of the tight spot in the 'ladder' ,in .2gr increments (or whatever your preference is). You should get pretty tight groups pretty quick.
 

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are you using the same brass? trimming to OAL? same primers? i'd stick w/ 41.5 gr and be happy w/ a 1/5" group. unless your shooting prarie dogs that should be good enough accuracy out to any distance a 243 is likely to leave a mark.
 
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