Welcome to the board!!!
About 12 years ago I asked myself the same question...I had always used the 100gr Remington CoreLokt...They did fine as I had already killed about 75 deer with that load but I wanted to try all the different factory loadings in that cartridge so I would know for myself what they did...
I was looking for a loading that gave reliable pass throughs on lung shots with a good sized exit hole but would also bust through a shoulder blade in case I needed to drop the deer on the spot...
Of course, you do realize that you need to try a few different loadings in your rifle to make sure they are accurate...But after that here are my top factory loadings...I could use any of these and feel very comfortable out to a good 300 yards...
1) 100gr Remington CoreLokt...Yep, I'm prejudice, who wouldn't be???
When it was all said and done, this bullet preformed as well as any and a very good price...In addition, my gun just likes them...I'm talking groups you can cover with a dime at 100 yards...This past season I dropped a buck in a soybean field at a lasered 327 yards...It's hard to beat results like that...I'm closing in on 100 deer killed with this bullet and 3 black bears...
2) 100gr Hornady Custom InterLock...Great bullet, does the job, one of my hunting buddies uses this round but I get 1 1/2 inch groups at 100 yards with this bullet...If your gun shoot this bullet better than the CoreLokt then that's what you should use...
3) 100gr Federal Premium Sierra GameKing SPBT...Also a great round, not as hard as the CoreLokt or the Hornady, but plenty hard to break down both shoulders...
4) 100gr Nosler Partition...Good round, deer do run further on lung shots with this round than the others because it's the hardest of the lot...If your bucks run larger than average, this might be the ticket...
5) 85gr Federal Premium Sierra GameKing HPBT...This is THE long range bean field bullet of choice among long time .243 shooters...
Factory velocity is posted as 3320fps...That's faster than any of the 90-95gr ballistic tips and this bullet is made with a thicker jacket and harder lead so it penetrates better than the ballistic tips that I have seen used...
When I first heard about this bullet, I thought it was a ground hog bullet...I even loaded a CoreLokt behind the 85gr expecting the bullet to break up on rib bones and anticipating a quick 2nd shot...Well, the first deer dropped on the spot, the 2nd deer ran after the CoreLokt passed through the lungs, identical hits, similiar sized deer and range...
I have now killed about 40 deer with this round, thought I had messed up one evening...I was sitting over a huge soybean field expecting a 300+ yard shot when a doe came running through the swamp behind me...I stopped her, put the bullet through her shoulder blades and she dropped, the range was only 50 yards...
The beauty of this bullet is that you can sight in 2 1/2 inches high at 100 yards and you are only about 3 inches low at 300...
For hunting fields where shots start at 150 yards, this bullet is the ticket...In my gun the CoreLokts happen to hit 2 inches high at 100 yards and the 85gr HPBT hits between 2 1/2 - 3 inches high...So, if I'm in the woods or swamps of eastern NC, I used the 100gr CoreLokt...If we have beans on our farms and I'm over a 100 acre bean field, I'm shooting the 85gr Sierra HPBT...
Hope this helps...Good Luck...