Haha, I hate the idea of stroking his ego in any ways but...the steps I follow I affectionally call the "fireman process" of reloading. He gave me a concise, detailed instructions of what he does and I've been using it since.

My gut told me it had something to do with powder vs the weight because it was hard to find load data for tac on bullets over 69gr in 223.

Forgot to mention that after the 2nd split neck of about 40 shots, I quit.
I hate the idea of using my varget since it work3d so well in my 308.

So I guess I'm giving up on tac and gonna try reloader 15. Good or bad?

As per the fireman's process, I got the bullet comparator kit and use it religiously. As for the magazine, I found a forum post from campfire, I think, that shows how to mod the stop mag to accept longer loading. It worked like a charm except for when u try to put all 5 shots. Up to 4 is pretty good.

IMR-8208

Bit of money, but new bottom metal and a different mag will give you more mag length room.

I do not have an ego, but I never get tired of being right.

TAC is a great powder for the 223, especially the heavies. So, TAC is fine. I have used a lot of TAC in the past. It meters great, also.

223 and TAC on page 30 below
http://www.ramshot.com/wp-content/uploads/2010/09/WesternLoadGuide1-2016_Web-1.pdf

I luv Tac

The fact that you have split necks tells me old brass so that could be an issue. Also 1/8 twist should stabilize that bullet but maybe not at the slower speed you are running it since you are seating into case capacity.
Try the new 73 gr and see it it tightens up. TAC has always worked well for me. I don’t have trouble with stabilization with the 75Gr but I run them near 3500pfs

Well the brass was only once fired hornady. As in I fired factory new out of this rifle and saved them.
As for the mag length, it wasn't an issue. I was fully able to seat it to where it kissed the lands and then push it in about 0.015". my modifiied factory tikka mag can accommodate about 0.200" more than stock.

Stroud, I don't have a chrono so have No idea the speed but dang! That sounds crazy fast for a 70+ grains bullet in a 223.

I couldn't get any of the Hornady bullets to work in my .223's either, so don't fret. They were all over the target.

I switched to AR-Comp and Sierra 77 grain SMK's (non-tipped like Chad recommends). In my case, I get .3 groups at 2775 fps regularly with a 1:8 twist LaRue barrel. I got my best accuracy using 23.2 grains, instead of 22.1 grains listed on Alliant's site. No, there weren't any pressure signs. You might try CFE-223 too.

I would try a workup for the 77's with a different powder. A lot of powders work well in .223.
Here are ones I would try with them that I have achieved stellar results in .223 with.
Varget- tops for me with heavy bullets.
H 4895- excellent combination of speed and accuracy for me.
IMR 8208 XBR-this stuff is like pixie dust in both of my .223's. In both my .223's it doesn't start to shoot well till just before pressure signs.
RL 15-right next to Varget on the burn chart and what I use when I don't have Varget. Makes good accurate velocity in my .223's and 7-08's.

I've been a little busy lately with 2 kids under the age of 2 so I haven't gotten back around to it but....

I've totally decided to give up on the 75 amax and go to 65gr gameking for both a hunting and paper p inching round. Given it's a 1:8 tikka, should I try tac or rl15?

There’s been a few other good powders mentioned. I would start with 8208 and AR-Comp. CFE 223 is good, but it didn’t perform as well as the others when using heavy bullets during my testing. 8208 and AR Comp are extruded, so you’ll have to trickle in order to have an exact charge.

A box of Sierra 77 SMK’s are cheap for a box of 50. It’s a small enough count to not worry about getting too invested.

For specifically the 65 gr Sierra GK, I have gotten excellent accuracy with that bullet. Varget, AA2230, and H335 all worked great.