Dry fit EVERYTHING before you begin! And stop and resolve all fit problems BEFORE you open the glue.
1) Liner into casing
2) Grains into liner
3) Sort grains by tightness of fit into liner (loosest to tightest) - install loose ones first as they have a long way to travel, finish with tightest ones
4) After you glue your grains into the liner, set (assembled) liner aside and let glue dry completely BEFORE you load it into your casing
5) Use a razor blade to clean any dried glue off the outside of your liner assembly before you install it into the casing
6) Coat casing and/or liner with spray silicone for easy assembly and cleanup
7) Load liner assembly into casing and attach end closures as usual
...That's how I do 75 and 98 loads. I learned this sequence painfully, after some expensive mistakes. It works for me. Good luck!