I would bet money (I could lose it!! ha ha), but, I think you have a chain that was "made up" from a smaller length chain ie --an 18" chain with links added to make it correct for a longer, chain. BUT possibly WITH THE WRONG GAGE of added links!
example- If the chain was 50 gage (.050), and any added links are the same pitch , BUT are 54. or 58. or other LARGER gage, it will NEVER go into a .050 bar.
Use a micrometer (or ask a machinist to do it- most love "idiots" that have no micrometer), but will check it for you. I'll bet they are .058 and your correct chain id .050. thus-too large by .008 in.
If this is not the case,you need a correct size "new" chain. Remember there are l2 important numbers in describing chainsaw chains. pitch and gage.