Depends on how long your leade/freebore is. If your leade is short, not much but if your leade is long, you will see measurable difference as more gas will leak around the bullet before bearing surface of the bullet will engage the rifling.
As to Hodgdon using 1.200" OAL, keep in mind that test barrel fixtures used to measure chamber pressures are single shot and do not feed from the magazine. So it simply means 1.200" OAL was used to conduct pressure tests and this does not mean the round will reliably feed from the magazine or minimize gas leakage from being too far from start of rifling. It does mean you can use load data if OAL is longer than 1.200"
I would suggest you determine the max OAL first using the barrel with the dummy round -
www.thehighroad.org/showthread.php?t=506678
Then function test by feeding the dummy round from the magazine and incrementally decrease the OAL until it feeds/chambers reliably from the magazine which is your working OAL.
If you look at the comparison pictures of factory 230 gr FMJ/RN, CCI is 1.270" while PMC is 1.255" and Remington is 1.258". For Berry's 185 gr HBRN (which has similar nose profile as 230 gr RN), 1.250" worked in Sig 1911 barrel with shorter leade and 1.255" worked in other 45 pistols (SA/RIA/M&P45/PT145).
Now if you are loading RMR 230 gr HM RN, which has shorter nose that increases bullet base length, you may need to load shorter to not hit the start of rifling (1.230" will work with most 45 pistols but need 1.200" for my Sig 1911 with very short leade, almost no leade)