Chamber Length?

[J.B. Books]

I believe from material I have read 2 5/8" 12ga shells were loaded to lower pressures than 2 3/4" shells. I am not sure when 2 5/8" in shells were discontinued. I have a VH from 1927 that was ordered to have 2 5/8" chambers.
The Remington Shur-Shot box below contained roll crimp paper shells and a warning to not use in Dam or Twist or chambers shorter than 2 3/4".

[Shep]

I have a DHE 12g that was made in 1928 on route and the seller says it has 2 1/2" chambers. I find it hard to believe a 1928 DHE would be 2 1/2" when many of the guns 25 years older were 2 3/4". Do you think he miss measured and they are 2 5/8"? If they really are 2 1/2" would it damage the gun to use 2 3/4" 3 dram 1oz 7 1/2 target loads? Thanks!