Bought a pair of forester gauges for the 378/416/460 weatherby I could help but notice they only offer go and field gauges. The go is .253 and field is .257 do they make a no go gauge? I bought these to occasionally check for lug setback. What would a no go measure .254 or .255? Thanks!

Four thousandths would be a normal no go tolerance. Field is like ten.
SAAMI allows a lot more than that between max chambers and min ammo.

SAAMI Spec for .416 Weatherby is .253 - .257”, so a “No-go” gauge would be .258” or so. The SAAMI reference I have does not show specs for the .378 or .460 cartridges but I presume they are the same.

SAAMI specs and manufacturers gauges are not necessarily compatible; each maker has his own set of parameters for gauges. Just because a bolt closes on a no go gauge it does not mean that the chamber is not still within SAAMI spec. And also, that is why you should not use gauges from different companies; each has it's own specifications for them.
For example, the belted mag gauges I use for barrel fitting have a go of .219 and a no go of .223.

If it makes you feel better, just crazy glue a shim on the "GO"

PTG gauges: NOGO = .257-258, Go = .254

Thanks for all the info!

just put 2 layers of aluminum ducting tape on the go gage and measure