"H" marking on Long Branch No. 4 barrel

Pictured below is the top of the barrel on my 1944 MP-marked Long Branch. The barrel itself is '43-dated. What does the "H" signify?

https://www.milsurps.com/images/impo..._barrel2-1.jpg

I did a little asking around when I first got the rifle a number of years ago (posted a thread about the purchase here), and never got a clear answer, so thought I'd bring it up here.

Thanks.

Hi Rangerover, If it was a Lithgow it would denote a Heavy Barrel, as it's a Longbranch my books show no H marks for any No 4 manufacturers.
I have a Shirley No 5 which has a T in the same place and I think like yours it is an Inspectors mark nothing more nothing less.

Cheers

:wave:

Inspectors mark I think.