have a no4mk1* (longbranch) myself and it never tolerated 150gn srounds -sprays em like a mad womens shit.
switch to 180gn and theyll happily trundle down the tube and onto the target(if my minds on the job)
old bloke I spoke to years ago at a deerstalkers shoot reckons it was all to do with the 2 lands/grooves stabilising the heavier round better.
180gnsoftnose are a tad hard on std 1/4"steel plate or hares possums etc inside 100yds so be warned if you want to eat it,think before touching the trigger(not the steel ya dolt)
as said above Tertle is ya man on ye old .303 ,he certainly helped me out.
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