Thread: 303 group-bad bedding?

Originally Posted by john m

A lot of worn 303 barrels do not like boat tail bullets. I picked up a tidy PH sporter that was shooting 10" groups at 100 yds with 150 gr. Tried 180 gr Highland (boat tails) 6-8" next, reloads with 180 gr flatbase 4" finally Woodleigh 215 gr flatbase 2.5" groups at 100 yds.

The other factor here is related to weight and boattails: the better grouping ammo types here have the bullet bearing surface increasingly further into the barrel throat when chambered. It may not be the boat tail as such that is to blame - more that a boat tail "costs" you front mass, putting the bearing surface further back, all other things being equal. (a boat tail needs a certain length of cartridge neck to engage with its side to be secure in it, so it needs to be seated deeper).

An engineering workaround the disadvantage of lighter bullets is when Britain replaced the round nose 212 grain Mk V with the 174grain .303 Mk VII spitzer. The Mk VII had a light filler up front which enabled the bullet bearing surface to engage further into the throat of the barrel when chambered. The point of snug/close engagement is that it helps the bullet to travel more concentrically through the bore, thus reducing wobble on exit. The wobble causes the bullet to fly in a spiral path but settles down eventually at some random point in the spiral and flies relatively straight after that - trick is to reduce the wobble in the first place. Imagine if you seat spitzers 1 degree off centre and fire them in a gun with a worn throat... It will make groups shaped like circles with a rare shot in the centre.

If you have a kinetic bullet puller, empty a case for safety and reseat the bullet to its original position, chamber and extract. Pull and reseat to increasing overall cartridge lengths, load and eject, to see how far out the bullet needs to be to engage the rifling lands. Seat your bullets for that gun a bit short of that. This guy here uses a sharpie on the bullets to help read the marks:



But before bothering to do any of this, tighten up and bed the action as advised above. @csmiffy, your groups are not circles, they are being whipped up to the left. You likely have a loose screw.. . (-: