Thread: An Interesting Visit to the Range

Originally Posted by No.3

Not just old cartridges sometimes, having the same problem with a current series Rem barrel 20" .308 in 1-10 twist. Accurate and on roughly at 100m and 200m for a 200m zero, not even on a sheet of newspaper behind the target at 300m. Supposed to be 9" drop off the factory chart, try 24" or more (hard to tell by rough guess and was expecting a left/right windage issue not a dive into the weeds so didn't take a tape measure!).

Thats a 2 feet drop at 300m, WTF? Exactly as you say, more testing required.

Something weird is with this one, as sub loads for this rifle (sub loads being the opposite of super's - velocity controlled by powder amount then length of barrel) require a whole grain of powder less than the 20" 1-12 barrel rifle my friend has as a comparison. Repeat, mine being a 1-10 twist which if the theory works out should have more friction than the usual 1-12" twist. Sub accuracy is fine almost 3 shots touching at 50m and 7" below point of aim which is workable, but the whole grain less of powder indicates that it must be a very 'slick' barrel. Also explains why the 'sub' loads I was getting off a guy a while back were a little louder than expected.

As far as the super's - I am guessing not enough time for the pill in the tube for the pressure to get up to where it needs to, for super loads. Pressure = velocity, rough calculation and all other things being equal. The small amount of reloading I have done for this did not show much promise, it either did not like the pill or the powder or me - and trying to work up a load I got to max on book and max for case full of powder with no signs of pressure but no real velocity to speak of. About 5" below point of impact for the factory load I ended up using and I kind of gave up while I scratched my head and went back to factory...

As you state more testing required - I suspect I may have more success treating it like a 15" "bushpig" barrel, going for one of the powders listed on the faster end for the cartridge and trying to get the pressure curve a bit steeper. My other issue is I am using a Magnetospeed chrony which seems reluctant to pick up the pill when fitted over the suppressor. I need to work out how much closer I need to get the chrony's bayo to the bullets flight path for it to work with the can on and get a decent speed reading off the thing...

Greetings @No.3,
I suspect that either your zero is closer to100 metres or your velocity is low. My bolt action .308 is zeroed at 172 metres to keep the mid range trajectory from being too high and it drops 360mm at 300 metres. Velocity is 2,750 fps in a 22" barrel and 2,700 in a 20" barrel.
Regard Grandpamac.