PDA

View Full Version : Another Question from the new guy...


EMTfromSeattle
July 17, 2007, 07:46 PM
So I went back to the range today... apparently everything is still tightened down with my rifle, as I was able to shoot 2 inch groups at 100 yards all day, with my best being 10 rounds at an inch and a half...was also able to terminate some stationary clay pidgeons at 200 yards...what fun...

So anyway, I was talking with the shooter next to me who, from the looks of him, has been shooting since flintlocks were in style...he said that I might want to try some 40 grain .223 rounds, and that might help tighten my groups a bit.

My questions is... what affect do the different bullet weights have on accuracy, and why? I currently shoot off the shelf 55 grain bullets, usually the BT FMJ American Eagle rounds... But when browsing, I have seen everything from 40 grain to 70 grain... help!

Ta,

EMT

boltgun71
July 17, 2007, 07:54 PM
Before we can answer what proper weight bullets you should use for the best accuracy we need to know your twist rate. The heavier the bullet you use the faster the twist is needed.

Heres my recommendation for the proper weight bullets for different twist rates in .223 Rem
1-14" or 1-12"= 40-55gr
1-9"= 55-70gr
1-8" or 1-7"=60-80gr

Hope this helps!

dmazur
July 17, 2007, 09:21 PM
As to the "why" part, bullets are stabilized in flight by rotation imparted by the rifling in the barrel. Well, if the spin rate is correct, all is well and the tip of the bullet doesn't precess or nutate. If the spin rate is too slow, the bullet wobbles in a less than predictable fashion and accuracy suffers.

At longer ranges, with improperly stabilized bullets, you can sometimes see a "keyhole" effect at the target, instead of a nice neat circular hole. Believe it or not, the bullet is hitting the target sideways!

44 AMP
July 17, 2007, 10:09 PM
Leaving out all else (shooter, ammo, wind, etc.) and looking at just the rifle, each one is an individual, and has it's own "harmonics". While it can't be seen with the naked eye, barrels "whip" up and down while the bullet passes through. If the bullet leaves the muzzle at the same point in this cycle of vibration, every time, the rifle is "accurate".

Lots of factors contribute to the harmonics, (bullet weight, rifling twist, barrel contour, velocity, bedding, temp, etc., etc.,)

Group size is a function of repeatability. Everything exactly the same each time, bullets go in the same hole. Benchrest shooters go to great lengths to get each shot as close to exactly the same as they can. That's why they get the groups that they do.

Each rifle is an individual, and there will be one combination of rifle and ammo that will shoot better than all the others, generally. There are rifles that show no marked preference, but they are often not really accurate with anything.

Some where out there is one bullet weight that your barrel likes better than the others. And often there is one brand of bullet that your rifle will like better than others. The only way to tell is to shoot them all, until you find the one that does the best for you. When you find it, stock up.

If none of the ammo choices gets you what you are looking for, then it is time to start thinking about working on the rifle.