Why do rifles love/hate a bullet?
- Thread starter Slowbalt
- Start date
I found the same with Campro .224 55gr FMJ. I measured and weighted a bunch of them, and they seem right on; just could not get them to shoot up to my standards; their pistol bullets are OK, in my 9mm I use their 124 gr CPHP with great results, although my other calibre pistols all shoot DRG cast lead better.
Hornady, Sierra or Speer were always my go-to bullets for rifles.
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Consider how many RPM a bullet spins as a result of rifle twist... the smallest imbalance in a bullet especially farther from the core will ruin accuracy. Compare your car tires to it: a car wheel rotates only hundreds of RPM on the highway but with all those pounds in mass, wheel weights weighing only grams are added for balance so you don't get vibration... and you only feel vibration because the wheel is restrained from wobbling away by the axle. The old adage "you get what you pay for" applies as usual. Simple physics, no magic: my 30-06 would yield similar results.
If bullets were perfect, we would not need rifling. Rifling Averages out imperfections. I think it may have more to do with the centre of gravity Round nose have the centre of gravity further forward; high aspect ratio (low Bullistic coefficient) tend to have the CG further back. Rate of rotation, when right prevents harmonics from throwing the bullet out of equilibrium and wobbling in flight.
The ops question is more complicated than it might seem.
There is of course the obvious ideal twist rate, muzzle velocity, bullet length balance thing, but there's more to it yet.
You have to think about why a cartridge like a 6BR has such a rep for accuracy... There is nothing magical about the name 6BR, the source is really the short case length.
The short case allows the barrel to be chambered with the bullet sticking as far as practical out of the case. That allows the free bore in the barrel to align the bullet to the bore. The value of this cannot be understated.
When a bullet has to be seated deep into the case, there is no such alignment. The bullet can start into the rifle at odd angles. That does nothing to improve accuracy.
Further is the magazine length... If you test the jam length of a variety of bullets in your rifle, you are likely to find bullets that jam with an over all length that is too long for the mag, or even too long to eject a live round.
This forces the reloader to short seating depth, excess jump and free bore is not utilized to align the bullet to the bore.
Savvy target shooters will select action lengths specifically to over come these problems and have reamers made specifically for the bullet they plan to shoot with the seating depth as long as possible and the freebore as tight as safety will allow.
If for example, if you want a high performance 308, build it on a long action, then you can eject 200 grain bullets and feed long seating depths from a mag. Short actions limit your bullet selection and throat length, or you need to hand feed ammo one at a time and remove the bolt to eject a live round.
There is of course the obvious ideal twist rate, muzzle velocity, bullet length balance thing, but there's more to it yet.
You have to think about why a cartridge like a 6BR has such a rep for accuracy... There is nothing magical about the name 6BR, the source is really the short case length.
The short case allows the barrel to be chambered with the bullet sticking as far as practical out of the case. That allows the free bore in the barrel to align the bullet to the bore. The value of this cannot be understated.
When a bullet has to be seated deep into the case, there is no such alignment. The bullet can start into the rifle at odd angles. That does nothing to improve accuracy.
Further is the magazine length... If you test the jam length of a variety of bullets in your rifle, you are likely to find bullets that jam with an over all length that is too long for the mag, or even too long to eject a live round.
This forces the reloader to short seating depth, excess jump and free bore is not utilized to align the bullet to the bore.
Savvy target shooters will select action lengths specifically to over come these problems and have reamers made specifically for the bullet they plan to shoot with the seating depth as long as possible and the freebore as tight as safety will allow.
If for example, if you want a high performance 308, build it on a long action, then you can eject 200 grain bullets and feed long seating depths from a mag. Short actions limit your bullet selection and throat length, or you need to hand feed ammo one at a time and remove the bolt to eject a live round.
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And then you can factor other variables to the equation...such as:
- chamber dimensions;
- headspacing;
- powder columns (shorter fatter powder columns have proven more efficient and produce more accuracy e.g. PPC cartridges);
- neck tension;
- consistent crimp on bullets;
- jump to lands;
- pressure spikes and curves as the powders burns, the gas expands and pushes the bullet down the barrel over a certain timeframe;
- barrel harmonics;
- a good rifle crown (the last contact between rifle and bullet on its path to the target);
- etc.
And there is no rhyme or reason as why consecutive barrels off of the production line will vary in their performance, despite being of the same length, diameter, contour, bore diameter, rifling created by the same cutter, button or hammering mandrel, with the same twist, and chambered with the same reamer, etc. Although, with every new barrel, there will be a minute amount of wear of the reamer, bore drill, rifling cutter/button/mandrel that may explain some of the variables in the chamber and bores.
Barrels will show a preference for certain bullets and/or cartridge combinations of brass, primer, powder, bullet, and coal.
The trick is to find the factory ammunition or handload that your particular rifle prefers, and use that with confidence!
- chamber dimensions;
- headspacing;
- powder columns (shorter fatter powder columns have proven more efficient and produce more accuracy e.g. PPC cartridges);
- neck tension;
- consistent crimp on bullets;
- jump to lands;
- pressure spikes and curves as the powders burns, the gas expands and pushes the bullet down the barrel over a certain timeframe;
- barrel harmonics;
- a good rifle crown (the last contact between rifle and bullet on its path to the target);
- etc.
And there is no rhyme or reason as why consecutive barrels off of the production line will vary in their performance, despite being of the same length, diameter, contour, bore diameter, rifling created by the same cutter, button or hammering mandrel, with the same twist, and chambered with the same reamer, etc. Although, with every new barrel, there will be a minute amount of wear of the reamer, bore drill, rifling cutter/button/mandrel that may explain some of the variables in the chamber and bores.
Barrels will show a preference for certain bullets and/or cartridge combinations of brass, primer, powder, bullet, and coal.
The trick is to find the factory ammunition or handload that your particular rifle prefers, and use that with confidence!
