CuRx Rimfire General Information
What are the Benefits of Using CuRx Monolithic Copper Projectiles in your Rimfire?
There are three main benefits with CuRx projectiles in your .22LR:
1. Increased long-range accuracy potential
2. Higher velocity with flatter trajectory
3. Reduced wind drift
1. Increased long-range accuracy potential: The CuRx projectiles are lathe turned solid copper and are more consistent in weight and dimensional symmetry than swaged lead projectiles found in factory ammunition. Additionally, when reloading, it is possible to maintain greater propellant charge consistency. I say accuracy potential, because the improved accuracy also depends on the reloading process and how fussy you are with it. See the CuRx Reloading Instructions.
2. Higher Velocity with Flatter Trajectory: Higher velocities deliver a flatter trajectory which mean less hold-over as the range increases, or less elevation adjustment on your scope. This becomes a big advantage at very long ranges, especially with first focal plane scopes, since as you increase magnification, you lose visibility of the bottom section of your reticle, right when you most need it.
3. Reduced Wind Drift: The big gain for long range shooting is from the higher ballistic coefficients (BC) of the two heavier projectiles (42grn & 50grn). The increased BCs not only retain velocity and therefore trajectory better, but they also provide significant reduction in wind drift, especially at longer ranges.
Why are higher velocities possible with CuRx projectiles?
At speeds above 1,300fps soft lead projectiles tend to significantly increase lead fouling. This is why most .22LR ammunition falls below this range. This can be reduced by increasing the lead hardness with additives, but this also increases the ammunition cost. The CuRx solid copper construction avoids lead fouling issues, so higher velocities are possible.
While lead is easier to engrave than copper initially, it remains ‘stickier’ than copper as it passes through the bore and has increased barrel friction. Once engraved, the solid copper projectiles actually have less barrel friction than lead.
Depending on the velocity, .22LR ammunition tends to reach its maximum velocity in 14 – 18 inches of barrel length. Beyond this, barrel friction starts to overcome the small propellant charge’s pressure, and the projectile begins slowing. To reach maximum velocity, subsonic ammunition requires less barrel length than standard velocity ammunition, while the high and hyper velocity ammunition require a few more inches of barrel length.
The CuRx projectiles can not only be loaded to higher velocities, but they utilise more barrel length to reach their maximum velocity, so your standard 20 – 24” rifle barrel is helping achieve more velocity rather than slowing it down, as happens with lead projectiles.
Things to Understand About the CuRx Projectiles
First of all, the Cutting Edge Bullets CuRx projectiles were designed for use with virgin primed brass, which CEB sell in the US along with their projectiles. With that in mind, the CEB die set comes with only a seating die, a crimping die and two shell holders.
However, the manufacturer of the virgin brass (CCI / Federal) will not export primed brass to Australia, so to utilise the CuRx projectiles here, you will need to pull projectiles from loaded ammo and replace them with the CuRx projectiles. As a consequence, in Australia, a resizing die is also required to remove the crimp from the pulled case, in order to be able to seat the CuRx projectiles without damaging the case mouth.
We purchased a quantity of resizing dies from Sharpshooters in the US, but these proved to be unsuitable in their standard form. The original die was too tight (swaging down the unfired cases) but the expander stem was too narrow to remove the crimp fully. As such, we have had to replace the expander stems with slightly larger ones, and bore out the die body. In future, we will have dies made here from scratch, which will actually reduce their cost, compared to importing them and then having to modify them.
Secondly, the CuRx projectiles come in three projectile weights which require different minimum twist rates to stabilise and have different magazine requirements. They are as follows:
Proj. Wt BC (G1) Required Barrel Twist Magazine Requirements
32grn 0.108 1 in 16” twist (std .22LR) Cartridge OAL fits a standard .22LR magazine
42grn 0.187 1 in 10” twist Cartridge OAL is longer than .22LR magazine
50grn 0.214 1 in 7” twist Cartridge OAL is longer than .22LR magazine
Lastly, the CuRx projectiles were designed for competition, rather than hunting. They do not expand at all. If used for hunting, they may be quite suitable for avoiding pelt damage, but shots should be confined to brain shots to ensure immediate and reliable humane destruction.
Suitable Firearms & Barrels
When using the 32grn projectiles, any standard .22LR rifle can be used. However, when using existing .22LR barrels with the monolithic copper CuRx projectiles, you first need to remove all traces of lead from the barrel before shooting the CuRx projectiles. If not, you will likely get unsatisfactory accuracy. This is easy enough to do, but use a compound with a good lead solvent such as Bore Tech Eliminator to get all the lead out.
When using the 42grn and 50grn projectiles, you will need a suitable twist rimfire barrel. The CuRx projectiles measure .223”, which is standard diameter for .22 cal rimfire rifles. Remember that centrefire .22 cal rifles (such as the .223 Remington or .22-250 Remingon) are actually .224” in the groove (and .219” between the lands). For .22 rimfire barrels the groove diameter is usually around .222” (can be between .221” - .223”) and between the lands measure 0216”. So rimfire barrels are smaller in diameter between both the lands and grooves, compared to centrefire barrels. Using .224 cal centrefire barrels will likely achieve little or no engraving of the CuRx projectiles by the rifling, which will result in unstable projectiles, and poor accuracy. Reduced pressure will also lower muzzle velocities.
When shooting long range, it may be beneficial to have a faster than minimum twist, even with the 32grn projectiles, in order to maintain stability beyond usual rimfire ranges. A twist like 1 in 14” or 1 in 12” may prove beneficial.
Allan Swan Gunsmithing in QLD can supply suitable .223 cal rimfire barrels with 1 in 7” twist (5R) rifling, 1 in 9” twists and 1 in 12” twists. Other Australian barrel manufacturers may also make suitable rimfire barrels, but we know that Allan Swan certainly does.
Additionally, with the heavier CuRx projectiles (42grn & 50grn) the cartridge overall length is too long for standard .22LR magazines, so single feeding may be required. Alternately, you could use a duel-length action such as the CZ 455 / 457 or Sako Quad models. These actions are built to accommodate both .22LR and the longer .22WMR, and have an interchangeable barrel system. The actions utilise a .22LR magazine with a magazine block which can be removed to accommodate the longer.22 WMR magazine. If you purchase a .22LR rifle, and also a .22 WMR magazine, you’ll be able to magazine feed the longer 42grn and 50grn projectiles.
Caution: Don’t fire a .22LR case in a .22 WMR chamber, as the .22 Magnum case is wider that the .22LR, which will likely result in case ruptures. Similarly, the CuRx projectiles are designed to fit a .22LR case and not a .22 WMR case.
Which ammunition to use with the CuRx Projectiles?
We trialled ammunition from CCI, Winchester, SK, Eley and RWS brands and had mixed results. Some of the match ammunition was very consistent in terms of charge weight, case weight and projectile weight, but they were not necessarily the best with the CuRx projectiles. However, rimfire rifles can be fickle with what they like and different rifles may prefer different ammunition, so testing will be required by you to determine what works best in your rifle.
CuRx Reloading Instructions & Load Data
The Reloading Instructions for CuRx rimfire projectiles are listed in the Technical Notes section under Ammunition Notes. To view click here.
The Load Data info also appears in the Ammunition Notes section. To view, click here.