4 Attachment(s)
Developing 6 MM 350 yd accurate Load pt1
I wanted to see if I could develop an accurate HV load to use in a 6x45 similar to the one developed for a 308W. The 6x45 is a low recoil, cheap to load, and extremely accurate round. The guns used for development are all Savage short actions with Shaw, McGowan, and Lothar Walther barrels all with 1 in 8 twists. To date, only modified PCed bullets based off a RCBS 95 gr mold (98.6 gr after PC) have been used. After casting, a gas check is seated and the front portion (bore rider) is sized and then the drive band/gas check is sized. After powder coating the same sizing sequence is used again. The first picture shows the main stages and the second show the bullet before and after the final sizing (.244/.236).
Attachment 195517
Attachment 195518Attachment 195519
Observations: Things found during testing that may be of interest.
- Copper was mixed in the alloy used. Similar to what was found in working up loads in 308W, the bullets will turn to dust at higher velocities when used in a fast twist barrel unless copper is added. It doesn’t take a lot; I am using 6 heaping tablespoons of copper sulfate (25.2% eq metallic copper) in a 20 lb batch. Caution- read threads how to mix safely.
- There seems to be a very interesting relationship between the alloy hardness, bore fit and PCing. In conventionally lubed bore rider bullets the forward portion of the bullet has no lubrication so if it presses very hard on the sides of the bore, it usually results in leading. When fired, if the pressure builds beyond the working strength of the alloy it will expand into the bore and lead the bore so pressures had to be maintained below the working strength of the alloy (as detailed in Lee Manual). A close tolerance or fit was required to have any accuracy. PCing seems to have changed some of the previous constraints of a cast bullet. Leading is no longer an issue. If the working pressure of the back portion of an alloy bullet is exceeded, it will suffer plastic deformation and retain the bore shape if the pressure falls below its working pressure before it leaves the end of the barrel. The bullet will be a perfect fit to bore and rifling will show full engagement on the bore rider portion. The harder alloys usually have a higher working strength and require higher pressures to cause plastic deformation. The above is based on the bullet staying together at high rotational speeds which is helped by copper addition. In all testing so far on both 308 and 6mm, accuracy makes a significant improvement when recovered bullets begin showing full rifling engagement to within 3/16” of bullet tip. The rifling engagement can be seen on the recovered bullet below which was originally sized .244/.236 (drive bands at .244 and bore rider portion at .236).
Attachment 195520
- A very large number of different PC powder coatings have been tried in the last few years. Even when properly cured (temp monitored with thermocouple), the powers tested resulted in varying amounts of buildup when shooting 50 rounds between cleanings which affected accuracy if shooting the higher velocities. At lower velocities and pressure almost any of the different powders work with no apparent buildup. The best powder tested to date is “Smokes” Bacon Grease which normally only requires one more patch than with jacketed bullets at the most. It has a lower ratio of polyester resin and its cross-linker to the other materials having a melting point near 1800’C.
- The die used for neck sizing is a home shop made holder using a purchased Redding neck sizing bushing. The approach angle was too sharp on the bushing as received, so a more gradual angle was ground using a Dremel tool. The increased angle allows the bullet to be (extruded or swaged) without shearing the bullet alloy or the PC.
- Bullet seating was done using an old C&H sliding bushing seater-die bored out to match the diameter of the bore rider portion of bullet.
- On trials made so far, it seems that the smaller 6 mm is more sensitive to neck pull and weight variations than the 30 cal. I have not been weighing bullets, and I use them as cast. More testing is needed to determine if fliers are the bullet or the shooter.
- Even weighing bullets have been getting one or two fliers in each 5 or 6 shot groups. I have been trying a number of different powders in the 6x45. Only small amounts of load data is available for 100 gr bullets and have found none for cast bullets so loads are started low and slowly worked up. Case volume is usually maxed out before any pressure signs are seen. On recent range trip, cases were checked with RCBS precision mike. Out of each group, 1 or 2 would show lower case length ( ˝ thousandth ) which matched up with number of fliers. Crimping and slightly faster powders will be tested next.
1 Attachment(s)
Bama's Arsenal Smash Test
Attachment 220094 The picture shows Bama's smash test of a water dropped bullet cast from Arsenal PC243-113-NR-BR-GC-AL mold and PC'd with Smoke's Bacon Grease. The mold is a PC specific design for 6mm with a 0.241 drive band, 0.0625 nose radius (NR), a 0.233 bore rider (BR) section, 0.233 gas check (GC) step and using Bamalloy to ensure a tough-hard bullet capable of auto loading (AL). As shown the PC bonds well with this alloy and increases the drive band to .244, and bore rider to .236 inches. Bama said his ballpeen hammer bounced off so he had to hammer it with a 3lb sledge. This actually is the Rotometal approximation to Bamalloy. The piece broken off and standing on edge shows an extra fine grain. Total bullet weight is 116gr. Idea is make it resilient enough to survive feed ramps and chambering without impacting concentricity. The mold casts undersize from most perspectives but this is necessary. Both cast drive band and bore rider are sized after GC is mounted and then again after PC applied. A lot of work but then the objective is a long range high speed accurate round.
