TEST OF THE 6.5 “CRUISE MISSILE”
Back a couple years ago when I did the 6.5 Swede HV test the individual who sent the GB 6.5 Kurtz bullet mould also sent a Lee mould for the 6.5 Cruise Missile” 175 gr cast bullet he acquired from Midway. This is one of them that casts bullets over size in driving band diameter and in nose diameter. The owner requested I test them when I got around to it. After moving from Washington State to Arizona and having most everything in storage for almost a year I finally got around to conducting a test. These are my trials and tribulations with this bullet.
Before moving I at first cast the bullets out of COWWs + 2% tin and WQ’d them. I found the driving bands to be .272 +/- and the very long nose to be .269 +/-. When seated to any reasonable oal in the Swede case and chambered the hard bullets would be pushed way down in the case a only the 1st part of that long nose would go up into the bottom of the chamber throat. Others reported this same thing. I attempted to sized the noses down with bushings in a modified H&I die in the 450 Lubrasizer. The bullets were too hard and they bent or the noses were swaged off center. A softer more malleable alloy was needed. The cast CMs went back into the pot. The alloy was changed to linotype with 20% lead added. This results in a usable CM cast AC’d bullet that at least could be sized down w/o destroying the bullet.
The 80/20 linotype bullets were first pushed through a .268 H sizer (I die removed) to size the driving bands and seat/crimp the Hornady GC on. The I die was replaced and they were then lubed in the same .268 H&I die with Carnauba Red lube. A .266 H&I die was put in the 450 Lubrasizer and bullets pushed in nose first up to the driving band to size the noses to .266. A .264 H&I die was also used the same way to partially size the nose half way back so when seated the ogive of the nose would be up into the throat at the leade. While I like a good challenge and enjoy casting bullets the gyrations I was having to go through to get these CMs to “fit” the 6.5 Swede throat were quickly getting out of the “fun” category to say the least.
Attachment 92324
We see in the above photo the 175 gr CM is a sleek “missile” indeed with the promise of that 1st kiss from a young maiden……and we all know how well that turned out……..actually though, we see that when the oversize CM is sized as such the driving bands at .268 “fit” the bottom of the tapered 6.5 Swede throat (all the milsurp M96s and M38s that I have measured have tapered throats as such) and the .266 to .264 of the nose allowed the bullet to slip up into the throat to just kiss the leade. As we also see the GC remains right at the base of the case neck which is good also. The actual cartridge OAL was 3.019”.
Thus the bullets sat until a few weeks ago when I finally got around to conducting the test. After sitting around that long the BHN was still at 18 and the fully dressed weight was 171 gr due to the linotype alloy used. I used the same cases that were carefully prepared for the 6.5 Kurtz test. They are formed from U42 ’06 cases. They were NS’d with a Lee Collet die to give .002 - .003 neck tension on the .268 sized CMs. Primers used were WLRs.
Since I only had enough bullets for one completely thorough test I chose to go with a slow burning powder to maximize potential velocity while maintaining minimal thrust on the bullet; in other words to lengthen the time pressure curve which is an important technique if one is to push the RPM threshold. Might be good to refresh our minds with what the RPM threshold is or at least what happens;
the bullet is unbalanced or becomes unbalanced due to obturation in the bore during acceleration. The unbalanced bullet is forced to conform while in the barrel and its center of mass is revolving around it's geometric center. When the bullet is free of the barrel's constraint, it will move in the direction that its mass center had at the point of release. After exiting the muzzle, the geometric center will begin to revolve about the center of mass and it will depart at an angle to the bore (line of departure). At 54,000 RPM to 250,000 RPM, depending on velocity and twist, the centrifugal force can be tremendous. It will result in an outward or radial acceleration from the intended flight path (line of departure) and will try to get the bullet to rotate in a constantly growing helix.
As stated many times and posted in a sticky the RPM threshold for regular cast bullets in rifles most often falls in the 120,000 – 140,000 RPM range. It can be pushed by using various techniques. I shall not go into all of them here as they are available in the sticky. Suffice to say increasing RPM has a distinct negative effect on this very long thin bullet. The 7.8 twist of the milsurp barreled 6.5 Swede rifles exasperates the RPM problem. I’ve measured the twist of my own four 6.5 Swede milsurp barrels and many others. The twist measurements fall between 7.7 and 7.9” so I just use 7.8 as the twist. Thus in the 6.5 Swede we find right at 1500 fps is close to 140,000 RPM. If we are to get any usable accuracy above that we must use an appropriate powder. With the very long nose of the CM I chose to go with RL 22 powder. Since load density would be below 80% a ½ - ¾ gr Dacron filler would be used also.
Not a lot of load data available for the CM so I just initially “SWAG”d” it. To initially get a feel for the powder/bullet loads I loaded 5 shot test strings of 30 – 44 gr RL22 in 2 gr increments. This would give me a quick assessment and I would then switch to 10 shot test strings for final testing and/or tweaking.
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Originally Posted by swheeler
