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SwedeNelson
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rsterne
To avoid any confusion, this bullet is too long for the .22 cal MRod and PRod magazines…. but it will fit the .25 cal MRod magazine with the .22 cal wheel installed in it…. The chamber may or may not require some work for the bullet to chamber easily…. Most air rifle barrels may not have a fast enough twist….
Bob
Al now has the thin RG pins sorted out…. so if this was to proceed to a Group Buy then RG2 ad RG4 moulds should be available in aluminum or brass…. That means you could cast Flat Nose, Hollow Point, or Cup Point bullets by selecting the pins you want from the three sets supplied….
I suspect that the 12″ twist rate specified above is likely faster than what would be needed…. Most of the BBTs seem to stabilize in a slower twist rate than calculated….
Bob
Since the 250-60 BBT has been so successful, and this is essentially a scaled down version of it…. I would love to see this mould go into production with the new thin RG pin system to allow a HP version…. I’ll do up another drawing with the HP to see if that encourages more interest so that we can lean on Al some….
Bob
Here is the new drawing for this design…. It would be 38 gr. as a FN, and 35 gr. as a HP….
It is the 2 caliber long .257-65 BBT scaled down to .217 cal, and then the boattail shortened 0.019″ so that it will fit in Hatsan and Marauder mags, and that shorter BT with a larger base will also allow it to work in a 14″ twist, according to the Kolbe Twist Calculator…. It is a shame that most airgun barrels are not a fast enough twist….
Alternately, we could use the same tooling and interpolate the diameter out to 0.224″, as there is an excellent TJ’s barrel available with a 14″ twist, and it should work great for that…. We could even leave the boattail full length, so that the bullet would be an exactly scaled down version of the 257-65….
Bob
Here is a drawing of the .224 cal version, with the full length boattail…. a scaled down version of the highly successful .257-65 BBT….
Although the Kolbe Twist Calculator recommends a 12″ twist for this bullet, we know that the 257-65 BBT works great in a 16″…. and the equivalvent twist in .224 cal is a 14″…. The TJ’s 14″ twist barrel should be just right…. and using the RG thin pin system the HP comes out at 40 gr…. The current high-powered PCPs are certainly capable of 80+ FPE to drive that at 950 fps or more…. I’d love to get an RG4 mould for this bullet….
Bob
donhansell
O48Twitch
I beg to differ…. There are many bullets where the nose rides the lands, and is much smaller than this bullet…. The nose on this design is the same as the groove diameter, and will be engraved very deeply by the lands and will have no problem loading and staying straight in the bore…. I have many BBTs that when you size them to (in this example) 0.224″ show a thin, shiny ring at the back of the nose when the drive band is sized down….
Airgun slugs are very frequently sized about 0.001″ under bore diameter, rather than over as in PBs…. They simply don’t have the high pressures available, and not only does the velocity increase when sized a whisker under the groove diameter, they usually shoot better that way as well…. I have never had any complaints that any of my BBTs were too small for the bore they are designed for…. In most cases they are sized a thou or two before shooting them, for best accuracy and velocity…. They are designed the way they are to ease loading AND minimize bore drag….
If you must have a larger version of this bullet, I would suggest that if and when it reaches Group Buy status that you ask in that thread if it is possible to purchase a slightly larger one…. That is certainly within the capabilities of NOE, as an example they are currently running a Group Buy where you can specify 0.225″ or 0.228″….
Bob
rsterne
donhansell
O48Twitch
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