boolit design vs stability

[fecmech]

I have run into a bit of confusion regarding bullet stability with a marginal 30" twist in my Rossi lever guns. The RNFP design( 158-165 grn) does not seem to want to shoot well at longer ranges(100-200 yds) while the Lee TLSWC which is slightly longer seems very accurate and stable out to 200 even at 1100 fps! The RNFP's will not make it to 100 yds at that velocity but will shoot less than 2"@50 yds. By bumping velocity up to 1300 fps I can get pretty good 100 yd accuracy (RNFP's) but they tumble before 200 yds. The Lee SWC has a slightly smaller meplat than both RNFP's and I wonder if the air acting on the bigger meplat destabilizes the RNFP's. If I plug the weights and lengths of all the bullets into a stability calculator along with velocities I get 1.58 and 1.56 for the FP's@1300 fps (1.5 is supposed to be good) while the SWC@1100 fps is 1.39 (marginal). I'm wondering if a RNFP with a smaller meplat would be more stable. The Lee 125 RNFP and 120TC are very accurate to 200 yds so the really short bullets do fine with the 30" twist.

BTW My Lyman 358429 @1600 fps (small meplat) with a stability factor of 1.23 is fairly accurate at 200 yds and holes in the target are nice and round. I would be interested in your thoughts on this.

[runfiverun]

think about buffeting when they slow down through the sound barrier.

[MtGun44]

I think run5run has it nailed.

This is common problem when bullets drop thru the 1100 fps (approx.) sound barrier. The flatter
nose will drop thru sooner (shorter range).

Bill

[Blammer]

that bit of a rounded nose edge and a tad smaller meplat is probably just enough... on the lee bullet

[runfiverun]

air does speed up when it travels over a round surface.

[44man]

From my handgun experience I don't see the meplat affecting stability even to 500 meters. Even a WFN will be accurate and cut round holes that far.
Getting the RPM's where they should be has proven so important. I don't think I could get a 1 in 30" to shoot. I know the Marlin .44 with the 1 in 38" was so sad at 100 I gave up and sold it.
Another thing I found was when I made my molds, one GG was not doing it for me so I use two and if room I put three. The amount of lube will be about the same as one large GG. I am not sure if it is important but seems to work.
A smaller meplat might give less drop at range but I will not say a large one shoots worse. I am going to say the problem is still RPM's.

[Shuz]

FWIW, in my experience with the .44 mag, a Lee 200g RNFP is much easier to get to shoot well than a Saeco 446-A., which is also a nominal 200 g boolit. I attribute it to nose profile. My loads are all below the speed of sound, so I know that is not an issue.

[fecmech]

Just for kicks I loaded the RNFP of my first post at a little over 1200 fps out of my Ruger GP pistol (16 or 18 twist, not sure) and went to the range. Got the hold over figured out and shot 5 shots at a piece of cardboard at 200 yds. All 5 bullets arrived at 200 yds point on in about a 10-12" group. Evidently if spun fast enough the flat point can make the subsonic transition OK. So I guess the take away from this is that stability calculators are predicated on "pointy" bullets and are not too accurate on RNFP's, at least not on the lower or marginal end. I guess I'll just keep lobbing those Lee TLSWC's and 120 TC's if I want to hit anything at 200 with my Rossi.