On Saturday, I tried shooting the RCBS 243-095-SP in a 1:14 twist 6mm. This bullet is about .925 long when ready to shoot after sizing and tapering to fit the throat.
This bullet is too long for this twist. Two bullets hit the paper sideways at 100 yds and 3 were nice, clean, misses. I'm going to pull the other 10 bullets for remelting.
These bullets used to shoot well in a 1:9 twist.
Attached Files
Greenhill comes up with a 9 1/2 inch twist for a .925 long 6mm bullet. You're probably going to have to stick with something about .650 long for the 14 twist to work. An LBT with a .5 radius ogive and one grease groove would get you the most weight out of the small package.
Attached Files
Ran a bullet of LBT profile through the JBM program with a length of .729. The program shows stability starting at 1116 fps with a stability factor of 1.7, and stays at 1.6 or 1.7 all the way up to a velocity of lead-melting speed. This might weigh 65 to 70 grains. One grease groove is about all that would fit. Do you think it would work without a grease groove and just lubing at the gas check?
Attached Files
I went to the JBM site and ran the bullet you mentioned through the Don Miller stabilty calculator and for a .732 long 70 gr bullet at 1116 fps in a 14 twist .243 the factor was 1.123. At 2000 fps it was 1.364 and at 2500 fps it was 1.469 so velocity is going to make a big difference. Personally I wouldn't go over a length of .700 and that would be after seating the check and tapering. I can tell you from experience it's better to err on the side of caution when spending money on a mould.
I don't know if the bullet would work with no grease groove but if you want to push it probably not unless it was pretty cold out. A small groove and a .5 ogive would get you the most weight for your length and still have a good form. The .5 ogive isn't as stream lined as the usual SP Veral makes so you'll gain a little weight by having more bullet body for length. The bullets I had cut for my 30x47 use that design.
If I remember right the jacketed 62 grain bullets used in the 6PPC are about .770 long and they're shooting them over 3000 fps in the 14 twist if that helps at all. I have some Bergers around here somewhere and if I can find them I'll measure one and let you know the length.
Attached Files
The picture below is of two 30 caliber moulds. The bullet on the left has the normal SP shape and the one on the right is the .5 ogive. The ogive length is about .090 shorter with the .5 on the 30 caliber. Don't know what it would be on the 6mm but it would still leave a longer body for more weight.
Attached Files
Pat,
Thanks for disagreeing. I found a mistake in my entry for the nose length which allowed the bullet to be stable according to the erroneous entry.
You are correct with the .700 maximum length. The .732 length would be an aggravating bullet with that twist.
Thank you for saving me money and face.
Attached Files
Pat,
The LBT mould arrived a couple days ago. Cast some for samples. It weighs a whopping 62 grains as cast; 63.5 ready to shoot. Diameter is .245. The length came in at .644 when sized and tapered.
The great part about it is that the gas check shank measures .2325 to .233. The Eagan has a shank about .235 and always shaves lead when seating. The gas checks go on it with no effort. A dummy round showed good engraving all the way around.
The JBM program shows stability at 1.9 thru 2.1.
Attached Files
Paul, I guess I'm late to thsi discussion. I didn't open it up back in August. I find it interesting that your 95 grain bullet wouldn't stabilize in a 14 inch twist. Per Ardito's information he shot that 214 grain Eagan bullet out of a 14 inch twist. I'd think the two bullet lengths should be comparable if barrel diameter was the same. Wonder why it wouldn't stabilize for you. Ardito probably pushed his at 2000 fps or higher.
food for thought
Attached Files
Paul I'm interested in how the new bullet works out for you so please keep us informed. You didn't mention it but I assume it's a 6PPC right? If so you should be able to crank that 65 gr bullet down range at a pretty good clip. What you're giving up in BC with weight using the lighter bullet you're going to make up for in speed so don't let that bother you. After running my 250 gr 30 cal bullet with a measured BC of .396 at 1750 fps compared to my 160 gr bullet with an estimated BC of .270 at 2550 through a ballistics program I found that they drift just about the same. Just a guess but I don't think you'll have any problem at all hitting 2600 fps with your new bullet in the 14 twist.
Attached Files
Tried the LBT 65 gr bullet on Saturday. Shot 2, 10-shot groups in 15 minute time limit without cleaning. Had 6 sighters for each target. The results were ok: first group 1.348, 2d one at 1.054 for a 1.201 agg.
Must have done something right with the Eagan 80 gr bullet. Same procedure. Shot 2 targets with no cleaning between in the 15 minute time limit. Group one was .786, group two was .928 for an agg of .857. Only took 3 sighters on the first target and none on the second.
The LBT load was the same as the Eagan. Both should have been about 2450 fps. The pressure was really low on the 65 grain bullet. Some more fitting of the LBT and some load development is in order before declaring the LBT less capable.
Evidently, stability isn't the issue with the Eagan bullet. A little more care was taken seating gas checks with less lead shaving. This may have helped accuracy.
Attached Files
Thanks for the update Paul. Just out of curiosity what load are you running with the 63 gr bullet? Reason I ask is that with my 30x47 I'm running 3 grs less of VV135 (or 39.5 grains) with the 160 gr lead bullet than the guys shooting 118-135 gr jacketed bullets are using. If it held true for your 6mm you might try starting at about 25 grs of VV133 and see what happens. Don't know what alloy or lube you're using but I use HTWW and LBT Blue.
Attached Files
21 gr H322 for both the 80 gr Eagan and the 63 gr LBT. Voodoo Red lube. Linotype. Sized .2435 and tapered to fit better.
Attached Files
Paul when you get a chance check your PM's. 32ideal
Attached Files
Glad you had success with your LBT mould, Paul. On this same note. I'm trying to understand the Greenhill Formula. Looking for a good bullet that's stable in an H&R 357 mag reamed to 357 max with a 1 in 16 twist, 22 inch barrel and a grove dia. of .358 inch. Looking at around 180 gr. bullet. Is the length used in the formula the total length of the bullet? I put the numbers in and came up with aprox. 1.2 inch length? The rifle has not been altered as yet, don't really know what bullet to use? Hope I'm adding to this tread and not hijacking it. Thanks, James.
Attached Files
Glad you had success with your LBT mould, Paul. On this same note. I'm trying to understand the Greenhill Formula. Looking for a good bullet that's stable in an H&R 357 mag reamed to 357 max with a 1 in 16 twist, 22 inch barrel and a grove dia. of .358 inch. Looking at around 180 gr. bullet. Is the length used in the formula the total length of the bullet? I put the numbers in and came up with aprox. 1.2 inch length? The rifle has not been altered as yet, don't really know what bullet to use? Hope I'm adding to this tread and not hijacking it. Thanks, James.
My Ruger #1 357 magnum stabilizes bullets to the 250g range fine (RCBS 250 sp and 358318)) at 1200fps.I belive the twist is a 1-16.My 35 Whelen also a 1-16 will stabilize this NEI 280 grainer just fine @ 1600 as well.The RCBS 200 FN should be a good one for your rifle in my opinion.Does well in both of the above rifles.
George
Attached Files
Thanks Goerge, for the info. I guess the Length used in Greenhills calc. is the total length of bullet, which seems to be the only logical answer.
Thanks, James.
Attached Files
Sorry I missed that question. Yes, total length governs required rate of twist.
A good example is the current US issue rifle, the M4. Shooting a 62 gr SS109 FMJ bullet requires a 1:9 twist, which is what the civilian versions use. The M4 has a 1:7 twist to stabilize the tracer round, which matches the SS109 ballistically, but is longer.
Attached Files
Thanx Bill somehow I thought the change in twist was due to weight in the M4!
George, have you (or anyone) measured the bullet from the RCBS 200 FN GC mould? Just to check Greenhills' formula.
Attached Files
Bryan Austin
20
fc60
15
Ed Harris
11
Bud Hyett
9
linoww
8
DanLH
5
Aaron
5
RicinYakima
4
Wilderness
3
9.3X62AL
3
