H&Hhunter said:
I've been trying to get my hands on some Vihtavuori as the data looks great. I can't get it down here. How are the real world numbers with VV540?
I started load development this weekend using the 250gr TTSX from Barnes, Vihtavuori N540 powder, Federal GM215M primers and Remington brass. The first problem is the lack of data for this bullet/powder combination. Barnes has load data for the 235gr and 270gr TSX bullets with N540 and Vihtavuori has data for the Sierra 250gr SBT.
235gr TSX
Min - 76.0gr @ 2,864 fps
Max - 83.0gr @ 3,062 fps
270gr TSX
Min - 72.0gr @ 2,636 fps
Max - 78.5gr @ 2,836 fps
250gr Sierra SBT
Min - 68.5gr @ 2,615 fps
Max - 74.4gr @ 2,808 fps
The first thing to decide is how fast should the 250gr TTSX leave the muzzle. Interpolating the Barnes TSX data gives a maximum velocity of 2,932 fps but that might not be a valid approach. The Sierra max velocity might be more reasonable at 2,808 fps. Anyway, here's some velocity data obtained over the weekend.
Bullet = Barnes .375 cal 250gr TTSX
Powder = Vihtavuori N540
Primer = Federal GM215M
Case = Remington (new)
C.O.A.L = 3.585"
Notes: Case mouth crimped into front cannelure
Rifle - Kimber Talkeetna 24" barrel
Chronograph - CED M2
72.4gr > 2,687 fps (avg of 5 shots)
72.7gr > 2,674 fps (avg of 5 shots)
73.0gr > 2,676 fps (avg of 4 shots)
73.3gr > 2,715 fps
73.6gr > 2,750 fps
73.9gr > 2,757 fps
74.2gr > 2,761 fps
74.5gr > 2,785 fps
74.8gr > 2,777 fps
75.1gr > 2,782 fps
75.4gr > 2,807 fps
75.7gr > 2,812 fps
76.0gr > 2,825 fps
76.3gr > 2,863 fps
76.6gr > 2,869 fps
76.9gr > 2,875 fps
77.2gr > 2,876 fps
77.5gr > 2,887 fps (avg of 7 shots)
77.8gr > 2,888 fps
I shot the first three loads yesterday but the velocity was too low so today I decided to figure out where I need to be with the charge weight to get to 2,850 fps or thereabouts. The 73.9gr to 74.8gr loads made one ragged hole at 100 yards but the velocity is only in the 2,770 fps range so I pushed on. I didn't see any obvious signs of over pressure with any of these loads (primers, bolt lift, O.D. in front of belt). The 77.5 gr load shows promise since loads either side of it had the same POI but after a long day of making loads and shooting prone and 17 bullets sent downrange the best I could do was a 1.4" 5-shot group with that load. I'm going to try three loads of 77.2, 77.5 and 77.8gr and do my usual "round robin" method next time to see if I have an OCW load. The loads listed are probably compressed from 76.0gr onwards and I don't think I can get much more than 77.8gr of powder in the case.
So what should the max velocity of the 250gr TTSX be?