My featherweight M-70 only has a 22 inch barrel: So I worked up loads that seemed to work OK in that rifle. The Winchester is much more picky than any of my Swedish Mausers. You are correct in that the US made brass has the wrong head size. Lapua Brass is the best for 6.5x55mm. Followed by Norma. They will last for 15 reloads so in the long run they are not really any more expensive than the 5 reload Winchester brass.
6.5x55mm Winchester MODEL 70 LOADS ONLY
Federal factory 140gr Soft Point: = 2,375 fps, 0.50 inch group.120gr Nosler Ballistic Tip: 46.5gr RL-19, Lapua, CCI BR-2, 3.085 col= 2,560 fps and a 1.0 inch group120gr Sierra Match King: 46.0 gr RL-19, Lapua, BR-2, 3.085 col= 2,508 fps and a 0.50 inch group.
120gr Hornady A-Max, 48.8gr IMR-4831, ww,ww, 2.964 col
= 2,925 fps and a 0.75 inch group Lee Crimp. High Pressure
129gr Hornady SST, 47.3gr IMR-4831, WW, WW Stand, 2.942 col
=2,808 fps and a 1.5 inch group. no crimp. Cratered primers
140gr Rem Accu-Tip, 47.0gr RL-22, Lapua Brass, CCI-200, 3.970 col= 2,640 fps and a 1.0 inch group140gr Nosler Partition, 47.0gr RL-22, Lapua Brass, CCI-200, 3.950 col= 2,569 fps and a 1.5 inch group140gr Hornady Soft
oint , 47.0gr RL-22, Lapua Brass, CCI-200, 3.850 col= 2,575 fps and a 2.0 inch group140gr Hornady SST. 46.5 gr RL-19, Lapua, CCI-200, 3.090 COL
= 2,570 fps and a 1.0 inch group
140gr Hornady SST, 44.5 gr H-4350, Lapua, CCI-200, 3.090 col
= 2,608 fps and a 1.5 inch group
140gr Hornady SST, 44.5gr H-100V, Lapua, CCI-200 3.090 col
=2,669 fps and a 0.50 inch group.
140gr Sierra Game King, 44.5gr H-100V, WW, WW, 2.930col
= 2,675 fps and a 0.55 inch group Lee factory Crimp, no pressure signs
140gr Hornady Soft Point, 44.5gr H-100V, ww, ww, 2.945 col
=2,680 fps and a 2.5 inch group. Lee Crimp. Some pressure signs
140gr Hornady R. N. 44.5gr H-100V, WW, WW 2.975 col
=2,620 fps and a HUGE Group, lee Crimp
140gr Hornady SST, 46.5gr IMR-4831, ww,ww, 2.995 col
=2,700 fps and a 0.75 inch group, primer flow
160gr Hornady Round Nose: 45.0 gr RL-22, PMC, Rem 9.5, 3.100 col= 2,288 fps and a 1.5 inch group
Winchester Model 70 Featherweight in 6.5x55 Swede Mauser.*This rifle has been glass bedded. At 100 yards, light snow, 32F. 6-8 knot wind.
Federal factory 140gr Soft Point: = 2,375 fps, 0.50 inch group.
120gr Nosler Ballistic Tip: 46.5gr RL-19, Lapua, CCI BR-2, 3.085 col= 2,560 fps and a 1.0 inch group
120gr Sierra Match King: 46.0 gr RL-19, Lapua, BR-2, 3.085 col= 2,508 fps and a 0.50 inch group.
140gr Rem Accu-Tip, 47.0gr RL-22, Lapua Brass, CCI-200, 3.970 col= 2,640 fps and a 1.0 inch group
140gr Nosler Partition, 47.0gr RL-22, Lapua Brass, CCI-200, 3.950 col= 2,569 fps and a 1.5 inch group
140gr Hornady Soft
oint , 47.0gr RL-22, Lapua Brass, CCI-200, 3.850 col= 2,575 fps and a 2.0 inch group
160gr Hornady Round Nose: 45.0 gr RL-22, PMC, Rem 9.5, 3.100 col= 2,288 fps and a 1.5 inch group