M96 vs CG63 6.5x55 Powder Preferences
Posted: 05 Nov 2017 12:38
This is a bit of a long post but I am hoping it is interesting to the reloaders and somebody may want to voice their opinion on the results I have presented.
I have two rifles chambered in 6.5x55. The first is a full military (except for a target crowned muzzle) all original Swedish M96 Mauser by Carl Gustaf 1905 dated. The second is a Carl Gustaf factory conversion for target shooting CG63 built on an 1906 dated M96 receiver. The conversion was done in 1973. Both rifles have 29 inch barrels and identical twist rates. Both are very accurate with the CG63 having the edge due to its free floated, heavy profile barrel and action bedding.
I should start by saying I weigh every powder charge on a digital scale and trickle up slowly to the charge weight.
I have been experimenting with powders and the M96 shines with 43.0 grains of Hybrid 100V pushing a 139 grain PRVI HPBT from Norma brass and CCI200 primers. The CG63 hasn't shown the best results for this loading and seems to prefer more velocity than H100V delivers even at maximum published load. The powder is pretty consistent in both rifles delivering:
M96 2637 FPS avg. SD 18.4
CG63 2698 FPS avg. SD 18.5
I think the slight speed edge of the CG63 may be because it has a nice shiny bore while the M96 has darker although still very good one. The CG63 chamber is a bit tighter too. The powder for both trials came from the same container so batch variation is not an issue.
My next powder to try was IMR7828. it is a slow burning powder and I figured it would bring out maximum velocity in those long barrels. Brass and primer were the same but I had some 140 Hornady match bullets I wanted to try. Checking my manual I chose to load from 44.0 to 48.0 grains with 48.2 being the published max. Now my manual says IMR7828 SSC but IMR/Hodgdon say the regular and small cut powders are the same burn rate and identical for reloading purposes. In any event, things got interesting.
The M96 at the 44.0 gave me an average of 2551 (SD 7.5) and the 48.0 grain load spit them out at an average of 2781 FPS (SD 15.3) and made a beautiful cloverleaf on the target at 50 yards. However there were small black swirls around the holes indicating to me the bullet was being spun too fast and starting to come apart. No signs of pressure but this speed is over 100 FPS above that of the published maximum load.
The CG63 from the first shot at 44.0 grains told me something was wrong. First the speed was 2672 FPS over 120 FPS faster than the same load in the M96. No pressure signs so I took a shot at each charge up to 48.0 grains checking for pressure. At 48.0 grains and 2879 FPS this was delivering 200 FPS over the published maximum load. The primer showed deformation into the firing pin hole and some flattening of the edges. I believe the bullet came apart in mid air as nothing hit the target. All the previous shots left pronounced black swirls around the holes on the paper. So what else to do but fire another string starting at the beginning. The first shot (44.0 grains) gave me 2704 FPS but again without pressure signs. At 48.0 it spit out the bullet at 2904 FPS but this time it hit the paper making a nice clean hole surrounded by a large black swirl. The primer was again badly cratered. I stopped shooting. So says I to me something is amiss with my loads. It has been since suggested to me that the long barrels coupled with the thin jacket of the match bullet was the culprit. This perhaps explains the black swirls and bullet failure but what about the apparent pressure issue in the CG63 at 48.0 grains. It wasn't a compressed load although very near case capacity. I checked OAL and that was okay although the CG63 was pretty darn close due to its newer and tighter chamber. Still not sure but not repeating that load again.
Last test was a comparison using the same powder at a reduced loading of 42.0 and 43.0 grains. I substituted the 139 grain PRVI bullet for the Hornady one. Here are the results.
M96
42.0 2272 FPS avg. SD 21
43.0 2294 FPS avg. SD 34
CG63
42.0 2415 FPS avg. SD 12
43.0 2501 FPS avg. SD 13
Neither of the loads was accurate, grouping between 1-2 inches at 50 yards. Once again the CG63 produced significantly greater velocity. I am not sure why but it is pretty obvious IMR7828 is not the best match for the CG63 and probably not for the M96 although it grouped well at 48.0 grains with the Hornady bullet. I may try it with the PRVI one as it has a thicker jacket. If I do I will report my results, promise
I have two rifles chambered in 6.5x55. The first is a full military (except for a target crowned muzzle) all original Swedish M96 Mauser by Carl Gustaf 1905 dated. The second is a Carl Gustaf factory conversion for target shooting CG63 built on an 1906 dated M96 receiver. The conversion was done in 1973. Both rifles have 29 inch barrels and identical twist rates. Both are very accurate with the CG63 having the edge due to its free floated, heavy profile barrel and action bedding.
I should start by saying I weigh every powder charge on a digital scale and trickle up slowly to the charge weight.
I have been experimenting with powders and the M96 shines with 43.0 grains of Hybrid 100V pushing a 139 grain PRVI HPBT from Norma brass and CCI200 primers. The CG63 hasn't shown the best results for this loading and seems to prefer more velocity than H100V delivers even at maximum published load. The powder is pretty consistent in both rifles delivering:
M96 2637 FPS avg. SD 18.4
CG63 2698 FPS avg. SD 18.5
I think the slight speed edge of the CG63 may be because it has a nice shiny bore while the M96 has darker although still very good one. The CG63 chamber is a bit tighter too. The powder for both trials came from the same container so batch variation is not an issue.
My next powder to try was IMR7828. it is a slow burning powder and I figured it would bring out maximum velocity in those long barrels. Brass and primer were the same but I had some 140 Hornady match bullets I wanted to try. Checking my manual I chose to load from 44.0 to 48.0 grains with 48.2 being the published max. Now my manual says IMR7828 SSC but IMR/Hodgdon say the regular and small cut powders are the same burn rate and identical for reloading purposes. In any event, things got interesting.
The M96 at the 44.0 gave me an average of 2551 (SD 7.5) and the 48.0 grain load spit them out at an average of 2781 FPS (SD 15.3) and made a beautiful cloverleaf on the target at 50 yards. However there were small black swirls around the holes indicating to me the bullet was being spun too fast and starting to come apart. No signs of pressure but this speed is over 100 FPS above that of the published maximum load.
The CG63 from the first shot at 44.0 grains told me something was wrong. First the speed was 2672 FPS over 120 FPS faster than the same load in the M96. No pressure signs so I took a shot at each charge up to 48.0 grains checking for pressure. At 48.0 grains and 2879 FPS this was delivering 200 FPS over the published maximum load. The primer showed deformation into the firing pin hole and some flattening of the edges. I believe the bullet came apart in mid air as nothing hit the target. All the previous shots left pronounced black swirls around the holes on the paper. So what else to do but fire another string starting at the beginning. The first shot (44.0 grains) gave me 2704 FPS but again without pressure signs. At 48.0 it spit out the bullet at 2904 FPS but this time it hit the paper making a nice clean hole surrounded by a large black swirl. The primer was again badly cratered. I stopped shooting. So says I to me something is amiss with my loads. It has been since suggested to me that the long barrels coupled with the thin jacket of the match bullet was the culprit. This perhaps explains the black swirls and bullet failure but what about the apparent pressure issue in the CG63 at 48.0 grains. It wasn't a compressed load although very near case capacity. I checked OAL and that was okay although the CG63 was pretty darn close due to its newer and tighter chamber. Still not sure but not repeating that load again.
Last test was a comparison using the same powder at a reduced loading of 42.0 and 43.0 grains. I substituted the 139 grain PRVI bullet for the Hornady one. Here are the results.
M96
42.0 2272 FPS avg. SD 21
43.0 2294 FPS avg. SD 34
CG63
42.0 2415 FPS avg. SD 12
43.0 2501 FPS avg. SD 13
Neither of the loads was accurate, grouping between 1-2 inches at 50 yards. Once again the CG63 produced significantly greater velocity. I am not sure why but it is pretty obvious IMR7828 is not the best match for the CG63 and probably not for the M96 although it grouped well at 48.0 grains with the Hornady bullet. I may try it with the PRVI one as it has a thicker jacket. If I do I will report my results, promise