M96 vs CG63 6.5x55 Powder Preferences

[Macd]

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

[Ranch Dog]

Don't have anything to offer that to say that I like reading reports like this, I find them interesting.

[GasGuzzler]

I’m not going to have those guns, those calibers, or use those powders but I’m with RD. I like reading stuff like this.

[Macd]

I searched around and found a picture of the target for the 48.0 grain load of IMR7828 in the M96 . Notice the swirls.

IMAG02851_zpsfolsqaox.JPG

[cj8281]

My first thought on this is check your cartridge over all length. To me, it sounds like the bullet is engaging the rifling upon chambering, this will cause high pressure and increased velocity, even from loads that are less than listed max. I believe the Hornady book has a section about that in the front. (Version 9)
The M96 might have a slightly longer free bore than the CG63. You might smoke a round, chamber it and then carefully extract it and see if the bullet is marked with the rifling.
Just a thought.

[RBHarter]

Higher velocities may be from the 29" barrels .
Book speeds are probably from 22-24" barrels . 5" with slow powders can be a lot .
I will tend toward you being right at a maximum load . See below .

The 6.5 regardless of case has twist rates at 1-8.5 and faster .
The bullet may be literally throwing the core out of the jacket .
A tougher bullet may be in order .

You do know that with H1000 2800 fps is a start load in a 264 WM for a 140 gr spire point in a 24" barrel ?
I shot a yellow with red Super X boxed Winchester 140 power point and it was at 2850 fps in the WM with 24" barrel with just about a start load .

The pig in question had a 5" exit wound at 125 yd broad side through the ribs .

[Macd]

Higher velocities may be from the 29" barrels .
Book speeds are probably from 22-24" barrels . 5" with slow powders can be a lot .
I will tend toward you being right at a maximum load . See below .

The 6.5 regardless of case has twist rates at 1-8.5 and faster .
The bullet may be literally throwing the core out of the jacket .
A tougher bullet may be in order .

You do know that with H1000 2800 fps is a start load in a 264 WM for a 140 gr spire point in a 24" barrel ?
I shot a yellow with red Super X boxed Winchester 140 power point and it was at 2850 fps in the WM with 24" barrel with just about a start load .

The pig in question had a 5" exit wound at 125 yd broad side through the ribs .

I agree regarding the tougher bullet. I have not measured myself but have read that match bullets have thinner jackets to help make them more concentric. The combination of high velocity and fast spin is the problem with bullet failure. The pressure problem is something else. I use a bullet comparator and OAL gauge to set seating depth off lands. With regard to being near maximum published load you are correct. That is why I won't be loading IMR7828 for the CG63 anymore and backing off on the load for the M96. The other possibility I haven't checked yet is the case capacity of the Norma brass.

Thanks for the observations.

[Macd]

Mystery solved and thank you cj8281 for putting enough doubt in my head to go recheck my data and setup.

My first thought on this is check your cartridge over all length. To me, it sounds like the bullet is engaging the rifling upon chambering, this will cause high pressure and increased velocity, even from loads that are less than listed max. I believe the Hornady book has a section about that in the front. (Version 9)
The M96 might have a slightly longer free bore than the CG63. You might smoke a round, chamber it and then carefully extract it and see if the bullet is marked with the rifling.
Just a thought.

When I receive a new rifle or new bullet I establish its maximum OAL using a comparator and gauge for each rifle that I load that bullet. I then make a dummy cartridge and set its OAL using the comparator from .015-.020 off the lands. A heavy factory crimp and it becomes my setup round for that rifle and bullet. I had the CG63 first and had made dummy cartridges for both the bullets so when I received the M96 I did my measurements and made two more setup cartridges. So far so good. However when adding the specific rifle label to the existing (CG63) and new (M96) cartridges I mixed up the labels for the Hornady 140 Match bullet on the two cases. I discovered this by redoing all the measurements and then checking my setup dummies. My reloading journal had the right measurements but I didn't confirm this until today.

Rather than type out a bunch of measurements I thought a picture (corrected labels) was a better indicator how much a .084 difference in a comparator measurement makes in OAL for the 140 bullet.

DSC00774.jpg

Making a mistake is never good but finding, correcting and learning from one is great.

[larryw]

Making a mistake is never good but finding, correcting and learning from one is great.

Agree 100%.. Glad you got it straightened out.

[Ranch Dog]

See, this is a good read with valuable lessons!