7.7x58 Beginning of The Velocity Chase
Ahh, the .311 diameter bullet, the unloved middle child of the thirty caliber family. This is hopefully the just the beginning of long series on my favorite of the .311 cartridges, the 7.7x58 Japanese and finding load data.
This series, while it is about the 7.7 and load data, it is not about just regular loads as you can find data fairly easily. It is more specifically load data for cast bullets and short (er) barrel lengths. The starting test bed is a sporterized Arisaka with a 19-inch barrel. I had fun doing a few things to this rifle so I’ll will more than likely do a write up in the future on what all I did to this rifle.
Some backstory: A short time prior I had developed a load for the 7.7 of 16 grains of trailboss under a 155 grain coated lead non gas-checked bullet sized to .311. I tried and tried in vain to get this load to be accurate. To even hit paper if we’re being honest. I was finally able to get enough hits on paper to see that the bullets were keyholing. “So,” I think to myself, “the bore must be pretty worn on this one” since it is a pretty common occurrence for the bore and/or the throat to be worn in the rifles. I decide I am going to get a bigger mold and finally am able to procure a Lyman 314299 mold which casts a (they say round nose but it is halfway between a spitzer and a round nose) 200 grain .314 diameter bullet. On a whim I decided to load some more 155 grain to shoot but this time I put on a gas check. Well wouldn’t ya know they shoot very well to about 1-1.5 moa at on hundred yards. So feeling a little bit stupid that it took me that long to figure out something so simple, (I do not now or ever claim to be a professional or know it all) this is where we pick up the story.
My plan is to find a cast load that balances fast enough velocity to be a viable hunting cartridge but not try melt the bullets or necessarily achieve jacketed bullet speeds. There are plenty of people who have a good light load for target shooting for these guns, but they are mostly all weak loads. I don’t like weak loads. My goal is to try and find a load that gets about 2000-2100 fps but try and keep the recoil a little bit on the tame side for myself. Felt recoil is perceived differently from person to person so all I can do in that department is report what I feel and let people take it as they may. On the trip out to the range I started with four different loads:
my control load: 150 grain coated cast bullet, 16 grains of trailboss, converted 30-06 brass and CCI large rifle primer,
and my three other loads: 155 grain gas-checked cast lead bullet, 29 grains IMR 4895,
200 grain gas-checked cast lead bullet, 37 grains IMR 4895,
200 grain gas-checked cast lead bullet, 38 grains IMR 4895.
I was able to collect good data on everything except three rounds of the 29 grain loads which I will explain at the end.
Here is the data that I did manage to collect:
Control load of 150 grain coated cast bullet, 16 grains of trailboss, converted 30-06 brass and CCI large rifle primer:
This is a very mild target load and one that I would load to just have fun and plink some targets.
The next two loads:
As you can see the 38 grain load is getting closer to the velocities I am attempting to achieve, but still not quite there. The 37 grain load wasn’t terrible if you ignore the one shot at 1752 fps. It would appear that there were some other factors that attributed to that huge drop in fps. Now for the 29 grain load:
Here is a long winded explanation of why I only had two shots with the 29 grain loading. The 7.7 military loaded ammo was 175 grain bullets with an OAL of 2.27 inches. Loading 150 grain bullets presents some problems as they aren’t nearly as long as the 175s or higher weight bullets. To load most cast 150/155s to correct OAL, you have only the bottom drive band on which to crimp the neck of the case. This leaves the bullet loose in the crimp and susceptible to being pulled out of the case which is exactly happened with the last three rounds of the 29 grain loads. Now this could be easily fixed of you just seat the bullets deeper in the cartridge and that might work depending on your rifle. However, though it was a Mauser copy, it seems Arisakas tend to have a less than a smooth magazine. The guns that I have do not feed the shorter length l50 grain cartridges well at all and tend to jam because the shorter bullet will catch the end of the magazine and stick, hence loading them to correct OAL. What I will probably end up doing is single feeding them instead of utilizing the magazine. It still doesn’t fix the problem of the bullets pulling out of the case if you partially chamber and have to reopen the bolt. Perhaps a heavier crimp may be needed.
Conclusions:
The 38 grain load is starting to tickle the numbers I am looking for, but not quite there. I have many different test planned for the 150/155 grainers as well heavier bullets. I was a little bit surprised at the low velocity of the 29 grain IMR load so it will be interesting to see what kind of velocities I can push. Once I find a good velocity the next thing I will be working on is accuracy. The accuracy for all the IMR loads were terrible. I believe a lot of it was due to my very unstable shooting position. I had to use stacked sand bags but it still to low for a good cheek weld. Also my scope wasn’t zeroed for any of these loads. Hmm what other excuses can I use? All kidding aside its just another problem to solve and more data to gather and record. Hopefully this will be of some help to someone. I will keep collecting data and post my findings here on this website as well as videos covering the same material.