Need advice for load in a 7.7 Jap

[waltham41]

Hodgon has the following starting load for a 7.7 Jap...

180 GR. SIE SP Hodgdon BL-C(2) .311" 3.150" 37.0 2054


The load is for a Sierra bullet, I am using cast 180-185 gr and want a minimum starting load.... how much different would it be for the same powder but the cast boolit?

Thanks

[curator]

I have used Hodgdon's Bl-C2 for cast boolit loads in my 2- 7.7 Jap M99 rifles. I found anything over about 32 grains lost accuracy. 28 grains and a tuft of dacron gave best accuracy in both guns, The Medford rifling in these guns makes high velocity difficult with cast boolits. My best accuracy was with 3 thousandths over grove diameter (.315) and gas-checked boolits of water-drop-quenched wheel weight alloy (BHN 22-24) Softer alloys did not group, they patterned along with significant barrel leading. Bullet design is also critical. Pick one with long bearing surface and short nose of at least .005 over land diameter.

[waltham41]

What kind of range are you shooting at with this load? What kind of drop are you experiencing?

I was shooting a light load of 180 cast with 10g Titegroup behind it and was having to use 400m on the sights at 200 yds.... very good accuracy close up at 25 yds but not so good at the longer distances.

[bruce drake]

I use LEE's .323 170Gr RN sized down to .314 and Lubed with BAC Carnauba Red during the gaschecking at .323 and then relubed with LEE Alox after resizing down to .314 for my Arisaka T99. I first tried .311 and .312 sized boolits but accuracy with the rifle was abysmal until I used a larger bullet to better fit the Metford style rifling.

I use 12.5gr of Red Dot or 13gr of Unique normally for a good 100 yard load for the rifle. You will have to use the higher sight settings to get out to 100 yards. I normally set my sights at 600 yards for most of my 100 yard shots with this same powder load in my 8mm, 7.7 JAP, 303 Brit, 308 Win and 30-06 Cast boolits. Accuracy with the load when combined with a properly sized lead bullet is between 2-3 inches depending on the condition of barrel as well.

Bruce

[Shiori357]

I would like to share some of my experience here, under several different powder charge with Arisaka Type99s.

I have two different production of Arisaka type 99 currently and I shoot both in past 2 years.

One; Kokura Arsenal series 22 with mismatching bolt.
Two; Under Kokura Arsenal / Toyo Kogyo series 23 also with mismatching bolt.

I did miner trigger tune for both rifles and complete front sight wintage adjustment as well.
(Miner tune; polishing contact surface and modify contact angle for sear to firering pin, I got to be done slight offset set up from original Arisaka. I did for only Toyo version, this work improve a lot difference at 100 yard bench shooting.)

I try two boolit weight so far, Lyman 314299 (200gr) and Lee C312-155-2R (155gr).
With my old Chronograph (Pact I 24") and track all of my load in last two years.

Use straight W-W metal for this cast, so it is not hard enough cast boolit for Arisaka metford type rifling, which I knew.

Both of my type 99 has .312 to .313 groove diameter, it is very hard to figure by slag method, so I should say it is not super accurate dimension in my both Rifles.

However, I sized to my cast .314 size that most of time "just lube and GC seating and it is actuary not sizing" that I feel, it is water quench, better not to give boolit has strain force during re-sizing process anyway.

Arisaka Type99 has 1-9 3/4 rifling twist, which just same as 1-10" as most of US 30 service rifles, so 200gr boolit may need to reach MV 1800 to 1950fps of speed, if Arisaka barrel has conventional Enfield Style Rifling. (but, it's NOT!)

Here is trick, I use softer W-W material for this load, plus over sized .30 cal. in this rifle.
I got good grouping pattern at 100yard by MV 1600fps range with 155gr.

Most of 3 shot by 2 MOA, 10 or grater shot about 3" to 4" grouping pattern @ 100yard.
It is not much different @ 1450fps on 200gr (314299 Alliant 2400 16.0gr) or 1600fps on 155gr (C312-155-2R Alliant 2400 16gr) or 1600fps on 200gr (314299 Alliant 2400 20.0gr)
All require 300m of radder sight setting at 100 yard shoot.

But, I got 200m radder sight setting by 314299 (200gr) with Hodgdon H4198 30gr load.
It is still mild load, but very consistent with this powder charge. (MV,1850fps it is to fast for W-W cast which I assuming for Arisaka Methford rifling, I could not track grouping at this test because guy next to me shot my target obviously)

Sight issue is big matter to me regarding discuss about constant 2" grouping / accuracy at 100yard bench shoot, especially we would like to keep original mil spec sight in this rifle, and would like to have fun to shoot all day without shoulder pain.

I just cast Lee C312-185-1R boolit today afternoon, I will figure this load as soon.

Shiori Okamoto