6.5 Japanese bullet accuracy issues.....anybody out there load for them?

[Muskyhunter1]

I have an Arisaka Type 38 Carbine in 6.5 with iron sights. It shot great till today.................

A couple of weeks ago I loaded up a bunch of rounds that were 140 grain Hornady SST boat-tail spitzers with 30.0 grains of IMR 3031. I fired an awesome 10 shot group that pretty much took out the orange bullseye at 50 yards. I was a happy boy and was ready to take the old gal hunting.

Today, I tried 120 grain Sierra hollow point boat-tail with 31.5 grain of IMR 3031. I got a group of about 8 inches at 50 yards. I was not impressed. To make myself feel better I pulled the last 6 rounds from my ammo box that were still loaded with the 140 grain Hornady SST spitzers and fired them at the same target at 50 yards. I got a 2 1/2 inch group but to my horror 2 (maybe 3rd started) of the bullets key-holed now That load and bullet shot really well a couple of weeks ago what has changed? Even with the bullets turning sideways it is a decent group for my old eyes with iron sights on a milsurp at 50 yards.

I did some research and it appears the Arisaka rifles were made with metford rifling (click link below to see metford rifling) and as such apparently don't like boat-tail bullets????? One fellow even claimed he got much better groups with heavier 180 grain Sierra Pro Hunters?????.

http://www.google.ca/imgres?client=firefox-a&hs=8Si&sa=X&rls=org.mozilla%3Aen-US%3Aofficial&channel=np&biw=1280&bih=861&tbm=isch&tbnid=Jyena3SFKSHc6M%3A&imgrefurl=http%3A%2F%2Fforums.gunboards.com%2Fshowthread.php%3F21117-Metford-rifling&docid=C90rDxbWn42oiM&imgurl=http%3A%2F%2Fphotos.imageevent.com%2Fbadgerdog%2Fgeneralstorage%2Fpiclinks%2FEnfield%252520Rifling%252520_Medium_.JPG&w=800&h=444&ei=Hgb3UufHM8fuyAGl-4DIDg&zoom=1&ved=0CGsQhBwwCA&iact=rc&dur=2055&page=1&start=0&ndsp=20

Does anyone have any experience with the 6.5 Jap as far as flat base and boat-tail and heavy bullets go. It seems 139/140 grain was pretty much the milsurp weights during WW II. I have been shooting a Lyman 140 grain cast GC sized to .266 with so so accuracy but they don't key hole. I also tried cast 170 grain cruise missiles GC also sized to .266 dia and they were not that great. I can see the rifle wants to shoot I just need to find the right combination. The bore looks decent.

Any solid advise will be greatly appreciate. Thanks

 

[bearhunter]

The Arisaka likes 140 grain bullets and heavier. I've never noticed them not liking boat tail ammo.

I have three rifles chambered in 6.5x50. All have slightly different bore diameters. One of the rifles is a Type I, made in Italy for Japan.

I also have a Thai conversion which doesn't count as it is rechambered to 30-06. I sold a Chinese example chambered in 8x57 a few years ago. The fellow paid through the teeth for it. I have only seen a couple of them chambered in 8x57 that were in decent shape. They are usually beat to hell.

I also have a 7.7 Type 99 and a Japanese made Siamese Mauser.

OK, I have stated what I have and what I can see down the bores. None of them have Metford type rifling. One of the 6.5 rifles has worn rifling that could be mistaken for Metford type. I have also seen many other Japanese rifles that the owners claimed had Metford type rifling. IMHO, the bores were standard type cut rifled or maybe hammer forged but they had sharp lands and grooves about half way up. Metford type has rounded edges all the way through.

OP, I think you have figured out your own problem. Short, light bullets.

One thing about 6.5 Jap bores, they can range from .260 to .270, depending on where they come from. Some of the Chinese made Arisakas used left over barrel blanks from their 6.7 Mauser rifles. They will have large bores. If your rifle had one of those bores, it wouldn't shoot any weight 264 dia bullets.

 

[Muskyhunter1]

Thanks Bearhunter. Looks like I need to slug the bore and check out the proof marks to determine make and origin. I checked thru the cupboard and found a box of flat base 140's so I will maybe give them a try today. Hard to believe a boat-tail design would have that dramatic effect causing the bullets to key-hole at 50 yards. I guess the boat-tail does change the center of gravity of the slug. I still can't understand why it shot so well a couple of weeks ago and now not good at all.

Thanks

 

[bearhunter]

Thanks Bearhunter. Looks like I need to slug the bore and check out the proof marks to determine make and origin. I checked thru the cupboard and found a box of flat base 140's so I will maybe give them a try today. Hard to believe a boat-tail design would have that dramatic effect causing the bullets to key-hole at 50 yards. I guess the boat-tail does change the center of gravity of the slug. I still can't understand why it shot so well a couple of weeks ago and now not good at all.

Thanks

Like I said, boat tail bullets don't make any difference in my rifles. light, short bullets do.

Your rifle shot well before with 140gr flat base bullets. I'm willing to bet it will shoot just as well with 140gr boat tails.

 

[Andy]

Keyholing can be caused by:

- insufficient twist (i.e. too long a bullet);
- undersized bullets; or
- a damaged/worn barrel (typically at the crown).

As pointed out, use of boat-tail bullets is not a cause. As also pointed out, cleaning your bore thoroughly, followed by slugging your bore is Step One.

 

[Tinman204]

I had the same problem loading for another 6.5 rifle that is natorious for bore sizes all over the map, the carcano. my bore slugs at a tight .268" (tight for a carcano )

I experienced good hunting accuracy while shooting 140 grain Winchester flat base bullets. When I switched to 120 grain Hornadays the group doubled in size. The hornadays where very short compared to the winchesters. Lastly I tried some 140 grain BT Hornadays and I was getting 2 tumbling bullets out of every 5 shots.

My thoughts after testing is that a long flat based bullet stabilizes well due to the large amount of bearing surface contacting the rifling. Also I've tried fast burning powders like IMR4198 with great success, it seems to bump the back of the bullet making it fit the bore a little better. (do so at your own risk)

If your bore slugs on the big end you can try some 160 grain .268" Hornadays from trade ex. They are made for Carcanos with sloppy bores and are very long and stabilize very well.