Metford rifling and the patch ????

So my Dad bought this 6.5×50 Japanese Arisaka 1927 type 38 rifle about a year before he passed , so it's been sitting about 5 yr and who knows how long before that .

I don't post often but I've been patching for several years with good success following the basics with my 50/50ish pistol alloy . I even killed a mule deer with a 200 gr PP in and 06' .

The Arisaka bore was a little dark and some scrubbing with brass brushes and a few passes with steel wool knocked most of the gravel out of the bore leaving a little bit of sticky not really drag or bind with a patched jag . Slugging showed me .258×.268 more or less but it would chamber a .278 as far out as .375 from the case mouth in formed 35 Rem . It's only about .280 in proper Norma brass but it touches the neck enough to scrub soot off .

Bare cast with a 270-140 FP NOE , 280473 and a .277-130 PC left an impressive even coat of gray haze with a couple of goobers . Accuracy ranged from palm sized with the NOE to 14" with the 280473 .

I proceeded with SOP and assorted bullets a 280473 sized down to .265 which wiped the grooves and the GC shank step . It shot about 4" with 9.9 Unique at 50 yd with the 280473 and just 46-48" with the Loverne 266473 both sized .265 .

Moving on , I expected very little with 160 gr start loads of H4831 at 35,35.5,& 36 gr . I was instead rewarded with about an 8" triangle at 35 gr and at 35.5 a roughly a 4×6 football shaped group . 36 gr delivered more or less point of hold for 2 shots about 3" and 3 off in parts unknown . I did get some confetti a bit of land marked and what was a still folded base . Mostly just poof dust .

With that known , I dry wrap , folded tails , from some old school calculator tape . The goal was to clean up the bore not shoot groups but if you're doing it you may as well do it right . I should add that the trigger is 2 stage of about 3.5# of take up , 7# to break , and the sights leave a little something to be desired . But I feel like my hold is good and follow through isn't horrible . The last part is that this is Metford rifled so I doesn't have a hard edge to cut patches in fact I can see where if the patch doesn't spin or parachute off and stays intact it could ride along quite a ways .
I'll try to get some pictures of the bore as is with a picture of what I started with .

Any experience with Metford rifling or other no hard edge polygonal rifling ?
Am I headed the right way when I go to green bar paper ?
Should I write a whole process of getting there like it's new ground ?

Try patching against the rifling so it wants to come off instead of twist tighter.
May help.

Bright Idea Alert

258 bore
268 groove
278 300 into bore
Hmmm
Maybe try patching 268-270 with lined note pad 2.5 thou or 3thou paper.
Fill the free bore /leade up.

The act of forcing it into the bore could/would/should size it to bore size.
There will be no support for a bit but the paper jacket.

I would say you should get a clean powder burn and pressures may spike a bit from suggested loads.
But I’m no guru on how powders are going to react.

Just a thought.

Maybe wrap some copper foil around them.
Wonder if that has been tried.
Or maybe a long copper cap to put them in then taper the front over to a point..
:Bright idea:

I tried some "fill the throat" naked cast in the 280473 with a check . Results were ......less than enthusiastic . JW Phillips helped with some formed brass and coated 277-130s that might work with a check . Those and the NOE bullet were seated to full bore seal or at least a full contact circle on the nose .

With things as they are here now it's unlikely any of those new fangled copper clad bullets are available in a once common .268 dia .

I think they were wrapped right hand .......I have to reverse the angle as the tape paper wants to curl around as is . Shouldn't be too big a deal , I'll have a .272 sizer die in about 2 weeks . Ammohead is making me one but needs some .278s to test size .

I have a 7mm-168 I could run through the .278 push through sizer lubed lots of bearing surface .
I have the sister mold to the 473 with standard lube groove and plain based I could size it .265 ...... I suppose I could try the 473 unsized its really only biting the bottom 4 bands .......

I kind of thought treating the Metford rifling like Micro groove would be the ticket .

Not quite Metford rifling but a very worn Enfield rifled bore. I loaded it to the minimum to disintegrate the patch before heading out into the field. It shot great until the bore polished up and the patches no longer disintegrated. I was using H4227 in the 303 with 208gr smooth sided fairly soft alloy boolits, sized to fit an unsized neck and fill the throat. So What I was finding was that with the rounded rifling, I needed enough pressure to disintegrate the patch. Once the bore polished up I had to increase the charge. So for me the optimum velocity-pressure worked out with the faster powder. I haven't tried a rifle powder in the rifle so that's all I have. Don't forget that the Martini Henry does not have sharp cutting edges and that fired paper patched boolits.