PP a two groove 303 Brit. Need advice.

[A pause for the COZ]

I have a two groove 303 Brit. .303 bore and .317 grooves.Chamber is .316
This thing shoots jacketed loads just fine. Accurate enough for my tired old eyes any way.
But it refuses to shoot cast bullets.
When I say refuses I mean refuses. Every load I have tried with varying sizes and bullets. End in Key holes if they hit the target.
One bullet I did try that did not keyhole but still patterned 12" at 100 yards was a boolet that drops at .316 I tumble lubed them and did not size. I had to seat them so deep just to get them to chamber. Yikes!!!
I did a little reading and I guess this was a war expedient way to put out some barrels. Cutting wide and deep two grooves.

Any hooo. I want to try PP this old girl to see if I can get a load. But I have no idea where to start.
What size should the bullet be before patching? What size should I end up with?

[docone31]

If you size to .314, then wet wrap two wraps of lined notebook paper, you will get .316-.317.
I use start load data for jacketeds of the same weight, no crimp, and use auto wax for lube.
I use a cigarette roller for the wet patches.

[A pause for the COZ]

I think I can do that. I have the 314299 bullet. Maybe I will just patch them as cast.
Off to the basement!!!!

[Nobade]

I think that is a mistype - shouldn't it say .304 rather than .314?

-Nobade

[Hardcast416taylor]

You didn`t mention what charges of what powders you are using. Start with the starting jacketed bullet load of a similar weight. Adjust the loads upward slowly. I have had fair luck with a RCBS 180 gr. FN .30 cal. I wrapped with wet copier paper as cast. When dry I light lubed with JPW and loaded them.Robert

[docone31]

I have wrapped as cast at .314, or, I have sized them to .308, then wrapped. I got equal results with both.
Once the crud is out of the bore, the groups tighten up. The barrel gets hot fast though. The .303 is a real sweetheart to wrap. At least I think so.

[303Guy]

I've never had key-holing but test tube results show a lot of rifling shear with two grooves. On one the two driving faces are too rough and they cut through the patch and core. With low enough velocity/pressure, they get through the bore with the patch just cut. Hard cast don't shear but I haven't range tested them. To fit a boolit in the throat it might be worth trying a bare bore-ride nose section with a patched driving band section. The nose should just enter the bore for nose support with the patched bit contacting the taper of the throat. Tough paper may be called for to withstand the cutting of the drive faces.

It may be prudent to go lower rather than higher in powder charge for lower pressure. Perhaps a slower powder with more of it. Powders like Varget and W748 can be loaded quite low and still burn clean but I'd use Dacron to position the powder.

The thing with both my two-grooves is the shape of the throat. They start at .318 and taper to .304 with a 3° included angle. This makes boolit fit difficult. I made a mold to match the throat taper and test tube results were encouraging but the .318 bases get squashed out of shape as they swage down to .304. I did get some accuracy with Lee 311 180 boolits patched to the ogive with heavy tracing paper (.004"). It shot OK out to about 40yds before they went which ever way. I didn't try slowing them down.

Oh, you can expect groove diameters up to .318 with two-grooves with .304 bores. The grooves are narrow, taking up 20% of the bore.

If your boolit is under groove diameter you can use wheat bran as a filler which seems to form a sealing wad and prevents gas cutting. For light loads it doesn't raise the pressure all that much but for 'normal' starting loads one must reduce the powder a bit to compensate.