I finally got around to determining my land-to-land bore diameter is 0.323 (finally got around to slugging the chamber).  It is a High Wall in 32-40 made by K R Breisen of Warsaw, NY.   

I've tried many cast bullets (that I've been able to find for sale on-line).  I've found 0.322 bullets stink and 0.323 cast aren't that impressive. I've been using various loads of IMR 4227, various bullet weights and shapes, using 13.5 grains and plus/minus .5 grains at .1 grain increments.  Even bought a breech seater, I really haven't seen much improvement with breech seating.

The only source for a 0.324 cast bullet was some cheap ($26 including shipping) 170 grain bullets from "Hunters Supply". I haven't tried these yet...

I think my twist rate is 1 in 13 inches or so (counting turns pushing a patch on cleaning rod).

Questions/advice seeked:

1. My "internet education" tells me that maybe I should be using a cast bullet 0.001 over bore diameter. WHERE DO I FIND SUCH BULLETS (0.324 cast)?   

2. Any caution I should have loading jacketed bullets? I find lots available that are 0.323 (e.g. 8 mm bullets)

Thank you in advance. if I don't reply its because I don't have much time to internet during day...AND I AM A ROOKIE so help me stay safe 😂😀

Thanks!

And yes, bore is fine, shiny, and it's a beautiful rifle (heavy target barrel). But best 100 yard groups are really in 1.5" to 2" range. Using a 20x Lyman tube scope. Breisen made a nice rifle, but trigger isn't that great for a target rifle (6 lbs). 

My Winchester 52's .22 rimfires outshoot this dandy of a "target looking" 1885 High Wall. Even my M1A's shoot as good... I'm looking forward to changing that!

Timber
If you are new to shooting single shot rifles, 1.5 to 2 inch groups (3, 5 or 10 shot groups?) are not bad for your initial shooting session(s). Your bullets don't fit the rifle and unless you get bullets that fit, it isn't likely to shoot any better. With a proper fitting bullet, my recommendation would be to up your powder charge to 14.0 grains of IMR 4227 with a maximum of 14.5 if that's what it takes to get good groups. Your High Wall rifle can certainly handle such powder charges.
With a 1:13 twist your rifle should stabilize 200 grain bullets but I recommend about 190 grain approximately 1.0 inch long if a blunt nose and cast 1:20 or 1:16 until you master shooting that rifle. Commercial bullets of .324 are certainly a problem. I poked around online for a while and found nothing worth considering. I would cast you some to try but my largest diameter 32 cal mold is a full thou smaller than you need. Perhaps you could plead your case here on this forum and another member might be able to cast you some .324s for you to try?
For a long term solution, I guess is you will have to look into casting bullets for that rifle. A possible alternative might be to purchase a suitable mold for your rifle, contact one of the custom bullet suppliers and have them cast bullets for you.
Somebody or other wrote a book on shooting traditional Schuetzen rifles. You might want to take a look at it. It's available on this web site. Contact Laurie Gapko the ASSRA Archivist at: secretary@assra.com
That old Breisen bench rest rifle should be a shooter and with a good bore should easily last for the rest of our shooting career.

In addition to what the others said ( especially about casting your own bullets, that's pretty much essential ), I'd have a good single shot gunsmith take a look at that 6 lb trigger.  I can't imagine that it left his shop that way.   Does it have set triggers?

Chris.

Wow! THANK YOU ALL! 

Seriously, that is good stuff y'all have and gives me lots of ideas and paths.  Thanks for confidence on upping powder charge. Thanks for bullet information.  Trying to leave custom mold off list for a little while (I don't have much free time yet, work and commute to go that level YET).

Didn't know the breech seating trick (push bullet out and measure) described either.

And yes, 6lb trigger pull on a beautifully done target rifle is PERPLEXING!  Fixable, but surprising.

Again, THANKS for taking time out of your day. I'm not in a rush with this, but trying to take paths of least resistance and cost for now.

Question - Since Mr. Breisen knew barrels and barrel making, I was wondering if he intentionally sized the bore to take advantage of the variety of jacketed bullets for 8 mm? Or, just to make a novice have to go through learning pains instead of instant results? 😀   

Well...I don't know how to post a picture that's for sure....

I suppose it's possible that you can make a mistake measuring twist rates and getting to fast of a twist but, more likely, because of slippage, the error is in it being to slow.

Ken Breisen, made barrels of any twist rate that was requested. My local slug gun shooters used him all the time, to suit their fancy in groove diameter and twist and I bought one of his last 44 1/2 actions.

Even if it happens to be a 15 twist, you can successfully shoot a bullet 1.16" long. Ron Long made that length bullet, just for the 15 twist.

This is a my match result at 200 yds using that bullet with that same 14.8 gr load and the 16.5 gr 100 yds group.

Frank

Frank that is yummy looking scores and target! That's the stuff right there! Heck, time to get a home equity loan and get all the right goodies and quit my putzing around!

Yes, I'm not confident of barrel twist rate I stated.

Thanks for sharing, that is very inspirational.

If there is a threaded hole, behind the trigger, it's a single set trigger. If not, it's a plain trigger.

Frank