I'm shooting a Browning 38-55 Traditional Hunter with fixed ammo.
I've tried all the recommended loads and reloading advice from the forum using the Saeco 300 gr. spitzer bullet.  My groups are not great; 2+in at 100yd and
4+in at 200.  I'm shooting better groups with my 60 year old .22cal BSA martini 12/15.
My question is, can I or should I try breech seating using a factory chamber?  If I can does anyone know of a bullet that would or has worked in that rifle?  The bore is .376.
Thank you for any and all help 

I have 2 of these fine rifles and both will shoot very close to 1 inch at 100m..  I use cast pills that are .377,  another that is .378, and have used both .379, and .380.
I use 9 gr Uniq with both std and mag primers, depending on the temp,  and they will all group about 1 inch, some times even clover leaf..
Using browning tang sight and Lyman 17 with shaver inserts..
In fact I will leave for the range for a Ram Bash taday using one of these rifles...

britt had the earlier Winchester version of your Browning 1885 Traditional rifle, I found that it shot the 255gr Saeco actually about 257gr cast from 25:1 lead/tin alloy bullet much better, could never get the 300gr Saeco to shoot near as well. My best load with the 257gr Saeco was 23 grains of H4198 and WW standard large rifle primers, bullet seated just deep enough to touch the rifling, came close to outright winning some CBA matches with this load and rifle. 
I also used a older Hoch tapered 295gr .376" bullet with a load of 22.7 grains of Vihtavuori N120, Federal Large rifle primer, bullet seated about .250" deep (photo of bullet and it seated in case), this bullet shot much better than the Saeco 300grain bullet, have no idea what the difference was.

My rifle shot very well off the bench at 100 and 200 yards, I'd say it averaged 1.25" at 100 for ten shots and under 4" at 200 yds and when I did my part as small as 3", understand when I shot that rifle often it was in CBA with a 24x scope and on score targets.

Good luck with your rifle, I know they will shoot you just have to keep after it, bought mine to hunt with originally and when I started to reload for it and tried different bullets and powders I was amazed how accurate it was, been sorry every since I sold it, but the CPA Addiction hit me   and that was the end of the W1885.

MIKE-T

I'm sure you can order a Hoch they are pretty much a custom made mould, my mould has a base band diameter of .376" cast from 25:1 alloy. ( (You need to Login or Register to view media files and links) )

The Saeco 255gr is just the short version of the 300gr it is still listed on the Redding/Saeco web site, and as I remember the base size on the 255 was the same size as the 300gr bullet. Do not have the actual base size since I sold both moulds with the rifle. 
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Buffalo Arms has the Saeco moulds, they are listed as .378" Diameter
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britt all my 38-55 bullets were/are shot as cast, pan lubed.

I'm actually looking for the short Saeco 38-55 225gr version for a youth project.

MIKE-T

britt I'm sure you can find someone to make a mould to fit your rifle, do a chamber throat cast/swage and send it to whoever you select to make your mould, I really like the Hoch, but Paul Jones also builds a fantastic mould as does David Mos.
A shooting buddy uses a version of the PJ mould #38003 300gr Chicken bullet (his is sized & tapered to fit his rifle, breech seated) in CBA competition and he does very well at 200yds.

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Good luck on your quest,  
MIKE-T

That Saeco mold is the one I use for fixed smokless powder in my CPA.  What I hear rather than what I know guys tell me the Starline 38/55 brass is thinner wall and will accept bullets that the others won't.

Something to the effect of Winchester Brass actually drawn for .375 Winchester just trimmed and stamped different while the Starline being a bit thinner accepts fat bullets better. Do a search over on the Marlin Collectors forum and a whole lot on the topic.

Saeco 571 with W-W brass is fine in my CPA. loaded fixed there is no buldge or sign visable were the bullet is seated in the case  However I do use a Lyman M die to expand the neck and flare when loading.  That's about essential in any cast bullet fixed ammo load.  You can also get the M Plugs custom sizes to suit your particular bullet. .382 is pretty fat though. A cheap way to find out would be to get a custom Lee bullet size die. They push through from the bottom using your loading press.  Cut it down a bit and see if the problem goes away. You could use a harder alloy too which would throw a smaller bullet.

Of course the next question is expanded neck will the cartridge still chamber. Thing about 38/55's is there is a lot of varation in barrels and chambers.  Old guns were mostly 380 bore while new made barrels most made from .375 blanks. .375 being a more common size for .375 Win 375 H&H  and other modern cartridges the barrel makers just make that size 

Weather has me behind on casting but if I get a few good days next week will have some 38's out of 3 molds,  Saeco, LBT and Hoch I can mail you samples to try fits. Will also put the mike on my M die plug just to see what size it is.

Boats