Marlin 336 30-30 load info

[Newtire]

Shot some great loads in my 336 20" RC microgroover this weekend.

They were:
Lyman mould 311440 and Saeco #316 sized to .310" water dropped WW and Felix-Lube.

Primer=CCI 250 mag. (not the first choice in primers for this load I know!)

Powder=SR 4759 @ 17.5 grains and then @ 19.0 grains.
The 17.5 grain loads were just so-so but the 19.0 grainers were very accurate with both boolits.

Only shot at 50 yds. so need to take these ones out to the 100 yarder and see.

I had some others sized to .311 but the 336 wouldn't digest them and had to shoot them in the old '93 which liked them.

[pls1911]

While it is possible that you have an unusually tight chamber in your MG 30-30, I think it's unlikely that the .311 sizing is your problem. After heat treating, I regularly seat gas checks, then size & lube in a .312 die, rarely touching the sides of my cast slugs.
I load and shoot slugs for the major designs in my newer and very old Marlins with the following considerations:

If yours won't fully chamber, you're likely engraving the bullet on the rifling. Try seating the .311 slugs a little deeper for the microgroove barrel. I find that my very hard Ranch Dog profiles (optimized for Marlins and BIG meplats) need to be seated about 1/16" deeper (shorter OAL) than the other 30-30 FN slugs from Lyman, RCBS and SAECO.
The newer Microgroove barrels have VERY short throat/forcing cones, and are therefore more sensitive to "close tolerance " ogives on bullet noses.
I adjust the RD's to just kiss the MG rifling, and they're deadly accurate.
The flat points from lyman, saeco and rcbs are more bore rider (nominally .301-ish) and work wonderfully when crimped in the crimp groove. (You'll see a tiny shoulder at the base of the nose section which is still just under groove sized on these bullets)
The pre-microgroove guns (pre 1953-ish) in 336, 36, and 93's, and all Winnies in my experince are much more forgiving in this area.

[Newtire]

If yours won't fully chamber, you're likely engraving the bullet on the rifling. Try seating the .311 slugs a little deeper for the microgroove barrel.

I only resized the boolits and then they chambered fine. Seems the 336 I have is just tight chambered. Like you say though, the older '93 is a little more forgiving.