Polyfill on cast loads?

I am now using lyman 314299. Bullets drop at .3145 and are around 200gr. I was wondering since the 155gr boolit I shot that was .311 after being sized did not hit paper at 50yds, will polyfill help with accuracy with the 200gr? Thanks!

What cartridge are you shooting? (You have probably mentioned it before, but they stopped making replacement parts for my rememberer a long time ago.) Have you slugged your bore? Any question about relative bullet diameter is moot until you actually know what you're working with. And you have to measure your slug with a mic, not a caliper. If you've never slugged a bore, go here: http://www.castpics.net/subsite2/How...the%20Bore.pdf

When you know what sizes you are dealing with, then it will be much easier to answer your question. In general, I do not advocate the use of fillers for a number of reasons, the first and foremost being that they are usually not necessary if the proper powder is found and used. Sometimes they are the only way to tighten up groups, but as I shoot mostly .30 & .35 cals, I seldom have found a need for them. My focus is hunting, not target loads though, and that does make a difference. I know that with larger bores, especially the .45-70, .45-90, etc., fillers can often make the difference between a shotgun pattern and a group.

When in doubt about a new load, I will shoot at a target centered on a 4'x4' backstop, using newspaper or brown paper to cover the backstop so I can see where the bullets are hitting and if they are actually grouping, even if far from POA. That's how I discovered my worst cast group ever (38" 5shot 50yds), and a fairly good one (1.25" 5 shots 100yds) that was 20" off POA. You might actually be shooting decent groups and not realize it. Back off to 25yds and move out from there.

fillers are generally used as powder positioners.
they keep the powder against the primer for better ignition consistency.
the fast shotgun [bullseye-2400]powders are usually not position sensitive, the medium powders such as h-322 up through 4064 usually do much better with fillers as it keeps the extreme velocity spreads much lower, the slow powders [h-1,000] usually fill the case to 100% or thereabouts and don't need fillers either.
the majority of my very most accurate loads use a medium powder [and sometimes a pistol primer] and a filler.
but i can usually come fairly close with another powder and no filler and that accuracy is sufficient for plinking or informal target shooting.
if you use a filler make sure it touches both the powder and the base of your boolit without a gap.

I am loading for my mosin nagant, 7.62x54r. I have slugged my bore at .314. When I tried to slug it with a .312 boolit it goes in easy and then drops through about halfway through. That was my indication I needed a bigger boolit. I have IMR4198, 2400, and unique. I shot two 5 shot groups at 50 yds and got both groups to have touchong holes. Not bad for my first cast and using polyfill. Thanks for your input on the subject!

You do need a bigger bullet, the question is how much bigger? If all you have done is to drop a .312 bullet into it (How do you know that was the bullet's actual size? What it said on the mould's package? Caliper? Ouija board?), that is not "slugging it to .314". Follow the link above for instructions, use an oversized bullet like an 8mm or hit a .30cal end on with a mallet to bump up its diameter. Then measure it with a micrometer for some real numbers and we'll be able to give you some useful advice. There is no rifle out there for which it is more important to get an exact measurement than a Moisin Nagant. Groove diameters in them can vary from .307-316". Only a caster can make many of them shoot decently because the optimum bullet size can vary so much from one to the next.

With a little attention paid to the details, you should be seeing accuracy like you got at 50 out to 200yds.