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I've got a Marlin 1894 Microgroove Barrel in 44 Magnum that has had an ongoing leading problem.

I'm now using some 0.432 Shellhouse boolits that fit the bore which slugs at 0.4305. I initially tried bullseye as I had on previosly tried smaller diameter commercial cast bullets and always got a ring of lead in the throat and evidence of lead on the cylinder walls. I presume this to be evidence of gas cutting. Tried a slower powder, 6 grains of Alliant Unique with noticeably less leading than bullseye but it's still a problem. Should I up the charge, lower the charge, try a different powder or try something else.

I know the stock answer is to cast my own, as commercial are too hard but the investment isn't worth it for the once a month outing to our club's turning target session which I use the gun for.

You have identified the key cause, too hard an alloy.

Hard alloys really only work if you have perfect bullet fit, you say that your bullets fit the bore but when using hard alloys they must also fit the freebore, in fact this is the crucial fit.

A freebore slug/cast is essential so that you can then choose a design/size to fit the shape/dimensions of your freebore.

Are you using magnum or special cases and do they extend to the chamber/freebore "step"?

What do you mean by "cylinder walls"?

I'm using magnum cases and have loaded the boolits to the maximum overall length that will feed/fit on the lifter - 1.657". I made up a dummy round and gradually reduced it's length untill it would chamber in the barrel without the bolt in, this measured 1.782" so I am a long way from the chamber/freebore step.

I believe you can modify the lifter to take a 0.100" longer OAL round, but then I'd be crimping on the lube groove.

When I say cylinder walls, I mean the sides of the chamber. There was evidence of greying forward of where a cartridge case would extend. This wasn't powder residue with the effort it took to remove.

Correction, dummy round maximum OAL to fit chamber is 1.710" with Shellhouse boolit. It was 1.782" with a Dodgy Rog 429667. Either way would still be crimping on the lube groove.

Greying isn't an issue usually, so long as it isn't cumulative it is not a problem.

It is hard know how good your bullet fit is with out a freebore/chamber slug/cast, there is more to fit than just length.

It isn't just about the length to fit the freebore but also the diameter to fit the freebore, that is more important than reaching out the the lands.

A gap tween the case mouth and the start of the lands is a fouling/leading trap which sizing the the freebore diameter helps a lot with. If your freebore diameter is large and you cannot get a bullet of a suitable diameter, then the only other way to overcome the problem is a soft alloy especially in low pressure rounds such as the 44 magnum.

Thanks Adam. So it looks like I'm stuffed unless I decide to make the investment in casting my own after taking a chamber cast. Plus it would be in the back of my mind that Beagle of beagling a mold fame at cast boolits gave up on the micro groove barrel in 44 magnum.

I have asked Shellhouse what size their boolits drop from the mold. That might be an avenue worth trying if not I'm most probably not going to be able to source any commercial boolits that fit in this country.

You really need to take that chamber/freebore slug/cast and then you will know what you need and then you will know whether what is available is any good, at the moment you are guessing as to bullet suitability.

If you go the casting route then Tom at Accurate will cut you a mould to your exact specification at no extra cost.

Thanks, I'll give the Texas Mac article in the library another read. I got a headache last time. Why can't you just wack a soft lead ball into the freebore and measure that impression?

Because as it is unsupported it is unlikely to give an accurate reading as it won't fully obturate.

Flowers of sulphur is a quick and dirty method, good accuracy but fragile, I usually mix 3 parts flowers to 1 part graphite powder and this makes it a bit more robust.

Just to add micro grooves can be finicky feckers, I have never had an issue with them with well fitting soft alloy bullets but I know other micro groove owners who have lost the will to live trying to get them to shoot cast.