Haven't even had a chance to do a bit of a web search for published data loading this bullet in .303 British.  Neighbor just walked up and informed me I'm being voluntold to develop some loads for this bullet for his uncle whose goats are being pestered by coyotes.  He's already bought the bullets, so there's no point in trying to talk him into using one of my cast bullet designs to do the job.

He would be shooting at less than 100 yards, thinking of where his goat pen is, so I have no intention of trying to get anywhere near maximum velocities; I imagine anywhere around 1800 - 2000 fps should be just fine.

Anyone with previous experience of doing something similar with this bullet in their Lee Enfield?

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Example, I load 125 Speer TNTs in the .30-06 with 44.5 gr H4895. There is a lot of airspace with this load and very light pressures, but very good accuracy.  Hornady website gives guidance in how to do reduced loads on their website. 

There are probably other good powders for these types of loads, but also some that will not reliably ignite, or have flash-overs that can lead to high pressure spikes. Best to do some research on this, especially if you’re loading for someone else. 

I don't think you can load the .303 British case down sufficiently to get that bullet down to handgun velocities safely.

My only experience with light loads for the .303 British was using surplus 123 gr. .3105" bullets designed for the 7.62X39 and it was difficult to those velocities down without using a filler of some sort.

Well, being as the bullets have already been purchased, that's what it's going to be.  If he would have asked first I would have loaded him up with the WFN design target cast load I had Ron at Accurate Molds cut for me.  His moulds are incredibly good, the price is more than reasonable, and you can pretty much have whatever you want in the way of measurements and design that you specify.  That 180 grain bullet trundling along at 1200 fps or so would do just fine.

I very much doubt these handgun bullets are going to completely come apart on leaving the barrel, but if they do I'll certainly see it in the very first shots.  As I said, I'm not going to try and make these loads screamers - pretty much anything centerfire is going to kill a coyote if it hits them in the vitals. 

I've never hunted coyotes for sport; I usually admire the way they get along with their lives.  But the times I have shot them because they crossed the line, I've shot them with what was handy, and the average one weighs less than our WPG bird dogs weigh.  Take away the fur coat that makes them look bigger and they don't measure much side to side; the adults around here probably weigh about 20 - 25 lbs on the average. There isn't enough to them for any of these bullets hitting them in the ribs or shoulders to be just a "superficial" wound.  Cue the Black Knight: "It's just a flesh wound!"

The only time I used fillers was when Ken Mollohan schooled me on the use of Super Grex when he was helping me start casting for my Lee Enfield back in the early 1990's when there weren't forums - just Fidonet. I was having trouble sorting a decent target load out.  Super Grex disappeared from the market about that time and I switched to trying cream of wheat.  Then I decided changing other things about my loads would be far less annoying than playing with fillers, and there hasn't been any of them on my reloading bench since then.