Reluctant to rocket

Full sized barrel makes a lot of sense … at least to eliminate some variables.

I will look out for one locally, they aren’t so easy to find around here, I had to drive 30 miles for the purple one, which is ridiculous.

There might be a halfway house.. somewhere around 150 litres which would maintain my clearances

Nick, I have never seen the book you quote so I still dont know the dimensions of your system.
I do know how important is is to have the right formula,
If it at all possible to give us the size of your fire box, burn tunnel and riser that will help eliminate the most basic factors that can hold back a stove?
Also can you confirm you have insulated  the fire box and burn tunnel.
PS I think Thomas  meant a single load will last 45 minutes,…. you can burn it all day long if you want to.

You should be able to get an oil barrel from any service station  garage for free, I have videos showing how to remove the paint and how to repaint.
My own 6” J tube will happily  run at around 400-500c above  the riser.

Ah .. thanks James (fox?)  - re burn time

Attaching image of dimensions

I am of no help, but it is heartening to watch experts troubleshoot something they are passionate about.

Bravo folks, I hope to see this rocket purring.

Fire box and burn tunnel,

Not as well insulated as they might be, I have 1 inch of ceramic fire blanket on top of the burn tunnel (as a saddle right through), but the sides are just cobbed in, the feed area is not well insulated, I plan to ‘backfill’ with perlite once I know the damned thing works.

Inside the barrel, the (brick) bottom of the riser is not insulated .. ‘the book’ didn’t specify what to do here

See pic

There’s definitely scope for improvement here, but my gut feeling is it doesn’t account for being so short of the mark

Everywhere I hear, “ oh mine melts diamonds” .. which is what makes me feel something is wrong .. I would settle for 500f at half throttle

Well I have build a few j tubes and from my first hand experience, I can tell you the dimension and insulation  do make a big difference to performance.
I understand that you are not too concerned about absolute max performance however, these type of stoves are designed and are required to work at very high temperature.
This is the whole concept and why these stove work so well but you need to build them to a known spec.
I am not saying you have not followed a book or you have done something wrong but to solve the issue we need to check the basics first.
There are dozens of folk who post on this forum with teething problems, normally the issues can be solved but we really need every detail as there is not that much leeway between working and not working!
For example I dont know how you built the riser or what percentage of perlite you used?
How have you designed the 8” pipe to go up a 10” square chimney, is there any insulation in the outside chimney?

The riser was made inside a 350mm diameter steel former (0.7mm mild steel) .. with a standard 200mm ID duct pipe forming the core, I wrapped the inner pipe in a sacrificial layer of corrugated card to facilitate removal after the first firing(s)

The refractory mix was to Lawrence Fines recipe, based on his success and experience .. it is approximately 85% perlite, 5% fire clay (slip), 5% furnace cement, and 5% Waterglass (sodium silicate 40%), mixed until light snowballs could be formed in the hand, thrown and caught intact. This was then tamped/compacted in 4” layers into the form

The final fired result is quite delicate, somewhere around double the density of expanded polystyrene … fairly sure it would float (without its steel jacket)

It’s basically perlite .. compacted about 20% and stabilised, within a mild steel outer jacket

The inner (galvanised) former core was remove after the first (and only) rocketing burn .. I think the soot went the way of the zinc … or perhaps my temperature surge was a brief metal fire

Lawrence is of the opinion that the rough inner surface is a *good* thing, and that an accumulation of fine ash is also a positive, he has an awesome stove to back it up

Pics attached, I did don’t think I got any of the mix itself, it was dark and raining … damp and dirty perlite forming clusters of a dozen or so grains.

The interface between the round (8”) pipe and the ‘square’ 10” (I’m guessing) chimney is a simple register plate, cut from a washing machine side panel, the 8” pipe pokes 6” through the plate and points it the general direction of the square ‘funnel’ … there is a 45 degree ‘dog leg’ inside the chimney.. which I understand is normal.

Again, the seal is imperfect, pending a working stove, but there is no leakage there, which perhaps tells us something… I.e.  the chimney is sucking harder than the barrel is blowing

Is that wrong ?

The (existing, masonry) chimney is not insulated, no, never has been it’s always drawn well.

Nichrome tumbleweed …  ‘glow plug’ igniter/sustainer/catalyst  idea …

Nope, no detectable difference .. still ‘hits a wall’ at 175c (actually the laser IR says more like 200c, but I tend to believe the bimetallic contact thermometer more .. or at least that’s the benchmark I’ve been working with)

Just going to burn it for a good few hours now, a couple of logs at a time and see what happens (and see if I can get some heat into this mass)