GTS break barrel

[Tony.T]

Absolutely fascinating- keep the progress reports coming please...

[bozz]

Ace nice to see you are still managing to put a bit of time into both newborn's, the rifle will all way's need to come second, enjoy the little one while you can, it only feels like yesterday that we had our first but he is now 26 his brother 24 and there sister is now 21. Where oh where did the years go. Take care and enjoy it while you can. Graham.

[TonyL]

Cheers for the update, Dan.

Sounds like you have more than enough on in getting that work, family and play balance in harmony at the moment. Take it easy.

[cooper_dan]

Thanks for the messages. The wee man is #1 in my life right now. Most break barrel work is happening during his naps!

Opened transfer port out to 2.8mm and checked over chrono today.
Exact = 4.91 ft-lb
Express = 4.92 ft-lb
RS = 4.92 ft-lb

I'm liking how equal the different weights are. But it would be nice if the output was a bit higher! More experimenting needed. Either going to open out the port a bit more, or have another look at the piston seal bore and fit. Will sleep on it.

[Shed tuner]

Thanks for the messages. The wee man is #1 in my life right now. Most break barrel work is happening during his naps!

Opened transfer port out to 2.8mm and checked over chrono today.
Exact = 4.91 ft-lb
Express = 4.92 ft-lb
RS = 4.92 ft-lb

I'm liking how equal the different weights are. But it would be nice if the output was a bit higher! More experimenting needed. Either going to open out the port a bit more, or have another look at the piston seal bore and fit. Will sleep on it.

that is not going to be a port problem. A 2.8 mm port will (just) support enough flow for 12 FP.

My guess is your pistons are accelerating way too slowly, so the pressure in turn builds way too slowly, and kills power. You could either lighten them, or get stiffer springs (the total energy when compressed need not be higher, but they need to get up to speed quicker).

Or you have a massive air leak someplace, but I figure you'd have sorted that...

[cooper_dan]

that is not going to be a port problem. A 2.8 mm port will (just) support enough flow for 12 FP.

My guess is your pistons are accelerating way too slowly, so the pressure in turn builds way too slowly, and kills power. You could either lighten them, or get stiffer springs (the total energy when compressed need not be higher, but they need to get up to speed quicker).

Or you have a massive air leak someplace, but I figure you'd have sorted that...

Acceleration is definitely a bit slower than planned. about 20% less than my TX for example. Good thinking. Should be easy to test too as as I can just run the single working piston, half the weight and double the acceleration. Unfortunately I don't have any stiffer springs, so might need to do some spring shopping.

I've had big air leaks from the breech seal, and the breech plug so far. Both of those are sorted, but I'm not ruling out piston seal issues just yet

[cooper_dan]

Think it's about time for an update!
So the break barrel was put on hold for a bit. The first prototype (up to about 10 ft-lb) finally let go and made a mess of its cocking linkage (due to a design oversight on my part!) And at the same time we had a baby so life changed a bit!

However in the last couple of weeks there has been some progress. A new cocking linkage has been designed which should be far superior to the first one. Parts for that are in production now and should be 3 weeks or so before I get them.
In the meantime I need to sort out a stock. I reckon you need all the leverage a stock provides to really test the limits of the cocking linkages.
Unfortunately my 'prototype stock' fund has just been wiped out by an unexpected car bill

So I've had a dig around and found my old TX200 frankenstock. With some modifications I think I can get the prototype to fit. Then do some major reshaping to get it looking sensible.

I've also re-worked the piston (in CAD only at this point) which brings the dynamic mass from 400g down to roughly 280g. This should really help give the spring an easier time and give an efficiency boost (400g was just too much to accelerate properly).