GTS break barrel

[cooper_dan]

Another weekly update (do let me know if this is boring and I'll do less of them )
I've now mostly fixed the cocking linkage to the point I can sit and shoot the thing as much as I want without anything breaking. Probably had about 100 shots this weekend.
So now I can start testing in earnest! First job is to get the power up to something reasonable.

The stroke has been upped to 63mm (38.8cc volume). Unfortunately I only seem to own quite soft springs (i.e TX200 mk3) which isn't ideal for this bore/stroke. Muzzle energy has stalled at about 4.75 ft-lb @ 20% efficiency.

Next step is to have a final tweak to get to 65mm stroke and fit a higher rate spring (maybe something like a Titan #7 or an OEM equivalent from something). Then start slowly increasing TP diameter to see where the sweet spot is.
Hoping to get up to around 10 ft-lb, then I'll start balancing the masses and see how much recoil can be removed.

[TonyL]

We'll never tire of these updates, Dan, so keep them coming.

And good luck with the continuing research and progression.

[tom24]

Love it
Please keep them coming
atvb tom

[MartynB]

Likewise Dan, this is very interesting for us that are interested in the subject

[nick-nic]

Keep em coming Dan, good to see how things are progressing.

[cooper_dan]

It's that time of the week again!
So this weekend I was going to start opening up the T.P but I changed my mind. Instead I decided to use this quite inefficient version of the action to develop the counterweight buffer a bit. This is one of the most important parts of the whole action. Get it wrong and it would result in damage to the gears and racks.

The thinking was this: currently there is enough spring in the action to provide about 27.7 ft-lb of energy to the piston. I'm hoping the action will end up being maybe 35% efficient, which would give 9.7 ft-lb with this spring. However it's only actually about 18% efficient (5 ft-lb) because it's being throttled by a small T.P. this means there is a lot more energy ending up in the buffer then there should be. Perfect time to make sure it works!

Long story short, the buffer is now working well and using a BSA breech seal. The end intention is to have the buffer and breech seal be the same part number to simplify spares, and it's looking like that's going to work out quite well (although there is still lots of testing to do).

I also had a bit of fun with my new phone camera which records in slow motion. Made up a sling to suspend rifles in and allow them to move freely. Check the link to see the video. It's not a serious test as there was too much wind and the triggers were all set differently, so just a bit of fun. First is a short stroke MK3 TX in a walnut stock. Second is my HFT TX in target stock and MK2 piston. Third is the bare action break barrel.

New video

[RobF]

If you have an old fashioned cable release and don’t mind drilling a trigger guard it will solve that .


Interesting seeing it progress

[Shed tuner]

cool...

[cooper_dan]

So it has been a month since the last update, and not too much to report. Day job has been hectic, and most spare time has been spent with the baby (now 4 months old!) and enjoying the recent spate of nice weather with the family.

Break barrel progress has mostly been 1 step forward, 2 steps back unfortunately. Had some recurring issues with the cocking linkage and some strange wear on the pinion gears, both of which have put the power issues on the back burner. This weekend I finally started opening out the transfer port, and power dropped even further! Seems I now have a leaky breech to deal with!
On the plus side, I have been able to shoot the rifle quite a lot and certain things are looking promising. The counterweight, buffer and gear system (i.e the recoilless bits) are working pretty much spot on, and the new hardened pins (which are used in various places) are holding up well with no signs of wear or bending.

Getting to this point has been frustrating, but the glimpses of a fully working action are there. Will keep plugging away and report back when the pellets are coming out a bit quicker

[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