GTS break barrel

[cooper_dan]

This looks jolly exciting.

I know it took John Whiscombe a decade to bring his rifle to market, it’s remarkable how fast the world can work these days.

All the best with the project, loving the regular updates.

Richard

I'm approaching 2.5 years on this to date. Although a lot of that was ticking over for various reasons. Hoping to have the production intent prototype done by the end of this year.
However the jump from production intent to actual production is the most difficult one!

[cooper_dan]

Managed to get a few hours on the break barrel today.
New cocking linkage is working well. Maybe 200 shots in total today and no real issues. Got a bit of metal to metal contact during cocking, will investigate that tomorrow.

Was playing around with single piston (recoiling mode) and efficiency is now up to 31% with a 10 inch .177 barrel. Still a bit more to do but it's getting there.
Added the recoilless piston back in but by this time I was being summoned back indoors. Had a couple of shots and it felt goooood. The tiniest little movement, but the weights still aren't balanced.
Will try to get back out tonight to chrono in recoilless mode.

Motivation has been boosted by those couple of (almost) recoilless shots.

[tomdavies9]

Managed to get a few hours on the break barrel today.
New cocking linkage is working well. Maybe 200 shots in total today and no real issues. Got a bit of metal to metal contact during cocking, will investigate that tomorrow.

Was playing around with single piston (recoiling mode) and efficiency is now up to 31% with a 10 inch .177 barrel. Still a bit more to do but it's getting there.
Added the recoilless piston back in but by this time I was being summoned back indoors. Had a couple of shots and it felt goooood. The tiniest little movement, but the weights still aren't balanced.
Will try to get back out tonight to chrono in recoilless mode.

Motivation has been boosted by those couple of (almost) recoilless shots.

Very exciting mate, always enjoy your updates!

It rare such an insight into the creation of a new rifle is given, and the maker in me loves reading through your posts.

Keep up the good work, and keep the updates coming

[cooper_dan]

Very exciting mate, always enjoy your updates!

It rare such an insight into the creation of a new rifle is given, and the maker in me loves reading through your posts.

Keep up the good work, and keep the updates coming

The efficiency increase was from increasing piston weight from 200g to 252g (in 9 steps of 5.8g each). Because its 28mm piston I'm guessing peak efficiency will be somewhere between 280-320g.
Then I need to do it all again for different TP sizes.
Then I need to do it all again for different calibres.

[tomdavies9]

The efficiency increase was from increasing piston weight from 200g to 252g (in 9 steps of 5.8g each). Because its 28mm piston I'm guessing peak efficiency will be somewhere between 280-320g.
Then I need to do it all again for different TP sizes.
Then I need to do it all again for different calibres.

Good job you enjoy tinkering with it, got your work cut out

Im sure I don’t need to tell you this but all this effort you’re putting in now will pay dividends in the end! And everything we’ve spoke about so far also tells me that when you land this it will be a very special piece of kit.

[Neil54]

How do you measure efficiency?

[cooper_dan]

How do you measure efficiency?

Energy out/energy in.
Energy out measured over the chrono.
Energy in measured by the spring rate, preload, and stroke.

There are some assumptions. The spring rate is calculated rather than directly measured so might be a little bit off. And I don't bother weighing pellets because it takes too long.
But it's good enough for what I need, and as long as I do it the same each time, the comparisons are valid.

[Shed tuner]

for a 28mm bore unless you have a v. small tp, I'd expect around 250-280g piston weight to be optimal.
If your port is at an angle (right angles) then this will obviously reduce flow, so I'd not bother testing with anything less than 3.2mm.

.22 will need less piston weight than .177 as you know

[cooper_dan]

for a 28mm bore unless you have a v. small tp, I'd expect around 250-280g piston weight to be optimal.
If your port is at an angle (right angles) then this will obviously reduce flow, so I'd not bother testing with anything less than 3.2mm.

.22 will need less piston weight than .177 as you know

TP is a bit small at the moment (3mm). The reason being, a bit of bounce reduces the load on the gears and protects them a bit. The problem is that there are so many different pellets that I'm not sure how to settle on a TP and piston mass. If I optimise for popular pellets, there might be some odd outlier with super low start pressure that will end up damaging the gears.
Need to have a think about it.

[Geezer]

TP is a bit small at the moment (3mm). The reason being, a bit of bounce reduces the load on the gears and protects them a bit. The problem is that there are so many different pellets that I'm not sure how to settle on a TP and piston mass. If I optimise for popular pellets, there might be some odd outlier with super low start pressure that will end up damaging the gears.
Need to have a think about it.

And high start pressures might do something similar?

I feel your pain on that, though can’t offer a great solution.

Not long ago, almost all .177” pellets varied from 7grn (Hobby etc) to around 10-11 (Bis Mags, Baracuda). Maybe 6.5 for plastic-body Prometheus.

And when M&G made Giss guns, they were all for 10M match, so 7-8.2 grn wadcutters only.

Now you have to contend with everything from the non-lead tin stuff at 5-something through more conventional lead and potentially up to H&N Sniper Mags (14.97) and Piledrivers (21grn).

With the market you are looking at (small, knowledgeable, conscientious enthusiasts) it wouldn’t be unreasonable to specify required ammo linked to warranty. Just like some cartridge handgun makers advise against +P or +P+ loads, or heavy bullets, or light fast ones, because of durability issues.

[BTDT]

The efficiency increase was from increasing piston weight from 200g to 252g (in 9 steps of 5.8g each). Because its 28mm piston I'm guessing peak efficiency will be somewhere between 280-320g.
Then I need to do it all again for different TP sizes.
Then I need to do it all again for different calibres.

275-280g would have the same sort of sectional density as the 25mm HW77 and TX200, Dan.

[cooper_dan]

for a 28mm bore unless you have a v. small tp, I'd expect around 250-280g piston weight to be optimal.
If your port is at an angle (right angles) then this will obviously reduce flow, so I'd not bother testing with anything less than 3.2mm.

.22 will need less piston weight than .177 as you know

275-280g would have the same sort of sectional density as the 25mm HW77 and TX200, Dan.

This is one of the reasons I will keep posting updates to the forum
Just because I've designed a rifle, doesn't mean I know that much
I think 280g is probably going to be a real stretch due to the piston design and gear drive, but I'll have another look next week with some fresh eyes!

Thanks all.

[cooper_dan]

And high start pressures might do something similar?

I feel your pain on that, though can’t offer a great solution.

Not long ago, almost all .177” pellets varied from 7grn (Hobby etc) to around 10-11 (Bis Mags, Baracuda). Maybe 6.5 for plastic-body Prometheus.

And when M&G made Giss guns, they were all for 10M match, so 7-8.2 grn wadcutters only.

Now you have to contend with everything from the non-lead tin stuff at 5-something through more conventional lead and potentially up to H&N Sniper Mags (14.97) and Piledrivers (21grn).

With the market you are looking at (small, knowledgeable, conscientious enthusiasts) it wouldn’t be unreasonable to specify required ammo linked to warranty. Just like some cartridge handgun makers advise against +P or +P+ loads, or heavy bullets, or light fast ones, because of durability issues.

I do have a plan, although I'm not sure if it will work or not yet. One of the pistons is relatively accessible without stripping down the whole action. It might be possible to have a series of tapped holes with grub screws in. The other piston could have 'power washers'. For different pellets, you could adjust the amount of grub screws and move the corresponding amount of washers from one end of the spring to the other. This would subtly change the dynamic mass. Whether this will be enough mass variation or not, I don't know!

[cooper_dan]

And some properly unscientific videos to look at. These don't really prove anything without any context or a proper jig to hold/fire from.
But at the moment I'm just one person in a shed so it's all you're getting for now

My current favourite recoiling springer (Walther LGV comp ultra).
https://photos.app.goo.gl/cYaFzdFdS5qMa4FWA

And the break barrel (better with sound on). The piston balance is about 30g off at the moment, so you'll see it does move.
https://photos.app.goo.gl/zbaCfGkh3w8U1jmY8

Like I said, doesn't actually prove anything, just might be of interest. You'll have to just trust I was trying to hold them both as loosely as possible

[Shed tuner]

that looks excellent Dan.. very impressive. What power output and calibre is that ?

BTW On port size, 3.2 will still be quite restrictive, but still flow a good deal better than 3.0
if you are goign to max out your piston weight at more liek 265g, the 3.2 will still be on the tight side.