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PostPosted: Sat Mar 07, 2015 7:00 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
I've sent off details to Brocock in case they're interested, and of course it's only fair to share this stuff with you good people who might be interested in taking twice as many shots with your Brocock airguns. I've still not quite managed to get the whole shot string sub-500fps with RWS Hobby 11.9gr pellets, but will continue to work on that. It's hard without a regulator. But I've had decent success in bringing the shot strings a lot closer to the ideal flat line than it was as purchased.

When I bought the Atomic in .22" from rrdstarr (swapped him for a Concept, also from SSSO) it was giving me a string which started around 460fps and went up to about 505fps then back down to 450fps, when pumped to the recommended 200bar pressure. For about 35 shots with these same Hobby pellets. Not exactly stellar, but okay. So I set to work tinkering, as I'm a tinkerer. Within a few efforts which primarily involved shortening the hammer spring and adding shims for spring pre-load, I managed to get it to shoot 25 shots within the range of 490fps to 510fps, then shortened the hammer probe (a long set screw running through the heavy hammer weight) such that I got this to about 30 shots ranging between 475 and 495fps with a fill to about 2,800psi. Which was cool. Obviously lost 5 shots compared to stock, but tightening up the velocity curve so well really helped with consistent accuracy.

I've since played with the internals the odd time, tinkering away, trying to find a sweet spot. The Atomic was always really loud, no matter what I did with the settings, so I knew the 7.5" long barrel was just too short for the power plant and obviously dumping a lot of air behind the pellet when it had already left the muzzle. So this past week I spent a couple of sessions attacking the thing yet again, trying to find a shot count suitable for Hunting Field Target which I've recently undertaken informally at the Mission FT shoots. Those sessions are 40 shots plus the odd shot to reset a target or two further out which don't have pull string resetting. A minimum of 42 shots seemed to be the goal. My Crosman 2240 carbine is giving me 60 good consistent shots, but that comes at the cost of having to follow a strict RVA dial-down schedule. Ridiculous really. But it works, getting me fairly impressive accuracy through those 60 shots. However the 2240 trigger is junk. Or rather the sear action is. It's gritty and too hard, and no matter how I've fussed with it the darn thing just won't get much better. And with such an awful trigger I tend to yank my shots, missing the knock-down paddle quite a lot when my crosshairs were right on target until I had to fight with the trigger. Usually to the lower-right. Anyway, the Atomic's trigger isn't the best, but it's relatively brilliant when compared to the Crosman. Going back and forth between them always makes me giggle a bit at how nice the Atomic's trigger feels. So if I can, I'd like to use that one for the competitive portion of those fun shoots.

So now getting to the point of what I've done to get to this point, where I'm getting 65 shots with Hobby 11.9gr pellets starting with a 200bar fill:

- Enlarged transfer port to 0.125" - probably mostly irrelevant, though I've found that TP diameter being over-sized isn't terribly important so long as other elements are in balance.

- Reduced hammer spring length to a very short 29mm, increased spring preload to about 20mm - a combination of a 10mm tubular spacer inside the hammer and an Ertalyte rear cap made to allow use of a wire stock, same depth as stock endcap but with only a 1mm recess for the spring.

- Reduced hammer mass to 41grams (including added plastic liner, adjustable probe, and aluminum locknut) by carving away steel just behind the bearing groove, then replacing this with a snug-fitting 'Ertalyte' plastic sleeve, slotted almost all the way to the back for the hammer guide pin.

- Reduced hammer probe bolt length to about half, reduced aluminum bolt fixing nut length to less than half.

- Reduced bolt probe projection to about 1mm proud of hammer face. Stock projection was about 11mm, which dumped a HUGE amount of air from the valve without increasing power.

The result is this string, using RWS Hobby 11.9gr pellets, measured using a Chrony F1 in feet per second:

457, 434, 447, 436, 456,
464, 467, 471, 465, 467,
466, 466, 464, 465, 468,
439, 459, 459, 462, 469,
460, 450, 500, 506, 501,
507, 522, 498, 507, 510,
515, 509, 510, 519, 530,
522, 529, 526, 537, 525,
497, 534, 512, 532, 543,
529, 533, 526, 517, 529,
519, 514, 510, 505, 498,
490, 487, 484, 474, 477,
465, 457, 452, 451, 438.

Average velocity is about 490fps or 6.35fpe. Obviously I need to tweak slightly further to flatten the curve still more and keep the maximum below 500fps, as this is still a pistol even if I'm using it in carbine format. Just a matter of smaller adjustments to preload, spring length, and hammer probe until I get it right. My next job toward the goal is to make a smaller transfer port, probably boring it to about 0.090" or so. I think this should slow the valve dump enough to give me a maximum velocity just below 500fps. Then I can further adjust the hammer probe and perhaps spring pre-load spacing to get the minimum velocity up as high as possible, ideally above 480fps. Such a setup should enable as many as 70 shots per fill, or DOUBLE the advertised shot count for the Canadian export version of the Brocock Atomic. Even as it is, with a bit of a swell a bit after the middle of the string, this is an impressive shot count increase using the recommended fill pressure with the stock cylinder volume. This is not the Elite version, which is advertised as giving 55 shots in the .22" version. That one should go to about 100 shots with my modifications.

Here are a couple of bad snapshots of what I've done to the hammer and probe. The aluminum probe lock-nut/spring guide was well over twice as long but I've chopped that down to allow for more more pre-load tubular spacer in the front end of the hammer hollow. The probe itself was about twice as long initially but most of that was wasted inside the nut. Carving away more than half the steel behind the sear bearing groove (the sear is just a 1/4" ball bearing) was challenging on my small lathe, but a carbide cutter used at the right speed managed to get the case hardened layer away and then it was easier. I made a press-fit Ertalyte sleeve to bring it back out to full diameter then glued it in place with CA wicked in, then carved away the groove for the hammer guide post/cocking bolt. The sear bearing rides along this low-friction, very tough plastic better than it did with the stock hammer steel. These operations aren't easy, but manageable for a hobbyist gunsmith. If intimidated I'd suggest making a new hammer from scratch, using brass, keeping the mass as low as you can by cutting away metal wherever it isn't needed. Too much hammer weight just tends to dump air in such a configuration. With my 2240 I've reduced the hammer mass dramatically and this has helped a lot in shot-to-shot consistency.

Image
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PostPosted: Sat Mar 07, 2015 7:17 pm 
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Joined: Tue Jan 29, 2013 6:54 pm
Posts: 2411
Location: Northeastern Ontario
Those are some impressive results. You have really done some stellar work on your Atomic. Congratulations.


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PostPosted: Sat Mar 07, 2015 7:44 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
Well, knowledge is a good thing. Since I was a little boy, tinkering (mainly ruining perfectly good machines for the first few years) has been my central hobby. Love taking things apart and finding out how they tick, making them work better. The Atomic is so simple it kind of begs to be modified. And all the Brocock airguns share a similar power train so they're relatively easy to modify, with relatively little risk. The biggest problems are with the very soft aluminum, which tends to shear when tightening bolts back down. It's an unnecessary bolt anyway as the hidden bolt under the plastic pellet tray is very substantial, but the one which secures the upper to the main tube stripped out after a couple of dozen dis-assembly/re-assembly cycles. Another was just about as bad, so I've drilled and re-threaded for a larger bolt on the trigger frame. But it's a solid platform for experimentation. I know SSSO sold at least a few of these things in Canada, so perhaps my long hours of fussing might help others get better results from their Atomics, Super-sixes, Concepts, Contours, what-have-you. More importantly I really hope Brocock adopts such simple modifications into their next-gen airguns as that would really benefit airgunners and their sales figures besides. Their new 'green series' looks interesting in terms of style for a compact airgun, but shot count and consistent performance are far more important.


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PostPosted: Sat Mar 07, 2015 7:48 pm 
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Great results! I *think* you're ok with the hobbies going a little over 500 as they are lighter than standard. If I remember correctly, a 14 gr pellet is considered normal weight in .22. Something like the Crosman HP would be good for testing.

Jim


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PostPosted: Sat Mar 07, 2015 10:42 pm 
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Location: Vancouver
It might be okay, but playing it safe with an air pistol is probably better. And I'm after ultimate consistency in the shot string so will be pushing o get that bottom of the string a bit faster. Something less than 10% extreme spread would be great.


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PostPosted: Sat Mar 07, 2015 11:36 pm 
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Location: Victoria, BC and Clarkston, WA
Gerard, you are the consummate tinkerer! Even your expensive Pardini K12 you fidled with! I have so little time I should give you my Benjamin Discovery and tune it for a good consistent velocity for Hunter FT.

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Pardini K10
Brocock Concept .22
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Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
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PostPosted: Sat Mar 07, 2015 11:45 pm 
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Location: Vancouver
Yeah, well, I don't really have the time. I just take the time. My business suffers the odd time but since I'm the boss (don't tell my wife I said that) I'm the only one who suffers.


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PostPosted: Sun Mar 08, 2015 5:33 am 
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Joined: Tue Oct 13, 2009 1:27 am
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Location: Vancouver
Staying up WAY too late, but it's really hard letting go of a tune-up once it's in my head to get something resolved. After a bunch of testing with a few different diameter transfer port holes and various slight adjustments of the hammer probe I've settled for now on an average of 508fps with 11.9gr Hobby pellets, ranging from lows at beginning and end just under 490 and a middle peak of 531. Extreme spread of 46fps, or just under 10%, which seems tolerable for an unregulated and rather small PCP.

Tried a TP with a 0.060" hole but it just wouldn't shoot over 440fps with this much-shortened spring. 0.060" was the supplied port size, but the hammer spring was almost twice as long and the hammer weighed about 40% more so it delivered about a 480fps average for 35 shots. I'm now getting a 508fps average for 50 shots. I can probably squeeze out a few more shots per fill, take the average to just below 500fps, but from what I've seen it's unlikely I'll get the string as consistent as this. More likely I'd have to pump to only 190bar or so just to keep the first few shots above 480. So I'll use it like this. Gives me a solid 50 shots for HFT, with probably no more than 5mm vertical displacement from slowest to fastest shots on the furthest targets. Good enough. Here's a very bumpy graph showing each shot. Should smooth out a little over the next tin of pellets.

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PostPosted: Sun Mar 08, 2015 6:16 am 
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Looking great. You're right, better to play it safe with the fps as that's peaking way over the 4.2 ft-lb limit that forms the second part of the CC definitions. I'd forgotten how that is much more of a factor with .22. With .177, using a light pellet like the 7 grain RWS basic you need 520 fps to hit 4.2 ft-lb.


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PostPosted: Sun Mar 08, 2015 10:44 am 
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Joined: Tue Oct 13, 2009 1:27 am
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Location: Vancouver
Yeah, I'll be working on it. When I stock up on Hobby this week. Burned right through a 500 pellet tin doing these changes.


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PostPosted: Wed Mar 18, 2015 5:02 pm 
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Joined: Tue Oct 13, 2009 1:27 am
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Location: Vancouver
Well I grabbed a little time this afternoon and tinkered a little more on the Atomic. Managed to get it up to 70 usable shots with just a few between shots 30 and 50 sneaking over 500fps with 11.9gr Hobby pellets. Seems close enough at less than a 5% speeding violation in those few cases. I tried taking slightly more off the top but the bottom fell out at each end, if that makes sense, making for a considerably shorter usable shot string and having to stop pumping at something around 2,600psi. And the remaining 50 shots or so got worse in terms of unevenness. So double the shot count and a string which looks like this:
Image

It's piling up pellets neatly at home, just have to see how it fares at greater distances at Mission on the 29th. The steel knock-down targets don't get further out than about 30 metres I think so the limited utility of about a 480fps average shouldn't be a problem, just need to account for the steep trajectory for those between 20 and 30 metres.


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PostPosted: Sat Mar 21, 2015 1:20 pm 
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Joined: Sun Jul 15, 2012 10:49 am
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Location: Victoria, BC and Clarkston, WA
Hopefully your bringing that next Sunday???

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Pardini K10
Brocock Concept .22
3 Custom Crosman 2260
Benjamin Discovery .22 w/Joe Hickey stock!
Crosman 150 pistol .22
4 Crosman MK 1 pistol .22
Mrodair CP-1M .22 and .177


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PostPosted: Sat Mar 21, 2015 3:14 pm 
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Joined: Tue Oct 13, 2009 1:27 am
Posts: 2514
Location: Vancouver
Sure am. While the 2240 carbine is a bit more accurate rested, the much crisper, easier trigger of the Atomic makes for tighter groups when not rested. So I'll give it a try, see if it improves my knock-down rate. The Boyd's stock certainly helps too, increasing both comfort and mass so the Atomic is a bit more stable.


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PostPosted: Sun Mar 22, 2015 10:39 am 
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Oh, did you know that if it goes over 500fps and you don't have your rpal, it's illegal? It was pointed out to me last week by a forum member that illegal mods are not to be discussed on the forum :butthead:

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Cometa lynx .22-hawke sport 3-9x40 ao
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PostPosted: Sun Mar 22, 2015 11:34 am 
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Joined: Tue Oct 13, 2009 1:27 am
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Location: Vancouver
This has been pointed out some hundreds of times in the forum, so yes, i am aware. As received from SSSO, this pistol tested on my Chrony F1 to shoot about 35 shots per fill. It started at about 430fps using RWS Hobby 11.9gr pellets, peaked around 508fps if memory serves, and finished around 430 again before dropping into the 300's for a couple then the 200's, which I didn't count in the total. I have sought to even out that curve, which was problematic in terms of actually hitting the target, while also increasing shot count and reducing blast noise. I have succeeded in these goals.


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