Well im hoping to be able to repeat soren’s results with slugs and also hoping to push 13 jsb to 815 accurately. I like the ballance standing with my 25 ghost so i think it might improve my ft scores!
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BRK Ghost Review
- Thread starter Franklink
- Start date
In the last week I've learned more about springs than I ever wanted to know. That was the lead up to spending a couple hrs with the chronograph the other night. Goal: tackle the problem of being ever so slightly over the 20fpe limit with the 13.73grain .20 JSBs.
This is a bit of a conundrum though, because I want to be able to just spin the power wheel up from the field target tune to get the .20/15.89s to 915-920fps. And I don't want to have to change the regulator pressure or remove the buttplate dropdown to swap hammer springs.
For reference, per field target rules, the maximum speed for the 13.73s (without being over 20fpe) is 809fps. Unless I'm willing to rely on the 2% variance allowed in the rule books, and I'll really like to be safer than that. So a baseline field target tune producing something like 800-810fps with the .20/13.73s would be just about ideal.
For starters.....
This is going to be technical and potentially boring, but there are some nuggets of information within that might be worthwhile, specifically about the Ghost's valve....
Since I first thought that reducing the hammer strike energy could solve the problem, I started with the 0,031" wire hammer spring. @ reg pressure of 75bar, "6" on the power wheel was getting me 797-811fps....perfect. With one huge problem, this spring won't push the 15.89s fast enough. 750fps was where they'd max out, even with power wheel on MAX. So I tried to increase the reg pressure and this particular spring won't push the 15.89s past 850, no matter the regulator pressure. That's a good, consistent tune for the 13.73s for field target, but not ideal for my desires to also be able to shoot the 15.89s by just spinning the wheel.
On to the 0.047" hammer spring.....reg pressure of 75-80bar produce 850-860fps from the lighter pellets with the power wheel on MIN. The fps decreases as the regulator pressure is increased. I went as high as 140bar and, quite surprisingly, arrived at my desired 800-810fps. For me this seemed very counterintuitive. My understanding ( after some pondering) is that more fps is produced with a lower reg pressure because the regulated air isn't pushing on the poppet as much, so an equivalent hammer strike allows more air to exit the valve at 75-80 bar than it does at higher pressures. As the reg pressure is increased, the increased force the air is exerting on the poppet allows less and less air to exit the valve with each hammer strike, thereby reducing the fps. And this configuration allows me to push the 15.89grain pellets up to 1000fps, so it accomplishes that goal. @Arzrover suggested that I might see a low fps first shot with such a high reg pressure (relative to power output) after the gun has sat and he was spot on. I let the gun sit for 48hrs and the first shot with the 13.73s was 775fps. The next and all subsequent shots were in the 800-810fps range like they should be. So, if I settle on this tune, I'll have to understand that the first shot for the lighter pellets is going to be reduced fps. I need to determine if this is a occurrence that happens over days or minutes before I decide if I'm willing to deal with it. For now, I don't like it. I don't want to have to blow one off before I get consistent shots.
Sparing a lot of detail....when we found out that lower reg pressure was INCREASING fps with the 0.047 spring, arzrover suggested that I shim the valve return spring to keep it from opening as much/for as long at lower reg pressures. The above testing was with two 1.5mmx5mm 90D orings sandwiched together on the poppet, under the return spring. I tested the above springs with and without the valve return spring shims and they had an effect with the 0.047" hammer spring, but didn't seem to matter much with the 0.031. I can only assume that slight difference in the spring rates are keeping the lighter one from overpowering the force of the regulated air (at low BAR), while the slightly heavier 0.047 is enough to either knock it more open or hold it open (when unshimmed) for too long, or some combination thereof.
Shimmed valve return spring here....
So where to go from here.... I've got two "tunes" with two different hammer springs, that produce the desired fps from the lighter pellet. And both have compromises. The 0.031 hammer spring doesn't allow use of the heavier pellets, at least not at desired speeds. And the 0.047 hammer spring has the problem of low fps first/cold shot, but DOES allow use of the heavier pellet. As initially mentioned, quite the conundrum........
At this point, I'm considering dropping my 38grain hammer weight back in the nose of the hammer, and seeing if that'll make the difference of getting the 15.89s up to 915fps, while still allowing the 13.73s to be shot at 800-810fps, all while using that lighter 0.031 hammer spring and a reg pressure of 100-120 (lower reg to avoid the low fps first/cold shot that I'm getting now with the higher-reg-pressure-than-necessary for the power level). I also still have the heavier HP hammer that could be dropped in the gun for testing. If neither of those two options has the desired effect I'll have to decide which compromise I want to live with from the two above "tunes."
The BRK Ghost's valve is VERY sensitive to the delicate balance between: hammer weight, stroke length, hammer spring, reg pressure, projectile weight, transfer port size, caliber size, and barrel length.
This is a bit of a conundrum though, because I want to be able to just spin the power wheel up from the field target tune to get the .20/15.89s to 915-920fps. And I don't want to have to change the regulator pressure or remove the buttplate dropdown to swap hammer springs.
For reference, per field target rules, the maximum speed for the 13.73s (without being over 20fpe) is 809fps. Unless I'm willing to rely on the 2% variance allowed in the rule books, and I'll really like to be safer than that. So a baseline field target tune producing something like 800-810fps with the .20/13.73s would be just about ideal.
For starters.....
- the 0.052" wire diameter OEM spring has a rate of 17lbs/inch (this is the spring that came with the .22 HP barrel)
- the 0.047" wire diameter OEM spring has a rate of 10.8lbs/inch (this is the spring that came in the gun as a .177 Carbine)
- a 0.031" wire diameter spring from local hardware store has a rate of 9.6lbs/inch (same length as OEM, a couple fewer coils)
This is going to be technical and potentially boring, but there are some nuggets of information within that might be worthwhile, specifically about the Ghost's valve....
Since I first thought that reducing the hammer strike energy could solve the problem, I started with the 0,031" wire hammer spring. @ reg pressure of 75bar, "6" on the power wheel was getting me 797-811fps....perfect. With one huge problem, this spring won't push the 15.89s fast enough. 750fps was where they'd max out, even with power wheel on MAX. So I tried to increase the reg pressure and this particular spring won't push the 15.89s past 850, no matter the regulator pressure. That's a good, consistent tune for the 13.73s for field target, but not ideal for my desires to also be able to shoot the 15.89s by just spinning the wheel.
On to the 0.047" hammer spring.....reg pressure of 75-80bar produce 850-860fps from the lighter pellets with the power wheel on MIN. The fps decreases as the regulator pressure is increased. I went as high as 140bar and, quite surprisingly, arrived at my desired 800-810fps. For me this seemed very counterintuitive. My understanding ( after some pondering) is that more fps is produced with a lower reg pressure because the regulated air isn't pushing on the poppet as much, so an equivalent hammer strike allows more air to exit the valve at 75-80 bar than it does at higher pressures. As the reg pressure is increased, the increased force the air is exerting on the poppet allows less and less air to exit the valve with each hammer strike, thereby reducing the fps. And this configuration allows me to push the 15.89grain pellets up to 1000fps, so it accomplishes that goal. @Arzrover suggested that I might see a low fps first shot with such a high reg pressure (relative to power output) after the gun has sat and he was spot on. I let the gun sit for 48hrs and the first shot with the 13.73s was 775fps. The next and all subsequent shots were in the 800-810fps range like they should be. So, if I settle on this tune, I'll have to understand that the first shot for the lighter pellets is going to be reduced fps. I need to determine if this is a occurrence that happens over days or minutes before I decide if I'm willing to deal with it. For now, I don't like it. I don't want to have to blow one off before I get consistent shots.
Sparing a lot of detail....when we found out that lower reg pressure was INCREASING fps with the 0.047 spring, arzrover suggested that I shim the valve return spring to keep it from opening as much/for as long at lower reg pressures. The above testing was with two 1.5mmx5mm 90D orings sandwiched together on the poppet, under the return spring. I tested the above springs with and without the valve return spring shims and they had an effect with the 0.047" hammer spring, but didn't seem to matter much with the 0.031. I can only assume that slight difference in the spring rates are keeping the lighter one from overpowering the force of the regulated air (at low BAR), while the slightly heavier 0.047 is enough to either knock it more open or hold it open (when unshimmed) for too long, or some combination thereof.
Shimmed valve return spring here....
So where to go from here.... I've got two "tunes" with two different hammer springs, that produce the desired fps from the lighter pellet. And both have compromises. The 0.031 hammer spring doesn't allow use of the heavier pellets, at least not at desired speeds. And the 0.047 hammer spring has the problem of low fps first/cold shot, but DOES allow use of the heavier pellet. As initially mentioned, quite the conundrum........
At this point, I'm considering dropping my 38grain hammer weight back in the nose of the hammer, and seeing if that'll make the difference of getting the 15.89s up to 915fps, while still allowing the 13.73s to be shot at 800-810fps, all while using that lighter 0.031 hammer spring and a reg pressure of 100-120 (lower reg to avoid the low fps first/cold shot that I'm getting now with the higher-reg-pressure-than-necessary for the power level). I also still have the heavier HP hammer that could be dropped in the gun for testing. If neither of those two options has the desired effect I'll have to decide which compromise I want to live with from the two above "tunes."
The BRK Ghost's valve is VERY sensitive to the delicate balance between: hammer weight, stroke length, hammer spring, reg pressure, projectile weight, transfer port size, caliber size, and barrel length.
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Starting to sound like im not going to achieve my goals with the hp model. I ve been fighting with my 25 also just can’t seem to figure out the right place to have things set to get consistent results.
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Don't let my reporting discourage you. Remember that what I'm most recently doing is WAY out in left field. I'm using a caliber in which the gun isn't even manufactured. As previously stated, I'm also using a hammer that was never meant to be in the guns in the US (UK sub 12fpe market).
While I tried to report results for potential owners for a long time, as a sort of reference point, I'm out in the weeds now.
What I'm doing with the .20 isn't as simple as just swapping barrel kits and adjusting reg pressure and hammer tension.
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Still on the .20 kick ehh Cole? Glad to see you get to play with this before launch. Hope you've been well!
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Hey Dillon! Good to see you back.
Yep, I still really like the .20. Small caliber joy, doesn't take a lot of air, REALLY accurate, wind-resistant, and with the 15.89s, can extend the useable range for a 30fpe airgun to much further than most would think possible.
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With the 25 100 yd benchrest with 33.9 jsb. With the 177 i would like to shoot 13 jsb in ft and be able to adj up to 28 fpe with 16 gr zan or 15 gr nsa
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I think you guys will be fine.
As far as I know, all Ghosts in the US have the same valve and same plenum size. The exhaust port in the valve that came in the .177 Carbine is MASSIVE and it tames down to sub 20fpe just fine. One of the main methods of power restriction seems to be the transfer port size in the .177 Carbine barrel. But there's also the ability to change hammer springs, lengthen the stroke, lower the reg pressure, and potentially even use the lighter skeletonized hammer (I was told just this evening by somebody who recently bought a .22 HP that AOA told him they have/can get the skeletonized/lighter hammers. That's news to me as I was previously told that the lighter hammers weren't meant for US guns. Frankly, if this rumour is true that's a good thing, as I like how this one shoots with the lighter hammer much more than how it shoots with the heavy hammer).
So, just like any other mechanical gun, some components will need swapped out to go from 60fpe down to sub 20 fpe, but the guts (valve and plenum) seem to be universal parts across all Ghost configurations.
I'll remind you guys that this review started with a .177 Carbine at 19fpe, and went up to a .22 HP at 50fpe, then back down to a .177 Carbine at 19fpe (for about a week) and now a .20 in 20 or 30fpe.
As far as I know, all Ghosts in the US have the same valve and same plenum size. The exhaust port in the valve that came in the .177 Carbine is MASSIVE and it tames down to sub 20fpe just fine. One of the main methods of power restriction seems to be the transfer port size in the .177 Carbine barrel. But there's also the ability to change hammer springs, lengthen the stroke, lower the reg pressure, and potentially even use the lighter skeletonized hammer (I was told just this evening by somebody who recently bought a .22 HP that AOA told him they have/can get the skeletonized/lighter hammers. That's news to me as I was previously told that the lighter hammers weren't meant for US guns. Frankly, if this rumour is true that's a good thing, as I like how this one shoots with the lighter hammer much more than how it shoots with the heavy hammer).
So, just like any other mechanical gun, some components will need swapped out to go from 60fpe down to sub 20 fpe, but the guts (valve and plenum) seem to be universal parts across all Ghost configurations.
I'll remind you guys that this review started with a .177 Carbine at 19fpe, and went up to a .22 HP at 50fpe, then back down to a .177 Carbine at 19fpe (for about a week) and now a .20 in 20 or 30fpe.
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Chris at AoA (with Robert's input) provided the above about availability of the lighter hammers. I'd been concerned that my new 22 HP wouldn't be able to tune down to a smooth-shooting 12-20 fpe.
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I just spent another couple hours testing every possible combination of hammer spring, stroke length, reg pressure and hammer weight that I have available to me, and this is the best I can do for the .20 Ghost, with the express goal of being able to rely on ONLY the power wheel to go from 13.73gr to 15.89gr at the two aforementioned desired speeds.
With the 13.73grain JSBs, the above produced the following 30 shot string. This will be my 20fpe field target "tune."
With the 15.89grain JSBs the above produces an average fps of 755fps (15 shots), with and ES of 13.7. Would need to rely on the 2% rule to be legal at sub 20 here.
Leaving all other parameters as above, with the exception of increasing hammer wheel to "12" the 15.89s average 918fps, with a 12.3fps ES. This will be the hunting/pesting/long range tune.
Yes it is possible to get a tighter ES for the sub 20fpe tune with various combinations of lower reg pressures, weaker hammer springs, heavier hammer weights, but none of those combinations will allow the desired 915-920fps with the 15.89s through only adjustment of the power wheel.
As it stands now, I'll have to settle for blowing off that first shot (low fps as previously discussed) when shooting the 13.73s at 20fpe. The tradeoff to dealing with that first low fps shot is that I'll be able to shoot the 15.89s at the desired fps for pesting/hunting by only cranking up the power wheel. The ES is also a little larger than I'd prefer for the 20fpe tune, but again, the tradeoff is being able to shoot the 15.89s at 915-920 by only adjusting the power wheel. I've won multiple matches with a non-regulated gun that has greater extreme spreads, so it doesn't concern me greatly here.
I just cleaned the barrel after all that chrono testing (EXTENSIVE and LOTS of pellets). So next comes working through my dope from 10-55 yards as many time as possible in the next 3 weeks between now and the match in Duncan, AZ. That makes me happy to think about getting to shoot alot, as I always enjoy the shooting side more than the tinkering/tuning side.
- Reg pressure of 140 BAR
- 0.047 wire OEM spring
- nearly max stroke length (about 1/8 of an inch of threaded nose extended)
- skeleton/lightweight hammer
- "MIN" on power wheel
With the 13.73grain JSBs, the above produced the following 30 shot string. This will be my 20fpe field target "tune."
- LO of 798.5
- HI of 817.6
- Ave of 809.6
- ES of 19.1
- SD of 4.79
With the 15.89grain JSBs the above produces an average fps of 755fps (15 shots), with and ES of 13.7. Would need to rely on the 2% rule to be legal at sub 20 here.
Leaving all other parameters as above, with the exception of increasing hammer wheel to "12" the 15.89s average 918fps, with a 12.3fps ES. This will be the hunting/pesting/long range tune.
Yes it is possible to get a tighter ES for the sub 20fpe tune with various combinations of lower reg pressures, weaker hammer springs, heavier hammer weights, but none of those combinations will allow the desired 915-920fps with the 15.89s through only adjustment of the power wheel.
As it stands now, I'll have to settle for blowing off that first shot (low fps as previously discussed) when shooting the 13.73s at 20fpe. The tradeoff to dealing with that first low fps shot is that I'll be able to shoot the 15.89s at the desired fps for pesting/hunting by only cranking up the power wheel. The ES is also a little larger than I'd prefer for the 20fpe tune, but again, the tradeoff is being able to shoot the 15.89s at 915-920 by only adjusting the power wheel. I've won multiple matches with a non-regulated gun that has greater extreme spreads, so it doesn't concern me greatly here.
I just cleaned the barrel after all that chrono testing (EXTENSIVE and LOTS of pellets). So next comes working through my dope from 10-55 yards as many time as possible in the next 3 weeks between now and the match in Duncan, AZ. That makes me happy to think about getting to shoot alot, as I always enjoy the shooting side more than the tinkering/tuning side.
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I think your best bet would be to find a machinist or maybe contact AOA. Pure conjecture, but I think there'd have to be some sort of minimum # of people interested in the .20 before AOA/BRK would be willing to go down that road.
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.20 Ghost @ 20fpe is just ridiculous. These are at various distances. Center dot is about the diameter of the lead in a wooden pencil, outer circle maybe 3/8 inch. Strelok matching perfectly. Oh, from a bum bag.
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That's exciting! Look forward to more as you begin to shoot a lot & further dial in. That .20 barrel kit--plus your secret sauce--could be a big seller!
Sorry if previously explained, is the function of the buckets to trap & contain lead? Keep targets out of wind & rain? Keep neighbors from seeing what you're doing?
Sorry if previously explained, is the function of the buckets to trap & contain lead? Keep targets out of wind & rain? Keep neighbors from seeing what you're doing?
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Glad to be back Cole! I don't blame you id love a .20 myself. My little Evol in .20 would be awesome I'd think! Love seeing how its coming together looking good.
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@Franklink I gotta figure out how you are able to match strelok that closely. I can tweak bc, scope height, velocity, etc and match at one or two ranges but not at all yardages…
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