B50 Detune

[GarthThomas]

Just a question for anyone who has been able to bring their B50/51 to below 12fpe. I have the lighter spring, turned the striker out 2 1/2 turns and replaced the transfer port to 3/32 (2.38mm). So far I average 13.2fpe. I'll try 5/64 (2mm) next and maybe 1/2 turn more on the striker pin. Plenty of stuff on souping up but not as much detail on the detune.

[rsterne]

Concentrate on the transfer port.... Lowering the striker force will result in having to drop your fill pressure....

Bob

[GarthThomas]

OK, thanks. I have been making transfer port baffles by cutting a disc of brass shim stock and drilling the desired hole then setting it in before the stock TP. Sandwiching it all in there shouldn't hurt? I have done two so far but I read somewhere going below 2mm might not be good for the gun?

[Ribbonstone]

Assume you'd prefer not to do anything to it that can't be un-done. 

At least in  mine, the transfer port is a good fit.  If I were to add anything under the port, would lengthen it enough that the breech would not quite fit flush.  Good news is that you can shape new ports out of delrin and drill them to whatever size you'd care to try. Even without a lathe, could make ports with an electric drill (black delrin is easier to hand shape as it seems a bit harder than white).

 

[TimmyMac1]

B50'sd have too much hammer weight, too much hammer spring and too Big a Exhaust valve. By Bringing the OD of the exhaust valve down the entire Momentum of the hammer and spring can be relaxed considerably by removing a few coils of spring and nearly half the Spring guide mass.
This gun suffers from the battle of the springs vs pressure when the reduction of the Diameter of the exhaust valve will always be the best solution for longievity by taking all the stresses out of the equation and letting the system balance it self with less trigger forces to deal with as a added benefit.
It seems the Chinese engineered themselves into a Corner and had no choice but to stand on it. The B50 exhaust valve will not last over 2500 rounds if the hammer forces are not reduced as well as the pressure and even after we relieve the stresessed out system the thing still only lasts 6000-7000 rounds. The Factory Exhaust valve is a lousy part and they have refused to improve it. I'm sure they made up 10,000 and they are only half way thru them yet. To make mass quantiities of a BAD PART  and then charge people who want to buy more of the bad part is BAD BUSINESS! That made me say No More B50. If they are unwilling to fix what is wrong with their gun I lose interest immediately.
If you want a good exhauist valve in a B50 I'm afraid your going to have to have it fabricated cause the factory is clueless and even after I sent them a Perfectly working Mac1 Tuned gun they asked me "why did I do that?". What was I thinking? They need to sell what they have not make it my way. The gun started life as a 12 fpe gun and with port restriction and the aformentioned valve and hammer group mods this gun can probably shoot forever with the weak exhauist valve cause it sees very low stress at that power level.
It is a copy of the venerable DayState Huntsman so it was based on a 12 fpe gun, not 25fpe. The blunt force trauma arrangement does not have to be even if you want to make big power. The Chinese did not go the elegant route of have someone who knows how to do it partiipate in the project. Even when I laid a perfectly working gun at their feet, they did not get it! Maybe they never will.
If it looks like a pellet gun and shoots it is done. I know that now. It's Chinese and good enough for the guy who pays the least.

Later

Tim

[GarthThomas]

I read everything I could find on these guns, so I was ready for anything and as you say they have been fixing their problems as far as I can tell. This rifle was flawless when it came but I was intent on tuning it right away so I never shot a string at the original settings. The person who originally bought it has decided that it is too much work with a PCP,  he prefers powder burners and CB longs in his rimfire are more to his liking. In order to buy it from him I had to get the power down to Canadian non PAL limits which a 1.6mm transfer port has just done.
I must say that this is a very easy gun to work on, the only set back is all the pellets it takes to be sure of its settings. When I shoot it at 12yds I don't need to draw a target on the paper just make a hole with the first pellet and then put the rest in that hole, after struggling with my springer for so long I get a strange feeling shooting results like that.

[Ribbonstone]

I seldom give detailed instructions, but for this I'll try.

This is for a .22 BAM 50/51

1. Inside the striker is a spring guide...its a darn heavy one.  It moves with the striker, so it counts as part of the weight of the striker.  Lessen that weight, and the gun runs best at lower pressure (something in the 2100-2000psi range).  I substituted a plastic (Delin) copy of the steel guide.

Original is on top, substitute plastic one on bottom. Ran out of Delrin, so used a Craftsman screwdriver handle (which probably was made from some type of Delrin).  Would have to look it up, but its a s-load lighter.


Figured that was sure to break....been almost 2 years and its not broken yet.

2. This takes lots of time.  Test shoot for shot count with various settings of the striker adjustment screw (which is in the nose of the striker and sets the stroke). Are looking for the LONGEST consistent shot string, REGUARDLESS of the energy (but it will be over 12 foot pounds). Want the LONGEST sweet spot.

3. Make new transfer ports.  I made them from Delrin, but you can make them from metal if your care to.  Start small, test, and SLIGHTLY enlarge before retesting.  If you go past your 12 foot pound limit, will have to start over.

4. If you have an energy limit, would test with heavy weight pellets.  These seem to earn more energy (less velcoity, but works out to more energy).

[GarthThomas]

I think I have the transfer ports figured out so I guess I'll try a Delrin spring guide to save on the weight and try to gain some life time for the exhaust valve. I was sort of inquiring a source for after market improved valves but I think if it breaks I'll have to try to make one on my own.
Thanks for the inputs, I know you have all been through this before and so far my rifle is working great so I shouldn't jump the gun worrying about what may or maynot happen.

[TimmyMac1]

The B50 is a great gun but it had issues the factory didn't address when they should have and left the dealer to sort out the failures and what should have been warranty while forcing the dealers to buy more bad parts or make the part themselves.  It is good to hear people have done just that and it is a good source of information here to know who does what. GTA is a fantastic resource for just that sort of thing.
Delrin Guide is a great idea
The timing of the factory fix is typical. Just about the time they factory gets it right the distributor gives up.
The Disco did a job on this gun even tho it is no where near the potential. If the factory had any QC at all they could have built this gun to last, stood behind it and still have a rocking market. Instead they did what Chinese usually do. ZIP till it was too late.
Nobody is going to make me do their warranty and buy/make the parts to do it. Just like the Koreans the Chinese love to abuse dealers and ignor problems. As a servicing dealer who stands behind what he sells, that is hard to tolerate. Till they start standing behind their products properly they are a no go.
As the world turns only major manufactures can make that connection.

[Ribbonstone]

Really only find two problems with the BAM 50/51, but can see how just those two could drive anyone involved with warranty work crazy.

1. They used too heavy a striker and spring to bump the gun up in power. Got the idea (*sigh* probably correctly) that power sells PCPs in the US.  Would have made an easy to operate 30 foot pound gun.  Of course, then you'd have owners trying to jack it up rather than jack it down in power.

2. The valve stem is  little fragile (and that kind of goes along with #1). Not only does the striker smack-the-&^^& out of it, they machined it with a right angle corner where the spring connects.  Right angles tend to focus stress, so most valve stem seals tend to crack right at that 90degree corner (of course, being smacked by that heavy weight striker and being compressed so deeply against a stiff valve stem return spring has part of the blame).

Not having a good supply of replacement parts was always a problem.  QB's have thieir issues, but at least you can easily get parts.  A little more attention to the consumer, a bit of down tuning, lighter spring guide, a tougher valve stem and this gun COULD have been the QB of PCPs.

[GarthThomas]

I made a new spring guide from Delrin today but I used the dimensions in the "Book" and it has less preload about 0.3" less.
I was previously getting about 650fps but after trying the new guide I was down to 450, so I turned the striker pin back to stock and that got me up to 470 with a 2mm transfer port. I still am going to try the stock transfer port. I made a spare spring guide blank so I will cut it to the same as stock dimensions tomorrow and see what difference that makes. I was using the same drill battery to run the light for my Chrony that I was using to make extra transfer ports with and its dead so I'm at a stand still for now.

[Ribbonstone]

One of the things I farted around with (not keeping strict notes) was a thin-headed guide.  Could stack up washers on that guide (steel/brass/Delrin) and end up with nearly any combination of striker weight and pre-tension. From very light (stacks of delrin washers) to very heavy (home made lead washers).

One of the things i forgot to mention (BUT IS IMPORTANT) is that the original guide has a hole though it for a reason:VENTING.  The striker also has a small vent hole. Without that, can have the striker compress air ahead of it as it moves forward, which acts as a pneumatic cushion to slow it down. 

Rather than drill a hole though my Delrin made spring guide, I filed a shallow (about 1/8") slot across the face of it and back up the head of the guide.  That fixed it. If the guide is  slightly loose fit into the striker, won't need the slots up the side of the guide's head.

[GarthThomas]

I managed to get a hole in my new guide, I will make some Delrin washers tomorrow as well. I just tried it with the original TP and was still getting 450- 470 fps. I have some brass washers that I can spin down to match the diameter of the spring guide but with what Timmymac1 said about keeping the weight down to prevent breakage. When he talks of the exhaust valve is that what the book scematic calls the firing valve.

[Ribbonstone]

I do agree about not smacking the valve too hard.

By lowering the striker weight, the operating pressure also got lowered.  So it may be that the gun is filled to too high a pressure to run at full speed. Only fill it to 1800-1900 and try again.

Could also be that the trnasfer port is a touch too small.

Light strikers tend to have a narrow range of operating pressure.  Often just 10 or 15 BAR seperates valve lock from the start of normal operation.  Know that when I had mine running its best at 140BAR (2050PSI), if it got filled to 155BAR (2450psi) it was valve locked and unable to spit a pellet out of the barrel.

[GarthThomas]

I have only been filling to 1450 or so as it is my sweet spot would start almost right away. I just tried a new Delrin spring guide the same dimensions as original and the preload has put it back to 750fps range with original TP and striker setting so if the total hammer weight is down that has to be a good thing. I am going to try a full string later and see whats different.

[Ribbonstone]

Sounds like you are on the right track.  Small internal changes can have larger than expected results.

Not knowing where the upper pressure limit is, always have the risk of valve locking the gun.  Have had experimental fills (still much loer than the tube's rating) that took as many as 80 slow shots before I bled off enough pressure to get to the "good stuff".  Have also had over estimated fills that locked the gun up, not letting enough air out to let the pellet shoot at all.

If that last happens, then open the end cap back up, slip out the spring and delrin guide, and put the original heavy weight guide back in...that weight will get her shooting.

[GarthThomas]

I was thinking about reducing the exhaust valve spring should I ever need to get inside the reservoir, but I haven't found a reference to a replacement other than possibly cutting down a hammer spring.  Thats if I have read the book correctly. By the way I've got it down to 12 fpe by the use of a 2.5mm TP and one turn to shorten the stroke, 50easy shots using about 30bar.

[Ribbonstone]

Screw it all down and shoot it.  Does seem to be what you can expect with a light striker: low fill pressure, narrow range of pressure, lower energy, and a lot of shots.

[GarthThomas]

Well the detune is a bust, I took it out to the field today and if I had never fired it before the detune it would probably be good enough but now. I just can't be happy with 12 ftlbs so its at 16 and I'll give that a try. In the process today I deburred the breech port, big difference on loading and might even help the longer range shooting. Tried RWS super points and they don't work so still on the cphps.

[TimmyMac1]

I was thinking about reducing the exhaust valve spring should I ever need to get inside the reservoir, but I haven't found a reference to a replacement other than possibly cutting down a hammer spring.  Thats if I have read the book correctly. By the way I've got it down to 12 fpe by the use of a 2.5mm TP and one turn to shorten the stroke, 50easy shots using about 30bar.

Don't change the return spring. It has little to do with the problem this gun has. The valve head clearance to the throat determines firing volume and that diameter is the problem. If you reduce the Firing valves diameter the area it covers on the seat will be substantially reduced requiring far less hammer momentum to get the valve to unseat. Once the diameter has been reduced you can cut hammer spring guide weight in half and also take a few coils off the hammer spring and the thing will still like the high pressure and shoot hard without the stresses associated with an enormous sealing area. Best of all you can get a good bell curve going. That change absolutely transforms this gun into a gun that has an easy to pull striker, awesome trigger and great self regulation. What the chinese copied was a 12 fpe set-up that was a layout John Bowkett popularized as the best solution for Daystate guns to be self regulating for the Euro Market.
The Chinese knew they needed more power so they created the battle of the hammer vs valve and valve spring where they could have reduced the head size to make the gun do 20+ fpe and nothing else would of needed to be changed sans transfer port.
The inhouse China Developement turned it into a gun that had a continually declining velocity from the first shot to the last. But the first shot was over 1000 fps with light .177 ammo so the Chinese figured they had arrived. They had achieved a gun that would be a starting point for a good tuner but not much else straight from the box.
That really is the difference. Americans needs something to be refined and we have the tuners to accomplish that but the factories only focus on outright power because that is what they know is most important for max sales. Till someone convinces them otherwise that is what we will get from China. The customer making the biggest order from the manufacture dictates the guns set-ups and there has never been a darn thing anybodywith smaller orders can do about that. Money talks even if it is ignorance doing the purchase decision. After all, more is better right?
I gave the factory a tuned gun on a silver platter and they commented how gutless it was compared to their set-up. They asked me why I sent it. They never tested it for accuracy or consistency since that matters little. They had a more powerful gun and who would want less? ME & maybe YOU!