BAM B-51 - Better Late Than Never

[moorepower]

moorepower, your Inbox is full....

Bob

Drained. 

[Ribbonstone]

Always seems better for me to start out with some goal in mind. Could be power related, could be shot count related, or it could be both.  Just figure out what you want it to do FIRST, then work in that direction.

Can’t have everything. Power works against shot count, increase one and you’ll decrease the other.  A more efficient tune can give you more shots than an inefficient one, but there is no real magic here: energy in vs energy out, there isn’t going to be some magic formula to reverse that.

So pick what you want to do, read “The Book” and read the threads here on the BAM. Should be able to get where you’re going if it is in the  rhelm of possibility.

Probably better to do a “gut-check” to see if you goal is likely.  Use this calculator, putting in your fill pressures, 196cc’s as the air volume, etc.

http://www.calc.sikes.us/1/

 By playing with the shot count, look at the fpe-cuin results.  Stuff in the 1.4-1.5 area would be a good tune.

[GarthThomas]

This is what I've done so far to the valve, I shaped a poppet to 5/16" and made the thinner washer as well I flattened the ends of the spring.
I drilled the hole in the valve body larger to 5/32"

I made a thinner acetal spring guide for the hammer and installed the M-C spring. I screwed the threaded striker flush but I could see it was obstructing the vent hole so I ground a little off to clear the hole. Also to add to less than stock preload I had previously drilled the end cap larger so the MC spring could turn easily. I'll post the string later.

So just some numbers ,I left the factory TP in but it looks like I will have to try a smaller one .
110bar/JSB18.1  Sot down to 62bar I stopped there because I was past 4%
702       756       775      776       749
706       756       782      772       740
695       761       777      769
720       767       777      765   
699       760       773      761       
727       753       778      755   
735       763       778      757   
752       759       772      753     
755       767       773      747   
749       771       773      745     

It's also very easy to pull the bolt back now, I am going to take the hammer out and check for debris or a burr on screw #26 the string seemed a little erratic. What do you think?     
     
       

[Motorhead]

 By playing with the shot count, look at the fpe-cuin results.  Stuff in the 1.4-1.5 area would be a good tune.

1.4 - 1.5 fpe-cuin at high power ( Yours & Bobs ) would be phenomenal !!

[Ribbonstone]

Bob tends to change things for best possible results.  Modded valve stem, lightened strikers and top hats, modded transfer ports, various springs, spring adjusters, etc.  All great stuff, and it works.

I tend to just fiddle around with the issue parts, doing minimal mods.

His results are better, either by power or by shot count.

Think the point is to decide ahead of time what it is you want. 

[rsterne]

Yes, I was shocked to see 1.40 FPE/CI  at 41.2 FPE average, 1.46 FPE/CI at 38.7 FPE average, 1.51 FPE/CI at 37.1 FPE average, and 1.61 FPE/CI at 34.8 FPE average, but that's what the gun got with the 18.1 gr. JSB Heavies.... Those kind of efficiency numbers are usually reserved for lower powered target rifles, and even then they aren't easy to obtain.... I still think part of the reason is the draggy sear design preventing hammer bounce from reopening the valve.... Heck, I'm even more amazed that I got 1.23 FPE/CI at 49.1 FPE average with the 25.4 gr. Monsters.... It's not easy to hit that kind of efficiency in .25 cal at 50 FPE, let alone with a .22 caliber....

Bob

[SpiralGroove]

Oh Ribbonstone,
You've got one of the nicest Bam B51 stocks out there!  I think it's greatly improved with the longer forearm tip; it balances the gun much better than the OEM.
I still can't decide if I want to go two tone or not?  I really wanted to re-do my stock because I felt it wasn't dark enough.
It got dented today somehow, so that's next for me.  I had originally used a light maple stain, intentionally not wanting to overpower what little grain there was.  But I don't like it.  I bought some pre-stain and will use it so I can use something darker and not have to worry about totally overpowering the Blah...wood.  Stock work is my favorite airgun, tinkering activity - I think?

http://i113.photobucket.com/albums/n227/kirk_schwarz/BAMB50-4_zps2f43e012.jpg

Sorry for going off topic

[Ribbonstone]

Not my stock work, bought it used that way; previous owner had the talent.

Can tell the stock started off as an issue BAM51, but I’d never have gotten it to look like that.

[bubba zanetti]

BZ, since you are doing FT, have you considered installing an in-tube regulator? In .177, you can get a ton of consistent shots with a moderate pressure setpoint.  It would need some porting and a lightened striker as compared to stock.

My son's QB79 fitted with a 1000psi 13ci Ninja bottle gets over 100 15fpe shots on a fill.  The volume is larger but I did not install an RVA to fine tune the striker preload so it's wasting air, so I would not be surprised if you could extract 60-70 shots from the B51 with some tuning.

PM sent.

BZ

[GarthThomas]

I posted my first string on my picture post above if you interested. More power than I need but the range of adjustment has opened up greatly. My goal is as many shots as possible around 15ftlbs. or less.
Thank you Bob for relighting the fire.

[SpiralGroove]

Hey GarthThomas,
If you spend $80 for a Milo74 regulator, you should be able to get 110 shots at 800 fps (14.9 fpe) using 10.5 grain CPUM.  I'm estimating you would be using air from 3000 psi down to 750 psi.  Make your setpoint about 800 psi (55 bar). 
This assumes a 1.14% efficiency, which could a sticking point, also the regulator's pressure flexibility. 
I'd go for it, but I've been labeled enthusiastic by the masses . 
 

[Ribbonstone]

I skipped some different weight pellet testing as the daylight hours after work are real short this time of year. 


Before this post, was happy with this tune:




Then I started reading these posts and started changing things.

1.Got back into the rifle and ground off part of the striker nose to lengthen the stroke. 
2. In doing  #1 discovered the vent was mostly blocked, so arranged for that to be clear as well.
3. Reduced the spring tension slightly.

With the above changes, shot this string:




Wanted to trade some of that “extra” energy for shot count, so partly took the rifle apart (just the top half, didn’t even have to destock the air tube) and measured the transfer port.

The transfer port measured .135”.  I reduced it to .125” (basically roughened the inside, filled it with Devcon, let it cure, and drilled it to .125”).

Did do a couple of shots with the 15.9gre. pellets at the middle of the expected shot count.   Those few shots averaged 911fps (about 29.3 foot pounds).

Did one full string of shots:



So the end result of this was:

1. The longer stroke let me get away with a lighter striker spring tension, which makes cocking a little easier.

2. The +30 foot pound shot string increased by 10%.

3. The difference in efficienty is within normal variation, would have to keep track over several to get a reasonably good approximation.

Probably worth the trouble.  The little extra in the shot count is a plus, the lower cocking force is a plus...am sure the amount of work it took will diminish in my mind over time, so will rate it a "win".

[rsterne]

KEWL !!!

Bob

[GarthThomas]

 

Hey GarthThomas,
If you spend $80 for a Milo74 regulator, you should be able to get 110 shots at 800 fps (14.9 fpe) using 10.5 grain CPUM.  I'm estimating you would be using air from 3000 psi down to 750 psi.  Make your setpoint about 800 psi (55 bar). 
This assumes a 1.14% efficiency, which could a sticking point, also the regulator's pressure flexibility. 
I'd go for it, but I've been labeled enthusiastic by the masses . 
 

I was hoping to get as close to those numbers without spending anything, 

[Ribbonstone]

Can tell the smaller transfer port leveled off the "plateau" a little better (which is really waht restricting the port does), even though the shot count isn't drastically different from the first shot string.  Looking at the 2% shots, first string got  14 shots and the last one 18, so while there isn't a whole lot more shots, they're a little more "level".

[SpiralGroove]

Hey GarthThomas,
I'm sure you could, just the regulator should give the whole string an ES of less than 3%

[SpiralGroove]

Hey Ribbonstone,
Yeah, "all in all", given our tweaks to our BAM set-ups (time spent vs change), I would put the results in the Marginal category.
Sure yours performs a little better and mine does too (mostly affected by the removal of the sail), but in hindsight, I would say the old addage "If it ain't broken, don't fix it" -> applies.  OK, my trigger feels normal now too.......
In my case, working on a low pressure string (venting & shortening the hammer) pretty much gave me more hammer -> something I really didn't need.  I needed more efficiency - period.  So, what more hammer gave me was the ability, within the Delrin hammer/spring guide realm, to use the MC spring vs stock (clipped by 3 coils).  So less wear and tear on the machine.  To summarize, for those enthusiastic, perfectionists --> Go for It!!!   Because you gotta find out   ------ otherwise --> Don't.

My Two Cents ................

[Ribbonstone]

Just tend to set a goal for each gun, either in terms of shot count, or power, and occasionally both. 

Probably the only think I’ll try past this is going back to the original striker spring strength, up the fill to 170BAR,  and reduce the transfer port a little more.  Still want my upper energy limit to be 30 foot pounds, but I might eek out another couple of shots in a string that way.

[rsterne]

Quite likely....but harder to cock, though....

Bob

[Ribbonstone]

True...might get a couple more shots per string, but enjoy it less.