Author Topic: First Forray into the Darkside - B-51 Mods  (Read 9954 times)

Offline scottinharwood

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First Forray into the Darkside - B-51 Mods
« on: September 05, 2008, 10:42:20 AM »
Well I am going to do it.  Tropical Storm Hannah is coming up the coast and it looks like no work outside tomorrow (Saturday).

What to do?

I know, I am going to follow all of the blurbs and great info on this site and start to mod my stock B-51.

I have the new lower-strength springs from McMaster-Carr.  Ordered them yesterday, got them today, standard post - its a sign I tell you, a sign!

My goals for tomorrow, shoot some strings at 2700#, 2300#, 2000# and 1700# to baseline the gun with Crosman Premier Heavies.

Then, replace the hammer spring and polish and lube the hammer weight and trigger assemblies then shoot some more strings.

That will probably take my day. Later I may try the mod to make the hammer pin protrusion length variable.  One step at a time though.  I would really like to be able to fire off a string of 30 to 40 CP Heavies starting with a 2300# fill.  The Benjamin Discovery I have has made me well aware of just how breath-taking going to a 2800-3000# fill can be.

Its not going to be sunny out so I will have to rig up some lights over my Chrony
AA S400Xtra 0.177, BAM B51 0.177, Crosman Discovery 0.22, IZH M-46, RWS-54 0.177, Crosman 1377C, Crosman Storm XT

Air Gun Tuner\'s Motto, \"At least do no harm to the existing airgun accuracy and power!\"

Offline DanoInTx

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Re: First Forray into the Darkside - B-51 Mods
« Reply #1 on: September 05, 2008, 01:20:49 PM »
My Big Ed tuned B51 has the McMaster Carr spring and shoots its best from a 1700psi fill.  If I filled it to 2300psi it wouldn't even shoot because the valve would lock.  Just something to think about when you start shooting strings with the new spring, better to start with a low fill pressure then increase till you get the curve you want.  No fun filling it up just to find out it wont shoot and having to dump air and start over.

If you DO overfill with the lighter hammer spring then you can easily dump some of the air.  Here's how I do it:

1)  Connect hose to pump/bottle
2) start adding pressure VERY slowly until you hear the pin valve in the fill nipple open
3) slowly, slowly, slowly open the bleeder on your fill rig and slowly let air out.  Of course close the valve on your tank first if using a tank rather than pump.  If you open your bleeder slow enough the pin/check valve in the fill nipple wont close and you can slowly dump air till you get to the correct pressure.  I've used this technique on both of my BAM's and it worked great.

Good luck and happy modding!

Oh yea, do you have a copy of "The Book"?
Dan

Current shooters: Beeman HW97K .177 with Hawke Eclipse 4x16x50SFAO and Steve C. stock, Beeman R9 .177 with Hawke Airmax 4-12x40AO and Gene\'s Midas touch, Air Arms S200 with Bushnell Banner 6x24x40AO Rowan brass bling and Steve C. custom stock, BAM B25, BAM B40 .177 with BSA 3x12x44AO, Benjamin Marauder .22, Benjamin 397 pumper.

\"repeat this mantra:
Air gunzzzzzz, air gunzzzzzz, air gunzzzzzzz!!!  ...You will feel better\" T.E.C.2008

Offline scottinharwood

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Re: First Forray into the Darkside - B-51 Mods
« Reply #2 on: September 05, 2008, 02:09:26 PM »
Hi Dan,

Yes, I printed 'The Book', that is why I am going to attempt all of this.  I was hoping to send it to BigEd for a full work up but no replys to my last couple e-mails.  I figure he is really busy or taking some needed time off.  I believe he was going to do some work ups on both a 0.177 and a 0.22 Discovery.

Good to know on the starting fill pressure though.  I will work my way up from 1000# and see where it locks

So here I go tomorrow, as soon as I rig some lights for my Chrony.

Scott
AA S400Xtra 0.177, BAM B51 0.177, Crosman Discovery 0.22, IZH M-46, RWS-54 0.177, Crosman 1377C, Crosman Storm XT

Air Gun Tuner\'s Motto, \"At least do no harm to the existing airgun accuracy and power!\"

Offline DanoInTx

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Re: First Forray into the Darkside - B-51 Mods
« Reply #3 on: September 05, 2008, 06:16:00 PM »
Mine goes from 1700psi down to 1200psi with 34 shots in between.  This is a .177 shooting Crosman heavies 10.5 grain between 850 to 875 then back to 850 for a nice curve.  Ed is taking a 2 1/2 week break to catch up on backlog and also to prep his gun for the Nationals.  He posted on the Chinese Yellow forum a couple days ago to mention that he'd be closed during that time.  His tune is really worth it, trust me I've owned both an untuned B50 and a Big Ed B51.  Ed claims that most of what he does is in "The Book", but there is some magic in there somewhere too:)  The only thing I've done to my B51 since I got it from Ed was to rebend the trigger and make a custom cocking knob:





They sure are fun guns to mess with for the price.  Have fun!
Dan

Current shooters: Beeman HW97K .177 with Hawke Eclipse 4x16x50SFAO and Steve C. stock, Beeman R9 .177 with Hawke Airmax 4-12x40AO and Gene\'s Midas touch, Air Arms S200 with Bushnell Banner 6x24x40AO Rowan brass bling and Steve C. custom stock, BAM B25, BAM B40 .177 with BSA 3x12x44AO, Benjamin Marauder .22, Benjamin 397 pumper.

\"repeat this mantra:
Air gunzzzzzz, air gunzzzzzz, air gunzzzzzzz!!!  ...You will feel better\" T.E.C.2008

Offline scottinharwood

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Re: First Forray into the Darkside - B-51 Mods
« Reply #4 on: September 06, 2008, 12:23:31 AM »
Dano,

That post came in a 2:16AM EST, its past midnight for you - get some sleep man.

Thanks for the info on Big Ed.  I was hoping to get a barrel, de-pinger and other stuf from him, if possible, I will see if he can do the work too.  I will still do the main spring change, thats easy.  Might even to the power adjuster screw mod too, depends on time and my ability to chrony today.  I really like the idea of a lower fill pressure!

I really like your cocking lever knob.  As you can see from the picure, my B-51 is older than yours so one thing that would be nice to do is to replace the whole bolt knob assembly with a prettier and better feeling one.

How are you flattening your trigger?  I would be afraid of breaking it.  I was thinking of making a wood overlay that would reduce the curvature and widen it a bit.  Could do it with PVC pipe bit too I guess.  Either way, I will polish and lube every thing.  I have a Maccari spring kit for my RWS 54, in it he includes Tar, White Grease, and lots of Moly.

I will keep all posted on shot strings and mods I do - this is going to be fun.

Looks like a lot of rain and wind today.  We are in HArwood MD, east of DC by about 30 miles so we should get some of the heaviest rains.  Gutters are clean so it should be OK.

Scott
AA S400Xtra 0.177, BAM B51 0.177, Crosman Discovery 0.22, IZH M-46, RWS-54 0.177, Crosman 1377C, Crosman Storm XT

Air Gun Tuner\'s Motto, \"At least do no harm to the existing airgun accuracy and power!\"

Offline DanoInTx

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Re: First Forray into the Darkside - B-51 Mods
« Reply #5 on: September 06, 2008, 06:51:01 AM »
To bend the trigger without it breaking you need to anneal it between bends.  First I straightened it out, then I reshaped it using a piece of round stock and a ball peen hammer....like an old school blacksmith.  To anneal the trigger I used a propane torch to heat it up to a dull red color then let it air cool, I've heard you can also quench it in water, but air cooling worked fine for me.  Brass is pretty easy to work with, just go slow and anneal between any heavy bending....I think you can get a replacement trigger from Best Airgun for about $5 if you break it, or so I have been told.  The biggest problem with the B51 trigger blade is the "hook" and how far forward it's set.  I removed the hook and also moved the reach back quite a bit.  They polish up pretty nice when you're all done.  I made the bolt handle on the lathe and then bent it the same way as the trigger.

Good luck and enjoy your tinkering.
Dan

Current shooters: Beeman HW97K .177 with Hawke Eclipse 4x16x50SFAO and Steve C. stock, Beeman R9 .177 with Hawke Airmax 4-12x40AO and Gene\'s Midas touch, Air Arms S200 with Bushnell Banner 6x24x40AO Rowan brass bling and Steve C. custom stock, BAM B25, BAM B40 .177 with BSA 3x12x44AO, Benjamin Marauder .22, Benjamin 397 pumper.

\"repeat this mantra:
Air gunzzzzzz, air gunzzzzzz, air gunzzzzzzz!!!  ...You will feel better\" T.E.C.2008

Offline scottinharwood

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RE: First Forray into the Darkside - B-51 Mods
« Reply #6 on: September 06, 2008, 06:58:57 AM »
Ok here is what I did:

Disasembled the B-51.

Found the breech block screws to not be too tight.  When I removed the breech screws I found that the top transfer port o-ring had about 25% missing - a bigchunck of the diameter just gone and I never suspected it.

The bottom transfer port o-ring was shot too, had the funny middle spit that bad o-rings get.  So I replaced them both.

Second, the trigger assembly components were really rough, as though they were machined quickly then slaped in with out polish.  I burnished the contacting surfaces with a diamond hone than polished the same surfaces with oiled 1000 grit wet-dry sand paper.  I used a white greese to lube the rub and pivot points.  The action is now very smooth and light now and because of this I no longer seem to mind the trigger shape.

The hammer and hammer spring guide were in the same shape, rough.  I chucked them into my wood lathe and polished them first with 600 grit then 1000 grit sand oiled sandpaper.  Now the hammer moves back and fourth with vey little friction.

I polished the bolt and lubed it with white greese.  Replaced the probe o-ring too.

I cleaned and oiled everything.

I replaced the main spring with the McMaster Carr spring.  Boy can you tell the difference before you even put them into the gun.

Slapped this thing toghether, filled it to 2000# and it was locked.

Bled it to 1750 # and I was shooting in the high 100's

I kept shooting and at about 1600# velocities jumped to about 700.

I think I will try the power adjust mod with the olds spring.  Or I will put a 1/2" spacer on the spring guide to tighten up the new M-C spring a bit.
AA S400Xtra 0.177, BAM B51 0.177, Crosman Discovery 0.22, IZH M-46, RWS-54 0.177, Crosman 1377C, Crosman Storm XT

Air Gun Tuner\'s Motto, \"At least do no harm to the existing airgun accuracy and power!\"

Offline DanoInTx

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Re: First Forray into the Darkside - B-51 Mods
« Reply #7 on: September 06, 2008, 07:16:50 AM »
Try increasing the spacing between the pin valve and the hammer before shimming the spring, leave just a little bit of the hammer screw poking out the front of the hammer and see if the FPS comes up, maybe 1/16".  If that doesn't work add washers one at a time until you get to desired power.  Mine gets about 17fpe with Crosman heavies at 1500psi.
Dan

Current shooters: Beeman HW97K .177 with Hawke Eclipse 4x16x50SFAO and Steve C. stock, Beeman R9 .177 with Hawke Airmax 4-12x40AO and Gene\'s Midas touch, Air Arms S200 with Bushnell Banner 6x24x40AO Rowan brass bling and Steve C. custom stock, BAM B25, BAM B40 .177 with BSA 3x12x44AO, Benjamin Marauder .22, Benjamin 397 pumper.

\"repeat this mantra:
Air gunzzzzzz, air gunzzzzzz, air gunzzzzzzz!!!  ...You will feel better\" T.E.C.2008

Offline Jaymo

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Re: First Forray into the Darkside - B-51 Mods
« Reply #8 on: September 06, 2008, 07:35:09 AM »
I thought about putting a weaker valve spring in the valve. Any thoughts on that?
15th Battalion, Mississippi Sharpshooters, CSA.

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Offline scottinharwood

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Re: First Forray into the Darkside - B-51 Mods
« Reply #9 on: September 06, 2008, 11:10:39 AM »
Hi Jaymo:

The McMaster Carr spring shown in 'The Book' is a much weaker mainspring.  I decided not to futz with the main pressure reseviour spring at all.  I do not think you need to either.  

I went back into the cave and continued my tweaking (I am an electrical engineer so the term is appropriate for me).  I turned down the hammer striker screw until only a little bit was showing, maybe 1/10 of an inch or less.

Knowing I wanted a main spring tension some where between the stock BAM B-51 spring and the McMaster Carr spring, I stacked 3 size -111 o-rings on the spring guide to take up about 1/2" more ofr spring space (added tension).  I put it all back together and charged the gun to 1950#.

My shot strings started at the low 600's - not too good but I decied to fire to see if the gun would hit 875fps.

It took a few shots but I finally hit 877fps.  I then used my Hill pump and pumped until I read the reseviour pressure; it was 1700#.

I continued to fire, my next thirty shots started at 906.8, slowly crept up to 931.9, then crept down to 899.  

Thats thirty shots with an average of 915 fps and a standard deviation of 6 to 7 fps.  The ES was under 20.

I think I have hit my sweet spot on this tune.  I will continue to fire it and see.

Again, I shoot lubricated Crosman Premeir Heavies (10.5gr).

I am happy so far and the tune cost me about $20.

Scott in Harwood
AA S400Xtra 0.177, BAM B51 0.177, Crosman Discovery 0.22, IZH M-46, RWS-54 0.177, Crosman 1377C, Crosman Storm XT

Air Gun Tuner\'s Motto, \"At least do no harm to the existing airgun accuracy and power!\"

Offline DanoInTx

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Re: First Forray into the Darkside - B-51 Mods
« Reply #10 on: September 06, 2008, 01:56:59 PM »
Sounds good Scott!  Not so sure about using o-rings for spring spacers though, springs like to rotate when they are released and might start to shred your o-rings giving really odd FPS numbers.  I'd stick with polished steel washers if possible, but what do I know:)  Might get a slightly flatter curve with a little loss of FPS by shimming just a tad less than you have, but I guess it depends on what sort of power you're going for.  Using steel washers instead of the o-rings might add a little bit of mass to the hammer also, giving you a bit more smack on the valve stem.  These guns are fun aren't they?

Dan

Current shooters: Beeman HW97K .177 with Hawke Eclipse 4x16x50SFAO and Steve C. stock, Beeman R9 .177 with Hawke Airmax 4-12x40AO and Gene\'s Midas touch, Air Arms S200 with Bushnell Banner 6x24x40AO Rowan brass bling and Steve C. custom stock, BAM B25, BAM B40 .177 with BSA 3x12x44AO, Benjamin Marauder .22, Benjamin 397 pumper.

\"repeat this mantra:
Air gunzzzzzz, air gunzzzzzz, air gunzzzzzzz!!!  ...You will feel better\" T.E.C.2008

Offline scottinharwood

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Re: First Forray into the Darkside - B-51 Mods
« Reply #11 on: September 06, 2008, 10:25:14 PM »
Hey Dano:

All those thoughts went through my head, but the o-rings were right there in front of me and I would have had to really scrounge for hours to get correct sized steel washers; my mantra in my basement shop is 'I know its in here somewhere....' and then three or so hours later I got to Home Depot anyway.  The hammer spring guide and inside of the hammer are n0ow polished to a bright shine and lightly lubricated so there is plenty of rotational capability on at least that end but I will just have to fire a bunch of pellets through it to see the effects - oh darn ;)

I found something out about my Beta Chrony in all this.  If I do not accurately place the muzzle of the rifle at both the same distance (that I knew) and also at the same angle, it can throw off the readings.  In that nice 30-shot low 900fps or so string, I had two, widely seperated low 800 value shots.  I was disapointed after the first one, thought hte tune did not take.  On the second one I noticed that I had canted the barrel up a bit and angled it from side to side over the chrony.  I really think those two shots out of 32 were bad data points so I did not include them.  I watched my angles and distances in the last 15 shots and they all came out low 900's where I wanted them.

Live and learn I guess.  I have never run so many pellets over the chrony before.

Oh yeah, read all the warnings took lots of precautions, go the safety ball bearing and srping off OK, put it back together and had to rotate the safety plate and sproing! there went the ball bearing and spring.  So I am safety-less now, but I never used the safety before anyway so no big loss.

I am going to run a careful set of chrony numbers today sometime and post before and after data.

Scott
AA S400Xtra 0.177, BAM B51 0.177, Crosman Discovery 0.22, IZH M-46, RWS-54 0.177, Crosman 1377C, Crosman Storm XT

Air Gun Tuner\'s Motto, \"At least do no harm to the existing airgun accuracy and power!\"

Offline scottinharwood

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B-51 Mods - Whoops forgot one thing
« Reply #12 on: September 06, 2008, 11:35:32 PM »
When I initially put the gun back together, I reinstalled the dreaded screw #26.  It locked the hammer.  I turned it a bit in then out a bit to reorient the screw head and depth, finally got the hammer to move but not nearly as cleanly as without the screw.  Sooooo, screw 26 is no-more in my B-51.  So far, I am not missing it at all!

Now, I finally hear a ping when I shoot.  What is it from? and where does a de-pinger go.  I saw some pics in 'the book' and could not figure that out.

Thanks

Scott
AA S400Xtra 0.177, BAM B51 0.177, Crosman Discovery 0.22, IZH M-46, RWS-54 0.177, Crosman 1377C, Crosman Storm XT

Air Gun Tuner\'s Motto, \"At least do no harm to the existing airgun accuracy and power!\"

Offline tat2dman

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RE: B-51 Mods - Whoops forgot one thing
« Reply #13 on: September 07, 2008, 01:21:12 AM »
A de-pinger is basically a baffle that goes in the air tube.
Barry Jackson-765-602-1351
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Offline scottinharwood

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I Spoke Too Soon
« Reply #14 on: September 07, 2008, 02:07:27 AM »
Well:

Sat down and ran more shots over the chrony, carefully.  Those odd ball low 800's readings that I got two of in a string of 32 nice 900+ shots turned out to be real.

I shot 50 more over the chrony and I keep getting the occasional low velocity shot, sometimes two in a row.  I raised the fill pressure from 1700 to 1800 and noted the same thing.

Then I put the scope back on, three shots to zero it - sort of - then began shooting 5 to 10 pellet strings at targets.  I am set up on sand bags so my gun is steady as a rock.  The groups open as you would expect with a steady lowering FPS.  However, there are some shots that just show that the velocity has dropped for that shot.

So its back to the drawing board.  I am thinking of trying to shorten the stock spring in increments.  Who out there has or sells a replacement stock spring for B-50/51's.  I always need to be able to get back to where I started from.

Thanks

Scott
AA S400Xtra 0.177, BAM B51 0.177, Crosman Discovery 0.22, IZH M-46, RWS-54 0.177, Crosman 1377C, Crosman Storm XT

Air Gun Tuner\'s Motto, \"At least do no harm to the existing airgun accuracy and power!\"