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PostPosted: Sun Dec 21, 2014 10:54 pm 
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Location: Komoka Ont.
I had to do a bit of smoothing on my B50 to get the accuracy going.The crown didn't look real good so I redressed it and I found a burr at the transfer port that was scoring pellets so that had to be removed and finally when pushing pellets through the barrel it felt rough so I did some amateur lapping. At 13.5ftlbs I've gotten 1/2" groups at 40yds with CPHPs but when I'm at 25ftlbs then JSB 18.1 are even more accurate. Those are the best pellets for this rifle that I've read of so far and I believe it.

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PostPosted: Sun Dec 21, 2014 11:25 pm 
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Location: Coalmont BC
Hopefully, Kim, my other projects will arrive soon, this was kind of a filler I finally got around to (after 2+ years).... Besides, the only spare .25 cal barrel I have is an LW Poly and it's 16mm OD so would hit the air tube.... Do you have any experience with the Polygonal rifling?.... I've never used one....

Bob

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PostPosted: Mon Dec 22, 2014 12:25 am 
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Location: Alberta Canada
I personally havent tried one. But randyhub has one upon his AF Condor as it is a very very accurate bbl even out to 80-90 yrds. Being that I believe its only 14.5 in length.
When he first got it, the slug tests with a variety of ammo showed a very suttle compression upon the pellet. Bbl crowning IMHO is the key with the bbl accuracy.
He swears by it, and Ive seen him make some amazing 100+ yrd shots with it upon gophers.

Been teasing the idea with it but another one of them projects upon the books. Because something else always teases my mind. :shock:
Like someones BT65 in 30 cal that was in my garage today. Tore down and apart in minutes. An hour latter after micrometers and all kinds of speculations proposals and such :rolleyes: . Assembled instantly :( It vanished :cry: to be determinded upon its potential come January 3rd 2015.
My wife described it as like two little kids at Christmas tearing into a gift just to find out that the wrapping paper got the most attention. :lol: :lol:

Sorry for the off topic bit. Guess it becomes one of them twisted choice things to use or not to use....hmmmmm.

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PostPosted: Wed Dec 24, 2014 2:06 pm 
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Location: Komoka Ont.
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.
Image
Image
I also drilled the hole in the valve body larger to 5/32"
Image
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.
So here are 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?

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PostPosted: Wed Dec 24, 2014 3:56 pm 
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It depends on what you are after.... You are filling to a very low pressure, and even then, the first 7 shots are more than 4% below the peak velocity (and the last shot), so you are only able to effectively use a fill pressure of ~ 100 bar.... I think it's a good string, but not sure why you would want to fit a smaller transfer port as that will drop your performance even more, and you're only at 24 FPE, although you are getting 34 good shots....

If you want a bit more power, and you don't mind a higher pressure fill, I would increase the preload and try again....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Dec 24, 2014 6:50 pm 
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I want to flatten the curve and get more shots, I like the low fill pressure and I'm hoping to find a point that I can get 50-60 shots at the best curve what ever power level that ends up with. I will rarely shoot over 50yds and I don't enjoy the extra care required to shoot higher power levels, it's just my personal choice. I know that with the valve as it is I could get a cannon and I would have drilled the valve larger if that was how I wanted to go.

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PostPosted: Wed Dec 24, 2014 7:19 pm 
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Ahhhhhh.... well if you want 50-60 shots, then dial the power way back by reducing the port diameter.... which begs the question why did you drill the valve exhaust port out?.... Of course the best way for what you want would be to install a regulator and go to a full 200 bar fill.... As a rough rule of thumb, if you want 50% more shots, then reduce the FPE by 33% to about 15-16 FPE....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Dec 25, 2014 10:39 am 
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Location: Komoka Ont.
I drilled the valve so I would have a greater range to tune without having to take it out again, I figure by varying the TP, springs, spring guides etc I could come up with a combo for what ever suits my purpose. Your post has really given me a lot of confidence for this rifle, I am so glad you waited this long to give it a go. Over the past few years I have watched your knowledge grow from a level I can't attain to the stratosphere for airgun physics and in a very short period you thoroughly worked this rifle over without wrecking anything.
I just put in a smaller TP (3/32") I'll see what happens, I can still take a little preload off the spring guide.

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PostPosted: Thu Dec 25, 2014 11:44 am 
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Location: Burlington, Ontario
I can't wait for my b51 to arrive next week. Thanks for posting all this.

@Garth, I appreciate you sending me a new spring! My goal is 12-14fpe on .177 and a decent shot string. The "book" will hopefully make more sense once I have the rifle in hand.

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PostPosted: Thu Jan 01, 2015 4:32 pm 
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Location: Burlington, Ontario
So I am trying to tear down my b51 using the book. Question on removing the hammer, I removed screw #26 and the hammer moves freely but I can't pull it out completely. Only the spring guide comes out. Do I need to remove screw #16 as well?

Thanks

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AA S400SL FT .177 Bushnell 8-32x40
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PostPosted: Thu Jan 01, 2015 4:50 pm 
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Location: Coalmont BC
You have to pull the trigger and lift the sear up (away from the tube) to allow you to withdraw the hammer.... same thing to reinstall....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Jan 01, 2015 5:06 pm 
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Location: Burlington, Ontario
Thank you. I am waiting for a smaller tp and mc spring to arrive. Just getting it ready.
Do you guys think I need to adjust the striker at all if I'm installing these two things to reduce fpe?

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AA S400SL FT .177 Bushnell 8-32x40
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PostPosted: Thu Jan 01, 2015 7:27 pm 
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Nope, not likely.... maybe just use it to fine tune....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Fri Jan 02, 2015 9:57 am 
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Joined: Wed Dec 14, 2005 11:34 am
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Location: Gatineau, Qc
Nice going there Bob,

Its been a while since I've posted, my problem I have is my factory poppet keeps cracking, I haven't figured out why or if its just too brittle.

Yves

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PostPosted: Fri Jan 02, 2015 11:29 am 
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Location: Coalmont BC
I think it is because of the valve spring going coil bound combined with a heavy hammer strike and low air pressure or firing the gun while empty (of air).... The poppet stops and the stem tries to keep going....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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