B51 Project

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Mac
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B51 Project

Post by Mac » Tue Nov 13, 2012 9:44 am

Bought a B51 recently, cleaned it up, reassembled and took a few shots.

B51 Exploded. Not difficult to work on at all.
B51 Exploded.jpg
B51 Exploded.jpg (1.58 MiB) Viewed 321 times
Here are a couple pics of the gun reassembled. Dan picked me out a nice one.
B51 Left Side.jpg
B51 Left Side.jpg (1.68 MiB) Viewed 321 times
B51 Right Side.jpg
B51 Right Side.jpg (1.43 MiB) Viewed 321 times
He is a quick five shot group I shot off my bum bag at 10 yards. Definitely shows promise.
B51 5 sh at 10 yards JSB 14.3.jpg
B51 5 sh at 10 yards JSB 14.3.jpg (1.38 MiB) Viewed 321 times
It is shooting the JSB Express 14.3 gr pellets in the 860s. That is as low as I could get it by simply adjusting the hammer travel. He hammer travel is maybe a quarter inch.
I have not shot a full string to see the velocity curve and may not until I have managed to decrease the velocity to about 825fps with these pellets. I may try a softer hammer spring or replace the actual threaded piece that hits the valve stem with a longer piece that will allow me to shorten the hammer travel even more.

Tim
Tim
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Mac
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Re: B51 Project

Post by Mac » Tue Nov 13, 2012 9:45 am

Went to Len's to take care of a few issues with the gun. Sharp edges had to be removed from the edge of the breach where the bold pushed the pellet i and the o-ring seal on the bold had to be replaced. Sharp edges were removed from the grove for the bolt where it pulls the hammer back. Also replaced the set screw at the end of the hammer that actually hits the valve stem. Replaced it with a set screw that was double the length, so I was able to have more adjustment for the length of travel for the hammer.

When I reassembled it, I kind of guessed where the set screw on the hammer should be set to get approximately 800fps with the JSB 14.3s. Shot it over the chrony and got readings from 794 to 803fps. Sometimes you get lucky.

Thanks for the help, Len.

Next step is to fill with air and shoot a string over the chrony. Will report when this is done.
Tim
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Mac
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Re: B51 Project

Post by Mac » Tue Nov 13, 2012 9:46 am

Predictably, the very short hammer travel translated to fairly low fill pressure. Even at 2500 psi, the velocity was in the 600s. At about 2200psi or 150 bar, it started shooting in the high 770s. I started my string of shots there, using the JSB Express .22 at 14.3 gr. The velocity quickly rose to 800 fps by the end of the first 10 shot string. Was shooting 820 fps by the end of 20 shots and peaked at 829.4 fps on the 25th shot. Down to 826 by the 30th shot and 804 by the 40th. The 50th shot was at 779.2 fps, so I ended it there.

The overall average for the 50 shots was 807 fps and the extreme spread was 51.9 fps. For field target I would cut 10 shots off each end of the string to lower the spread (25 fps ES for 30 shots), but for hunting and plinking, the 50 shots will all be very usable.

My next move will be to decrease the size of the port to restrict the amount of air getting through. I will lengthen the hammer stroke as well, which I hope will flatten out the trajectory some and also allow me to fill to a higher pressure level, resulting in more usable shots. My S400 seems to like the combination of a small port and hard hammer strike, so I'll see if it works here as well.

A regulator set at about 1800 psi would presently give me a big long string at about 825 fps. Not ready for that yet, as I would like to get the peak velocity down some, get the max fill up higher and the number of usable shots increased. I may tune for just under 20 ft/lb to make it usable at the Port Club and still have lots of power for hunting.

It certainly is fun messing with this gun. Snowing hard right now so these indoor activities will have to do for now. Looking forward to getting out to see what it will do at 50 to 55 yards. Now to get that new port made up. I may get a variety of sizes and settle for the one that yields the best performance according to my way of thinking.

Be back later.

Tim
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Mac
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Re: B51 Project

Post by Mac » Tue Nov 13, 2012 9:47 am

Was out at the Port Club doing some shooting because it was just too nice to stay indoors. Sunny and 18 degree in the afternoon.

After taking over 100 shots with my FWB 300 from the FT sitting position, I dragged out the B51 to see what it would do. I was not real steady by then after sitting in this position for such a long time. When I did my part, I was hitting a .375" dot at 35 yards. I then tried at 50 yards and was doing about 1" holding over a mil dot and a half to two dots for wind. I hit a 1.5" spinner at 55 yards holding three dots up and three dots right. There was a pretty good breeze out there.

I put in the small transfer port that Len made for me and tuned the gun to shoot JSB 14.3 pellets at 750fps or just under 18 ft/lb. The transfer port opening is 0.082".

I have not run a full string over the chrony, but will get to it sometime.

Looks like more good shooting days coming up in the next week, so I may do some testing off a decent rest when I first get there.

Later

Tim
Tim
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