B51 .177 gets a makeover

I have had a B51 for about 3 years…but the last 6-8 months it havent seen much action….

i had it tuned nicely, and its accurate…but the 410 took over…

so it has been sitting in the basement untouched for a while…i had a dream of turning it into a .308…but budget keeping me back from investing $$$ into a new barrel.

also sitting in the basement was a 23″ poly .25 barrel ready to drop in an Af rifle….but the talon is busy being a .457…..sooo i cut the breech of the barrel, and started to turn it

Barrel
B51 barrel are 12mm barrels…and the .25 i had was a 16mm barrel…so i turned most of it down leaving the front 2-3″ 16mm so the barrel band has to be pushed on from the back side, before the barrel is mounted in the breech, this adds a nice barrel weight plus allows for a ½” unf thread to be cut for extra gadgets ;-), alternatively you can mount a 16mm barrel theres plenty of room for it, then it just has to be cut to fit the breech…i tried this and it seems plenty sturdy, and has about ½mm space between the tank …..reason i cut the barrel down was i wanted a light rifle…and the 16 vs 12mm barrel actually removes quite a bit of weight

Breech….the breech has to be drilled a little bit, its allready .245 so i upped it to .255″ where the Oring touches…, the probe got a slightly bigger oring…transfer port got bore out to .25″…and then that was done

the coupling between the breech and valve, which is a brass port sandwished bewteen 2 orings got replaced with a piece of tubing i had that fits perfectly but allows alot more flow.

the valve, well….without any changes from the 18 fpe (but all above changes made…it shot a crowmagnum at 850 fps…i forget the 42 grain speed but it was quite a bit of power….

the valve got drilled out to .25″ in the transferport too….be carefull with this part , as there is not much material…return spring got swapped for a lighter one….the endcap of the valvebody has a small hole in it towards the tank this got bored out to .308

the valve got the original hammer weight/springguide to add some preload and weight..plus 5 washer on the hammer to further tention it up.

42 grain pellet loaded up, 200 bar…..and booom 983 fps(90 fpe), second shot 920 fps, 3rd shot 884 fps….not excatly consistent….but quite a bit of power for allmost carbine size rifle with 20″ barrel…..(will add FPE as soon as i get chairgun downloaded)

removed the washers so it became a stock hammer setup….and power sterted at 885 fps, and dropped 10 fps pr shot, until it hit 840 then i got about 3 shots before it hit 830(63 fpe) which is more like it… but still too much hammer force is mu guess….have swithced the hammer parts to my optimized ones….but…..originally the barrel is glued in place…and i had just mounted it with nothing but firction hoping it would stay in place…but it started to move forward with each shot…so epoxied it to the breech and it is drying as i type this…..

what i wanted was a light hunting rifle…the AA410ERB is great, but im having a bit of trouble shooting it offhand….and when i got home i picked up the B51 and shot it…and it just felt more easy to get on target, so im hoping with this mod, to get a powerfull rifle at about 55-60 fpe(800 with 42 grain, 900 with kodiac), thats light and pointable .

to be continued……