My Hayabusa PCP - The Experiment Continues

[AirGunEric]

Maybe hollow out the hammer and fill with something heavier- i.e. lead (or gold if you have some extra laying around ) ?

[rsterne]

Apparently Tungsten isn't that hard to machine, and twice as heavy.... but I can't imagine having a 1 lb. hammer.... it's over 8 oz. now....

Bob

[rsterne]

It turns out I had another hammer spring here to try, which allowed me to examine what the maximum performance was.... It was actually two 3" long springs of 0.062" wire instead of the single 4.5" long spring of 0.072" wire.... This gave me about the same force when cocked, but instead of having no preload when uncocked it had a preload of about 10 lbs.... That gave more hammer energy, so I was able to find out where the velocity plateau was at 3600 psi.... It turns out the gun maxes out at about 870 fps (340 FPE).... I couldn't back the preload adjuster out far enough with the long spring to get down under 800 fps, but by using the original spring I was able to plot the velocity profile.... Once I established that the best place to tune the gun was with the original spring maxed out, I then shot a string, recording all the shots within 5% of the peak....



The best choice for a hammer spring would be one about 5" long, made of 0.062" wire, and I can get a 10" one from Trakar and then cut it in half, which is the eventual plan.... However, I was able to get 9 shots with 5%, of which 7 shots were within 3% ES.... The average velocity for those 7 shots was 819 fps (302 FPE), and I would refill at about 2500 psi, and the efficiency is 0.76 FPE/CI....

I think this will prove to be an effective short range Grouse gun.... It doesn't have the smack of a powderburner, but if I can get decent patterns with the #8 shot I think it will do the job....

Bob

[rsterne]

Today was quite a day.... After a couple of years of planning and a year of work, I shot my Hayabusa .457 for the first time today, and saw over 550 FPE.... I tested three kinds of ammo, found the maximum that the gun would do at 3600 psi with all three, and found two great shot strings.... The bullets used were a 143 gr. roundball, and two Lee bullets, a 216 gr. RN and a 336 gr. FN.... In order to find the velocity plateau I had to use the two 3" hammer springs like I did on the .410 shotgun, and here are the maxed out results....

143 gr. RB - 1101 fps (385 FPE)
216 gr. RN - 993 fps (473 FPE)
336 gr. FN - 859 fps (551 FPE)

Needless to say, all the work and frustration has paid off and I've got a pretty big smile right now.... I put the 4.5" long 0.072" wire spring back in and shot the following strings....



With the spring just shy of coil bind the roundball showed the first shot fastest at 1070 fps.... The 216 gr. RN had the 2nd shot fastest at 960 fps.... Both bullets had 5 shots before falling more than 4% below the peak.... With the 336 gr. FN bullet I got a very nice 7 shot string peaking at 815 fps (496 FPE).... That string averaged 800 fps (477 FPE) with an efficiency of 0.96 FPE/CI.... I then backed the preload down a turn and shot another string with the 216 gr. RN and got 8 shots peaking at 929 fps (414 FPE) and averaging 913 fps (400 FPE) with an efficiency of 0.99 FPE/CI from 3600 psi down to 2400....

To say I'm pleased with this performance is an understatement.... I was hoping this gun would break 500 FPE, I never though it would break 550, nor did I think it would give me 8 shots at 400 FPE on a fill.... Time to just bask in the glow of satisfaction for a while.... I need a break.... and a drink....

Bob

[rsterne]

This will give you an idea of the power.... I taped four clear Cedar 2x4s together and it blew through two of them and imbedded completely in the third....



This was the 336 gr. Lee FN travelling at 792 fps (468 FPE), which is the first shot of my 7 shot string.... Here are the exit holes and bullet in the third 2x4 (edge view)....



The 2x4s were a foot long and taped tightly together at both ends with duct tape, and the 3rd one where the bullet stopped was split from end to end.... They were against a solid backstop to prevent movement....

Bob

[rsterne]

I wasn't very happy with the hammer spring I was using, it had no preload and must have required 40 lbs. to cock it, so I searched for a longer spring of smaller wire.... I couldn't find anything ready to use, but I did manage to find a 10" long spring made of 0.062" wire, and when I finally got it in the mail, the first thing I did was "set" it to collapse the coils so that in future during use it wouldn't get even shorter.... It's a good thing I did, because it lost 2" in length, ending up at only 8".... I cut 2" off and tried it, but the preload was too much, I could hardly install it, and it turned out that I didn't need that much, so I cut it down to 5.5" and that worked out great.... I can still max out the gun with the 336 gr. bullet at 855 fps, with a bit of preload left, and even at that setting the gun was much easier to cock.... I tried it with the 216 gr. bullet and it did 979 fps (460 FPE), and I had to back the preload down 6 turns to get a proper string, and at that setting it was MUCH nice to cock.... I shot three strings at different preloads, and the results are below.... The caption on the pressure line is wrong, that was at -8 turns....



At 6 turns out I get three shots within 10 fps and two more before the velocity has dropped by 4%.... The first 3 shots average 965 fps (447 FPE) and the 5 shot string works out to 0.86 FPE/CI, not too bad for that much power.... At 7 turns out I got 6 shots averaging 934 fps (419 FPE) at 0.90 FPE/CI, and at 8 turns out I got 7 shots averaging 922 fps (408 FPE) at an efficiency of 0.96 FPE/CI.... Any of the three strings would be fine, but the first one, with 3 nearly equal shots at almost 450 FPE with two more within 4% looks very tempting....This pretty much completes the development of the .457 version, when I get a chance I will test the .410 shotgun with the new spring....

Bob