My Hayabusa PCP - The Experiment Continues

[rsterne]

The black Hatsan stripper, to me, seems to actually make it quieter shooting inside my shop, but I'm sure that's just perceived as all it's doing it venting the gasses to the sides.... and I'm shooting with earplugs in, so who really knows.... You can't tell the accuracy at 20', one hole is one hole, pretty much.... The gun is, however, LOUD....

I found my hammer cocking handle was rubbing on the side of the breech slightly, so I ground/filed the notch slightly wider.... I think that seems to have made the shot to shot variation slightly greater and may have shortened the string a shot or two.... I'm topping up my SCUBA tank right now, tomorrow I will try and find a tune that starts 4% below peak velocity right at 3000 psi.... ie the fastest possible string where all shots are 96%+....

I'm pretty sure I was getting hammer bounce on the first string yesterday when it was REALLY loud and the first shot the fastest starting at 3000 psi.... I'm wondering if I can figure out how to make a Hatsan style hammer latch to stop the hammer on it's first bounce (while travelling backwards) and prevent a second strike of the valve stem.... Lifting it out of the way to allow the hammer to be cocked is the trick, because withdrawing the bolt is a separate operation to cocking the hammer.... On the other hand, if I can get over 1 FPE/CI at these power levels, it is maybe a moot point / waste of time....

I'm effectively only using about 1" of hammer travel (well it's only being accelerated for the first inch, and then coasting the next 0.2" up to the valve).... so you shouldn't have a problem with a 1" travel and a QB spring....

Bob

[remtom1200]

I see the same operation for the debouncer in this application as it is with the hatsan, and i'm guessing you have to cock this setup with the bolt open which would allow the hammer to move freely? The trick could be where and how to pocket the little spring for the debouncer.

[rsterne]

Actually, I load the bullet first and leave the gun uncocked until ready to fire, so I'm cocking it with the bolt closed.... I think I have enough depth in the breech under the bolt to hide the toggle, and I can always use a hairpin spring.... On the .22/.25 cal breech I could close the bolt with the hammer cocked, on the .30/.35 cal breech, which has 1.5" hammer travel, you can't rotate the bolt down to the locked position with it cocked.... At this point it's just a thought, anyway....

If the hammer toggle/bounce preventer in the Hatsan was really improving the efficiency compared too, say, a modded Disco at the same power level and pressures.... you would expect that the Hatsan would have much greater efficiency numbers.... It doesn't.... I am still of the opinion that a properly tuned PCP shouldn't need a hammer debouncer.... They seem to be useful if you are running too much hammer strike for the pressure.... eg. on the latter part of an unregulated shot string, or in a regulated gun running at maximum velocity for the pressure....

Bob

[rsterne]

Sean: RE polishing the barrel with Bore Brite (red).... I pulled the barrel and did the chamber area until the felt pucks weren't quite so tight in the bore (maybe 20 strokes).... I then assembled the rod full length, added fresh paste, and did 20 strokes full length, not quite out the muzzle, then reloaded it and did 30 more.... I then removed a section of rod, reloaded with paste and did 15 more, took off another section, reloaded and did another 15.... So, the full barrel got 50 strokes, and the breech end about 100.... I still have yet to clean it and reassemble.... Any suggestions RE the method I used?.... How often should I do this?.... I probably shot about 100-150 rounds already (1 bag)....

Bob

[rsterne]

I took SeanMP's advice and polished the bore with Bore Brite (red) today, and true to what he said, I picked up a few fps and the groups tightened up.... I tried the RVA at 2.5 turns out as well, with a 3000 psi fill, and got just about what I expected.... Although the first shot wasn't the fastest, the peak of the bell-curve was only at shot 5, and the efficiency was just under 1.0 FPE/CI.... so that's a little too hot.... I retested at 3 and 3.5 turns out, and the results of these three tunes are below.... All started at 3000 psi except the 3.5 turns out, which required only a 2800 psi fill....



The best tune is 3 turns out, which allows me to use a full 3000 psi fill and get 20 shots within a 4% ES and 13 within 2%, using an average of 44 psi per shot.... There are 16 shots within 25 fps between 1004 and 1029 fps, so that makes a pretty decent sweet spot using a 2900 psi fill and a 2200 psi refill, which works out to 1.13 FPE/CI at an average of 95 FPE.... If I was running the gun on a tether, I would fill to about 2700 psi, shoot a 5 shot group, and refill at 2500.... or use a regulator set for 2600.... That would give me 5 shots within about a 5 fps ES (0.5%) by running right at the top of the bell-curve....

When I shot the last string after I reset the RVA to 3 turns out after the days testing, I shot four 5-shot groups.... They were all just ragged holes, but one was exceptional.... It is the first time I have ever had a gun pass the "Feinwerkbau Test"....



I realize this was only at 20', but it's still the only time I could put a bullet in the hole made by a 5 shot group and have it remain in the single sheet of target paper.... The testing and tuning on this gun is now complete until I can get it outside to stretch its legs this summer.... The .257 cal barrel and my new bullet molds should be here this week, so the plan is to work on that next....

Bob

[SeanMP]

Bob
A hearty congratulations ... Having a gun produce hole on hole is a heck of an achievement.

Your intuition was good. I definitely would have done the same routine on a barrel like this because it's such a large tight fitting slug it's going to be depositing a lot of lead.
From here all you need to do is a full length swabbing with Bore Bright, perhaps ten strokes, followed by a tight patch lightly oiled. This will knock off the high spots of deposit leaving the behind the material in the scratches and pores.
I personally would continue that routine for another 5 sessions or until I was really convinced the barrel was at its peak. As long as your seeing improvement in velocity or accuracy it's worth continuing

Again, nice work! I can't believe how awesome that build is right off the hop.

Gophers beware!

[remtom1200]

Is the oring on your valve the only thing keeping 3000psi from leaking by? Thats pretty amazing if it is and is that a duro 90 oring?

[rsterne]

Yep, just a single 70 Durometer O-ring.... Why would that be amazing?.... Two O-rings are in theory no better than one, the second one only works if the first one leaks....

Bob

[SeanMP]

A 70 duro Oring is certainly feasible but the gap is critical at 3000psi

PRESSURE-DUROMETER.jpg

[Doc Sharptail]

How about some pix? At least of the completed gun....

Regards,

Doc Sharptail