Air Gun Home :: View topic - 2260 PCP Rifle

rsterne · Moderator

I finished my 2260 conversion today.... This once 10 FPE CO2 rifle is now capable of up to 50 FPE using an 18 cu.in. 3000 psi tank regulated to 2000 psi.... I shortened the stock 5" and used the part I cut off to make a raised cheekpiece which I customized to line my eye up perfectly with the 4-12 x 40 AO Bushnell Scope....

The rifle weighs just 6 lbs. 10 oz. all up.... and balances perfectly, right on the front trigger retaining screw.... Just in front of that there is a Disco gauge mounted in an extended front end on a (modified and bored out) Disco valve which moves the pressure seal ahead of the roll-stamp on the 2260 tube.... This, in conjunction with a QB79 tank block modified with the addition of a 3/16" shear pin plus an extra 8-32 screw with the head in shear make sure that the gun can stand the loads of a PCP setup.... The 2260 tube was shortened to just in front of the serial number so I won't have a problem with the CFC (the gun is already registered).... Rolling Eyes

The rifle is equipped with an RVA of my own design, which allows changing out the hammer spring without disassembling the back of the gun.... To enable me to fully utilize the 2000 psi pressure of the regulator I had to change out the hammer spring for one made from 0.040" wire.... I have a total adjustment range of 1/2" (8 turns).... which gives me the ability to adjust the power from 8 FPE to 50 FPE with the turn of a screw.... The transfer port is drilled to 0.166" and the barrel port to 0.169".... Cool

At the maximum setting, the power ranges from 34.7 FPE with 11.9 gr. RWS Hobbies (1145 fps - supersonic) to 50.5 FPE with 32.4 gr. EunJin Pointed (838 fps).... This setting uses a lot of air, and turning the adjuster out 2 turns gives about 50% more shots with virtually no power loss (33.8 FPE) with the lighter pellets.... although the heavier ones suffer and the highest energy is now with 28.7 gr. EunJin Domes at 43.9 FPE.... Backing the adjuster out another two turns (-4T) flattens the power curve even more to a level of about 33 FPE with most pellets.... and increases the shots to about 45-50 per refill.... At this level, 18 gr. JSB Heavies shoot at 920 fps and 21 gr. H&N Baracudas (Kodiaks) have a muzzle velocity of 850 fps.... At 6 turns out, the power curve is virtually flat at 21 FPE, and should be 80-100 shots per fill.... At minimum power, the gun is just under 8 FPE (498 fps with 14.3 gr. pellets) and is likely in the 250-300 shots per fill range.... Shocked

The targets above were shot indoors at 20'.... They were only done to sight in the rifle and find out if this thing was going to be sensitve to pellet selection, which is obviously isn't.... All 3-shot groups were shot at 4 turns out (31-34 FPE) except the last two on the bottom row, which were shot at maximum power.... Small squares on the targets are 0.1".... 8)
Top row L to R: JSB Exact 15.9 gr, RWS Hobby 11.9 gr, JSB Express 14.3 gr, JSB Heavy 18.0 gr, H&N Baracuda 21.0 gr....
Bottom row L to R: H&N Rabbit Magnum 24.8 gr, EunJin Domed 28.7 gr, EunJin Pointed 32.4 gr; then EunJin Domed at 838 fps and JSB Exact at 1059 fps....
The gun shot so well without the barrel band I decided to leave the barrel floating.... Wink

All in all, I'm very pleased with the results.... This gun has been in development now for nearly a year, through my 22XX PCP project experiments.... I decided that it would balance OK with the 18 cu.in. tank, so that was the governing factor in the final configuration.... My 13 cu.in. tank will be used for my next project.... Twisted Evil

Bob

broommaster2000 · Moderator

Geev!!!

To be honest, I don't think that that big tank looks that good on a small slender rifle like this... I guess it's the only way to go with that manometer though. Neutral

And well, a 2250 doing 50 Fpe is not to shabbay. It's something I'd write home about. Mr. Green

rsterne · Moderator

Kinda like racecars, Broom.... Rolling Eyes

Pretty ain't always fast.... but fast is ALWAYS pretty.... Twisted Evil

Bob

AirGunEric · Site Admin

Bob's a nut! Really- he's gone totally whacko- making 50fpe 2260's! Crazy/Loopy

Teryx · Veteran Member

I'm writing home right now! Shocked

I just hope Bob's "compound" doesn't become the Canadian "Waco" Shocked

Teryx

broommaster2000 · Moderator

rsterne · Moderator

I did a bit more playing around with this rifle today.... I found that at 4 turns out (32.4 FPE) when it went off regulator the velocity actually climbed almost 40 fps from ~900 to ~940.... I tried a few other settings and found that at 3 turns out on the RVA the velocity over the entire pressure range is MUCH flatter because the peak of the non-regulated shot string is at the regulator cutoff pressure (which is actually 1900 psi).... Shocked

This gives me a virtually flat shot string of 47 shots starting at 3000 psi and continuing 200 psi lower than the setpoint to 1700 psi.... the performance (and noise) is up of course.... The average velocity over the 47 shots was 968 fps plus/minus just 2% (with the exception of 3 shots that spiked down to ~935).... That works out to 37.4 FPE and an efficiency of 1.09 FPE/c.i..... Cool

When you break up the string into 10 shots groups you get the following:

shots 1-10; average 966 fps (2 low shots)
shots 11-20; average 970 fps (1 low shot)
shots 21-30; average 967 fps
shots 31-40; average 974 fps
shots 41-47; average 960 fps

The velocity got more consistent as the pressure dropped.... As this is the first string I have shot at this setting, I don't know if the gun is settling in or if the valve opening is slightly erratic at the higher pressures and improving as the pressure drops.... In any case, even with the low velocity shots thrown in, all shots are within 95% of the maximum so within 50 yards, if won't make any significant difference in the POI.... Rolling Eyes

I will be doing some accuracy testing at this power level.... but just to satisfy my curiousity, I shot 5 shots over the Chrony with 21 gr. Kodiaks, 25 gr. JSB Monsters, and 28 gr. EunJins.... The FPE creeps up slowly as the pellet weight increases:

H&N Baracuda 21.0 gr @ 898 fpe = 37.6 FPE
JSB Monster 25.2 gr @ 823 fps = 37.9 FPE
EunJin Dome 28.4 gr @ 779 fps = 38.3 FPE

It is pretty obvious that I'm right on the sweet spot for pellet weight between 18 and 28 gr.... the variation in energy is less than 1 FPE.... Cool

Bob

Slavia · Moderator

As far as aesthetics, I'll put it in terms that Bob can understand:

Using that bit of wood to raise the comb was an elegant solution.

BBgunNoob · Veteran Member

whats your next project ? Smile

BBgunNoob · Veteran Member

and that is amazing that you turned a 2260 into a killing machine that beats out 500 dollar guns lol

broommaster2000 · Moderator

Hey Bob, could you make a cost estimate? I wonder if it really does what BBGN says. Mr. Green

rsterne · Moderator

broommaster2000 · Moderator

Thanks Bob,

Hahaha, wooh, are YOU glad you did the job yourself or WHAT! Not hard to see how you're satisfied with a kit when you put it like that. Mr. Green

VENI VIDI VICI · Member

rsterne · Moderator

I designed and manufactured High Tech R/C Model Racing Yachts (sail) for 30 years.... the kind that win International Championships.... I spent the last few years working in a machine shop part time and ended up on a CNC Mill (plus manual mills & lathes)....

I started back into Airguns when I retired in Sept. 2007.... so everything I write about has been discovered since then.... mostly through my original research as what has been available is spotty, poorly documented, and anecdotal at best.... I'm trying to change that by sharing what I learn along the way.... Mr. Green

Bob