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All Springer/NP/PCP Air Gun Discussion General > "Bob and Lloyds Workshop"

9mm PCP Carbine

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rsterne:
For the last few weeks, on and off while thinking about my Hayabusa project, I have been working on a 9mm Carbine.... It is my intention to set this gun up as a non-PAL rifle shooting 77.8 gr. EunJin pellets at just under 500 fps (~42 FPE).... As with a lot of my projects, it's just to learn what is possible and/or practical.... I used a Disco valve with the throat of the valve bored out to 1/4" and the exhaust port milled to 3/16" on a 20* angle.... The inlet side of the valve is streamlined to increase flow into the valve.... The transfer port is a piece of 1/4" OD x 7/32" ID brass tubing fitting into milled recesses in the valve and barrel and the breech is sealed to the valve with O-rings.... I machined the breech from aluminum, along with the barrel band and RVA.... I used a Disco fill fitting and cover.... The barrel band features a shouldered hole containing an O-ring so that the barrel is semi-floated....  

The barrel is a 9mm barrel liner (1/2" OD) from Track of the Wolf.... I had quite a time getting the pellets to feed, and it required a long taper to basically "size" the pellets as they are fed into the rifling.... I blued the barrel after doing all the machining.... The hammer is a stock 2260 unit with a longer cocking pin.... and the hammer spring is from a Disco.... Once I finish tinkering, I will be fitting a stock (ie non-adjustable) 2260 rear plug and trimming the hammer spring to keep the strongest shot under 500 fps.... The steel bolt uses a probe to push the pellet past the transfer port, and a 10-32 bolt as a handle, fitted with an oversize brass knob.... I tried a flow-through bolt, but pushing on the skirt of the pellet damaged them, actually tending to shear off the edge while seating the pellet.... The probe pushing on the center of the pellet allows the skirt to collapse slightly while seating, avoiding this problem....  



I filled the gun to 2000 psi and started testing.... To my surprise, the peak of the velocity curve is at very low pressure, even with the hammer spring near coil bind.... As you back off on the hammer spring preload, you have to start at a lower fill pressure.... and the peak velocity occurs at an even lower pressure.... By the time I found a non-PAL setting, I was only filling to 1400 psi.... The velocity was peaking at only about 900 psi.... and in all cases, the last shot in the string (where the velocity was down ~10% from the peak) was at under 600 psi.... with the pressure reading about 400 psi at the end of all the strings....  



The efficiency is very high.... At maximum, the gun is delivering ~52FPE for 10 shots (514 FPE total) at 1.2 FPE/ci.... Two turns out on the adjuster, it is getting ~46 FPE (508 FPE total) over 11 shots for 1.4 FPE/ci.... At 4.5 turns out, it is returning ~40 FPE (356 FPE total) for 9 shots, again at 1.4 FPE/ci.... The limited number of shots is due, of course, to the relative small reservoir.... but it compares favourably to my .22 cal PCP Carbine Grouse Gun which gets 16 shots at 20 FPE from the same size tube (320 FPE total), for about 1.2 FPE/ci.... I may try restricting the transfer port to see if I can flatten the shot string for the non-PAL version and get more shots.... It should be possible to do so.... If not, I will likely use a regulated 13ci tank and shorten the stock....  

Bob

rsterne:
I know, I'm replying to my own topic....  :) .... This thread is copy/pasted from another forum because I wanted to use my latest project by way of introduction here.... I have added the information below to the thread already, so here it is....

Well, I had some time this afternoon to make a new transfer port from a piece of 1/4" brass rod.... I started at 1/8" bore which was too small, but showed I was on the right track.... I drilled it out to 9/64" (0.140") which just happens to be the same size as a stock Crosman TP.... This allowed me to crank in the hammer spring to just under 2 turns out, and get a flatter shot string.... The black line in the graph below is what it did previously in the non-PAL setup.... while the red line is the way it works now.... 



By the time I was finished, I ended up with a longer string (12 shots) that was much flatter (8% variation).... The average velocity was 487 fps with a low of 460 and a high of 499.... Average energy was 41 FPE for a total of 491 FPE over the string.... The starting pressure was now 2000 psi and the reservoir was down to 700 psi after the last shot.... That meant the efficiency was even better at 1.46 FPE/ci.... 

I'm only shooting inside, but the entire string goes into one ragged hole.... This gun is pretty much done until I can get outside in the Spring and do more testing at longer ranges.... I think the idea of having a non-PAL gun that puts out 41 FPE is pretty cool.... 

Bob

Rescue35:
Welcome and thanks for the information. This will help me a lot in my build. I'm currently working on a .45 and 9mm rifle. In fact I'm heading back to the lathe to finish working on the valve body. Keep us updated.

rsterne:
I've just swapped out the hammer spring for a stiffer one (0.040" wire instead of 0.035").... I'm out of EunJins but more on the way.... Once I get my pellets, I'll be trying to see what I can get for maximum performance before detuning it for Canada's wonderful under 500 fps limit.... I have my PAL (Possession and Acquisition License) but this gun I don't want to have to register....

Bob

lloyd-ss:
Bob,
Good to see you here!  A lot of talk about carbines and barrel lengths going on these days.  You said you are going to try and tune this carbine for max performance before dropping it to the non-PAL 500fps limit.  Just to make sure I understand, you will be trying to max out the fps with this set-up with the 16"  9mm barrel? That will be very interesting to see.

Regarding your efficiency numbers.   When you quote numbers of 1.2 FPE/cuin, you are referring to 1.2 FPE/standard cuin of air, correct?  Could you show us a calc to show how much air one of those 52FPE shots at 1500 psi would use in cc's.

Thanks for posting!
Lloyd

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