Air Gun Home :: View topic - .22 Uber-Carbine

rsterne · Moderator

If you frequent some of the other forums, you will be familiar with my 24” barreled .177 and .22 calibre Uber-Pumpers… I decided to use the same technology to develop a 14” barreled version in .22 cal for a compact Grouse gun… The goal was to substantially reduce the number of pumps required to reload, while not compromising the easy handling of a 2289 when getting in and out of a car, as I find most of my Ruffies just before sunset when they are chowing down on roadside gravel to digest their afternoon meal… There was little point in enlarging the valve with the short barrel (wasted air = more noise), and the longer valve I used in the .22 Uber-Pumper would just waste pump stroke in the 2200 tube (which is just a fraction shorter than the barrel)… besides, 600 fps is more than enough... Rolling Eyes

Technically, the basis is a 2200 pump tube (receiver) and pump linkage, and the gun will be registered as a modified 2200 using the serial number on the tube (so I can brag about numbers with impunity, as I have a PAL)… Most of the other components are modified 2289 parts (barrel, valve, trigger group, hammer, spring & seat, and the stock)… with a few custom machined parts (made by myself) as required to complete the build… The gun is topped by a long Crosman steel breech mounting a Leapers 4x32 Master Sniper scope in their medium height rings… I focus the scope at 20 yards, and the image is clear from 10 to 30 yards without having to fiddle with adjustments… This, combined with a 25 yard zero, gives me a point blank hold from 9 to 28 yards for 1/4” above or below line of sight, which covers basically all of my shooting requirements… holding on the bottom of the eye gives a Grouse in the bag, providing he doesn’t duck just as I squeeze the trigger… Twisted Evil

The photo below shows the modifications to the bottom of the 2200 pump tube:
Drilled a 3/16” hole to mount the rear of the trigger group
Moved the front of the sear slot forward 3/16” to clear the sear
Drilled & tapped an 8-32 hole for a set-screw to retain the valve

In addition, it shows the mods to the 2289 trigger group:
Drilled and tapped a through hole to accept two 8-32 screws (one each side) to fasten the front of the trigger group to the breech band
Lighter sear spring (Dynaline #24612) with tubing guide and travel stop, and Crosman trigger shoe
All trigger friction points polished, including the hammer (short, under 2 lb. pull & smooth as silk)

In the top of the next photo, you can see the changes to the top of the 2200 pump tube:
Drilled new 9/32” transfer port just behind the original one
Drilled and tapped a 4-48 hole for the breech retaining screw

Next down is the custom piston assembly:
Flat-topped piston machined from 5/8” aluminum rod, with O-ring groove, drilled & tapped 1/4"-20
Piston rod from 1/4”-20 threaded rod, with double nuts both ends
Yoke machined from 5/8” delrin rod, slotted and drilled 3/16”, length adjusted so that the intake port “just” opens when it hits the pivot block, to prevent the linkage from crashing into the barrel band

Below that is the modified 2289 valve:
Front end shortened to “just” remove the original mounting hole, without exposing the check valve, with a new O-ring groove
Flat (1/16” deep by 3/8” long) machined to allow the valve to move back
Recess for the new 8-32 set-screw in the pump tube which retains the valve

Bottom left is the custom breech band, machined from 3/8” thick aluminum, which mounts the front of the trigger group

Bottom center is the new pump pivot bolt, machined from a 1/4” stainless steel bolt to 7/32” diameter, with shoulder and two 10-24 nuts

Bottom right is the custom barrel band / pivot block:
Barrel band machined from 3/8” aluminum, with three 6-32 set-screws, two into the pivot block, one for the barrel flat
Pivot block is machined from 5/8” aluminum rod, slotted and drilled 7/32, with the portion inside the barrel band knurled and pressed in place

When I started this project, I set a goal of 500 fps in 6 pumps, and 600 fps in 10 pumps… I was able to achieve that with the only internal valve modification being a lighter spring, plus a 0.162” transfer port… 511 fps in 6 pumps, 604 fps in 10 pumps, and a maximum velocity of 631 fps at 12 pumps… After bringing the valve to the same specs as in my 2289, the following numbers were achieved:

2 pumps: 310 fps
3 pumps: 381 fps
4 pumps: 439 fps
5 pumps: 481 fps
6 pumps: 518 fps
7 pumps: 550 fps
8 pumps: 577 fps
9 pumps: 600 fps
10 pumps: 620 fps
11 pumps: 638 fps with a “fart” of retained air
12 pumps: 650 fps with a 218 fps 2nd shot
13 pumps: 647 fps with a 390 fps 2nd shot
14 pumps: 626 fps with a 477 fps 2nd shot
15 pumps: 600 fps with a 549 fps 2nd shot
16 pumps: 563 fps with a 601 fps 2nd shot

All testing was done with JSB Express, 14.3gr. pellets… The barrel port was drilled to 0.166” (#19) and the transfer port was drilled to 0.162” (#20)… The valve exhaust ports were streamlined, and the valve stem slimmed… A stock 2289 hammer spring was used, and a “set” 2289 sear spring was installed in the valve… this combination allows the gun to be pumped without the need to be pre-cocked… Higher maximum velocity could be obtained by using a 2200 hammer spring (and an even lighter valve spring), allowing more pumps before retaining air, but the gun would then have to be pre-cocked before pumping… A 24” barrel would also increase velocities, but my criteria was a Grouse gun that was quicker to reload than my 2289, while being just as compact getting in and out of the car… :wink:

When I was looking at the numbers, I found something interesting… With a bit of balancing on the springs, you could probably achieve two equal shots at 16 pumps, of the same velocity as the 8 pump shot (about 575 fps)… This would in theory give you several options while hunting: pump to 16 and have a follow-up shot available; pump to 16, take one shot and re-pump; or pump to 8 for each shot… I have no idea if the point of impact of the first and second shots would group together, as they have totally different pressure curves (the first shot has a short, high-pressure pulse, much quieter)… but I can see vAgRaNt just itching to try this… Laughing

This build took about a week and was a very satisfying experience… The initial accuracy tests show it to be at least as good as my 2289, and that gun accounted for 7 Ruffies this fall… I have no doubt that my Uber-Carbine will prove to be a great Grouse gun… and I think it looks trick enough to enter in this years contest (if we have one)... 8)

Bob

AirGunEric · Site Admin

Hello Bob- nice to see you pop in on us!

What is the overall length of your flat-top piston assembly? Does it occupy the same sort of space as a 2200 unit? (I don't have dimensions on a 2200 piston setup at the moment)

rsterne · Moderator

HI Eric....

I don't have an exact total length.... but I do know it's just over 6 inches but less than 6.25" ('cause I couldn't quite measure it with my calipers).... Laughing

The 2200 piston I have sitting here (brand new!) is 6.12" so they must be almost the same length overall.... BUT, my yoke is longer in front of the pump arm pin (1/2" instead of less than 1/4").... and of course you can't easily flat-top a 2200 valve.... of course my piston is adjustable.... Cool

When I tried a 2200 valve, I had to build up the sides of the cone with JB weld and then turn it flat.... I made the mistake of going right into the check valve area, and found that the check valve had a habit of extruding itself proud of the hole.... If you put my modified 2289 valve in a 2200, it would probably have the valve stem too far back to work with a stock 2200 hammer set-up... Rolling Eyes

Bob

thepaladin · Senior Member

Really nice looking, but here you can't legeally take grouse with an air gun.... Oh well.

rsterne · Moderator

Maybe not in Tennessee, but you sure the heck can in BC.... Rolling Eyes

Bob

thepaladin · Senior Member

I checked a few years ago and the way the law is written is, no game birds with an air gun. This brings up odd situations like, it's legal to shoot pigons but not doves...even though they're basicly the same bird. Comes from non-shooters and non-hunters writing the laws.

rsterne · Moderator

Welllllllllllll.... I made up a rear velocity adjuster (RVA).... I took a piece of 5/8" diameter aluminum rod about 3/4" long, drilled and tapped it 8-32 for the rear trigger and breech screws, then drilled and tapped the center out to 3/8"-16.... I took a 1.5" long 3/8" "button head" bolt (it takes a small allen-key), turned the head down to 3/8", and turned the end of the threaded portion down to 0.22" for a length of 1/4" for a spring seat.... By using a 3/8" bolt, the through hole is large enough that you can change the hammer spring without disassembling the rear of the gun.... Wink

It didn't take very long to balance out the two shots at 16 pumps so that they were nearly equal, but the velocity ended up between what I got at 8 pumps and 9 pumps, so I turned the adjuster in one more turn, and after a bit of fiddling, I got it to shoot two shots at 17 pumps at the same velocity as what I was getting at 9 pumps.... The valve is within a half-turn on the RVA of needing to be pre-cocked, and the hammer spring about the same amount from coil-bind, with this combination.... Shocked

I shot a ten shot string, alternating between 9 pumps* and 17 (2 shots).... with the following results:

589.0 *
575.2
599.5
587.9 *
587.0
595.1
593.4 *
584.2
587.3
591.6 *

The low and high were 575.2 and 599.5 respectively, the average was 589.0 fps, with a standard deviation of 6.55.... I then shot a second string with even better results: low of 580.2, high of 596.1, average of 588.9 fps, deviation of 5.65.... These are perfectly acceptable, better for instance that what you might get with a Crosman Discovery for consistency.... Remember, this is with a combination of 2 shots at 17 pumps and single shots at 9 pumps.... Cool

I then set up a target at 20 ft. with the following results:

From left to right:
5 shots at 9 pumps
5 shots at 17 pumps - 1st shot
5 shots at 17 pumps - 2nd shot
6 shots, 2 of each of the above

I was absolutely DELIGHTED with the results.... basically all the shots fall within one ragged hole.... Twisted Evil

The maximum velocity with the increase in hammer spring tension went up a bit to 664 fps at 14 pumps, and no air was retained in the valve until 13 pumps.... Wink

I will be doing more testing over the next few days.... vAgRaNt told me that he found some day to day variation with his RAP until he lightened the hammer.... I'll watch for that, and as weather permits I'll do some group testing outside at longer ranges.... so far, it looks like I can pump to 17, take a shot at a Grouse with a backup, and then pump to 9 if another shows his head.... Cool

Bob

vAgRaNt · Member

Well Sir, It would appear that this gun does infact deserve it's title as the Ultimate Grouse'r. Handy length, good
power, followup shot capable, and very good accuracy. Sounds to me like you nailed it - Bravo!!! Clap Clap

rsterne · Moderator

I've been doing some experimenting and have NOT found any variations from day to day.... HOWEVER, I have found that there is a temperature effect.... Rolling Eyes

The shot strings in the post above were taken with the gun "hot".... you can actually feel the heat of the valve through the pump tube when you are pumping and shooting continuously.... particularly when you are pumping to 17 pumps and taking two shots.... This is milder version of what I found when I was working up the 22 Uber-Pumper, where I actually MELTED the top of the Delrin Piston.... Delrin melts at 175*C (347*F).... Shocked

I remembered from a long ago Physics course that at constant volume, air pressure is proportional to temperature (in degrees Kelvin, which is Centigrade plus 273*).... I'm shooting in a cool garage (about 10*C, or 283*K), so if I'm getting only a 30*C temperature rise with pumping, that represents about 10% more pressure because of the heat in the air due to compressing it.... In other words, if the air cools 30*C, it's going to loose about 10% of it's pressure on cooling.... Evil or Very Mad

So what does this mean in practical terms?.... I spent the whole day pumping and letting the gun cool for various times before firing it.... I found that if the gun was "hot enough to feel the heat", it took about 15-20 minutes to cool to the point where no further cooling occurred (based on shot velocity).... If you were starting from a cold gun, the air in the valve lost it's heat more quickly (the metal around the valve was cold), and I found no difference in velocity from about 8-10 minutes onwards.... Cool

If you remember from the post above (with a hot gun), I was getting a nice shot string (about 589 fps) with a single shot after 9 pumps, or with two shots after 17 pumps.... If you pump and let the gun cool before shooting, it requires pumping to 10 pumps for the single shot, or to 20 pumps for the double shot, to get the same velocities.... I also noticed that if the gun is cold, you actually have to pump to 18 to get two shots of equal velocities (even fired right after pumping, the air in the valve cools enough to loose 1 pump).... Shocked

To summarize, for velocities of 585-589 fps:

Gun "hot" (ie continuous pumping and shooting):
single shot needs 9 pumps
two shots need 17 pumps

Gun "cold" when fired:
single shot needed 10 pumps
two shots needed 20 pumps

Gun pumped from cold and fired immediately:
single shot needs "9.5" pumps
two shots need 18 pumps

Basically, when sighting in, shooting continuously, you need 9 / 17 pumps.... Under typical hunting conditions, you pump to 20, and refill to 10 if you need a third shot.... Wink

Please note, these variations are NOT the same thing you see with a CO2 gun, and they don't occur with a PCP (unless you start shooting right after filling).... This is a specific problem with multi-pump guns caused by the heating of the air during compression.... and it's a LOT worse if you are using retained air for a second shot (because you are working with higher pressures, and therefore more heat generated).... With a true RAP, where you are always starting from a base preload, and then adding just a few pumps between shots, you will still notice this effect (ie shooting continuously will work differently than allowing the gun to cool between shots).... however, it shouldn't be as pronounced.... Rolling Eyes

Bob

ustilago · Member

Interesting. . . I observed something similar when I was doing the valve volume reduction research. Shot velocities would climb over the course of a shot string. And yes, the valve does get warmer. . . noticeably warmer. Hmmmm, I think I just found a new use for my IR thermometer. . .

rsterne · Moderator

I've been playing around with this thing long enough now to find another weird habit it has.... If you remember, I wondered whether the 1st and 2nd shots in the retained air setup would shoot to the same point of aim even though they were the same velocity.... I have some good news and some bad news.... Shocked

The good news is that the groups are so small that I can tell the difference.... Cool

The bad new is that there IS a difference.... Evil or Very Mad

I do my indoor shooting at 20', and group sizes I evaluate with the aid of a bench rest.... I am getting repeatable 5 shots groups that you can cover with a 3/8" OD washer at that range.... ie C-T-C of about 1/8"-3/16".... The only problem is, that the groups from the 1st shot at 17 pumps (hot) are about 1/8" - 3/16" higher than the groups from the 2nd shot.... and yet the velocities are very close (within about 10 fps, similar to the spread with 10 pumps).... When I shoot a 5 shot group at 10 pumps, the group is centered the same as the 2nd shot.... Rolling Eyes

Just out of curiousity, I reduced the temperature in the garage to 5*C (from 20*C), and did the same test again with the gun cold (pumped to 20, allowed to cool 15 minutes before firing).... the heights of the groups were consistent with what I found above (1st shots higher than 2nd shots), but they moved about 1/8" - 3/16" to the right.... same thing with the group at 10 pumps.... Neutral

I have no idea if this will be a problem when I start testing outside at 20-25 yards.... I may be able to reduce the velocity of the first shot slightly to compensate for the higher initial trajectory (or not).... or the opening up of the groups may hide the effect all together (or not).... Winter has now arrived, so that testing may well have to wait a couple of months.... I have learned enough to know that I have to test under conditions as close to what I hunt as possible.... Wink

In any case, there is no question in my mind that velocity isn't the only thing that effects group placement.... For my gun, at least, temperature has a slight effect.... and the short, sharp pressure pulse of the 1st shot in a retained-air setup also affects the point-of-impact slightly.... Rolling Eyes

Bob

rsterne · Moderator

I just got my order of two sleeves of 14.3 gr. .22 cal JSB Express pellets today.... actually I only ordered one sleeve, but D&L shipped (& billed for) two.... I'm REALLY glad they did, though, because this lot is wayyyyyyy better quality control than the last batch I had.... The previous ones were from 2007, these are batch # 1003008 (this years) and there are virtually NO distorted skirts, whereas last years were pretty bad (from 30-50% damaged).... Shocked

I set up the Uber-Carbine and did some more bench-rest comparisons indoors at 20 ft.... All were 5-shot groups, velocity 580 fps.... The small squares on the targets are 0.1", the black squares are 0.23"....

Left to Right:
9 pumps
1st shot @ 17 pumps
2nd shot @ 17 pumps

I noticed that the velocity was slightly reduced from the previous batch, but the variation between 1st and 2nd shots in the retained air mode has almost disappeared.... and the group size has shrunk to virtually one ragged hole just over 1/4" across.... All three groups (a total of 15 shots) would fall within a 3/8" OD group.... ie 0.15" C-T-C.... Very Happy

I continue to be impressed with the accuracy of the Uber-Carbine.... and these new JSB pellets are the icing on the cake.... Twisted Evil

Bob

rsterne · Moderator

We got a break in the snow today, and I got a chance to shoot some groups at 20 yards.... 14.3 gr. JSB Express at 580 fps.... Shocked

Left group: 9 pumps; 5 shots in 0.47" OD - 0.25" C-T-C
Right group: 1st shot at 18 pumps; 5 shots in 0.45" OD - 0.23" C-T-C

The gun is sensitive to the tension on the barrel band screw, especially on the POI of the 1st shot in the retained air setup.... the best setup I have found so far is with the set-screw just touching the top of the barrel.... Time will tell if Blue Loctite will hold that adjustment.... I have also found that 18 pumps in the retained air setup gives 1st shot POI closer to the 9 pump groups than I was getting with 17 pumps.... different barrel harmonics with the short, sharp pulse, I guess.... Rolling Eyes

Bob

Doc Sharptail · Member

Very interesting! There's a lot to digest here. It will take me 3 or 4 read-throughs to get gist of all of it. Good thing is I have a 14" .22 bbl that shoots extremely well. Now to round up a 2200 to play with...

Realistically, for hunting, how much are you gonna pump that thing? Inquiring minds wanna know Mr. Green

I find 15 pumps to be about right with my ftp'd 22-89 set-up, but it's not retaining air there, the way I have it set up...

Regards,

Doc Sharptail

rsterne · Moderator

The whole point is that I have a choice.... 580-600 fps is plenty for a Grouse, considering FPE and trajectory at the ranges I hunt.... so I can either pump it 9-10 times for every shot.... or pump it 18-20 times and have two shots available.... Cool

The exact numbers I decide on wil have to wait for more experimenting.... I just machined down a hammer to only 21 grams and can't wait to try it.... ustilago and vAgRaNt figure the lighter hammer adds to consistency with a RAP setup.... Wink

Bob