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Air Gun Home Forum Index » Rifles » Modding the Crosman 1077 Goto page Previous  1, 2, 3, 4  Next
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PostPosted: Sat Apr 11, 2009 7:20 am Reply with quote
Lescarroz
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Alstone wrote:
Welcome to airgunhome Lescarroz,
That’s just my findings with a similar system, someone who knows more about the 1077 will probably be able to help you more.

Al

Tanks a lot Al.

I'm a litle bit beginner on CO2 and PCP Embarassed

I understand that if the hammer is heavier, it should open up more CO2 and give a little more power and the spring as well. It's physical.

Perhaps my valve is to limit its possibilities, but I don't think Crosman manufactures different types.

Thank you for your interest on my problem. Shrug
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PostPosted: Sat Apr 11, 2009 8:14 am Reply with quote
AirGunEric
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What are your chrony readings?

It is possible that you have gotten the maximum out of your 1077 due to the valve design and the length of the barrel. When you've hit the limits of the barrel (it being too short) Co2 misting will come out the muzzle, no matter what the ambient temperature. The maximum velocity from a 1077 that I have ever heard is about 850fps using a 7.9 gr pellet, but that was achieved with a completely different, custom-made valve. The 1077 platform is, unfortunately, fairly limited. One of it biggest problems as well is the seal between the pellets in the magazine and the valve, often Co2 leaks out in this area (to compensate somewhat you could install a stronger spring behind the detent that rests against the pellet magazine).

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PostPosted: Sat Apr 11, 2009 11:01 am Reply with quote
Lescarroz
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Hi AirGunEric

The chrony speed it's 615 f/s with 8gr pellets.

The seal of the magazine is not very well done.
I try to improve it, with your advice.

The 1077 is with an 88g adapter, when I close the valve and empty pressure I need to fire several times (~10 ) to remove the pressure.
Is this normal ?

Thank you very much for your help Smile
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PostPosted: Sat Apr 11, 2009 3:39 pm Reply with quote
AirGunEric
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The built-up pressure is just Co2 that remains in the flow path, nothing abnormal there.

Your 615fps seems low, but maybe not. Try the stronger spring behind the detent for the magazine, and make sure you don't have a 'detuned' version (they did have them for the Canadian market) that slipped out the door in the wrong box. The valve in yours should have a black casing, a gray or brown casing mean it is likely the 'detuned' version and you will need to drill the port in the detent and the steel plate behind the detent spring out to a larger size to flow more Co2. Do you have any suspicion of leaks- i.e. around the valve or the flow tube between the powerlet and the valve? If you leave the rifle pressurized with Co2 overnight (turn off the 88g valve but do not fire the gun to relieve the pressure) do you still have pressure in the morning or has it leaked out?

What is the ambient temperature that you are shooting in?

If you check these things and everything seems OK, you can drill holes in the valve plunger (2 or 3) to allow more gas to flow when the hammer opens the valve. At that point you should start seeing mist out the barrel when you shoot under almost all conditions, meaning you need ALOT more valve (wasting tons of Co2) or a longer barrel to get more power- i.e. you've hit the limit for the 1077.

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PostPosted: Sat Apr 11, 2009 4:28 pm Reply with quote
Lescarroz
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My valve it's white !!
Probably a low power model. Embarassed

The ambient temperature was 22C°, good for CO2

I try to put a stronger spring in the valve and smooth a little the charger for a better sealing, and also leave the rifle pressurized this night.

Thank You very much.
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Individual Results 
PostPosted: Wed Feb 17, 2010 3:36 am Reply with quote
oherndon
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Thanks for all the modding tips. I performed some of these, and here are my individual results:

1) Replaced trigger spring (huge improvement - combined with other trigger mods, cut trigger pull weight in half)
2) Recrowned barrel (groups are, on average, 30-50% better)
3) Polished the breach end of the barrel (I didn't do any chrony testing before this mod, but I can tell you that it can't possibly have hurt things. From the factory, this aft part of the barrel was pretty rough and had sharp edges that were starting to chew up my clips.)
4) Shimmed the front of the barrel (fabricated a wooden "plug" around 2" long that fits snugly inside the barrel jacket just behind the front sight. I liberally coated it with spray silicon lubricant so the hole in the plug doesn't swell closed in high humidity, and this also helps with the sliding action of the barrel if I get a jam.)

Some other mods that weren't mentioned, but that I thought seemed like good ideas...

5) Removed the butt plate and filled the hollow stock with rice. Since I have the 88g AS conversion, my gun is really front heavy and this helps to balance it out.
6) Polished all trigger contact points. Ground down and polished the sharp edges on the stamped metal part of the trigger assy to reduce friction against the hammer assy for a smoother, lighter trigger pull.
7) Used spray silicon lubricant on all moving parts within the trigger assy - plastic and metal alike - to reduce friction.

I havent yet replaced the detent spring with a stronger one, but that's probably next on my list. The design of the whole chamber is just incredibly mediocre in this gun - it's definitely the weakest link as far as unnecessary CO2 loss is concerned.

I haven't made any changes to the valve itself or the hammer weight, and I probably won't. My gun mists when it's colder than 75 degrees outside, so the valve is already operating at great efficiency.

Thanks again for all the helpful hints.

- Orin
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PostPosted: Wed Feb 17, 2010 9:10 am Reply with quote
Slavia
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Welcome to the forum, oherndon! The rice idea was pretty creative.

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More Individual Results 
PostPosted: Sun Mar 07, 2010 7:21 pm Reply with quote
oherndon
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Thanks Slavia.

Two other mods I've since made pertained to the AirSource adapter, but these are more like fixes to factory defects than actual tweaks. 1) Every adapter (I've tried 3) leaked CO2 with the valve completely closed. 2) When I screwed in a fresh bottle, lots of gas would escape through the vent holes before I could get it tightened down.

To correct the first problem, I disassembled the needle valve (removed the allen set screw and it came right out) to inspect. The needle tip was slightly pitted and rough, so I polished it up with some 320, then 400, then 600 grit sandpaper. Inside the valve body where the needle seats, I could also see some burring, so I chucked up a long machine screw (round, slotted head) in a drill and used it to deburr the sharp edge. Finally I lubed the o-rings with some Pellgunoil and put it back together.

To address the second problem, I inspected the piercing needle (where the AirSource bottle screws in, not the one on the gun itself) and noticed it protruded beyond the rubber seal/washer. The bottle was getting pierced and spraying out CO2 before making contact with the washer (instead of it making washer contact and then piercing as it compressed the washer further). I pulled out the rubber washer, placed a very thin stainless steel washer behind it to act as a shim, and put the rubber washer back in place, using Pellgunoil oil between each layer. Now the tip of the piercing needle is virtually level with the surface of the rubber washer - right where it needs to be.

After making these mods, I crossed my fingers, closed the valve, and screwed in a fresh bottle. Presto! No gushing CO2 out the vent holes and no leaking valve. Smile

Also, I did finally replace the detent spring with a stiffer one - I used one with about twice the resistance. I also added an o-ring to the detent tip (the parts breakdown shows one, but mine was missing). The detent cap pops right off, so this is an easy thing to check if you've already got the gun torn apart. Without the o-ring, gas can escape between the detent body and tip instead of being forced through the hole in the tip. I lubed everything up, once again using Pellgunoil, and put it all back together.

Before the AirSource adapter mods, I was getting maybe 200, >400 FPS shots (70-80 in the 600's, 50-60 in the 500's, and 50-60 in the 400's), so I was losing a lot of gas when I screwed on a bottle. I haven't broken down the velocities since the fix, but I've put around 300 shots through the gun so far, and I'm still in the low 500's. I figure I've increased my shots per cylinder by 150 or more.

The detent mods have given me only a marginal velocity increase - my peak went up maybe 20 FPS (now 660 FPS on a 60 degree day... can't wait to test it in warmer weather) - but I have noticed much tighter extreme spreads. In a 10-shot group, my extreme spread is now less than 20 FPS (sometimes as little as 5 FPS), where it was commonly 30-40 FPS before. Of course this also depends on warm-up time between shots, but for these tests, I kept it around 2-3 shots a minute. One might say the gun is just breaking in, because it has less than 1000 rounds through it, but I've never heard anyone talk about break-in periods on CO2 guns like they have with springers.

All told, post-tuning, my gun shoots at least 50 FPS faster, the trigger is 50% lighter and much smoother, groups are 30-50% better, and extreme spreads in 10-shot groups are over 50% tighter. I couldn't be happier.

I hope this info helps other 1077 tweakers. Smile

- Orin
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co2 \ air 
PostPosted: Fri Apr 20, 2012 3:11 pm Reply with quote
lanceehansen
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can the 1077 be modified for compressed air?
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PostPosted: Fri Apr 20, 2012 3:44 pm Reply with quote
ZipSnipe
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I doubt it Lance, the internals are not up to par for compressed air. I looked into it when I got mine. You would need a new barrel, some type of pump and a slew of other changes.

I find the 1077 fine for what it is, I was going to do the bulk air mod but after using it for awhile now I am satisfied with the 12gram co2 , I would love to mod the magazine and get more shots outta of it!!!
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PostPosted: Fri Apr 20, 2012 3:52 pm Reply with quote
yourdaddyjoe
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No go on HPA Compressed air. The internal transfer tube can't handle it as it's set in plastic and there is not enough volume in the valve. You get more velocity from Co2.

Not safe and my attempt blew out all the seals at 1800psi.

On 1999 and newer models you can bulk fill the Co2 gas tube with an adapter that screws into the valve after you remove the seal retaining ring and seal. You will also need a fill port from a Benjamin Discovery. 100's of shots if you also use a 2240 gas tube extension from B&A.

Fun plinker, just not meant for hunting.

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lube 
PostPosted: Fri Apr 20, 2012 3:56 pm Reply with quote
lanceehansen
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OHH NOOO,
I used the wrong stuff to lube my 1077. 3 O-rings have melted.
the seal on the airsoft adapter the seal on the co2 seat and somthing inside the regulator is hissing.......
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PostPosted: Fri Apr 20, 2012 4:19 pm Reply with quote
yourdaddyjoe
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Not good, better give Crosman Customer Service a call for seals on Monday.

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PostPosted: Fri Apr 20, 2012 6:47 pm Reply with quote
ZipSnipe
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What did you use?

Tell us so no one else makes the same mistake!!!
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lube 
PostPosted: Thu Apr 26, 2012 12:31 am Reply with quote
lanceehansen
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I used a teflon spray and it ate the yellow O-rings. I called Crossman to order new ones and had a nice talk with the attendant who said not to use any patrolium product on the 1077. that if I didn't have the right stuff that I could use ATF fluid as a substitute cause it wouldn't distroy the seals. now I am waiting for the seals to rebuild my gun.
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Modding the Crosman 1077 
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