GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: sandman on February 10, 2013, 10:30:31 AM
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So I couldn't help myself and spent €105 on a crosman 1377 a couple of weeks ago. The original plan was to save up for a good springer, but when I found out that the 1377 has such a huge aftermarket
I just had to get my hands on one. The first thing that failed on me was the pivot pin, which slipped out to the right. This forced me to replace it with a regular 4mm nut and bolt (the shops here don't have american 3/16" ones), but that will just be a temporary solution. At this point I have to tell you that I'm totally new to modding and tuning airguns of any kind, but I want the finished product to have the following characteristics:
-being able to pump it more than 15 times without damaging the gun
-drastically upgrading power (able to achieve at least 700 fps with 7.9 grain pellets)
-sub 3 MOA accuracy out to 50 yards
-replace all the plastic with metal
At the moment, I think that the nearest dealer who sells custom 1377 parts is Gmac in the UK. I'm not bound to any limits in terms of power. What are the possibilities?
I'm about to order the following:
-steel breech with extended probe
-flat top piston
-stronger hammer spring with spring guide
-brass barrel band
-steel safety pin
-steel pivot pin
-18 inch barrel
-adjustable trigger sping
After that, I'm going to look for a nice scope OR an aimpoint/ eotech red dot (at the cost of accuracy). Might even go as far as buying a l By the way, does a flat top piston increase power, and can it handle more pressure than the stock piston? Do i need any specialised tools or expert knowledge to install these components?
Sandman.
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Pumping up the 1377 more then 10 times won't do you any good.
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A 24" barrel and a flat top piston and adjustable flat top valve alone should easily get you +700 fps at 10 pumps. For maximum safety I would recommend that you pin the valve in one or two more places to keep it rock solid.
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For maximum safety I would recommend that you pin the valve in one or two more places to keep it rock solid.
Pin the valve?
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http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,10015.0.html (http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,10015.0.html)
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My crosman carbine with 24" barrel .22 using 14.3 premiers does 735fps or 17+ ft lbs at 25 pumps. I would think that a .177 would do over 800fps.
Regards, Tom
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My crosman carbine with 24" barrel .22 using 14.3 premiers does 735fps or 17+ ft lbs at 25 pumps. I would think that a .177 would do over 800fps.
Regards, Tom
And you're pumping up your Crosman 25 times why????
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The sky is (nearly) the limit with that platform, as far as modding is concerned.... A Flat-Topped Piston and Valve eliminates the headspace, increasing the compression ratio and allow higher pressures to be reached on fewer pumps.... I have a gun I call my "Uber-Pumper", and it uses a 1377 valve, only slightly modified, with a 24" .177 barrel and a Crosman steel breech.... While the gun could be built on a 1377 pump tube, I chose to modify a 2100 tube and linkage for the job, and make my own flat-toped piston, because the swept volume is 50% greater, so that cuts the number of pumps by a third (ie 10 pumps on my gun is like 15 on a 1377 pump).... If you are using over about 20 pumps and an F-T-P you need the solid steel pivot pin, as the stock roll-pin will wear the hole in the linkage pretty quickly....
(http://i378.photobucket.com/albums/oo221/rsterne/Uber-Carbine/Uber-PumperwithScope.jpg)
With 7.8 gr. JSB Express pellets, I get 500 fps on 3 pumps, 800 on 10 pumps, 940 fps on 20 pumps, and 990 fps on 30 pumps.... It would take about 50 pumps with a 1377 pump and a good, properly adjusted F-T-P to do the same.... but it could be done.... This gun was extensively modified, and isn't just assembled from bolt-on parts, a lot of them I had to make or modify.... but if anyone tells you you can't get significantly greater performance from a 1377 over 10 pumps, they haven't really tried.... It can be done, and done safely, although the wear factor will increase the more you pump.... Even so, I have many tins of pellets through that gun on the original pump O-ring, in fact with no maintenance except the occasional drop of oil.... The keys to higher velocity are a longer barrel, an F-T-P, and more pumping.... All the other things are details....
Before you start on the quest for mega-power, you really need to ask yourself "how many times do I REALLY want to pump this thing?".... Personally, for 99% of people, I wouldn't even change out the hammer spring, as the stock one, without an RVA, is good for at least 15 pumps in a 1377.... With a 24" barrel and properly adjusted F-T-P, that will put you well into the 700's in .177 with a standard weight pellet, without any additional mods.... Beyond that is fun for bragging rights, but you will quickly tire of pumping that much, or at least I did....
Bob
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I'm currently getting 705fps with mine using JSB Exacts (8.44 gr), 24" barrel, ft piston/valve, stock springs, at 10 pumps. Mine retains air after 12 pumps.
For 10m target I do 4 pumps at about 500-540fps.
Imho - Pumping 25x sounds like a real pita!
JMJ
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Wow, Rs. That thing looks mighty fine. I certainly wouldn't mind having
something similar in my arsenal. Does installing an FTP take a lot of skill or
special tools?
Sandman
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Nope, but you need to get a flat-faced valve at the same time, or have a lathe to face yours off dead flat just in front of the O-ring.... The F-T-P just replaces the stock plastic piston and rubber pump cup with a Delrin or metal piston that is adjustable for length.... It must be set so that the flat face on the piston and valve JUST touch each other.... Too loose and you lose efficiency and the pump arm will fall open.... too tight, and the pump will be hard to close and you will overstress the linkage and pivot pins.... If you are going for REALLY high pressures, you may find a metal F-T-P is better as it's more rigid and won't melt (yes, I melted a Delrin piston in my Uber-Pumper)....
Bob
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One thing about building up a .177 is that there is little reason to port or increase inner volume in the valve. With a .22 more air is beneficial. Regards, Tom
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My crosman carbine with 24" barrel .22 using 14.3 premiers does 735fps or 17+ ft lbs at 25 pumps. I would think that a .177 would do over 800fps.
Regards, Tom
And you're pumping up your Crosman 25 times why????
I like to shoot at noise makers (large nitrogen bottle made into bells, circular saw blades, etc) that I have at 90 yards from my shop(rains a lot here). 735fps is about the minimum speed to dependably hit my targets at that range. At 10 pumps it gets 566, 12 606, 15 659, 20 707, 25 735, could probably get 750fps at 30 pumps but not worth the extra work. Regards, Tom
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Oh man another addict to the circle! Great advice has been given and the link the capof is going to be useful. Good luck and post pics! Thes crosman guns are super easy and highly addictive.
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Unfortunately I don't have an account there, and upon clicking "registrate" it says: "registration currently closed" >:(
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With 7.8 gr. JSB Express pellets, I get 500 fps on 3 pumps, 800 on 10 pumps, 940 fps on 20 pumps, and 990 fps on 30 pumps.... It would take about 50 pumps with a 1377 pump and a good, properly adjusted F-T-P to do the same.... but it could be done.... This gun was extensively modified, and isn't just assembled from bolt-on parts, a lot of them I had to make or modify.... but if anyone tells you you can't get significantly greater performance from a 1377 over 10 pumps, they haven't really tried.... It can be done, and done safely, although the wear factor will increase the more you pump.... Even so, I have many tins of pellets through that gun on the original pump O-ring, in fact with no maintenance except the occasional drop of oil.... The keys to higher velocity are a longer barrel, an F-T-P, and more pumping.... All the other things are details....
Before you start on the quest for mega-power, you really need to ask yourself "how many times do I REALLY want to pump this thing?".... Personally, for 99% of people, I wouldn't even change out the hammer spring, as the stock one, without an RVA, is good for at least 15 pumps in a 1377.... With a 24" barrel and properly adjusted F-T-P, that will put you well into the 700's in .177 with a standard weight pellet, without any additional mods.... Beyond that is fun for bragging rights, but you will quickly tire of pumping that much, or at least I did....
Bob
By the way, is that a bigger air reservoir? Am I going to need that? What effects will that have? What endless opertunity does that bring me? I WANT THAT, NOW! *realises own gun will never be that awesome, turns off computer and quitely starts sobbing in a dark corner of the room*
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The valve (ie air reservoir) is the same size as the one in your 1377, in fact there are very few mods to the valve.... Only the pump is bigger, so I don't have to pump as many times to get the same pressure and velocity....
I would strongly suggest you don't get greedy, at least at first.... Get a flat topped piston and valve and a longer barrel and a steel breech and find out what you can do with that.... I think you'll be pleasantly surprised....
Bob
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Unfortunately I don't have an account there, and upon clicking "registrate" it says: "registration currently closed" >:(
I ran into the same issue. Try this:
http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,9618.0.html (http://www.crosman-air-pistol-owners-forum.com/board/index.php/topic,9618.0.html)
Worked for me last month.
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Agree with rsterne, go with ft piston and valve and longer barrel. I went with a 14 in barrel ft piston and valve and steel breech and added 150 fps with just those. Mine has the old school cocking knob at the rear so anything over 12 pumps is a waste in mine as all the air wont get out of the valve. But with a new one that you can change the hammer springs it opens up alot more potential.
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Yeah, I'm certainly going to get a flat-top piston kit (which includes the valve), an 18 inch barrel, a power hammersping with guider and replace all the plastic with metal, so that includes the steel breech, a steel pivot pin, a steel barrel band (which will fix the wobble, I hope), and a steel safety pin. Wouldn't that be a nice little package? Would that enable me to put in, say, 50 pumps (if I would want to) without damaging the gun? What would be the safe maximum pressure for the air reservoir?
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I don't think anyone really has a good idea what maximum pressure you can achieve with a 1377 pump and F-T-P.... I can tell you that a 1377 with stock valve, hammer and springs will start retaining air at about 1500 psi.... It wouldn't surprise me if you could achieve twice that with a good pump, minimum headspace, and enough pumping.... What does that mean?....
The area of the valve (and piston, both 0.62" diam) is 0.302 sq.in.... That works out to 452 lbs. force at 1500 psi and twice that (904 lbs.) at 3000.... The main pivot pin is 3/16", so a solid steel pin (using tensile of 53K, and two ends) would have a predicted shear failure of 1765 lbs (ie a safety factor of nearly 2:1 at 3000 psi).... However, the holes in the tube would be expected to yield (ie start to elongate) at 1075 lbs (safety factor at 3000 psi is only 1.2:1, not really high enough, but should be fine at 1500).... The tube wouldn't be expected to yield until over 9000 psi (11K burst), so not an issue.... The other item of concern is the stake that locates the valve, along with the front trigger screw.... The stake is only 1/4" wide by 0.065" thick, so the area is only 0.0163 sq.in.... Using a yield of 40K for the aluminum valve, that is only 650 lbs. for the stake, but we can add the 8-32 trigger screw, which has a shear strength of 390 lbs. (assuming mild steel with a tensile of 53K), giving a total of 1040 lbs (safety factor of only 1.15:1 at 3000 psi, not really good enough, but again should be fine at 1500).... If you use a high tensile screw (eg. 180K), that would be much higher (1325 lbs. just for the screw) and that would be a very good idea if you plan on pumping a lot.... With that, plus the stake, you would be at 1975 lbs. (about 2.2:1 safety factor at 3000 psi), which should be OK....
So, providing you replace the front trigger screw with a high tensile one, and use a solid steel main pivot pin (I don't have the specs on the stock roll pin, and besides, they wear out the hole in the pump arm quickly), it looks like the first thing to fail would be the steel tube stretching/distorting around the main pivot pin, in theory at just over 3000 psi.... or the pump linkage, which could easily kink, especially if it gets out of line at all.... That is consistent with what I have seen in my Uber-Pumpers.... The first sign of pressure related problems is the back of the aluminum valve wearing/denting where it bears on the stake in the tube.... I would recommend you NEVER pump the gun more than a few pumps without the front trigger screw locating the valve, it's a large part of the safety of the design.... and replacing it with a high tensile 8-32 SHCS is a very good idea, and necessary if you want to pump over ~1500 psi.... The next sign of weakness is distortion of the tube around the main pivot pin.... and I've never seen that, which leads me to believe I have never exceeded 3000 psi.... By the time you get to those pressure levels, the holes in the linkage are going to start wearing and stretching anyway.... It certainly wouldn't hurt to increase the diameter of the main pivot pin to 7/32" to increase the bearing area in the tube a bit....
DISCLAIMER: This information bears no guarantee of safety at any given number of pumps.... It is simply a bunch of numbers representing my opinion.... If you pump past 10 times, which is Crosman's recommendation, or even just modify the piston, you're on your own....
Bob
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The sky is (nearly) the limit with that platform, as far as modding is concerned.... A Flat-Topped Piston and Valve eliminates the headspace, increasing the compression ratio and allow higher pressures to be reached on fewer pumps.... I have a gun I call my "Uber-Pumper", and it uses a 1377 valve, only slightly modified, with a 24" .177 barrel and a Crosman steel breech.... While the gun could be built on a 1377 pump tube, I chose to modify a 2100 tube and linkage for the job, and make my own flat-toped piston, because the swept volume is 50% greater, so that cuts the number of pumps by a third (ie 10 pumps on my gun is like 15 on a 1377 pump).... If you are using over about 20 pumps and an F-T-P you need the solid steel pivot pin, as the stock roll-pin will wear the hole in the linkage pretty quickly....
(http://i378.photobucket.com/albums/oo221/rsterne/Uber-Carbine/Uber-PumperwithScope.jpg)
With 7.8 gr. JSB Express pellets, I get 500 fps on 3 pumps, 800 on 10 pumps, 940 fps on 20 pumps, and 990 fps on 30 pumps.... It would take about 50 pumps with a 1377 pump and a good, properly adjusted F-T-P to do the same.... but it could be done.... This gun was extensively modified, and isn't just assembled from bolt-on parts, a lot of them I had to make or modify.... but if anyone tells you you can't get significantly greater performance from a 1377 over 10 pumps, they haven't really tried.... It can be done, and done safely, although the wear factor will increase the more you pump.... Even so, I have many tins of pellets through that gun on the original pump O-ring, in fact with no maintenance except the occasional drop of oil.... The keys to higher velocity are a longer barrel, an F-T-P, and more pumping.... All the other things are details....
Before you start on the quest for mega-power, you really need to ask yourself "how many times do I REALLY want to pump this thing?".... Personally, for 99% of people, I wouldn't even change out the hammer spring, as the stock one, without an RVA, is good for at least 15 pumps in a 1377.... With a 24" barrel and properly adjusted F-T-P, that will put you well into the 700's in .177 with a standard weight pellet, without any additional mods.... Beyond that is fun for bragging rights, but you will quickly tire of pumping that much, or at least I did....
Bob
Bob, I'm in the process of making a walnut version of the 1399 stock for my Benji HB22 and I'm interested in the mod you did to your stock. It looks like you shortened and raised it up a bit? I don't have a lot of experience with different stock geometries and at this point I'm just scaling down a 1399 pattern a bit to fit the HB22 grips. My pattern's overall length is about 13.5" now instead of the original 15". You probably had some good reasons to change the geometry and I'm wondering if I should do the same to my walnut version.
Would it be possible to take a photo of just your modified stock next to a ruler so I can scale things properly?
Thanks,
Eric
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The length was shortened about 1.25", so the LOP is pretty normal (~14.25").... Crosman's skeleton stock LOP is ridculously long at about 15.5".... You can see how far I raised the comb, about 3/4".... helps get your eye closer to the scope C/L....
HTHs....
Bob
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By the way, does installing a flat top piston and valve increase pumping effort?
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Not at low pump numbers, but at high pump numbers, yes, because the pumping effort is proportional to the air pressure in the valve....
Bob