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Air Gun Home Forum Index » Pistols » Modded 1377 FPS Goto page 1, 2  Next    View previous topic :: View next topic  Modded 1377 FPS   Posted: Wed Feb 25, 2009 9:48 am Mountain Man Member Joined: 03 Feb 2009 Posts: 17 Location: United States Hi guys/gals,I have put in my order for a modded Crosman 1377 with a 14in.barrel and flat top valve and piston set up from Roy Weid@Mountain Air Guns.Does anyone know what kind of FPS I can expect from this setup?What exactly is the benefit of the flat top setup?Will it increase velocity?Im just trying to figure,because if this set up isnt going to give me around 700fps or better,its not worth it,no matter how it looks.Thanks to all.   Posted: Wed Feb 25, 2009 10:09 am Jaxom Senior Member Joined: 06 Aug 2008 Posts: 927 What do you plan on using the pistol for? _________________ .22 2300kt Crosman Custom   Posted: Wed Feb 25, 2009 11:25 am rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC The Flat-Top-Piston & Valve makes the pump more efficient.... you will cram more air into the valve with every pump.... and it will continue to work at pressures the stock setup simply cannot reach.... I haven't tested a .177 with a 14" barrel.... but my guess is that it is going to take you about 10-12 pumps to achieve 700 fps but you should certainly be able to get that.... It will depend a bit on your choice of springs inside the valve and for the hammer where the gun will actually top out.... I have a 13XX with a 24" barrel and a pump from a 2200 (about a third more volume per stroke).... and I can get 990 fps at 30 pumps (7.8 gr. JSB Express).... I never use that, of course.... but that gun did 706 fps at only 7 pumps with a stock valve and hammer spring.... I would NOT recommend that you start hogging out the valve.... I have found that to be of limited benefit in .177.... and then only over 800 fps.... Below that a stock valve and transfer port work just great.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Wed Feb 25, 2009 1:28 pm Mountain Man Member Joined: 03 Feb 2009 Posts: 17 Location: United States Jaxom wrote: What do you plan on using the pistol for? Mostly hunting and critter control   Posted: Wed Feb 25, 2009 1:38 pm Mountain Man Member Joined: 03 Feb 2009 Posts: 17 Location: United States rsterne wrote: The Flat-Top-Piston & Valve makes the pump more efficient.... you will cram more air into the valve with every pump.... and it will continue to work at pressures the stock setup simply cannot reach.... I haven't tested a .177 with a 14" barrel.... but my guess is that it is going to take you about 10-12 pumps to achieve 700 fps but you should certainly be able to get that.... It will depend a bit on your choice of springs inside the valve and for the hammer where the gun will actually top out.... I have a 13XX with a 24" barrel and a pump from a 2200 (about a third more volume per stroke).... and I can get 990 fps at 30 pumps (7.8 gr. JSB Express).... I never use that, of course.... but that gun did 706 fps at only 7 pumps with a stock valve and hammer spring.... I will be using JSB PREDATORS.So if you can get 706fps with 7pumps,with stock valve,then I should be able to achieve 700 with the flat top set up What is hogging out the valve? I would NOT recommend that you start hogging out the valve.... I have found that to be of limited benefit in .177.... and then only over 800 fps.... Below that a stock valve and transfer port work just great.... Bob Re: Modded 1377 FPS   Posted: Wed Feb 25, 2009 9:46 pm DerekVinyard Member Joined: 04 Nov 2008 Posts: 90 A .22 can move at over 700fps with 12pumps with a 14" barrel... You should do fine, the FTP is required... Mountain Man wrote: Im just trying to figure,because if this set up isnt going to give me around 700fps or better,its not worth it,no matter how it looks.Thanks to all.   Posted: Wed Feb 25, 2009 10:23 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC That's really impressive.... I must obviously not know what I'm doing.... With a 14" barrel in .22 cal, I only get about 577 fps in 12 pumps with a stock volume pump.... and about 643 fps with a 2200 pump (35% bigger pump than a 2289).... The best I ever got with a 2289 volume valve in 12 pumps was 750 fps with a 24" barrel and a pump from a 1400 (twice the swept volume of a 2289 pump).... It took a bigger volume valve to get more than that.... All the above have Flat-Topped Pistons of course.... What the secret to getting 700 fps in 12 pumps with a 2289 pump and valve in .22 cal?.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Wed Feb 25, 2009 11:11 pm DerekVinyard Member Joined: 04 Nov 2008 Posts: 90 OMG... I'm sure you are correct, that was the 24" barrel... You know you play with too many pumpers when you can't remember the exact build. Looking at my scribbles, it was 750fps in 14 pumps on a 24" barrel. rsterne wrote: That's really impressive.... I must obviously not know what I'm doing.... With a 14" barrel in .22 cal, I only get about 577 fps in 12 pumps with a stock volume pump.... and about 643 fps with a 2200 pump (35% bigger pump than a 2289).... The best I ever got with a 2289 volume valve in 12 pumps was 750 fps with a 24" barrel and a pump from a 1400 (twice the swept volume of a 2289 pump).... It took a bigger volume valve to get more than that.... All the above have Flat-Topped Pistons of course.... What the secret to getting 700 fps in 12 pumps with a 2289 pump and valve in .22 cal?.... Bob   Posted: Wed Feb 25, 2009 11:20 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Even that's damn impressive.... Easy to forget which build did what, eh?.... That's why I keep my notes in a spreadsheet.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Wed Feb 25, 2009 11:23 pm DerekVinyard Member Joined: 04 Nov 2008 Posts: 90 I've completed a great deal of experimentation and learned, but I should document everything. I forget too much... I've almost completed a 1377 piston tester. I'm going to test piston designs on a stock flat faced valve and compare psi generated per pump. Just cut/threaded a gauge into the valve tonight. By the way, I would never do it for anything other than a bench test. Not enough material there to hold the valve safely. Then I'm going to move to valve volume, pressure and fps. This I will be documenting. rsterne wrote: Even that's damn impressive.... Easy to forget which build did what, eh?.... That's why I keep my notes in a spreadsheet.... Bob   Posted: Thu Feb 26, 2009 8:19 am Mountain Man Member Joined: 03 Feb 2009 Posts: 17 Location: United States rsterne wrote: The Flat-Top-Piston & Valve makes the pump more efficient.... you will cram more air into the valve with every pump.... and it will continue to work at pressures the stock setup simply cannot reach.... I haven't tested a .177 with a 14" barrel.... but my guess is that it is going to take you about 10-12 pumps to achieve 700 fps but you should certainly be able to get that.... It will depend a bit on your choice of springs inside the valve and for the hammer where the gun will actually top out.... I have a 13XX with a 24" barrel and a pump from a 2200 (about a third more volume per stroke).... and I can get 990 fps at 30 pumps (7.8 gr. JSB Express).... I never use that, of course.... but that gun did 706 fps at only 7 pumps with a stock valve and hammer spring.... I would NOT recommend that you start hogging out the valve.... I have found that to be of limited benefit in .177.... and then only over 800 fps.... Below that a stock valve and transfer port work just great.... Bob What does hogging out the valve mean   Posted: Thu Feb 26, 2009 9:14 am DerekVinyard Member Joined: 04 Nov 2008 Posts: 90 Mountain Man wrote: What does hogging out the valve mean Don't increase the internal volume of the valve. I'm going to experiment and document things, I'm not as organized as Bob. I've tried just about every barrel length... And just about every tube for building a pumper (1400, 2200, 2260 and 1377/2289). You will do well with the stock tube, but the longer the barrel the better your output will be. A .177 is easy to move compared to the .20 and especially the .22.   Posted: Thu Feb 26, 2009 9:20 am Mountain Man Member Joined: 03 Feb 2009 Posts: 17 Location: United States Thanks for all the replys   Posted: Thu Feb 26, 2009 12:06 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC By "hogging out the valve" I actually meant opening up the port behind the exhaust valve and/or slimming the stem.... IME increasing the volume between the valve seat and the pellet usually hurts performance in .177 until you are pushing it well over 700 fps.... With a .22, some moderate relieving seems to pay benefit, even at around 500 fps, but even in that caliber you can go to far.... Increasing the internal volume of the valve simply adds to the number of pumps required to reach a given pressure.... At relatively low velocities (for the caliber in question) pressure seems to be more important than volume.... When you are reaching for maximum performance, then you need both pressure and volume.... When you increase the internal volume of a valve, it requires more pumps (and hence more air inside) before it starts retaining air (which limits velocity).... Once the (now larger) valve begins retaining air, however, there is more potential energy available to be released.... Providing the passages can flow that (now larger) amount of air, you may get more velocity.... providing the barrel is long enough to allow the increased air to propel the pellet and not just make more noise.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Thu Feb 26, 2009 1:23 pm Mountain Man Member Joined: 03 Feb 2009 Posts: 17 Location: United States Excellent info there rsterne I have the choice of having my 1377 built with a ported and modified valve or the flat top valve and piston.From what Im understanding here is that the flat top setup will get me to the desired power level with less pumps,and hold more pressure without failure.Am I correct so far?Do you think the 14in.barrel will allow me to reach the 700fps range?I dont want it too long,I have a 2100 for that,but need it long enough to hit that 700.I will be using the gun on small critters,gray squirrels and birds at a distance of 25yards or less.Do you think my setup will be O.K.?I still have time to change my setup because he wont be able to start on it for a couple more weeks,so I can change the setup.What would you recommend to achieve the performance that Im looking for Modded 1377 FPS     Air Gun Home Forum Index » Pistols You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum All times are GMT - 5 Hours   Page 1 of 2   Goto page 1, 2  Next All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First  Select a forum Main Forums----------------AirGunHome Q&AGeneral Air Gun Questions and TopicsPicture GalleryTarget Shooting: Casual, Fun and CompetitionHunting, Pest Control, Varminting People/Events/Airgun Issue Discussion----------------Introduce YourselfThe BS TopicClubs/Events/Regional/Political Airgun Issues Maintenance, Modification and Reviews----------------RiflesPistolsAntique, Collector and Novelty AirgunsBB GunsPellets/AmmoOpticsAccessoriesAirgun Smithing Buy, Sell or Trade Forums----------------For SaleWant to Buy   Note: If you are seeing "Please enter your username and password to log in." 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