Low velocity after valve replacement?
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Low velocity after valve replacement?
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Topic: Low velocity after valve replacement? (Read 2195 times))
Greg_E
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Real Name: Greg
Low velocity after valve replacement?
«
on:
September 24, 2021, 12:27:53 AM »
I'm making some mild mods on my Bulldog and run across something I don't understand. Too late to air back up and do more testing, thought I would ask and gather info from more experienced shooters.
Porting the airway in my Bulldog. Shot a string of 125 grain powder coated rounds that I've had good consistency using. These are also really easy to cast so low effort to make more when I run low.
Before mod string: Fill to 3000psi, 5 1/4 turns out, following fps
751
774
790
794
780
771
758
745
731
715 - ending pressure about 1900psi
Mods: new valve body and valve, drill valve body port to #1 drill, drill transfer port and barrel to #1 drill. This changed valve body opening more than barrel opening. Polish the lip of the barrel transfer port to remove ammo wrecking burrs. Put everything back together and turn hammer back out 5 1/4 turns (I did scribe lines on the adjuster a while ago). 3100psi start.
426
679
Error
660
660
770
797
817
Error
804
Ending pressure about 2000 psi
So here is the question, do new valves need to break in? I did smear a very light coating of silicone grease on the valve stem, could this be my issue and I'll have to wait for it to blow off?
Just a touch faster on these 125 grain are right where I think I want to be, hoping that the first 5 shots will be around 830 or so. That should get 145 grain stuff well over 200fpe which I think is right where I want to be with this. This should also get the 80gr hollow points or 88 grain solids really smoking. Everything I'm going to shoot is going to be cast pistol ammo or the Benjamin Nosler or Griffin boat tail, but probably cast ammo for fairly obvious cost reasons.
I'll shoot another bunch during the day tomorrow and see if the first mag velocities come up, I can't imagine it is going into a hammer lock state when the real changes are transfer port size. I'm pretty sure all the ammo I used was cast of the same alloy at the same time. Same powder coat on all of them too.
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Ironman482
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Re: Low velocity after valve replacement?
«
Reply #1 on:
September 24, 2021, 09:18:56 AM »
I would c k the alignment of the barrel to transfer port , might be off a enough to restrict air flow.
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Lani52
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Re: Low velocity after valve replacement?
«
Reply #2 on:
September 24, 2021, 11:40:19 AM »
It looks like you need more hammer. If that port gets to be .30 and above, the. Bulldog turns into a 5 shooter, but your string is backwards.
Silicone grease is not what a valve stem likes.
The Pitbull hammer spring made a big difference on my 24 inch Bulldog, but you also need to change out to Pitbulls sidelever as that spring is stout.
RC
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rsterne
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Bob and Lloyd
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Re: Low velocity after valve replacement?
«
Reply #3 on:
September 24, 2021, 12:48:43 PM »
I agree, looks like you need more hammer strike.... It also looks like there is more power there when you get it sorted....
Bob
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Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
Greg_E
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Real Name: Greg
Re: Low velocity after valve replacement?
«
Reply #4 on:
September 24, 2021, 02:09:13 PM »
I was wondering about the hammer but thought that since pressure was about the same, and hammer spring in the same position, shouldn't it flow at least as much as the before test? Going to air it up soon and do more testing to see if the low initial velocity remains. The power increase down at 1900-2000 is really pleasing, hoping I can get a good 10 shot tune with the slightly larger port.
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Rob M
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Posts: 6308
Re: Low velocity after valve replacement?
«
Reply #5 on:
September 24, 2021, 02:31:00 PM »
no , because you now have more seating presure on the poppet. I also noticed you have a 1 to 1 throat to poppet , is that correct ?
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Rob M
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Posts: 6308
Re: Low velocity after valve replacement?
«
Reply #6 on:
September 24, 2021, 02:32:02 PM »
no text
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Greg_E
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Real Name: Greg
Re: Low velocity after valve replacement?
«
Reply #7 on:
September 24, 2021, 04:32:14 PM »
Not sure I know what you mean about 1:1 throat to poppet, but my guess is that you mean same diameters from valve body up through barrel port. If so then kind of yes. I did taper the valve body a bit with files, but after the thickness of the that piece, it is the same diameter.
I've read that you want a slight taper to the transfer port, big at the valve and small at the barrel. Stock was the opposite.
«
Last Edit: September 24, 2021, 04:34:16 PM by Greg_E
»
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Greg_E
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Real Name: Greg
Re: Low velocity after valve replacement?
«
Reply #8 on:
September 24, 2021, 07:18:32 PM »
Made some tests and changed the hammer spring some. Not sure I'm really where I want to be, but might be where I'm not going to gain anything.
125gr start 3k end 2600 psi, 5 1/4 turns
660
652
705
715
770
Same slug and pressure 4 3/4 turns
682
Changed to 4 1/2 turns
741
784
780
800
4 1/4 turns
738
Error
764
784
810 @ 2600psi
797
804
780
Error
731 end @ 1850 psi
4 turns
Error
774
E
E
804
804
E
774
744
738 ending at 1750 psi
I then loaded up a few 147 grain, I think these are a failure. They load hard and are slow, getting better energy out of the 125 grain.
659
662
699
731
754
748
735 ending at 2300psi
These 147 are flat nose and probably running into the rifling which is causing them to start accelerating more slowly. Just a guess but they shoot way lower than Benjamin Nosler. Think I need to find a pointy or 2r nose in similar weight. Maybe I'll size them down to .356 and see if there is an improvement.
All above ammo is sized, powder coated, and then sized back down to .357 again. Casting, then PC results in .360 or a little larger and more of a change than I want to make at one time.
I don't have many of the Nosler rounds, need to buy a bunch more and see what's happening.
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Rob M
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Posts: 6308
Re: Low velocity after valve replacement?
«
Reply #9 on:
September 24, 2021, 09:35:01 PM »
yes, transfer port being the same size as the throat is 1-1.. thats a minor issue , the tp should really be smaller by the area of the stem ( throat minus stem area = roughly ideal tp size..
anyway , is your little tp spacer removed ?? it seems to me , youve created some dead space from valve to barrel , creating a pressure drop.. id put that little stock restrictor back in , see if the numbers come back up. Im no bulldog export , but 186 fpe after mods is very low. should be in the 250s
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Greg_E
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Real Name: Greg
Re: Low velocity after valve replacement?
«
Reply #10 on:
September 25, 2021, 12:17:16 AM »
The little restrictor is in place, but drilled out to match the rest. I knew the little expansion and recompression would be an issue.
For the 125 grain, I thought the highest energy was pretty decent, just wish the spread wasn't as big. I'll have to send some of the last few Nosler through and see what I get. If the past repeats, I should see a decent power from them.
I should mention I still have the "return" spring on the front of the poppet, I know removing this helps with valve duration so I may need to remove it.
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Lani52
First to break 600 yards with 12 oz cola can
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Re: Low velocity after valve replacement?
«
Reply #11 on:
September 25, 2021, 12:52:05 AM »
What is the size of your transfer port? I know you said #1 what is that in inches?
I found the size, .2280.
Why such a small Tp?
Roachcreek
«
Last Edit: September 25, 2021, 12:59:03 AM by Lani52
»
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Bulldog ported to .30, heavy spring 260 FPE/178 grain thru the magazine
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Benjamin Kratos 25 .5L CF bottle
Hatsan Spark compressor
Molds: NOE 358-152, 257-420BT, Accurate molds 358-122 Lyman 358-429, 257420
Altaros Booster pump run by TWO CAT compressors
Greg_E
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Real Name: Greg
Re: Low velocity after valve replacement?
«
Reply #12 on:
September 25, 2021, 01:13:27 AM »
Want a small boost in power, but still have 10 shots per fill at 3000psi.
And yes .228 inch where most would go straight to .3 or slightly larger.
I do have the Pitbull spring, but not the steel handle, if I need more spring I may change to this stiffer spring. Not sure where coil bind might be on the stock spring, but going towards 3 turns out might be close.
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Rob M
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Posts: 6308
Re: Low velocity after valve replacement?
«
Reply #13 on:
September 25, 2021, 08:58:19 AM »
i made a mistake earlier i think , going back and rereading , it seems you never altered the valve throat diameter.
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sb327
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Real Name: David
Re: Low velocity after valve replacement?
«
Reply #14 on:
September 25, 2021, 09:37:21 AM »
I noticed that but I can’t really comment on the valve because I’m not familiar with it. If it is shaped like a lot of production gun valves, it is coned where it meets the throat. IF this is the case, it will probably take some shooting to get seated in and not be as sticky coming off the seat. Due to differences in production poppets, it may also explain some of what is being seen by the poppet being a little softer.
A softer poppet is more reliable (works in favor of the manufacturers) but takes a harder strike to unseat (works against end user). It’s a trade off.
With the amount of effort put so far, I’d go a little further and switch to a peek poppet.
If it’s doable on this gun, again, I’m not familiar with this specific gun.
Dave
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Greg_E
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Real Name: Greg
Re: Low velocity after valve replacement?
«
Reply #15 on:
September 25, 2021, 06:01:33 PM »
I don't have the tools to make a PEEK poppet, but if I find one I'll give it a try. And yes the poppet seals against a cone shape in the valve body. Pretty sure the poppet is delrin or something similar.
Going to check for bypass air around the bolt/probe with the heavy pellets and see if that is an issue, I have "better" o rings for that fault from Pitbull. Not running that o ring because it seemed to be too thick, I was getting some cutting from the probe.
I stayed away from anything around the poppet sealing area. I know some gains can be found there, but currently out of my experience range. I do think I want to find a weaker spring to go in front of the poppet, or maybe just take it out completely. That should let me back the hammer off a little. I'll think about this after I send more rounds. Only at about 40 since I changed the valve and ported the transfer ports. And none of those have been into a target, all into mulch.
And maybe I just need to shoot it more and let things wear in a little.
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Lani52
First to break 600 yards with 12 oz cola can
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Re: Low velocity after valve replacement?
«
Reply #16 on:
September 25, 2021, 07:05:30 PM »
I have had my Bulldog 4 or 5 years and although I have a spare poppet, I do om all my airguns, I have never had any poppet troubles. Bear in mind, I do keep mine fully charged with 3300 psi full time, and briefly as high as 3500 psi for testing.
If you want a 35 FPS boost without drilling a huge port, just take out that vrs.
Roachcreek
«
Last Edit: September 25, 2021, 07:07:51 PM by Lani52
»
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Roachcreek 615 yard shot 257 Haley 12 oz cola can Airgun-utube
Prod, Exclusive sidelever breech MMTJ barrel, Blue fork trigger group AR stock magpul forearm 16 “ shroud with AR birdcage Flash hider
Bulldog ported to .30, heavy spring 260 FPE/178 grain thru the magazine
Skyhawk, JSAR LW Poly choked barrel .22/45 FPE Huma reg Lee545 plenum and shroud
Airforce Texan 257 lss MadDog stock, cf .5L bottle ,no vrs, 25lb Hammer spring
Benjamin Kratos 25 .5L CF bottle
Hatsan Spark compressor
Molds: NOE 358-152, 257-420BT, Accurate molds 358-122 Lyman 358-429, 257420
Altaros Booster pump run by TWO CAT compressors
Greg_E
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Posts: 1380
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Real Name: Greg
Re: Low velocity after valve replacement?
«
Reply #17 on:
September 27, 2021, 08:55:44 PM »
In a moment of clarity, I remembered that I had a 125 grain hollow point version of the 147 that was giving me problems. These also load hard, but they seem to fly right around the same speeds as the previous 125 round nose. Fresh off the pump so a little hot and slightly higher 3100psi:
682
764
803
824
817
757
790
777
725
721
Some higher, some lower. Looks like I still need a little more spring but it also looks like I've already kind of wrecked shot count.
Rounds used left to right: Lee 356-125-2R, Lyman 356637, Lyman 356637 HP Devastator.
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rsterne
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Bob and Lloyd
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Re: Low velocity after valve replacement?
«
Reply #18 on:
September 28, 2021, 07:59:54 PM »
If you are having low velocity problems with some slugs, ie they are shooting significantly slower than others of the similar weight, or the velocity doesn't make sense.... Then you probably need to size them, they are likely too big for the bore, and therefore take too much force to push them through the barrel....
Bob
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1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
Greg_E
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Real Name: Greg
Re: Low velocity after valve replacement?
«
Reply #19 on:
September 28, 2021, 11:46:44 PM »
I've slugged the barrel, and measured recovered rounds from my mulch and both were .357 major diameter so that's what I've been sizing to after powder coat.
The 125 grain hollow point were moving about the same as the 2R round nose, but the hollow points still loaded hard. I'm thinking it is something with the weight, or with the alloy that the two Lyman rounds were cast from. My pure lead was a lot harder than it should have been. Waiting fresh stuff from Midway this time, should be actual pure lead.
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Low velocity after valve replacement?