Bulldog modification log .328 porting and more



Author Topic: Bulldog modification log .328 porting and more  (Read 8378 times - 1 votes) 
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Offline PCPhack

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Bulldog modification log .328 porting and more
« on: September 14, 2018, 02:07:29 PM »
Here I will log additional modifications to my Bulldog to make it hunting ready.

Already performed in an earlier posted thread:
-TP opened and polished to .3 inches
-JSAR SS valve installed
-Initial tuning for 2 shots at 285 foot pounds with Nosler 145gr or NSA 142gr slugs
-Shot accuracy after the above modification s are here: https://www.gatewaytoairguns.org/GTA/index.php?topic=148197.0

To-Be performed in this thread:
-Increase porting to .328 Done
-Longer dogbone linkage on the bolt to seat slugs to edge of .328 porting Done
-Deepen scalloped out area of bolt to maximize port flow Done
-Switch to handmade steel cocking lever (Thanks Matthew). Done
-Polish and lube the hammer Done
-Polish trigger group Done
-Reduce trigger 2nd stage pull length Done
-Reduce trigger pull to ~1-2 pounds Done. 1lb, 4oz
-Clean and polish the barrel with polishing paste Done
-Fire lap barrel with Wheeler kit Done
-Inspect the barrel crown and rework/polish as needed Done polishing and looks clean under magnification
-Install 5 barrel supports Done
-Install Pitbull extended reservoir Done
-Install JSAR titantium extended reservoir for 4500psi Done
-Install Pitbull regulator with custom length ordered plenum spacer Cancelled
-Install Pitbull long moderator Done
-Retune Done




« Last Edit: January 02, 2019, 04:03:36 PM by PCPhack »
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Offline PCPhack

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Re: Bulldog modification log
« Reply #1 on: September 14, 2018, 02:11:08 PM »
Hammer complete, including a careful 90 degree polishing of the face edge where the sear catches the hammer.

Before and after pictures.
« Last Edit: September 14, 2018, 02:24:15 PM by PCPhack »
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Offline PCPhack

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Re: Bulldog modification log
« Reply #2 on: September 14, 2018, 03:54:18 PM »
Based on the efficiency of existing shots with the factory reservoir, I will have to increase efficiency and/or come down in power to 270 fpe or so, to get the 4 shots on regulation with a custom Pitbull plenum length (assuming 1cc per fpe expected especially due to the SS valve). I estimated the receiver volume, and volume lost to the regulator body itself though, so will try to get those calculated exactly. This is rough estimation so far, with 21 inch plenum tube (1 inch ID), leaving only 10 inches for reservoir plus regulator itself , with 3000psi setpoint. Yes, I am aware of the risks. Existing shots at 285 FPE are using about 250 psi per shot with the factory reservoir. I will be back with more exacting numbers and the plan. I will likely work on the TP sizing a bit more to eek out a little more efficiency.

Edit: Took porting to .328 for more headroom with the power and efficiency.
« Last Edit: October 08, 2018, 11:17:23 AM by Rocker1 »
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Offline Tonycalves

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Re: Bulldog modification log
« Reply #3 on: September 14, 2018, 04:00:35 PM »
4500PSI seems a little high for a Bulldog. Subscribed as I'm looking for improvements for my Bulldog.
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Offline PCPhack

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Re: Bulldog modification log
« Reply #4 on: September 14, 2018, 04:09:27 PM »
4500PSI seems a little high for a Bulldog. Subscribed as I'm looking for improvements for my Bulldog.

It is high. The valve body (and especially its threads) and receiver must withstand the full 4500psi. The valve is not held in with valve screws though, but rather captive in front of a smaller hole in the receiver. Of course, that is no guarantee that the receiver can handle it.  At least anecdotally, other have had success without issue, but again that is NO replacement for proper pressure testing. I have understood the air tube has been tested to 10k psi, but not the entire assembly. It is important to understand that on this design, the valve thimble end threads (where the reservoir tube screws on) will always see the full 4500psi, while the receiver and rest of the valve body would see 4500psi in the event that the regulator failed (or in this case some psi between the 4500 and 3000 set point, since the plenum will be larger than the reservoir).

If anyone takes it upon themselves to exceet 3k psi, they do so at their own risk. The only claim for testing that I have seen in written format is that of the Pitbull reservoir up to 10k psi.

I am actually curious if JSAR has done testing to failure of their valve and its threads. If so, I am curious of the failure pressure.
« Last Edit: September 14, 2018, 05:33:51 PM by PCPhack »
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Offline PCPhack

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Re: Bulldog modification log
« Reply #5 on: September 14, 2018, 06:10:23 PM »
Trigger group set up outside the receiver, ready to start grinding, filing, and polishing.

A big thanks to Pitbull for their Youtube video. While it may seem obvious what to do, the video has good reminders about finer points like grinding and polishing in the right direction to preserve key angles on edges, and etc. There are a few ways to adjust trigger, so I suggest reviewing past work of others to decide what you want to do.
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Offline oldpro

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Re: Bulldog modification log
« Reply #6 on: September 14, 2018, 06:13:42 PM »
4500PSI seems a little high for a Bulldog. Subscribed as I'm looking for improvements for my Bulldog.

It is high. The valve body (and especially its threads) and receiver must withstand the full 4500psi. The valve is not held in with valve screws though, but rather captive in front of a smaller hole in the receiver. Of course, that is no guarantee that the receiver can handle it.  At least anecdotally, other have had success without issue, but again that is NO replacement for proper pressure testing. I have understood the air tube has been tested to 10k psi, but not the entire assembly. It is important to understand that on this design, the valve thimble end threads (where the reservoir tube screws on) will always see the full 4500psi, while the receiver and rest of the valve body would see 4500psi in the event that the regulator failed (or in this case some psi between the 4500 and 3000 set point, since the plenum will be larger than the reservoir).

If anyone takes it upon themselves to exceet 3k psi, they do so at their own risk. The only claim for testing that I have seen in written format is that of the Pitbull reservoir up to 10k psi.

I am actually curious if JSAR has done testing to failure of their valve and its threads. If so, I am curious of the failure pressure.
The valve and threads are not the weak point in the system they are more than capable of handling 4500psi its the air tube thats the weak point it is very thin where they threaded it and anything over 3200 psi is well below the 3 to 1 safety margin and unsafe.
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Offline PCPhack

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Re: Bulldog modification log
« Reply #7 on: September 14, 2018, 06:20:49 PM »
Thanks Travis.

They claim it was tested to 10K psi, so at 4500 psi, is only 2.22 times the working pressure. I am curious why they stopped at 10K psi, and what the actual failure point is or was (or did they actually go to failure).
« Last Edit: September 14, 2018, 06:22:52 PM by PCPhack »
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Offline FuzzyGrub

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Re: Bulldog modification log
« Reply #8 on: September 14, 2018, 06:26:53 PM »
My power goals are in the opposite direction to yours.  The Huma reg does not have much leeway with vent hole, so make sure you you have your plenum design final.  That could be an expensive hole.

I would think that the BD hammer and spring are more than enough for a SS valve.  A no pre-load and gapped spring might buy you some efficiency. 
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Offline oldpro

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Re: Bulldog modification log
« Reply #9 on: September 14, 2018, 06:28:35 PM »
Thanks Travis.

They claim it was tested to 10K psi, so at 4500 psi, is only 2.22 times the working pressure. I am curious why they stopped at 10K psi, and what the actual failure point is or was (or did they actually go to failure).
I would be curious if they had a failure at 10k my math says no but real world might be another story.
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Offline PCPhack

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Re: Bulldog modification log
« Reply #10 on: September 14, 2018, 06:48:22 PM »
I wish Pitbull published a test to failure video like JSAR did for the Marauder tubes. The material they used (2024 aluminum) and thickness would seem to indicate it is ok, but it needs more investigation!
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Offline PCPhack

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Re: Bulldog modification log
« Reply #11 on: September 14, 2018, 06:51:09 PM »
My power goals are in the opposite direction to yours.  The Huma reg does not have much leeway with vent hole, so make sure you you have your plenum design final.  That could be an expensive hole.

I would think that the BD hammer and spring are more than enough for a SS valve.  A no pre-load and gapped spring might buy you some efficiency.

I am considering ordering the plenum tube a little long, and making the final tweaking cut after testing. The hole for the Huma is needed long term, but for a few shots at stable temperature, pressure, and altitude should be ok without it. I will definitely not drill the hole until I am certain where I want it.

The Bulldog hammer has plenty of mass for the JSAR valve, and the factory spring is too strong for the JSAR valve. I used up 10 dollars in slugs confirming it (should have started at the weakest end of the spring). Travis knows what he is doing, and the spring they ship with the Bulldog valve is perfect.
« Last Edit: September 14, 2018, 06:58:16 PM by PCPhack »
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Offline PCPhack

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Re: Bulldog modification log
« Reply #12 on: September 14, 2018, 07:00:47 PM »
I heard back from Pitbull. They tested only to 10k psi, because that is the highest their hydraulic pump could go, but it did not fail there.

I have asked them if they are willing to donate a tube to video being tested further if I can find a tester.

Edit: They are willing to donate only for a certified pressure tester who would also certify it. Anyone know of such a resource willing to play? I would guess that for a variety of reasons, a certification would not be free, even if the tester was willing to donate the time.
« Last Edit: September 14, 2018, 07:11:50 PM by PCPhack »
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Offline FuzzyGrub

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Re: Bulldog modification log
« Reply #13 on: September 14, 2018, 07:24:08 PM »
Didnít know Travis included a spring.  Youíre good then.  Good luck with your quest.
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Offline PCPhack

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Re: Bulldog modification log
« Reply #14 on: September 14, 2018, 10:44:25 PM »
Thanks John.

I had a little shop time, so went out and did the trigger group tasks. Wow, in the picture with flash, you can still see it is not a mirror polish. To the naked eye it looks very smooth, and it feels very smooth. I lubed them and put the trigger group all back in with the pins. It is very smooth now, breaks on the second stage much sooner, and I did weaken the spring to ease the overall trigger force needed. ;D

« Last Edit: September 15, 2018, 01:17:07 AM by PCPhack »
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Offline PCPhack

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Re: Bulldog modification log
« Reply #15 on: September 15, 2018, 06:29:30 PM »
Extended reservoir preparation done. Here is how I opened the stock at the front. First, I put a few of the front screws into the two stock halves to hold it together. Then I used a large step bit, followed by 50 or so turns of 220 grit sandpaper taped to the oem reservoir. I have always liked how step bits make clean cuts in plastics, and is much faster than the dremel way.

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Offline FuzzyGrub

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Re: Bulldog modification log
« Reply #16 on: September 15, 2018, 07:35:58 PM »
I used a bench grinder for the rough in, but alum tube and different grades of sandpaper to finish it off.


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Offline PCPhack

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Re: Bulldog modification log
« Reply #17 on: September 15, 2018, 08:09:24 PM »
That also looks very clean John! I have often used a bench grinder to shape plastic, but it's not my first choice for a circle. My largest step bit was almost perfect, but the hole needed to be just a tiny bit larger, thus the sandpaper.
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Offline soolio

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Re: Bulldog modification log
« Reply #18 on: September 16, 2018, 03:14:09 AM »
Youíre really making me want a bulldog! Would really like to see some pics of the full gun as you go along for reference.
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Offline PCPhack

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Re: Bulldog modification log
« Reply #19 on: September 16, 2018, 01:17:19 PM »
It's still all apart right now, but will post some pictures of the whole gun once I start final assembling a bit more.

« Last Edit: September 16, 2018, 01:41:52 PM by PCPhack »
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