Tuning Pitbull AKC measurments (modified bulldog) with questions for tuning pros

Jump to latest Follow Reply
bd2021

bd2021

Member
Nov 18, 2021
379
16
MN, United States
Questions based on data below:

1. Is my hammer spring too strong?

2. Is my ammo too light? How much heavier should I go?

3. Can I turn the hammer spring back more than two turns from flush?

So now that I have a compressor, and some time, I took some measurements.

Using Griffin .357 135 Grain Dish bowl hallow points.

Series 1: Hammer three turns back from full tight

Series 2: Hammer turned all the way back so that it was flush with housing.

Series 3: Hammer turned back an additional turn from 2

Series 4: Hammer turned back an additional turn from 3

Since I am a newb, I am not sure how much further back I can turn it, and if bad things might ensue (such as a spring popping out).

Here is the data:



2.1650850747.png




3.1650850788.png




In closing, I am liking that I can get 8 or 9 shots by turning the hammer spring way back. I am wondering how much farther back I can go, though. Is it possible to go too far?
 
I did not like how many turns I needed to have the pitbull spring turned out, so I modified it. There is a little plastic guide with a thick spacer on the end. I cut the spacer in half which is good for at least a full turn, but probably more like two turns.

I'm at 8 turns out right now after changing it, seems to be close to where I had the stock spring by feel. Ill have to get to testing later thins week.

Since you are not going for maximum power, I would suggest you cut half of the spacer part off and see if you can get to 10 shots on the regulator. The amount of air might change with a heavier round like the 155 I sent.
 
Upvote 0
And I just did a test on my very limited supply of Benjamin eXTREME 145 grain bullets. (If you know where to get these, or something better, please let me know).

Okay, so now I am fairly happy. 8 regulated shots at an average of 250 ft. lbs. of energy (881 fps) with an extreme spread of 14 fps on the regulated shots. This is I think better performance than they advertised, which is 215 ft. lbs with 142 grain ammo.. 

Moral of the story:

1. Buy a compressor and a chronograph when you buy a pitbull or any other big bore gun. Pitbull might suggest this during their checkout, or in the printed instructions that I am recommending they generate and send with their guns.

2. Pitbull really should include some printed instructions for newbs like me. E.g., from what I can tell, this is likely great performance (pending me getting somewhere I can shoot at 50 and 100 yards on a target). The hammer spring adjustment and bullet grain recommendations. E.g., too light of a bullet and this gun is just wasting air as far as I can tell.

I have a lot of 85 grain and 110 grain ammo I bought from NSA that I think is clearly too light for this gun, or might require a weaker hammer spring. They did include the stock hammer spring so I might test that. I think the Pitbull power spring will waste too much air with light ammo.



4.1650858034.png

 
Upvote 0
I did not like how many turns I needed to have the pitbull spring turned out, so I modified it. There is a little plastic guide with a thick spacer on the end. I cut the spacer in half which is good for at least a full turn, but probably more like two turns.

I'm at 8 turns out right now after changing it, seems to be close to where I had the stock spring by feel. Ill have to get to testing later thins week.

Since you are not going for maximum power, I would suggest you cut half of the spacer part off and see if you can get to 10 shots on the regulator. The amount of air might change with a heavier round like the 155 I sent.
Click to expand...

I missed your post but thanks again for the tips! 

I think 8 shots is pretty good. I might tweak it some but testing is getting expensive, and I am running out of my coyote killer ammo.
 
Upvote 0
If you put the stock spring in, you are going to need to have it somewhere in the 3 to 4 turns out to get slightly less power. This was more compressed than I wanted it to be, but might still need to go back to it.



And yes, I think the lighter weights might be wasting air, that's a whole tune I have not looked into yet, been mostly focused on getting the heavy rounds where I want them, then need to back down to the 125 and 84 grain rounds that I have.



To be economical, you will need to start casting your own ammo. Alternate to the Benjamin Nosler, you might try the new Benjamin 357 that they have out now, I think most places have it in stock and it's $0.50 per shot so more affordable. There was a thread somewhere, but can't find it now https://www.pyramydair.com/product/benjamin-357-slugs-147-grains-flat-nose-100ct?p=1817

Not something I'm going to buy, there are similar molds from Lee that are similar prices and I'm all set up to cast my own. But fourth box is free (normally), I would buy one and see how it shoots.



Word of warning... Lube or powder coat your ammo! I'm about to try this stuff because application is simple. If it works I may not PC as much stuff. https://lsstuff.com/store/index.php?main_page=product_info&products_id=11 Supposed to dry which limits mess, I coated some 50 cal last night and can report later if it actually dries or stays sticky.



Also word of recommendation, buy a decent cleaning kit, these need to be cleaned similar to firearms, especially if you are not lubing you ammo. I also suggest buying a cheap borescope, Teslong makes a few and if you get that brand you should buy the extra mirrors to use with the larger bore. The cheap flexible 20 cal camera has a $20 mirror kit that covers up to 40 cal, and make life much nicer.
 
Upvote 0
Should also note that Benjamin has changed the description of the 357 version, they no longer list this for big game, only pests as big as coyote. I guess things change when you finally build a bigger and more powerful option. Also some hunting laws say at least 40-45 caliber and some say at least 400fpe, neither of these are currently met with any 357 BD variant. Most I've seen is around 300fpe with a 3 shot limit (which is still smokin' for air). Corrections welcome on the above.
 
Upvote 0
I just tested with the pitbull spring, and the cut down spacer, in meters per second

8 turns out 239, 238, 233

7.5 turns 218

8.5 turns 237, 235, 238, 236, 237, 236

These are all with powder coated 155 grain pure lead from a Lyman 356637 that I cast, sized to .357.

There are only a few more turns I can pull out of this and keep enough thread engagement to handle the spring pressure. I may want to cut the spacer a little more, or make something different if the plastic it too thin. I'd like to get back to nearly flush with the receiver.

But the extreme spread of 9fps isn't too bad on the last 6 shots. Ill have to try and see what a 125 grain round will produce now, hopefully I won't need to back off the spring much more since it just isn't there to back off.
 
Upvote 0
My experience with the PITBULL hammer spring is that it is just too tight. Like you, bd2021, I had to back it out 2 turns from flush with the receiver to have it shoot without being over powered. It used a lot of air and was pushing 300 FPE. I went back with the stock spring 3 turns from bottomed out. I did however take a lot of material off my poppet valve and made it more of a bullet shape. I think it not only reduced the weight of the poppet valve, but made it easier to open with the new shape. My poppet valve return spring has also been eliminated, I cut it down at first, but ultimately decided to eliminate it all together and removed even more material from my poppet valve and shaped it even more. My gun uses the same amount of air regardless of bullet weight. I can shoot 97.5 grain pellets at 977fps average 206 fpe, all the way to 142 grain slugs at 901 fps average 256 fpe without changing a thing. All give me 12 full power shots ending at 2900 psi. I can still get an additional 6 shots if I shoot down to 2000 psi but they won't be regulated. I believe the shape of my poppet valve may play a role in why my gun uses the same pressure for each shot regardless of ammo weight, but I don't know for sure. I only changed the shape of my poppet on the front side, not the stem side as it is a mating surface so I was careful not to nick or scratch that side. My next upgrade will be to install a balanced valve that I have, but I am in no rush to do this, as I love my current set up. I think your numbers are looking good. Is there a difference in how your gun behaves with the 2 different springs? Mine was violent with the PITBULL spring and very calm shooting with the stock spring. With it being so smooth and calm I find that it is more accurate as well, it doesn't jump or recoil as bad helping me stay on target and follow through better after each shot. I have taken her out to 200 yards thus far and can hit the target consistently now. I guess my point is also pay attention to how your gun reacts to each spring and choose the spring or set up that makes it shoot nice and smooth as this will help with accuracy once you meet your power/shot count goals.



-JP
 
Upvote 0
Mine has no difference with the spring change, but note I cut an 1/8 inch off the included spacer, otherwise I was going to be like 10 turns out which doesn't leave enough thread engagement to hold the spring pressure (in my opinion). At the 8.5 turns out I have roughly the same pressure as the stock spring at 3 turns out. If I ditch the valve return spring, I'd need to lighten the hammer spring even more and then it again becomes an issue. I may decide to shorten the Pitbull spring a bit, it would be nice to have a small amount of free play when the bolt is released to cut down on valve bounce, I don't think I have bounce now, but I know I don't want any.



I do know that I'm whacking the back of the valve retaining nut if I turn the spring in a little, that's why the 7.5 turns immediately went slower. I have marks on both hammer and nut for the testing in the past.
 
Upvote 0
Crosman-Benjamin-Bulldog-357-exploded view.1651157482.jpg
Poppet valve would be located on the front inside of part 3 in that diagram on the part 4 oring side if that makes since. Valve stem, attached to the poppet valve would then go through part #3 and your hammer hits that valve stem when you press the trigger, opening up that port for a fraction of a second.

Part number 33 here.

poppet.1651157976.PNG


-JP
 
  • Like
Reactions: bd2021
Upvote 0
Is there a difference in how your gun behaves with the 2 different springs? Mine was violent with the PITBULL spring and very calm shooting with the stock spring. With it being so smooth and calm I find that it is more accurate as well, it doesn't jump or recoil as bad helping me stay on target and follow through better after each shot.



-JP
Click to expand...

I haven't gotten around to trying the stock spring yet. I want to but I'm juggling a lot at the moment. Worse, I have to order some wood for a deck soon. Debating hiring somebody or using some vacation time to do the deck. Problem with that is, as it will be the first time I built a deck, I'll end up making about $2/hour. I'd do it a lot quicker on the second deck but I only need one.
 
Upvote 0
Mine was violent because I couldn't turn the PITBULL spring down enough. 2 turns out from flush with the receiver was still too much and I didn't want to modify the PITBULL spring at that time. Maybe cutting some coils or modding the spring guide would have helped. I just know my gun shoots very smooth and quiet now. What I mean by quiet is the mechanical noises when you pull the trigger, You can hear the tune of your gun once you get to know it real well and understand pcps better. I have been working with mine for 2 years and I am still learning. Don't know if the video will show, but listen and watch how non dramatic my bulldog is. It is just on it's bipod and rear sandbag. Not in a vice or gun grip. Wasn't like this before tuning it. That's 250ish fpe.

download.png




-JP
 
Upvote 0
OK, yes mine does have a little more noise now, hard to tell how much because I wear hearing protection when I shoot it.



I think that we need a spring half way between the stock spring and the Pitbull spring once you open the transfer port. Wish I knew how much force was on each, hard to get a real value with a scale and pressing it with your thumb.



Also, the ES above is really good, I was getting 9fps spread and your worst was 7fps.
 
Upvote 0
So I got some 147 Grain Flat Nose Benjamin .357 Slugs from Pyramid air for a little less than they are being sold for on Amazon thanks to the buy 3 and the fourth is free deal they offer.

I did some testing (no accuracy....maybe later this week) on the Modified bulldog (Pitbull AKC), testing fps and power versus turns back from full tight on the hammer spring cap, starting at 4500 psi and stopping before the pressure fulls below 2700 psi, which is the regulated pressure according to pitbull air.

Here is my data:

1.1651368411.JPG


Looks like I get 7 shots before the pressure falls below regulated for 255 or so ft. lbs at 884 fps with an extreme spread of 21 at 9 turns back of the hammer spring cap from full tight. That is really far back.

2.1651368571.jpg


At 10 turns back, I was getting pretty consistent velocities of 852.7 fps average even beyond 2700 psi.

I still suspect I will need to design a new hammer guide (item 23 on exploded view diagram) to get a reasonable number of shots. Even at 10 turns back I am getting 238 ft. lbs and a lot of shots, but that is a lot of turns back.
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu