Bulldog Upgrades.3

Part 3:

Take always in account when reading these notes, that many of the upgrades we do are achieved by using whatever we have at home first. It means we try to resolve the issue without having to spend more. We work around the matter due to not having immediate access to a lathe, milling machine, etc. If you are willing to spend more, then you can look for a machinist and re-make new parts with the specifications you want. But for a common person like me, every cents count, we just cannot go and burn $ without making first infinite calculations.

Repaired trigger, assembled the Bulldog again, and had a first try at home, checking fps, after the tune up with TP and Valve with 1/4 opening. There are some changes, more starting speed. Still, we are going to keep trying because we want to achieve at least 950 fps with a 95 gr. DrillDog Big Bore Pellet; same with the others... an increase.

The hammer spring has a washer used as a shim (thickness = .97 mm), and all-the-way-in minus one turn. With that set up, from 3000 to 2000 psi I shot seven times with the 95 gr. slug and we were able to achieve over 900 fps there (not before as you will see); however, after the third shot the string is similar. So we are going to add a second shim and see if it improves even better. If not, then the next step could be a heavier spring.

As in its factory condition with a 95 gr. slug:

1- 890 fps (167.13 fpe).
2- 885
3- 869
4- 868
5- 852
6- 839
7- 824

After the first tune up, and one shim:

1- 936 fps.
2- 910
3- 901
4- 860
5- 846
6- 838
7- 830

Once adding a second and third washers we are happy with the results. First we tried an 80 gr. pellet and this Bulldog shot it at an amazing 1011 fps with 3000 psi!!!


With 95 gr., two washers (.97 + .97 + .97 mm), all-the-way-in, minus one turn; from 3000 to 1900 psi:

1- 953 fps (191.63 fpe).
2- 944
3- 925
4- 901
5- 862
6- 835
7- 815

Sometimes if you give the spring more room, like minus three turns, it can shoot even better than all the way in, so we may try that at some point. But in reality a heavier spring will give you the choice of not having to use shims + so many turns in; it means less pre-load which is good. If you compare the factory data we posted under our page Bulldog FPS/FPE; you now realize that on each DrillDog Big Bore Pellet, and after this tune up, we will surpass those speeds easily.

The Bulldog's factory hammer spring data, after I measured it, is:

- 21 full rotation coils.
- Wire diameter 0.069 inch.
- OD 0.478 inch.
- ID 0.333 inch.
- Length 3.080 inch.
- Space between the coils is 0.095 inch.

From this data you can go up in strength and try what works best.
~ * ~

We were not able to find on the internet the exact just one spring I needed without paying for a bunch of them directly from some manufacturer. So, I went to an Ace Hardware Store I have not that far from home and bought the closest size they had, a compression spring #114, UPC 7 46071 79114 9; however, as you see in the next picture it is a little bit wider in diameter. Just a hair, and that made it to get behind the hammer with way too much pressure. Nevertheless I added the Info here because this spring could be used in another rifle.

Both springs. Factory at the top, and the Ace # 114:


Also bought a Clevis Pin Single Hole to check if I could use it with the spring as a guide after not finding a brass one same diameter; but as this set up was not the one I finally used, then I did put it aside. Nonetheless we are adding the picture because if you keep your rifle as from factory, then you can replace it with one like this which is of a more durable material. It fits like a champ and you can grind it if necessary. In the next picture it shows longer than the black one, because I already had cut it off when adding shims. This Clevis is 5/16 x 1 1/2 inches.


Next step, if I wanted to remove the shims at all, and not having the spring compressed all the way in, was then to find the solution at home...and found something! A plastic bushing that fitted with precision not only inside the the spring nut, but also the factory plastic guide was the same size that inside the bushing's head. This bushing was originally 0.490 inch (12.46 mm) in diameter, and 0.683 inch (17.37 mm) long. The head or widest part that connects to the factory's spring guide is 0.595 inch (15.12 mm) wide.



The purpose of this set up is to remove the 3 washers I had use as shims which did the job, but not without having to screw the hammer nut all the way in. Said that I sanded both: the spring guide and bushing to a point that I could cock the rifle with the hammer's nut all the way back. Acomplishing that means also that anytime I could increase the tension of the spring even more.

Once the guide and bushing were cutted off (sanded) the final measurement is: 

-Spring guide==> 1.083 inches (27.52 mm).
-Nylong bushing with head==> 0.402 inch (10.21 mm)



Now we do not need shims. I can screw-in the nut for 5-6 full turns of more compression. If the cocking operation is affected, all you need to do is to shorten the spring guide a little more, or as far as you want to go inside in the thread.

If you have a milling machine, now you can make just one single piece out of steel, which can include the two items (guide + bushing) in one. Or if you keep it as I did, the advantage will be that it weights less, the nylon will help in cushioning the blow, and you can modify it just by sanding it more.

May 2018.

For Part 1 of Bulldog upgrades go to:

For Part 2 of Bulldog upgrades go to:

For Part 4 of Bulldog upgrades go to:

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