Bulldog modification log .328 porting and more

[PCPhack]

Thanks for the reassurance. I ordered the Wheeler fire lap kit and added it to the list of modifications to perform in the first post. The kit should arrive by the weekend.

[Coyote]

Thanks for the reassurance. I ordered the Wheeler fire lap kit and added it to the list of modifications to perform in the first post. The kit should arrive by the weekend.

David, now I'm going to tell you what I should have in the first place. I did many hours of research over a period of a month. Too much research. I couldn't find any evidence of anyone destroying a barrel. I used 180 grain cast ammo. I prefer NSA swaged but the ammo I used had a lot of surface area to contact the barrel. I shot twenty rounds with each grit with a good cleaning in between each grit. I borrowed a bore scope and holly cow. It shined. The proof was that after shooting sixty rounds that accuracy hardly changed. I'm no professional but I hold my own. Hope this helps dispels any doubts.

[PCPhack]

Thanks David! Feeling pretty confident now. Between the titanium reservoir and the lap job, my Bulldog will be ready for the next level. 

[Coyote]

Thanks David! Feeling pretty confident now. Between the titanium reservoir and the lap job, my Bulldog will be ready for the next level. 

I'm excited to hear how it turns out. I'm planning to do about the same...

[PCPhack]

The next chapter is starting. 

[PCPhack]

WARNING: THIS POST AND ALL FOLLOWING REFER TO MY CUSTOM BULLDOG UTILIZING A TITANIUM RESERVOIR. DO NOT FILL A STOCK TUBE FROM BENJAMIN TO MORE THAN 3000 PSI!

It is installed and pressurized to 4200 psi. I can tell right now that I probably won't use it over that or even 4000 due to practicalities of performing fills. Granted, the reservoir was empty, but my big tank was full at 4500, and could only get it to 4200. I won't want to have to run the compressor THAT often. Of course I will do a few shots at 4500 just to see what it can do.

We have guests coming over for the evening, so it will be late or tomorrow before I can post some numbers.

[MJP]

Now this is getting interesting, and done properly with a safe custom airtube.
Pictures and shot strings please. 

Marko

[PCPhack]

I am going to guess right now that it makes 375 FPE at 4500 psi. I know it will do a bit less with the tiny jet that I am using on the SS valve (to overcome first shot stiction with a smaller jet and more spring), and as it should do 400 with the regular or large jet. I can't wait to see what it really does.

[rsterne]

The force backwards on the bolt for a .357 cal at 4500 psi is 450 lbs. (50% more than stock).... a 3:1 safety margin means it should be able to stand 1350 lbs. of force.... Just thought I would mention that.... Stay safe....

Bob

[PCPhack]

Bob, yes I believe that anyone trying this should consider beefing up the bolt system, lever, pins, and linkage. My linkage is steel, as is my lever, which is a good start. The pins are stock, and one ought to do the calculations for those shearing off, but we don't know the metal type. Anyway, yes I will be proceeding with caution.

In worst case, a pin could shear off and the linkage bust through the plastic housing where ones cheek is welded in firing position. For this, I am considering a metal plate over the area as an extra safety measure just in case that ever happened. Another idea is to drill horizontally across the breach behind the bolts seated position and then use a pin through it to limit the bolts backward movement ability, but that would be fiddly, and one might forget to set it. I need to study potential travel distances with the linkage all detached. Another outcome could be the bolt itself slamming further backward into the lever rear pin bolt area. At this point I am not sure it will be an issue though; the existing linkage pins may be strong enough.

Tests will come tomorrow. I won't go out and test while tired. The tube is pressurized, so I will see in the morning if everything has a good seal.

[rsterne]

The problem with a bolt/linkage failure is that the parts, once given momentum, become a hammer themselves, with all the consequences of that.... You can't push a nail into a board with your hand, but even a light hammer, swung gently, will generate enough impact force to drive the nail.... It all boils down to the conservation of momentum (the mass of the bolt being accelerated backwards by the air pressure) and how quickly it stops (the distance in which that momentum is lost to whatever it hits)…. Lloyd did an experiment a while back that showed an open bolt shearing through a 1/4" steel bolt, and bending a 5/16" one (if I remember correctly)…. It was crazy the impact energy the bolt had, and what it took to stop it....

Bob

[Kinetic45^]

Physics 101: Equal and opposite reactions!

I'm eagerly following this to see what you guys come up with to determine the limits of the strength of the stock action and what can be done to beef it up, if anything.

[PCPhack]

Initial tests with me taking cover for safety. Some may be disappointed here, but note the small jet I use to combat stiction, which cuts down on the FPE.

In earlier tuning, I had cut 2 loops off of my factory spring. With the smaller than as shipped jet that I am using on the SS valve and this cutdown spring, the peak of the curve is 4200 psi. As such, I can't perform a maximim test right now. However, this yields a nice 2 shot tune which is what I use for hunting anyway. This is with the cut down spring turned all the way in. Both shots were exactly 1004fps, so one shot on each side of the curve. This is 318 fpe and more than enough (and would be around 328 if shot at the peak at 4200 psi). Note that in earlier testing I always saw over 50 FPE less with the tiny jet that I am using now, but the upside is that I have no stiction issues after the gun sits a while, which is critical for hunting. I would have to order a new uncut spring and open the jet back up to do a max test.

Travis, if you guys have factory springs, or just stronger ones, then I probably will get them for further testing.

In other thoughts, I may even back the tune down some as I have ran the compressor twice today topping off the tank. Lol.

Name: Ti Test 142gr
Notes: 4400 end 3834
Shots: 2
Average: 1004 ft/s
SD: 0 ft/s
Min: 1004 ft/s
Max: 1004 ft/s
Spread: 0 ft/s
Power Factor Average: 142
Power Factor Low: 142
Power Factor High: 142
Barometric Pressure: 29 Hg
Temperature: 59F
Weight: 142.0 gr.

[PCPhack]

After the string. You can see the speed and psi at the end. I have ordered some Realtree Xtra vinyl wrap to cover the few inches of air tube that extends from my stock.

[PCPhack]

A bit of feedback for anyone considering the titanium reservoir; it adds a very noticeable weight increase. Consider very strongly to just take the factory length and not longer like mine is (3 extra inches) if this may be an issue for you. I can really tell the difference while free holding the rifle. Granted, with the bullpup design it's not really a big deal, but some may not like the slight weight increase.

[PCPhack]

Another observation is that I get about 10 less FPE with with 178gr NSA of the same design as the NSA 142gr slugs. I believe it is due to barrel friction, as the slug is much longer. I will retest that after fire lapping the barrel (kit should come tomorrow). I may need to get a 356.5 die, as these are 357, but with 356 I lost accuracy. Benjamin Noslers at 145gr shot within a few FPE of the 142gr NSA slugs.

[Coyote]

The force backwards on the bolt for a .357 cal at 4500 psi is 450 lbs. (50% more than stock).... a 3:1 safety margin means it should be able to stand 1350 lbs. of force.... Just thought I would mention that.... Stay safe....

Bob

Thanks Bob. Very good to know. I too am planning to upgrade to the titanium air tube.

[PCPhack]

The force backwards on the bolt for a .357 cal at 4500 psi is 450 lbs. (50% more than stock).... a 3:1 safety margin means it should be able to stand 1350 lbs. of force.... Just thought I would mention that.... Stay safe....

Bob

Thanks Bob. Very good to know. I too am planning to upgrade to the titanium air tube.

I think for myself, I will settle on something less than 4500. More like 4000. This is still 34 percent over factory. Filling to 4500 is just too impractical when 4500 is my tank pressure.

[Coyote]

The force backwards on the bolt for a .357 cal at 4500 psi is 450 lbs. (50% more than stock).... a 3:1 safety margin means it should be able to stand 1350 lbs. of force.... Just thought I would mention that.... Stay safe....

Bob

Thanks Bob. Very good to know. I too am planning to upgrade to the titanium air tube.

I think for myself, I will settle on something less than 4500. More like 4000. This is still 34 percent over factory. Filling to 4500 is just too impractical when 4500 is my tank pressure.

I was thinking the same thing. My compressor and SCBA tank both max out at 4500 and having to constantly top off would be a pain.

[rsterne]

I think that is why most PCPs running more than 3000 psi use a 250 bar (3600 psi) fill.... sometimes 3800....

Bob