Bulldog modification log .328 porting and more

[PCPhack]

Actually, the end of the dogbone link closest to the lever needs to be a little more narrow than I made it. I noted it now with the marking in the paint as seen here. It only keeps the bolt from retracting a tiny amount, but I will fix it.

[rsterne]

That cocking lever in Reply #116 appears to be on the verge of breaking, IMO.... Perhaps that has something to do with the testing you did at over 4000 psi, on a gun designed for 3000 ?!?!?....

This may very well be a perfect example of how important it is to address ALL safety aspects when considering increasing the operating pressure.... or caliber and hence operating force.... on any PCP....

Bob

[PCPhack]

That cocking lever in Reply #116 appears to be on the verge of breaking, IMO.... Perhaps that has something to do with the testing you did at over 4000 psi, on a gun designed for 3000 ?!?!?....

This may very well be a perfect example of how important it is to address ALL safety aspects when considering increasing the operating pressure.... or caliber and hence operating force.... on any PCP....

Bob

Point taken, but I do not think this is the case. Two shots did not do that. It is worn down. If it had happened in two shots, I do not believe it would be so smooth. Anyway, a new one is easy enough to order. It may be that in general it will wear out with the modified setup that I have.

[ShakySarge]

I will concur that the warping of the pin hole has nothing to do with fill pressure. I don't overfill mine either yet it has also warped in the same manner. My guess is that when the spring tension is great enough, the thin aluminum cannot withstand the leverage and gives some. It wasn't an issue with mine until I started turning up the spring tension.

[rsterne]

Perhaps the wear is because it got bent from those two shots.... or perhaps not.... It certainly appears to be bent, it will be interesting to see how a new one compares when you replace it....

One of the problems with bolt lock-up mechanisms is not that they aren't strong enough to take the static (pulse) load on firing.... The problem is that if that mechanism fails, or it the gun is fired with the bolt not properly latched.... the bolt can accelerate backward at high "g" over the entire "sealed" distance (how far the bolt travels until the breech O-ring clears)…. and some distance after that, depending on how close the tolerances are.... This gives the (quite heavy) bolt a significant velocity and a very high momentum.... When it hits whatever is there to stop it, the instantaneous force it generates is much higher than the static force that launched it....

Think of a hammer, and the huge forces it generates when it comes to a halt against a nail.... There is no way you could push that nail into a board by hand.... and yet a relatively gentle swing of the hammer, generating momentum which comes to a sudden stop.... creates HUGE force....

It is easy to focus on one thing when looking at the safety of a PCP.... for example the tube strength, or the valve attachment screws.... while forgetting what other things we may be overstressing.... and the consequences that some other, unexpected failure could produce....

I'm as guilty as anyone, even though I try very hard to think of everything....  …. I'll bet you have never fired your barrel through a Chrony, have you ?!?!?.... Setscrews that didn't bite properly into the very hard epoxy of a CF tube, a material that had a very low shear strength, were responsible for that.... and no, I didn't get a Chrony reading on it.... 

Bob

PS, is the spring tension from cocking not in the opposite direction on that lug/fork?.... I think that bend/wear is from bolt recoil....

[PCPhack]

I believe the material is just too weak. By nature of the bolt dragging on the oring when it retracts, any play in the pin area there is opened up. Then upon firing, the bolt is slammed backwards, just as you explained Bob, and any small play is closed up. This back and forth wears the hole out over time, especially when it shoots slugs at around 50 percent over factory FPE. A small steel sleave or shoulder washer for this hole, epoxyed in place may be enough, but it is an awfully small area to modify like that. I would actually prefer an entirely stainless cocking lever.

[triggertreat]

Is it possible to attach a ND magnet set under the lever?  This may help/prevent it from opening when fired.

[PCPhack]

I don't see how any magnet would help, as the lever doesn't come up any when firing. It can't actually due to the lock up of the bolt in a slightly retracted position when that pivot point crosses the center line of the bolt.

Looking at this closely, it may have some wear, but I think most of the oval shape is due to elongation of the hole, as in the aluminum has stretched here or bent as Bob put it. Hard to tell which. Maybe some of both.

[ShakySarge]

It very well could be both the force of cocking and the "blowback" of the bolt. Makes sense, seeing as how there really isn't a "locking" position, so to speak, of the bolt. Instead of locking into place, the arm simply returns back into a linear position behind the bolt when closed.There is plenty of room for failure to remain fully locked IMO.

I was thinking about getting with a CNC guy about making a new cocking lever and a retractable blot probe that would additionally lock into a milled slot on the receiver to further lock it down. I may have to do some drawing to figure it out but if it is feasible, heck, why not?!

[PCPhack]

I will concur that the warping of the pin hole has nothing to do with fill pressure. I don't overfill mine either yet it has also warped in the same manner. My guess is that when the spring tension is great enough, the thin aluminum cannot withstand the leverage and gives some. It wasn't an issue with mine until I started turning up the spring tension.

You can see in this picture of mine, the handle hand area is also bent out a bit. This is from cocking it, so yes there is a lot of stress while cocking as well as during firing.

[PCPhack]

It very well could be both the force of cocking and the "blowback" of the bolt. Makes sense, seeing as how there really isn't a "locking" position, so to speak, of the bolt. Instead of locking into place, the arm simply returns back into a linear position behind the bolt when closed.There is plenty of room for failure to remain fully locked IMO.

I was thinking about getting with a CNC guy about making a new cocking lever and a retractable blot probe that would additionally lock into a milled slot on the receiver to further lock it down. I may have to do some drawing to figure it out but if it is feasible, heck, why not?!

If several of us would want them, we could get a better deal than each getting a 1-off.

[ShakySarge]

I am game if anyone else would like to have one as well. I am working on a prototype for the bolt handle out of tooled steel that I started after my last post on the thread. I will start doing some drawing of a bolt with retractable probe as well and would be more than grateful for any other ideas or input. My thought is that the probe would extend past the concave of the bolt face about 1/4 inch that is easily retractable once cocked as well to ensure that the magazine can clear it. The part I have not figured out is the inlets necessary to lock it in without hampering loading a magazine or such but once the magazine is inserted, the probe would need to be fully extended to ensure it seats the round far enough and doesn't retract until I make it retract into the bolt after said round is chambered.

Any input would be appreciated. If it can achieve good enough numbers we may be on to something. The key is the retracting. I have experimented with several probed bolts already and so far only one design has had a significant increase of more than 40FPS. That being the 1/8 probe that is 1/8 at the rear and goes down in diameter to the tip. The issue is maintaining the concave on the bolt to help push the air in a forward direction instead of just straight up into the barrel.

[ShakySarge]

I will concur that the warping of the pin hole has nothing to do with fill pressure. I don't overfill mine either yet it has also warped in the same manner. My guess is that when the spring tension is great enough, the thin aluminum cannot withstand the leverage and gives some. It wasn't an issue with mine until I started turning up the spring tension.

You can see in this picture of mine, the handle hand area is also bent out a bit. This is from cocking it, so yes there is a lot of stress while cocking as well as during firing.

Oh yes, mine is quite similar! Mine even has a bit of a twist to it. Not great engineering on the cocking arm by any means.

[PCPhack]

Mine is not hard to cock with the JSAR valve being balanced, but it is the very end of the cocking, getting the hammer to catch the sear, that I need to pull harder. Mine has always been like that even brand new out of the box. I might see about making it catch easier on the next disassembly.

By the way, the longer linkage piece actually exacerbates the above cocking, hammer, sear issue, so I will definitely need to address it. So everything is normal you know...touch 1 thing and need to adjust 3 others, lol. 

[ShakySarge]

I agree. It isnt until its time for the sear to catch that it gets heavy. Perhaps a slightly heavier sear spring would help?

This is what I have so far from just brainstorming from the top see through view on a retractable probe.

[Kinetic45^]

Following since I have a Pitbull and shoot lots so expect this wear eventually.
Add me as interested in a better made kit of bolt parts to retrofit.

[rsterne]

Sounds like the bend/wear may be increasing the effort right at the end of the travel because there isn't quite enough travel to get the sear to latch properly.... If this is not a problem on a stock Bulldog, possibly the hammer spring is too long / wire too big, and it's going coil bound.... I would think the longer link piece would indeed make the problem worse....

There is an old adage about modding PCPs.... Making a change often requires two more.... and each of those two more.... etc.etc…. Pretty soon you have created a monster....

Bob

[ShakySarge]

Very true Bob, a little takes more than we think sometimes. I was thinking the same that the spring could be binding but it's still the stock spring. Gonna have to look into that a bit more and figure out what to do about it. Perhaps the same weight spring with a coil or two less may solve it?

[PCPhack]

I don't think it is due to the factory spring as mine has a few loops cut off. Before that, I was using the weaker JSAR supplied spring.

I think Bob was right here. The set point for the sear is at the end of the lever travel. When that hole starts to wear or stretch, the hammer is not quite pullled back enough to catch the sear.  So you start having to exert more and more force to the lever that is already at the end of its travel, furthering the issue over time.

I am thinking to either build up the catch spot on the hammer so that the bolt catches it sooner, or to take a little off the hammer edge where the sear catches so that it catches sooner (while maintaining a perfect right angle as this is critical for sear function and safety).

[ShakySarge]

That may just do it. Just a minute of amount of clearance may solve the issue.

Here is what I have so far for the cocking lever. Mind you, it is still in the rough stage and since it was the first try at it, I bent it in the wrong spot. I may be able to heat it up and bend it where the yellow arrow points as it must be bent there to ensure that it locks when returned forward after cocking. If it won't bend where I want it to, I will have to start all over again. We shall see.