Tuning Drilling or venting Hammer

[superchikn]

I drilled or vented the hammer in my Artemis PP 750 on Friday because I believe I was getting air bounce between the hammer and the valve. What additional tuning does this require? With no other changes my fps went from 722 to 760 with a 16 gr pellet.

I expected a minor pickup but definitely not this much.

The gun is ported to a hair over 5/32" at valve and TP, the thimble is a little more than that with the single port mod.
I have the extended plenum from Wes, designed by Bighun.
The reg. is still at <1,400 psi as it came from the factory.
10" barrel.

When tuned to 720 ish which I believe was around the "knee" the hammer spring adjuster was about one turn in from full out, another turn and a half was max power.

I drilled a 1/8" hole in the center of the hammer as the poppet pin is off center to the hammer face.
When I reinstalled everything with the HS adjuster the same # of turns in I had picked up 35 to 40 fps and would max out at about 765. I am now backed as far as the adjuster will go to roughly the new knee.

my shot consistency had dropped off a bit but not horrible.

Anybody have any thoughts on this?

I am not looking for max power but right now I am seeing 20+ shots at 20fpe. I am fine with that. just want to refine the tune.

Thanks

 

[nervoustrig]

The fact it picked up velocity after drilling the hammer sure suggests it was developing an air cushion in front of the hammer (and/or a vacuum behind it). But usually when that issue is alleviated, consistency (ES) will improve so I don’t know what to make of the results in this case.

 

[superchikn]

Thanks Jason,
Quite honestly it was windy and the sky was overcast enough that after 20 or so shots I started getting ERR 3 (Caldwell Chrono) which I believe indicates not enough light, so my readings may have been a bit erratic. I will have to have at it when I have daylight again.

The other side of this is 20+ fpe seems like a lot, in a good way for a reg. setting of 1,300 - 1,400 psi. and 22-24 shots. Does this seem right or am I just really lucky on this?

The hammer spring adjuster has little effect on the speed.

 

[superchikn]

Is there any drawback to venting the hammer?

 

[nervoustrig]

I know of no real downside, with the small caveat of the relationship between hammer mass and valve dwell.

Obviously venting the hammer reduces its mass a little but that will typically be an advantage—however slight—for most any gun shooting pellets. Whereas for slugs (or slugs shot from long barrels), the lost mass could be relevant. Probably not though since the amount of material removed is usually small. Simply add a little more hammer spring tension to compensate.

 

[Motorhead]

Many tuners have known this for many years having seen this issue crop up with many PCP designs.
Correct/ed VENTING on compression side as well back side venting on a hammer has aided quite a few AG's in finding not only a tad more power, but better overall consistency.

 

[HKVP9]

I am curious if venting the hammer on my Puncher Jumbo would be of any benefit? Or is this for just specific guns?

 

[nervoustrig]

Just depends. In many cases there are features both in front of and behind the hammer that allow air to move, such as a slot for a cocking pin and opening for the trigger group. However sometimes the receiver and/or stock will block these passages and introduce a lossy air cushion or vacuum when the hammer is released. With this understanding in mind, a visual inspection will probably give you a good idea.

 

[Dr. Kralenstein]

I am curious if venting the hammer on my Puncher Jumbo would be of any benefit? Or is this for just specific guns?

We have open slots above where the bolt probe is. No need to add anymore really.

 

[superchikn]

I know of no real downside, with the small caveat of the relationship between hammer mass and valve dwell.

Obviously venting the hammer reduces its mass a little but that will typically be an advantage—however slight—for most any gun shooting pellets. Whereas for slugs (or slugs shot from long barrels), the lost mass could be relevant. Probably not though since the amount of material removed is usually small. Simply add a little more hammer spring tension to compensate.

Thanks Jason,
Definite gain from doing this and the only drawback I've seen is that now I cannot back my hammer spring out far enough, Guess I'll take a coil or two off.

I know people have been doing this for years and for all I know they also did a B Staley mod too, but I was concerned that maybe the air cushion provided a buffer from the hammer smacking the back of the valve body. Just a thought.

 

[superchikn]

Many tuners have known this for many years having seen this issue crop up with many PCP designs.
Correct/ed VENTING on compression side as well back side venting on a hammer has aided quite a few AG's in finding not only a tad more power, but better overall consistency.

Thanks Scott,
Yes I had read about others doing this before, but any in-depth discussion of the pros and cons was probably before my time here.

Power gain is there, need to verify consistency is, although it is not looking like it at the moment, need to test again under better conditions.

 

[nervoustrig]

maybe the air cushion provided a buffer from the hammer smacking the back of the valve body.

Okay yeah that’s an interesting thought. With the right set of conditions, I suppose it would be possible for the air cushion to mitigate the potential of the hammer overdriving the valve stem. However in practice the problem that arises is the cushion’s spring rate isn’t consistent from shot to shot just based on variations in how the hammer travels from point A to point B. Sometimes air squirts around it more freely, sometimes less freely. So sometimes it’s a good air cushion and other times a bad one.

That’s the fundamental reason a hammer affected by an air cushion and/or vacuum tends to produce wild velocity swings.

 

[Motorhead]

Lets not forget either .... Most valves don't utilize poppet stem seals ( Some do, most don't ) and with that, as shot happens pressure from the valves throat leaks past the stem & if hammer has no front side venting it will act upon the hammer and forcefully send it backwards. This is NOT good either for a consistent shot cycle

 

[superchikn]

Okay yeah that’s an interesting thought. With the right set of conditions, I suppose it would be possible for the air cushion to mitigate the potential of the hammer overdriving the valve stem. However in practice the problem that arises is the cushion’s spring rate isn’t consistent from shot to shot just based on variations in how the hammer travels from point A to point B. Sometimes air squirts around it more freely, sometimes less freely. So sometimes it’s a good air cushion and other times a bad one.

That’s the fundamental reason a hammer affected by an air cushion and/or vacuum tends to produce wild velocity swings.

Very cool, that makes sense. Thanks for the explanation.

 

[superchikn]

Lets not forget either .... Most valves don't utilize poppet stem seals ( Some do, most don't ) and with that, as shot happens pressure from the valves throat leaks past the stem & if hammer has no front side venting it will act upon the hammer and forcefully send it backwards. This is NOT good either for a consistent shot cycle

This valve does not have a poppet stem seal. but I was wondering about that. So does a valve with no seal always "need" a vented hammer face?

 

[Motorhead]

This valve does not have a poppet stem seal. but I was wondering about that. So does a valve with no seal always "need" a vented hammer face?

Face of hammer ... Or a miens within the the hammers bore at the bottom to vent air out of that space. ( It can be on top such as a long cocking lug slot or bottom slot at trigger or a simple hole. )

 

[mubhaur]

Face of hammer ... Or a miens within the the hammers bore at the bottom to vent air out of that space. ( It can be on top such as a long cocking lug slot or bottom slot at trigger or a simple hole. )

What about Theoben and RAW design on this matter !

I understand that a good space for air vent is available. But have you tried ever venting the hammer in these platforms?

I see that there is a lot of air thrust when hammer goes to the valve stem. I don't know how much difference it creates in Theoben.

I understand that one of the reasons giving a vent hole on the side of FX Royal series guns, is perhaps to address this issue.

Thoughts needed.

 

[Motorhead]

What about Theoben and RAW design on this matter !

I understand that a good space for air vent is available. But have you tried ever venting the hammer in these platforms?

I see that there is a lot of air thrust when hammer goes to the valve stem. I don't know how much difference it creates in Theoben.

I understand that one of the reasons giving a vent hole on the side of FX Royal series guns, is perhaps to address this issue.

Thoughts needed.

Threw the years ... Theoben to RAW there w/o a doubt the hammers used have changed in profile on the forward / nose areas.
While there clearance with the receivers bore ahead of poppet stem are somewhat close, there not close enough to be semi sealing or of tight enough clearance IMO to create an issue.
As well the poppet stem on these PCP's has an O-ring sealing it to the valve body having near zero bypass of HP air coming into the hammer bore.

* yes one of the exceptions in having poppet stem sealing