.25 ultra se hammer issue

[clintwestwood]

hi all.

im currently re tuning the above (for sub 12 fbs accuracy smoothness etc).

i want to buy a couple of hammers to find the optimum level of legal power and reliability, hence 2, so i have 1 as a "control".

now this is the thing, ive see a few dudes selling them on evil bay, but they are saying they are caliber specific, i didnt think they was, and anyhow, they only seem to come in .177 and .22.      mine is .25.
the confusing thing is on all the actual airgun spares proper gun shop sites here they dont say or give any caliber options for the hammers on their sites, some parts are like probes etc, but not the hammers.

i wonder why the evil bay ones are stating caliber specific?


any thoughts?


dave

[Back_Roads]

 The material that the hammers are made with may be lighter or heavier depending on caliber.

[subscriber]

The hammers may not be caliber specific, as much as power specific.  For the UK sub-12 FPE market, that might be moot.  From a US perspective, all UK hammers are .177 cal hammers, unless they are "FAC" rated.

It might be useful to state what airgun's hammer is being talked about, as some enthusiasts make or modify them to have a specific mass and friction properties, for example.

[clintwestwood]

thanks guys.

it appears to be different weights/mass etc.


i got this   

[rkr]

So we are talking about BSA hammers here? They vary in weight and length, R10 hammer is the longest and heaviest as it is meant for regulated gun. 12 fpe SE models used very light weight hammer with longer strike. Then there's old style hammer which is heavier with the same strike length. Here's a photo of old style Scorpion hammer, R10 hammer and Hornet hammer from left to right. SE hammer has the thick part about half the length of the Scorpion hammer.

IMG_2832 by abbababbaccc, on Flickr

[rkr]

It is also worth noting that BSA does not change hammers for calibers, they may change the transfer port size and sometimes add a separate hammer weight. If you are looking for a smooth operating 12 fpe gun then the old Scorpion hammer, 1.2mm wire hammer spring and blast tamer is a very nice combination. No hammer bounce and easy to cock. Add PTFE or delrin washers or caps for spring ends and do the normal tuning.

[subscriber]

rkr,

You sound like the right guy to contribute to this thread.  Perhaps you could help me understand why BSA uses a heavier hammer for a regulated version of their PCP?  Regulating the pressure means the valve will operate at a lower pressure than that in the air tank.   So, I figured that a lighter hammer strike would work better for that. 

Of course, a lighter hammer strike can be achieved via a blend between hammer mass and hammer spring energy.  So a heavy hammer with a less energetic spring may provide the desired strike, but surely that makes the hammer slow and increases lock-time?

[rsterne]

Hammer mass changes the ratio between lift and dwell.... A heavy hammer will produce greater dwell for a given spring setup.... Perhaps they are attempting to achieve a longer pulse to make up for less pressure, while limiting the lift (less spring energy) so as to not waste air.... Just a guess, but not what I would do.... They may have found it produced less shot-to-shot variation as well?....

Bob

[Motorhead]

On the MAGAZINE guns within the Scorpion family, the inner core controls both weight and effective stroke having an extended nose as the 2 on left of picture have.  This nose is for magazine clearance as the hammer passes under the mag.  Make nose too short, larger body of the core will hit mag and valve won't be opened at all or very little !! 
The Core on left at full length & diameter I've never seen & curious what model it came from ( Or is it a custom core ? )

I've tuned on these guns for years and very savvy on changing tune output and mods that increase efficiency etc ...

[rkr]

Motorhead, I think you mean the hammer on the right as the left one is normal Scorpion hammer? The right one is from a single shot BSA Hornet, they had a bit different internals including a super heavy hammer that doesn't narrow down at the tip.

The story is that BSA was very concerned about the cocking effort of their guns (they had MMC cocking after S10) and thus wanted heavy hammer soft spring approach. Another concern was drop tests (i.e. gun dropped to the floor from certain height and should not go off) and I believe the soft spring approach worked better for that too. The Hornet has actually larger diameter very soft spring in addition to that long heavy hammer with very short hammer strike. It was a regulated gun and it had rather low operating pressure so I guess they wanted a bit more dwell to get most out of it with as low cocking effort as possible. That legacy was then transferred to R10 that runs around 80-90 bar pressure in 12 fpe, short strike and heavier hammer than it's non regulated cousins. The valve return spring in BSAs is also ridiculously stiff to flatten the power curve so they need that mass in the hammer if dwell is wanted. 3.2mm diameter valve stem is not helping dwell either, when I tuned my .224 BSA with stock valve I had to use extremely stiff valve spring to be able to reach 100 fpe. Swapped in 2.0mm valve stem and soft valve spring and I can now make the power with regular hammer spring, although it's now .172 and only shooting 60 fpe.

[Motorhead]

yes two on left are Scorpion types ... RIGHT side one for me is the unknown .. Typo error, oups

[subscriber]

rkr,

Drop safe is an important question.  To look at that we need to start with assumptions.  On a conventional PCP such as Marauder, if there is a pellet loaded in the barrel, the hammer would be cocked.  So with the hammer held by the sear, a strong blow from the muzzle end (dropping onto muzzle) may break the sear and shoot into the ground.  Here, the heavier the hammer, the greater its potential for breaking the sear engagement from dropping the air rifle on its muzzle.

If the safety is applied and all it does is to lock the trigger or the sear, then the risk of sear breakage is the same as above.  If the safety lifts the hammer off the sear, then the sear does not take the impact.

In single loading, it is possible to lower the hammer on a loaded chamber with a Marauder.  When using a mag, that results in double loading.  In any event, dropping a Marauder on its butt stock would tend to cock the hammer.  An impact just short of catching the hammer on the sear would then fire the pellet loaded in the chamber at near full velocity, with the barrel pointing up.  A much more dangerous situation than firing into the ground.

The latter accidental firing above, would be more likely with a heavy hammer and a soft hammer spring.  It is like dropping a blowback SMG on its butt stock and the bolt travelling back far enough under inertia to pick up a round off the magazine, but not far enough to catch the sear; then fire that round as the bolt moves forward due to the fixed firing pin extending from the breechface.

The counterpoint would be that using a lighter hammer and a stronger spring would be safer.  One could also make and argument that the chamber of a PCP should not be loaded in the field, until the quarry is in sight.  To not climb fences with a loaded chamber and the rules applied to carrying firearms.  The snag is that PCPs do not have extractors, so once loaded the projectile cannot be remove from the chamber easily.  In other words, extra care should be used about where the muzzle is pointing when carrying, or in the case the airgun is dropped or falls over.

Large bore airguns usually have very heavy hammer springs, which might make them less prone to the hammer moving far enough to strike the valve.  The PCPs that separate loading and hammer cocking may offer more options.  In any event having the ability to lock the hammer in a position short of resting on the valve stem might be a good option, so that dropping on the muzzle or butt stock cannot fire the airgun, or break the sear.

On large bore PCPs and the more potent "small bore" ones, I would like to see a disconnector, that prevents the hammer from dropping onto the valve stem, if the bolt or toggle are not fully closed and locked.   Firing a 20 FPE PCP with the bolt closed but not locked may not bend the bolt handle should it be fired "out of battery", but the larger caliber, and more potent PCPs will cause damage and can pose a risk to the shooter.

As a data point, my brother accidentally fired his 30 FPE FX Streamline with the bolt unlocked.  The pellet cleared the barrel and the toggle moved back abruptly and noisily on firing, but did not recock the hammer - perhaps because the trigger was still being held down.  Needless to say, my brother was startled by the event, but the PCP seemed undamaged.  I know that Lloyd has videos of him testing bolt handle strength for this very type of event.   I won't post them here, as I have already deviated from the question:  "is a light hammer spring safer than a heavy one?"  That said, a broader perspective on PCP safety is better than an overly narrow one.