Interesting observation of Webley Mk3 and Airsporter loading taps

[craig7]

I have recently been looking at the loading taps on Webley Mk3 and the BSA Airsporters inspired by the various MK3 versus Airsporter discussions on boards like these.
Results
They both have their advantage and disadvantage. It appears that the Mk3 must have had its tap drilled through and line broached from the transfer port as it is exactly the same size and displays identical broach marks. The advantage of this process must have completely eliminated possible errors for alignment for Webley. The pellet fired into lard reveals absolutely no clipped edge to the pellet skirts.
However, i recently noticed an article in Airgunner which details transfer ports upto a max of 4mm being ideal for power. It also details why the Anshutz 335 was never as powerful as its competitors due to a transfer port above 5mm because they mistakenly thought it would be more efficient.
At 12ftlbs limits, 3.8mm is suggested to be the optimum for power.
Its interesting therefore that the relative massive transfer port of a .22 MK3 of 5.6mm (that allowed line broaching through the 5.6mm tap) probably reduces the guns performance by a good 1ftlb to 2ftlbs and can even cause the pellet to fall from the tap into the transfer port when shooting upward into the sky as noticed by one poster on this board.
The Airsporter with its 4mm transfer port having some 2ftlbs lbs more potential power.
Also interesting is the tiny damage clippings to one edge of the pellet of 3 Airsporters i looked at under microscope.
Conclusions.
The Mk3 has to be potentially the more accurate gun with little or no chance of tap alignment issues.
To get to this perfect alignment we however lose 2ftlbs potential power due to the transfer port having to match the tap diameter and thus breaking the 4mm golden rule for diameter .
The Airsporter is ideal for power but you either get a good one or bad one in alignment/accuracy terms because alignment would be hit and miss based on the usual limits and fits tolerance system inherant in the manufacturing process.
My next tests will be run on the indoor range (chrono and target)

[ogilkes]

Extremely interesting, do keep us posted!

[Abasmajor]

I have recently been looking at the loading taps on Webley Mk3 and the BSA Airsporters inspired by the various MK3 versus Airsporter discussions on boards like these.
Results
They both have their advantage and disadvantage. It appears that the Mk3 must have had its tap drilled through and line broached from the transfer port as it is exactly the same size and displays identical broach marks. The advantage of this process must have completely eliminated possible errors for alignment for Webley. The pellet fired into lard reveals absolutely no clipped edge to the pellet skirts.
However, i recently noticed an article in Airgunner which details transfer ports upto a max of 4mm being ideal for power. It also details why the Anshutz 335 was never as powerful as its competitors due to a transfer port above 5mm because they mistakenly thought it would be more efficient.
At 12ftlbs limits, 3.8mm is suggested to be the optimum for power.
Its interesting therefore that the relative massive transfer port of a .22 MK3 of 5.6mm (that allowed line broaching through the 5.6mm tap) probably reduces the guns performance by a good 1ftlb to 2ftlbs and can even cause the pellet to fall from the tap into the transfer port when shooting upward into the sky as noticed by one poster on this board.
The Airsporter with its 4mm transfer port having some 2ftlbs lbs more potential power.
Also interesting is the tiny damage clippings to one edge of the pellet of 3 Airsporters i looked at under microscope.
Conclusions.
The Mk3 has to be potentially the more accurate gun with little or no chance of tap alignment issues.
To get to this perfect alignment we however lose 2ftlbs potential power due to the transfer port having to match the tap diameter and thus breaking the 4mm golden rule for diameter .
The Airsporter is ideal for power but you either get a good one or bad one in alignment/accuracy terms because alignment would be hit and miss based on the usual limits and fits tolerance system inherant in the manufacturing process.
My next tests will be run on the indoor range (chrono and target)

Hi Craig,

Thanks for this extremely interesting post. It's a good job we have some members with your obvious technical expertise to keep some of us less technically minded members informed.

Look forward to seeing the results of your range testing.

Regards

Brisn

[Prof51mtw]

I have recently been looking at the loading taps on Webley Mk3 and the BSA Airsporters inspired by the various MK3 versus Airsporter discussions on boards like these.
Results
They both have their advantage and disadvantage. It appears that the Mk3 must have had its tap drilled through and line broached from the transfer port as it is exactly the same size and displays identical broach marks. The advantage of this process must have completely eliminated possible errors for alignment for Webley. The pellet fired into lard reveals absolutely no clipped edge to the pellet skirts.
However, i recently noticed an article in Airgunner which details transfer ports upto a max of 4mm being ideal for power. It also details why the Anshutz 335 was never as powerful as its competitors due to a transfer port above 5mm because they mistakenly thought it would be more efficient.
At 12ftlbs limits, 3.8mm is suggested to be the optimum for power.
Its interesting therefore that the relative massive transfer port of a .22 MK3 of 5.6mm (that allowed line broaching through the 5.6mm tap) probably reduces the guns performance by a good 1ftlb to 2ftlbs and can even cause the pellet to fall from the tap into the transfer port when shooting upward into the sky as noticed by one poster on this board.
The Airsporter with its 4mm transfer port having some 2ftlbs lbs more potential power.
Also interesting is the tiny damage clippings to one edge of the pellet of 3 Airsporters i looked at under microscope.
Conclusions.
The Mk3 has to be potentially the more accurate gun with little or no chance of tap alignment issues.
To get to this perfect alignment we however lose 2ftlbs potential power due to the transfer port having to match the tap diameter and thus breaking the 4mm golden rule for diameter .
The Airsporter is ideal for power but you either get a good one or bad one in alignment/accuracy terms because alignment would be hit and miss based on the usual limits and fits tolerance system inherant in the manufacturing process.
My next tests will be run on the indoor range (chrono and target)

This is indeed very interesting. I'm working on transfer ports at the moment and what seems clear is that there is, unfortunately, no 'golden rule' for dimensioning the transfer port: the optimum size is power source and calibre dependant. The decisive factor appears to be the achievement of a critical level of mass flow choking inside the port. I've given some test results in the latest Airgun World for those who are interested, with more to follow.
Mike

[T 20]

This is indeed very interesting. I'm working on transfer ports at the moment and what seems clear is that there is, unfortunately, no 'golden rule' for dimensioning the transfer port: the optimum size is power source and calibre dependant. The decisive factor appears to be the achievement of a critical level of mass flow choking inside the port. I've given some test results in the latest Airgun World for those who are interested, with more to follow.
Mike

Hi Professor Mike


Are you finding any link between static compression ratios within a springer as regards the optimum transfer port size as well ?

Keep up the good work.

I'm looking forward to next month's AGW and the physics bit now.




All the best Mick

[spartan]

Ive done a bit of experimenting on mk3 transfer ports, my findings found,the best size was 1/8, I had a power increase, also consistency seemed to improved.

[Prof51mtw]

Hi Professor Mike


Are you finding any link between static compression ratios within a springer as regards the optimum transfer port size as well ?

Keep up the good work.

I'm looking forward to next month's AGW and the physics bit now.




All the best Mick

Good Morning Mick: Yes, the compression ratio or, more specifically, the peak cylinder pressure will have an effect on the optimum TP size. Whether lubricant vapour combustion is present also has an effect, as Jim has just pointed out to me, citing the fact that Weihrauch reduced the size of the TP on the HW55 when moving over to plastic piston seals.
Mike

[T 20]

Good Morning Mick: Yes, the compression ratio or, more specifically, the peak cylinder pressure will have an effect on the optimum TP size. Whether lubricant vapour combustion is present also has an effect, as Jim has just pointed out to me, citing the fact that Weihrauch reduced the size of the TP on the HW55 when moving over to plastic piston seals.
Mike

Thank God for that --- I thought I'd been imagining it.

As Jim has pointed out Weihrauch changed from a 4mm transfer port to a 2.8mm port when they went from leather to synthetic seals --- so in effect they doubled the static compression ratio.

I'm finding leather seals like to work at a sub 200:1 compression ratio and synthetic seals and O rings work best at 300 : 1 upwards.

The Webley MK3 has one of the lowest compression ratios I have found at 80:1, I am considering fitting a Diana 52 piston seal to one of mine and then sleeving the transfer port down to 2.5mm --- on paper this should make it a bit more user friendly.




All the best Mick

[craig7]

Thanks everyone and thanks Mike.
Yes im well aware of the various potential effects that swept volumes and cal. can have on transfer ports but i was offering a very averaged ideal and basing it on the .22 (the .177 cal. Mk3 is less subject to the same set of problems and my gun being .22) or i would have been here all night, or not started the post in the first place.

I did check out the majority of efficient springers i have which suggested something in the area of 3.5mm to 4mm seeming to be ideal at least in the .22 or where this maybe simply copying across models of the same maker.
The BSA Mercury (11.1ftlbs) Feinwerkbau Sport (11.4ftlbs) and a tuned BSA Supersport (11.6ftlbs) all relatively compact but good power guns with ports in the range i suggest.
Do we go smaller than 3.5mm to 4mm i ask but larger definitely appears to have negative effects at sub 12ftlbs.

Would love to hear how you go about correctly sleeving the MK3 port. Yes i have toyed with the idea but very concerned with potential problems. Here i am thinking of the bush not going in perfectly square, or even collapsing due to the thin wall, especially when working all the way down the bottom of the cylinder. Alternatively making an easier slide fit bush but getting knocked out during firing.
Initially without any testing, im thinking maybe a light slide fit for easy location and removing the potential chance for collapse but gluing it in place.
I have the skills to perform the mod but happy for feedback and ideal transfer port discussion first.

[bigtoe01]

Here is what I have found:

there is an optimum TP size for power, BUT this is not the optimum for surge.

the optimum for minimal surge comes with a further increase in TP diameter.

So...for example on my 77k optimum power was at 3.5mm, optimum surge was 3.7mm, but there was very little difference going to 4mm but much more becomes slammy

So...to go with what Mick is finding, as we increase TP diameter the static pressure comes down, there will be an optimum static pressure for power, we just need to look at how much less we need to maintain close to this power but to decrease the surge and time the piston bounce to be right at the end of the compression stroke.

To play around with TP diameter I have found m4 and m5 long grub screws work well, on a 4mm gun drill to 4.4mm and tap 5mm, then drill the m5 grub screw to the TP you want to test and machine to length...wash out the port with alcohol and glue in the new TP with hydraulic sealant.

I have a 1980 HW55, it was leather sealed and has a 4mm port, its presently using a Vortek seal and while not slammy is VERY gas rammy, the TP is quite short so im going to reduce it and see if I can make some gains in power (presently at 8.5FPE) and see if I can dial out the slammyness.
If I remember I will measure the stroke and work out the static pressure and update as I test different TP diameter's.

[craig7]

Nice one Bigtoe.
It does look as if my starting point best guess on the ideal seems about right then, as your HW77 (Great accuracy near 12ftlb gun) is in my suggested range and similar to the great old guns i have (3.5mm to 4mm)
Drilling and tapping using a 4.2mm drill (ill correct you bigtoe lol) and going with grub screw sounds like a resourceful idea for break barrels but how will we do this with a Tap loader like the MK3.
I will check out your site, it sounds interesting.

[bigtoe01]

Nice one Bigtoe.
It does look as if my starting point best guess on the ideal seems about right then, as your HW77 (Great accuracy near 12ftlb gun) is in my suggested range and similar to the great old guns i have (3.5mm to 4mm)
Drilling and tapping using a 4.2mm drill (ill correct you bigtoe lol) and going with grub screw sounds like a resourceful idea for break barrels but how will we do this with a Tap loader like the MK3.
I will check out your site, it sounds interesting.

I go with 4.4mm so there is no chance of the tap breaking in the port and rendering the gun scrap but yes it should be 4.2mm.

On a tap loader...we are looking at a brass bushing maybe with inset O ring and some means of gripping the bush from below with a grub screw....something like seen on the RB2 but the grubscrew is in the rifles breech and holds a polished bush in place.

its a tough one, I have an RB2 and thinking about it its a slightly easier gun to fettle than what you have, if its anything like a Webley Tracker i would say an utter nightmare LOL Its a shame you can not modify the tap to work backwards, you drop the pellet in upside down and make a TP reducer that it drops onto, so when the pellet is spun into position the reducer is behind it right on the compression cylinder....

[mallyally]

ITS ON THE WRONG SIDE

[craig7]

Some good notes there Bigtoe.
Yes, the tap loaders are a nightmare for having to work down through the cylinder to get at the port. I guess they should be left alone.
I have my MK3 running at at slightly over 10ftlbs which is fine for rats and rooks or most general 40 yd plinking that i do.
I also find mine to be very accurate, at least as good as the BSA Airsporter and Mercury if not slightly ahead with open sights but falling behind only when the Airsporter/Mercury is mounted with the 4x40.
I prefer its point ability and great quality build though when compared with the moderate quality BSA.
Also i do wonder if altering the transfer port dia might spoil accuracy but i have noticed that MK3s do buck a bit, suggesting they might improve and have less bounce if they had smaller ports but not sure.

[craig7]

Mally, I disagree.
I would not really put up a strong argument and i guess its what you get use to but try 10 quick shots with an Airsporter and then repeat with the MK3 and see if you feel the same.
However, for me and other members of my club we have found it much better to have the L/H free for cocking the lever and with a pellet in the R/H, flipping the tap and dropping the pellet in with the same hand.
Once you have gone with this technique, it is much nicer and quicker than the Airsporter even considering earlier Airsporters with auto opening taps.