Used BSA Ultra SE shot string

[VT23]

Hi all,

Firstly, Ive got to say that this forum is awesome! Im on a steep learning curve, but the knowledge journey is quite addictive!

So, i bought a used Ultra SE .177 and have been plinking targets in the garden. So far so good and it seems to perform well at the 20m range that I'm limited to. Of course curiosity got the better of me so bought a reasonably priced Chrono (Acetech 5000) to take some MV measurements with. Below are the results and was curious to hear some feedback. There is a Huma reg installed and the transfer port has been drilled out to 4mm. I believe the hammer and spring are standard.

Below are some shot strings i took. Strarting pressure was approx 230bar but i think a little less for the JSB exacts string hence slighty less shots before off reg.

Bisley Magnum 10.6gr:


Between shots 1- 50:

High = 678.1
Low = 660.5
Average = 667.4
Std dev = 3.8
Average ft/lbs = 10.5



H&N FTT 8.64gr:


Between shots 1- 50:

High = 768.9
Low = 712.1
Average = 747.7
Std dev = 7.9
Average ft/lbs = 10.7


JSB Exact 8.44gr:


Between shots 1- 43:

High = 770.6
Low = 749.7
Average = 761.7
Std dev = 5.3
Average ft/lbs = 10.9


The curves are a little erratic. Im also surprised that the heaviest weighted pellet yielded lowest ME. Thoughts?

If Ive missed any key details please let me know.

 

[sagalout]

Congratulations on an excellent buying decision.

Im also surprised that the heaviest weighted pellet yielded lowest ME.

Bis Mags are not the best pellet in an Ultra. Try JSB Heavy 10.34gr.

I have found 3.5mm TP to be the best. The standard hammer is 1.4'ish wire diameter and is too heavy for a regulated gun. Normal to change it to a 1.2mm diameter, 10 coil if you can find one or an R10 spring (1.2mm 12 coil).

Looking at your charts (difficult to be precise with the scaling) it could do with a fettle, but if it's accurate don't mess unless you have the MFS "must fiddle syndrome" that some of us suffer from.

Here's one I fiddled with earlier.

 

[VT23]

Thanks Sagalout, unfortunately, I too suffer from the incurable MFS lol!

The graphs seem a little up and down then settle a bit after 20 or so shots. Is this to be expected from an incomplete setup - going on the assumption that the previous owner just fitted a reg and sized up the port with no other tweaks?

Your graph looks pretty flat! Nice job!

 

[sagalout]

The graphs seem a little up and down then settle a bit after 20 or so shots.

The off reg portion looks very smooth, this suggest to me that the action is good. The reg is not in play here except for the air flow through it, it is below set pressure so is not controlling the plenum pressure which is just following bottle pressure.

My best guess is the reg seal is not very good and at higher pressures not giving a consistent plenum pressure. A trend line for the on reg portion of the string would be useful.

The first shot is low, this also suggests the reg is not sealing as it is allowing the plenum pressure to rise and that extra pressure is preventing the valve opening the same for thwe same hammer strike as later shots.

As per my previous post, do a string with JSB 10.34gr, and let's look at it again.

 

[VT23]

Thats an interesting observation. Ive ordered a lane pressure tester - it wasn’t very expensive and works with a variety of regs so will come in handy for the future. Ive also ordered some jsb heavies so will get back to you with my findings. Thanks for your expert help!

 

[VT23]

Out of interest is the 100bar default pressure setting optimal for the ultra se? I plan to do the lane 5 bar setup at some point.

 

[VT23]

The lane tester arrived, along with an O-ring kit from Huma. The regulator was set to 100 bar and held pressure overnight — that was my first test.

For the second test I purged air from the tester screw in successive short bursts. The cylinder pressure would drop to about 80 bar, then bounce back to ≈95 bar, and from there it slowly settled (30–60 s) to 100 bar. With a full bottle the regulator read 105 bar. When the reservoir pressure fell to 110–120 bar, the regulator read approximately 95 bar.

I rebuilt the regulator with new O-rings; the settling time improved slightly. However i still see a 10bar variation with the reg setting across between 230-120 reservoir pressure.
I have taken another shot string with JSB Heavies, 10.34 gr:



stats from 0-50 shots (230bar starting fill)

High = 704.1
Low = 686.9
Average = 696.1
Std dev = 3.9
Ave ME = 11.1ft/lbs

I noticed that after each reload the FPS increased (apart from the 2nd reload - i had to dry fire this one due to a suspected double load) Ive circled these shots in the graph. I wonder if this could be due to the regulator having more time to creep up from 95 to 100 bar during reload.

 

[VT23]

Worth noting that i didnt weigh any of the pellets. After 20 shots, i realised that i shouldve been more selective regarding pellet quality, as some pellets had dented skirts. It doesnt really show in the graphs, maybe the 20 before were mostly fine.

 

[BallisticBill]

It helps to know the underlying power curve, which you can find by setting the reg above ideal operating pressure and shooting a string off reg. You are probably going to knacker the valve seal disc, although, looking at your results and the creep, it's knackered already. Huma regs don't like being adjusted.

In my limited experience of Huma regs, they have fairly high cylinder-pressure dependency. This doesn't matter if the underlying power curve is flat over the range your reg is controlling to. Apart from the peaks, your string suggests the underlying power curve is too peaky for your reg control. This would result in the start and end of the full regulated string at lower MV than the middle. Over-large TP isn't going to do you any favours in this respect. Personally I'd keep below 3.5mm... 3.4mm for 10.34gr, 3.2mm for 7.97gr or lighter.

The chart below gives some idea of the underlying power curve and effect of plenum pressure variation.

Post in thread 'BSA Ultra SE huma reg'

Aug 25, 2025

This is really where you need a digital pressure gauge on the cylinder so you can measure air consumption per shot. I suspect the reg pressure may be too low and you are running at low air efficiency. Transfer port size may also not be optimum. Installing a blast tamer can improve efficiency by controlling hammer bounce but won't automatically maximise air efficiency.

There's a relevant thread here. I can give more info by PM.


This chart shows air consumption (dotted lines) vs plenum pressure for different TP sizes:



dBar scale is cylinder pressure drop per...

• BallisticBill

• 

 

[VT23]

Thanks, BallisticBill. Yes, I’ll give that a go. I don’t have a digital pressure gauge, but I’ve purchased an improved analogue gauge with finer graduations. Looks like 90-95 is the sweet spot!

 

[VT23]

So I decided to buy a Nate Chrono, and I’m glad I did! The results are much more consistent compared to the cheap chrono. I fired a bunch of pellets through the Acetech with the Nate attached. I don’t have the numbers, but the Acetech was very inconsistent, with extreme highs and lows and many no-detects. The Nate didn’t miss a beat!

Here’s the new shot string below (JSB heavy). Note that the averages are higher than before because I tweaked the HS over the weekend. The Acetech was acting up, so I didn’t complete the tune. Shot 2 was pretty hot (11.89 fpe), so I’ll dial it down a little.

 

[sagalout]

The first 2 shots are indicative of reg creep, and the reg is set to low.

Creep is suggested as the first 2 shots are higher than the rest, i.e. plenum pressure is closer to ideal operating pressure.

 

[rkr]

View attachment 824681
The first 2 shots are indicative of reg creep, and the reg is set to low.

Creep is suggested as the first 2 shots are higher than the rest, i.e. plenum pressure is closer to ideal operating pressure.

Can you explain what's causing the creep, has the reg leaked and plenum pressure is higher than set to start with?

 

[VT23]

View attachment 824681
The first 2 shots are indicative of reg creep, and the reg is set to low.

Creep is suggested as the first 2 shots are higher than the rest, i.e. plenum pressure is closer to ideal operating pressure.

I rebuilt the regulator so i wouldn't be surprised if i introduced contamination. I'll perform an overnight test.

 

[VT23]

Also the reg was set to 100 bar (as it comes from Huma). Ive not experimented with finding the optimal setting yet. However i did notice, on the reg tester, that the set plenum pressure drops as the reservoir pressure drops.

In the pics below the starting pressure is a little over 100 and drops to 95 when the reservoir pressure is approx 120bar.

 

[VT23]

I have a lane regulator aslo that i have installed yet. This behaves in a similar way - maybe they both need time to break in?

 

[sagalout]

Can you explain what's causing the creep, has the reg leaked and plenum pressure is higher than set to start with?

Yes, that's what I mean by creep. The reg is not maintaining the set pressure, it's leaking so plenum pressure rises. This can be fast or long term, after its been stored for a few days for example.

Here's a good photo (ie not mine ) of a knackered huma seal that creeps/leaks like a sieve. It could also be creeping because an O ring that should be hiding back bottle pressure ain't doing it's job, on the Huma reg for the Ultra SE it's the one on the set screw (red arrow)


On the FX AMP reg the O ring that can cause creep is X2-1 red. The seal on the AMP is either the entire piston if it's solid delrin, or the delrin insert in the brass piston (I'm saying delrin as a posher term than plastic, but I don't know what the material is).


Why do reg seals fail/creep/leak (pick you favourite term)?

 

[sagalout]

In the pics below the starting pressure is a little over 100 and drops to 95 when the reservoir pressure is approx 120bar.

It's normal/common for a reg (unless @hamngphilly built it) to exhibit some bottle pressure dependency. The Huma reg is difficult to fettle, the set screw has a fine pip that seats/digs into the replaceable seal, not much else you can do but relace the seal. Having said that I had a Hume reg in the cave the other day that was a complete arsehole and refused to seal properly. Inspecting the set screw under 30x magnification I think possibly maybe potentially there was a burr i=on the pip. I gave the pips a very gentle polish and that cured it.

I'm sure those with lathes and skills could touch the pip up in a more betterer way, but I have a drill press and bad eyesight. What's that you say sonny?

I have a lane regulator aslo that i have installed yet. This behaves in a similar way - maybe they both need time to break in?

The first and only Lane reg I've fitted needed to be polished to recreate the seal after finding the IOP. Dunno if I've mentioned it before but twiddling with the reg creates craters in the seal!

 

[Hmangphilly]

View attachment 824681
The first 2 shots are indicative of reg creep, and the reg is set to low.

Creep is suggested as the first 2 shots are higher than the rest, i.e. plenum pressure is closer to ideal operating pressure.

Good spot on those first 2 .
It would be interesting to know whether that string is just after a fill or if its been standing for a while .

i generally dont take much notice of the first few directly following a fill , fitting or adjustment .

 

[sagalout]

The first 2 shots are indicative of reg creep, and the reg is set to low.

Just a thought, the first 2 shots could be high following filling the gun with air and the blast overpowering the reg thus raising the plenum pressure. BUT if the reg set pressure is IOP the those first two shots would be low. So either way the reg is set to low.