Air Gun Home :: View topic

Alstone · Moderator & Site Supporter

My tx200hc was due for its yearly service the other day, so I decided to try and improve the lock time and reduce the action noise, also up the output to 11flb, it’s running at 10.5flb at the moment.

I should explain that in the UK we are allowed 12flb maximum output for a non FAC rifle, so 12flb is ok but 12.1flb and the law says that you have an unlicensed firearm which is 5 years in jail and the confiscation of all your guns, plus you have a criminal record, a bit like having a silencer in the States.
So most people set there guns at 11-11.5 because you don’t know which pellets the police are going to use when they test your gun, and the wrong pellet can push you over the limit.

Anyway after reading Slavia’s post a while back on action noise waveforms I decided to give it a try, I taped the microphone to the butt cheek piece so it would act as a sound board, and shot off a few pellets, so far so good.

After stripping down the TX washing all the old lube off and giving it a good clean, I decided to make a new top hat lighter than the original and insulated from the compression tube, this I did by making a steel base and a nylon top cap, the original weighed 27g whereas the new one was 16g, at the same time I changed the type of lube to clear velocity grease on the spring, moly on the spring guide and light oil on the outer compression tube, this is all intended to speed up the lock time and also help in cold weather.

The initial results are promising and according to the waveform chart the lock time should be quicker. ( I say “should be quicker” because the piston is getting to the end of the compression tube quicker, so the pellet should be leaving the barrel earlier, but I will know better when it’s had a few hundred pellets through it).

The output is now 11.2flb using AA fields 8.4g 4.52 (0.177) 775fps and will possibly creep up to 11.5flb over time, the noise level seems the same, but it’s interesting on the Audio chart the level of audio sound compared to the waveform, the lower chart has more hot spots than the top one, although the lower waveform as less aptitude, I haven’t figured that one out yet but I do suspect some clipping on the input recording.

PS: The Waveform program I used is Audiocity.

Al

Slavia · Moderator

The wave peaks in the second example do indeed look clipped. It also looks like the vibrations are being damped down more quickly at the end of the second graph.

I don't know that clipping is necessarily a problem, though. The absolute decibel level isn't important; it's the before/after comparison of the graph's "shape" that has value. On the other hand, I think you can use the time scale (as you did in determining lock time).

I held my microphone against the middle of the compression tube, rather than the cheek piece, as you did. How do you think that might influence our results?

Amigo · Veteran Member

Al:

With an 11 gram reduction in total piston mass/sprung weight, I'm curious what the results of your testing would be with a pellet weight in the range of 9.5 to 10.5 grains. Also wonder if there might be some piston bounce - although that could be irrelevant if you don't use heavier pellets.

I like the idea of the nylon insert for its potential dampening effect.

Thanks,

Amigo

Alstone · Moderator & Site Supporter

Slavia
I’m not really sure what difference moving the mike from the compression tube to the stock will make, I should think it cuts out the sharpness out but would introduce secondary harmonics to the graph. Anyway like you say it’s the comparison of the graphs that gives you the information. I’ll give it another go tomorrow on both the receiver and stock and see what the difference is.

Amigo
I have some 10.5g Bisley Magnums so when I do the test for Slavia I’ll put some through and see what sort of chart comes out?

BTW Amigo I haven't forgotten about the Tempering post, I have all the paperwork done just waiting for better weather to do the photos.

Stock Mike

Alstone · Moderator & Site Supporter

Ok then these are the results of a waveform sample taken from the stock of a rifle and another from the receiver, the first is from the stock cheek piece.
The stock sample appears to be a smoother graph, I suppose because the sound is more mellow with travelling through the stock.
The second taken from the receiver is more ragged?
Slavia which do you think gives the better idea of what is going on?

Amigo the second graph is again from the stock and receiver but using a 10.4g Bisley magnum .177 pellet.
The graph shows that the impact of the piston with the compression chamber is greater than with an 8.4 g pellet, which is what you would expect! But very little bounce?

Well that’s my basic interpretation of the results, if anyone has any other ideas on the results then please post them.

AA pellet 8.4g

Bisley Mag 10.4g

Receiver Mike

Al

Slavia · Moderator

Amigo · Veteran Member

Al:

Looking at the graphs, it appears as though the 10.4 grain pellet results in a smoother shooting cycle.

Did your physical tactile senses detect any shooting cycle differences (fore/aft recoil, torque etc.) between the pellet weights and or piston weight?

Thanks for posting your research!

Amigo