AirGunTech: Re Engineering Spring Powered Air Rifles for smoothness, consistency, and to better suit UK power levels.

Computers and chronographs…easy or hard?

Airgunning in the UK is really quite complicated, Brits by nature are 100% sure fire tinkerers, BUT with the law being so tight here in blighty we have to limit our tinkering to improving consistency over power increases in the most part. What this means is anything you do to your beloved airgun you need to make sure its performing on the right side of the law for unlicensed airguns…so you need to use a chronograph.

I use 2 here, a Combro 625 and a Beta Chrony…I know some of you guys will shake your head at their accuracy but on the whole they are within 2 to 3 FPS of what  the actual velocity is (worst case) and if you tune wisely and factor in the margin of error you stay well within the limit imposed for UK airguns. Here is the cool thing though for consistency testing they are pretty much as good as any chronograph available as you are looking at FPS variation more than anything.

Now you can use the old fashioned method of noting down each shots reading as you take it…or you can spend a small amount a cash and invest in a hookup cable to connect the chronograph to a PC.

The USB based connect cable I bought came via an advert in the classified section of the airgun BBS here in the UK, the actual site owned by the manufacturer, full drivers are available for windows and linux although I did not see any for Mac. Here I am using Windows 7 64bit  and no driver was needed on my workstation laptop…so you may just get lucky like I did !

First job was to install the chrono connect software which you find under the download tab at, this was really quite painless with no reboot needed ( for me anyway). Next  install the USB hook up and made sure it is recognised. Finally the connection to the chrony is made and the unit powered on…you now need to make sure you set the right com port, this is easy to do by looking at the installed com port under device manager in windows and setting the chrono connect software to use the same port. Now you can now check the chrony is communicating with the chrono connect software.

If all is well and the chrony or combro is communicating OK you are about ready to start testing.

At this time I am only using the demo mode so some of the features regarding saving data are disabled BUT you can still shoot 10 shot strings, save results and graph the outcome….once unlocked 10 shot strings for me will become 50 and 100 strings…how many shots you take is then completely up to you.

First test was using a freshly rebuilt and modified HW35k, this rifle is 28yrs old now and is generally shooting  better than she ever did although  the latest bout of modifications have rendered her in need of a partial reblue. Recent modifications are to smooth out the rifle, these include HW80 cocking shoe, re profiled cocking arm ( to work with the shoe) and PTFE guide,  fully internally Nylotron sleeved reduced diameter piston with integrated rear piston bearing and a 19.5mm dia Titan XS mainspring with custom Delrin spring guide and tophat. End results as you will see from the graphs are around 10FPE although I expect this to rise to around 10.5 after a tin of pellets loosens things up…then a final preload washer will I hope push her to 11FPE which I regard as a safe maximum… I will detail the modifications here on AGT soon with full pics.

For now though lets look at the software and what it reports.

Here I pushed 10 Umarex domb head .22 pellets through the HW35, these are a light weight .22 pellet (13.27gr), from the drop down menu’s you are able to choose rifle type/calibre, and pellet/projectile details. If the gun is not listed you are able to type this info in manually and also add pellet info and weight if you need.

So…you take your first shot over the chronograph,if a successful reading is reported you should hear a bong from the PC, 10 shots later you are greeted with the following:

Here we see number of shots =10, the minimum FPS was 575.90, the max 586.79 for an average of 582.49.   10.89FPS spread with 3.50 std deviation for an average energy of 10FPE. I only hope when in final tuned state it reports similar or better consistency results.

Hitting save capture creates a CSV which you can use open office calc to open or excel from Microsoft, the cool part though is you are then given an option to upload the csv file to a data base where a graph can be generated for you. Now…the graph once generated comes with a set of links for you to use on websites etc, I choose to screen capture and save my graphs to the laptop…the choice is yours though.

I know this is a basic graph but it does give you some idea of how consistent the velocity is and once unlocked your 10 shot string could well be a 100 shot string which when graphed would give a much more detailed view.

Here are results using Crossman Accupells:

So, overall chronoconnect looks to be an awesome piece of software, if like me you enjoy tinkering with your airguns it pays to have something like this in your toolbox. Knowing what energy the rifle is producing and how consistent the velocity is with your chosen pellet can only lead to greater accuracy at the range or while hunting. You can also keep a data base of pellet stats through the same rifle which should help tell you which pellets perform best. Here at AGT I will do just this and publish velocity data thru the HW35 as well as other rifles to help show how each pellet performs.

  • having found your site and have found some very helpful ideas on tuning HW air rifles.thanks

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