First shots off, WTF?!?! Possible causes

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broekzwans

broekzwans

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Mar 13, 2016
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the Netherlands
Almost sounds like a proper clickbait title right?Ā šŸ˜

I've read it more than once in the past weeks/months/years that airguns are suffering from the first shots being offĀ and what I mostly see is that the regulators are blamed. I thought it might be convenient to clarify some possible causes that can be fixed quite easily too (sort of troubleshooting guide):

  • A greasy hammer:Ā hammers will strike the most consistent when they run absolutely dry. Dry lubes are possible if you want to experiment with it but make sure the carrier fluid is evaporatedĀ before reinserting the hammer. Most hammers run in a pretty tight channel and oils and grease can act as a sealer which can cause pressure buildup in front of the hammer or vacuum at the rear of the hammer. They will also give pretty inconsistent results during shot strings and will behave differently every time the gun is stored and also depends on the way the gun is stored. So the rule this out cleanĀ the hammer channelĀ šŸ˜
  • Oily/greasy barrel:Ā When improper oils are used to clean the barrel it might leave a greasy substance inside the barrel, or just residue of the cleaning oil, which will slow down the first (few) shot(s) but this will be removed by the pellets you shoot. This will probably end up in a couple of pellets at lower velocities for the first few shots. One product I know that does this is ballistol, there is some type of resin in there which will solidify when left to dry so if you use it for cleaning make sure you remove it before use. Nothing wrong with ballistol by the way andĀ this isn't the only product that does this!
  • Sticky valve: If the airgun is stored for a longer time the valve might start to seat slightly different compared to right after the shot. Polymers will start to deform to the exact valve seating shape and oring valve seatsĀ might start to sort of stick to the seating area. Cleaning the seating area will help for oring seals and using proper materials for the polymer seating facesĀ (this is mostly influenced by the manufacturer since very little people make their own valves). This issue will be gone after the first or second shot generally but will re-occur each time the gun is stored if not taken care of.
  • Shooter needs to warm up:Ā This is oneĀ some people won't like, it might just be you who will miss the first shotšŸ˜± Hold is something really important when shooting and is mostly underrated by many. Building up the exact same hold every time you shoot is vitally important for accuracy. If you don't turn this into a routine there is a chance your hold might be inconsistent which can cause a wandering POI every time you mount the gun. This can even lead to re-sighting each time you pick up the gun to shoot.
  • Improper lubrication of the regulator:Ā During changing temperatures the lubricity of greases and oils changes and will influences the speed and accuracy of the regulator. Ask the manufacturer of the regulator for advice on the lubrication since I assume they've done tests to find the optimal grease or oil for their regulators. Also during use the oil or grease is redistributed to regain it's full function which might take a couple of shots.Ā This will probably be visible during the changing of the seasons or big fluctuations in temperatures.
  • Regulated chamber pressure increase due to temperature deviation:Ā This one is already mentioned by a few (including me) over here on the forum, when moving from a cold to a warm environment the plenum pressure will increase pretty much according to the gas law. This is easily cleared by one or two shots to get the regulator going again. So it is important to first let the gun sit in the conditions you're going to shoot in for a while, dry fire once or twice before use and get going.
  • Leaking regulator:Ā This is already kind of known for most. If the sealing surface of the piston is damaged there is a high chance the regulator pressure will rise quite an amount over time. But there is also another way it can leak, if the adjustment screw sealed the piston but the oring around the screw is dirty (a hair or something on the oring) there is a chance it will leak past this oring and fill up the regulated chamber, most probably, up to the fill pressure or slightly below.

A regulator is not failing miserably when it creeps only a couple of bars in a day. For most people it is really hard to stop this slight settling behavior of the regulator, there are enough machinists and tuners who can accomplish this but they know what they're doing and know what their looking for. If you don't feel comfortable modifying you regulator please don't! The risk of ruining the regulator is quite significant and in my opinion is not worth the risk over taking two dry firing shots before you go.

By the way, if you actually test it, a slightly creeping regulator (and I mean slightly, less than 5 bar) will most likely give you a higher muzzle velocity while in pretty much allĀ cases I read that the first pellet hits lower than usual. Quite the opposite of what you would expect right?! The BC is not changing that rapidly that only a couple of m/s faster will end up drastically lower because the BC deteriorates dramatically. Also the miniature pressure gauges aren't sacred, their needles will stick too and will barely respond to minimal changes.

So just some things to think about when you notice weird behavior on your first shots. First check the easy things like the greasy barrel and the greasy hammer if the regulator creep is minimal, then proceed to the other steps (and don't forget to doubt your own abilitiesĀ šŸ˜‰, had to accept this myself too at some point). Hope this helps. If I missed something please add it below and I can add it into this post if preferred.
 
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Great post my friend...may I add one: Incorrect screw on the moderator.

I have found that using aĀ wrong adaptor or even using an o'ring between the moderator and the barrel affect the POI and groups. A few days ago I was experimenting with that and to my surprise I had in 1 single 10 shot string 2 or even 3 different groups.Ā 

First discovery was using an m20 - 1/2 unf adaptor and a new moderator...that did not screw all the way in

Then I had about the same with DonnyFL and the impact shroud. I figure if I add an o'ring it will be sealed...but I had a similar condition 2 or 3 groups on a single string. I remove the adaptor in one and fixed...then I remove the o'ring in the other and fixed too.

My conclusion: the freaking regulator !!! jajaja :)
 
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@cmateraĀ This is especially applicable to hunting, if you don't know where your first shot is going to land you shouldn't be in the field ;) If you experience first shots being off than it is particularly important to look at the possible causes mentioned above.

The first three just mean proper cleaning of your equipment to rule them out, the 4th is a case of improving your skills, the 5th and 7th might be better to let a gunsmith do the job to avoid unnecessary risks and the 6th is something that is really hard to prevent up front. A large temperature deviation from cold to hot needs to be bridged by a shot to become normal again, from hot to cold isn't a problem in this case. So after stepping out of the car let your airgun get up to temperature, fire a shot and get going. There are barely any situations where you can't fire a shot with an airgun before starting the hunt.

For target shooting itĀ rarely ever is a problem to fire a couple of shots before starting to shoot targets.

It is still possible that the regulator is the issue but it might not be the actual problem and this might save the $$ for a new regulator.
 
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Firstly, broekzwans I want to compliment you on your well-articulated summary of troubleshooting steps and recommendations for improving the consistency of the first shot. It is a common problem and I think you have done a good job identifying many of the common causesā€¦particularly the unpopular one, the imperfect biological mass placed behind the trigger.



I do want to clarify one point regarding the symptoms of a creeping regulator. The hammer spring tension (HST) adjustment will dictate whether the first shot is fast or slow. In most examples that we read about, the user reports a slow shot and that is because they have adjusted the HST for efficient use of air. Thus after it has sat around for a while and the pressure has crept up, the first shot is slow because the hammer cannot adequately overcome the force of the additional pressure that is holding the valve closed. Valve lift and dwell are diminished and the velocity suffers as a result.



In other cases though, the first shot will be faster because the HST is adjusted too strongly. Thus despite the higher pressure against the valve, the hammer has plenty of energy to knock it open forcefully. Valve lift is high and dwell is long, therefore the velocity is higher than normal. I remember helping one user here on AGN whose first shot was hitting something like 1.5ā€ high at 50 yards. He had tuned it to around 850fps. Running the hypotheticals through Chairgun, it predicted his first shot was more like 1000fps. I remember telling him that if it were off that much, it really should be obvious from the muzzle report but he didnā€™t seem to notice anything unusual. Turns out when he tested the first shot over the chrony, it was almost exactly where Chairgun predicted. Again, it usually goes the other direction but that particular case was interesting because it was so severe.



Regarding the example you gave where the velocity is faster yet the POI is lower, I agree that it will certainly not be because of a change in the pelletā€™s ballistic coefficient. It would be due to something else, most likely barrel harmonics.



Anyway for the scenario where creep causes (for example) a 130 bar setpoint to climb to 140 bar overnight, that will have a negligible effect on velocity when the HST is adjusted properly. So while it is nice that FX includes a second gauge for monitoring the regulated pressure, it seems to have given rise to blaming the regulator in many cases where simply adjusting the HST would bring things in line. It appears to have done wonders for Humaā€™s sales though :)



Granted I know there are some circumstances where the creeping is so severe that something has to be done. Fortunately in my experience it has usually been easy to solve by dressing the seat with fine wet/dry sandpaper against a piece of glass or granite. In other cases such as Ninja paintball regulators, the seat is a little plastic ball that can be easily replaced.


 
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Firstly, broekzwans I want to compliment you on your well-articulated summary of troubleshooting steps and recommendations for improving the consistency of the first shot. It is a common problem and I think you have done a good job identifying many of the common causesā€¦particularly the unpopular one, the imperfect biological mass placed behind the trigger.



I do want to clarify one point regarding the symptoms of a creeping regulator. The hammer spring tension (HST) adjustment will dictate whether the first shot is fast or slow. In most examples that we read about, the user reports a slow shot and that is because they have adjusted the HST for efficient use of air. Thus after it has sat around for a while and the pressure has crept up, the first shot is slow because the hammer cannot adequately overcome the force of the additional pressure that is holding the valve closed. Valve lift and dwell are diminished and the velocity suffers as a result.



In other cases though, the first shot will be faster because the HST is adjusted too strongly. Thus despite the higher pressure against the valve, the hammer has plenty of energy to knock it open forcefully. Valve lift is high and dwell is long, therefore the velocity is higher than normal. I remember helping one user here on AGN whose first shot was hitting something like 1.5ā€ high at 50 yards. He had tuned it to around 850fps. Running the hypotheticals through Chairgun, it predicted his first shot was more like 1000fps. I remember telling him that if it were off that much, it really should be obvious from the muzzle report but he didnā€™t seem to notice anything unusual. Turns out when he tested the first shot over the chrony, it was almost exactly where Chairgun predicted. Again, it usually goes the other direction but that particular case was interesting because it was so severe.



Regarding the example you gave where the velocity is faster yet the POI is lower, I agree that it will certainly not be because of a change in the pelletā€™s ballistic coefficient. It would be due to something else, most likely barrel harmonics.



Anyway for the scenario where creep causes (for example) a 130 bar setpoint to climb to 140 bar overnight, that will have a negligible effect on velocity when the HST is adjusted properly. So while it is nice that FX includes a second gauge for monitoring the regulated pressure, it seems to have given rise to blaming the regulator in many cases where simply adjusting the HST would bring things in line. It appears to have done wonders for Humaā€™s sales though :)



Granted I know there are some circumstances where the creeping is so severe that something has to be done. Fortunately in my experience it has usually been easy to solve by dressing the seat with fine wet/dry sandpaper against a piece of glass or granite. In other cases such as Ninja paintball regulators, the seat is a little plastic ball that can be easily replaced.

Click to expand...

Thank you for your reply!Ā While I fully agree with the creep issue you're mentioning the example I gave was for a very smallĀ creep/settling behavior. If the shot ends up slower after a creep of only a couple of bars you're running on the edge of the adjustment. Most people will not reach that far but obviously it is also behavior you can see. Glad you're contributingĀ šŸ˜

Also, the muzzle report will not always become louder when the pressure and velocity rises. I've seen (and done) quite some tunes that gotĀ a lot more efficient after a vast increase of theĀ reg pressure. The hammer hits the valve with the same force but the counteracting force from the pressure on the valveĀ that it has to overcome is much larger with higher pressure which leaves less residual momentumĀ to push the valve open after knocking it loose. The loss of momentum leads to a valve that isn't opened as far as before but due to the higher pressure the pellet might still get the same acceleration profile which leads to a higher efficiency and a smaller chance of hammer and valve resonance after the first smack (also called hammer bounce). The hammer bounce is of course pretty much eliminated with the free floating hammer but the principle of the first smack remains the same.

All those possibilities and tuning options šŸ˜…Ā such a fascinating hobby šŸ˜ Thanks again for you reply!
 
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