is it normal to have first few shots way off

Not normal, or at least should not be normal. Maybe it's something you can live with on a target rifle, but it would never work in a hunting situation. Sometimes regulator creep can cause first shot problems, but it should be first shot only. It would be odd in my experience for the first few shots to be consistently off, and then return to POA. Don't really have an idea on that one, although I'm always suspect of any liner/sleeve barrel system. 

As Ed says, regulator creep is the most common cause but it also has a lot to do with how the hammer spring is dialed in.

Regulator creep is when the pressure rises slowly due to small imperfections in the regulator’s valve seat. Eventually it climbs high enough that it totally squishes the seat together and the pressure stops rising. If it rises a lot, the hammer may not strike the valve hard enough to fully overcome the pressure that is holding it closed (partial valve lock) and the resulting velocity is lower than wanted. To fix it at the source, you need to smooth the surfaces of the valve seat. If it’s a flat surface, you can use progressively finer grits of wet sandpaper to do it. If it’s curved or beveled, you can burnish the seat with a mild abrasive paste. 

However there are a couple of other things you can do first.

One is to check that the hammer spring tension (HST) is adjusted properly. When it is, the system will be less sensitive to pressure variation. What you do is gradually increase the HST until the velocity maxes out, then back it down to about 95% to 97% of that maximum.

The other thing is, if the regulator is new, it needs time to break in. Sometimes the surface irregularities will get ironed out after a couple hundred shots. Sometimes not.

By the way, I agree it could be something else. Creep often affects just the first shot but sometimes more. It depends on a number of factors:

1. Severity - how much pressure rise it experiences
2. Amount of hammer strike
3. Size of plenum relative to the tune’s power level
4. Regulator hysteresis – the amount the pressure has to drop before the valve seat reopens

Just to name a few. 

If that’s not it, the next most common cause we see is probably a wet hammer lube. It’s generally best for the hammer and receiver to be run dry with a dry lubricant like molybdenum disulfide powder, tungsten disulfide powder or graphite burnished into the surfaces. It those surfaces are rough, smooth them first with fine wet/dry sandpaper. 

A couple of questions to you which may affect the answers from others:

When you say the first few shots are way off, is this the first few shots after a refill? Does it do the same thing if you set the rifle aside for 30-60 minutes and then resume to shooting?

What pressure are you filling the gun to?

Have you ran it over the chronograph to see whats happening the first few shots? 

Jason has you on the right track. I would suggest dropping the reg to 95 bar and work your way up to max with the hammer spring. Being your 100fps slow on your first shot now, your velocity will probably be more than you want.

FWIW, that building velocity is symptomatic of the two causes I described above, either reg creep/insufficient hammer strike or hammer drag as a result of a wet lubricant.

TMH also asked a very good question. If you run the pressure down below the regulator’s setpoint and then refill it, that can produce the same symptom. It has to do with the nature of how the regulator’s valve seat cycles open and close relatively quickly under normal circumstances, but more slowly during a refill…thus it may achieve a different plenum pressure. The way around that is to go ahead and blow off a couple of dry fires after a refill, or stop shooting and refill before dipping below the regulator’s setpoint. However if it always behaves that way after sitting idle for a while, refer back to the other two causes.

Sounds like you just need to take your time and start from scratch and properly tune the gun. The honeymoon is over, so it’s time to get down to business. Set your reg, set your HS wheel on Max then back the spring off using an Allen wrench. Work your way up to your maximum speed for the reg setting using the Allen wrench to increase your hammer spring tension. If you are happy where it maxes out speed wise, back the wheel down to #4 and start shooting. Always keep an eye on your reg gauge. If you have it set at 110 and you grab the gun hours later to go shoot, makes sure it’s still at 110b. Tap it a couple times to make sure. My impact reg will show 115b after shoot each shot. When the bottle pressure gets down to 150b, my reg gauge will only show 110b until I tap it. Then is jumps back to 115b. 

I have had perhaps 10 different pcps over the last 10 years edgun,kalibrgun, fx in .22 and .25 calibers.

The only guns I noticed needed "settle" in time were my fx guns. 

My fx impact was by far the worst. It needed 5 shots before it started really getting accurate. I'm not going to lie. I'm glad it's gone. 

My edgun matador can sit for 3 weeks and hit dead center at 60 yards on the first shot. It is truly an engineering marvel. Absolutley dead on. Every time.

Course it has a huma reg. Not sure how it would be with edgun reg. 

I know that in a recent Shooter1721 video (Maverick?) he mentions that in his experience FX guns seem 'tight' to him after a refill and, IIRC, he says that he never fills them to the listed pressure (fills to 230bar even if gun is listed for 250bar). Then he proceeds with his chrono work in the video and his first 2-3 shots have a lower velocity than the subsequent shots.

I wonder whether FX guns function the same with a Huma reg installed...

What that describes is a regulator with poor input regulation characteristics. That is, its output pressure rises and falls along with the input pressure. All are subject to it but some more than others. I’m by no means an expert on regulator design but one source of this nonlinearity is a large orifice to the high pressure side. It aids in recovery time but sacrifices linearity. Another I suspect is the piston material, most being brass or stainless steel but some being plastic which makes it more subject to dimensional change due to the pressure applied.

If you are leaning it in a corner against a wall with the barrel, or in the safe leaning against something, that might be the cause. 

Just leave it stored at remaining pressure right at the reg set point and refill only when ready to shoot OR! just blow off the first one to four shots b4 doing any serious shooting like a lot of people do.

You can be fixing this phenomenon all you like but still won't guarantee an errant first shot at the least opportune moment that you won't know till you missed and wondered if it's was the guns fault or you. It can happen at any time.

Filling to 3000psi or less does help based on my personal regulated guns in general experience not limited to only FX.

Zero issues with the last 2 FX Impacts I purchased never filled past 3000psi and recently stored at regs set points to be proactive about any potential reg creep and just fill to 3000psi when ready to shoot then shoot down to reg pressure then put them away. If the remaining pressure stored is higher then set reg pressure just pop off the first couple shots it's as easy as that. Regardless if you know if it creeps or not just don't want that lucky errant missed shot to find out after the fact.

I would not advise unscrewing the bottles when storing them.

I do like the simplicity of non regulated guns that their first shot are always dead on no matter what (SERIOUSLY). Even my Hatsan Flash and Vectis and Benjamin Maximus believe it or not. It's one less thing that can throw your accuracy off at the least opportune moment. Better just to grab and shoot eh? I have come to really appreciate the Benjamin Kral guns lately.

On the flip side the Impacts are some of my most accurate long range guns that give my very old top 10 (give or take maybe more) unregulated guns a run for their money past 150 yards.

To date the best luck I witnessed with NO first shot (WTF?) Missed shots are my RAWs and HW100s and 110s and Taipans Vets and Mutants all Edguns all models and all Cricket rifles and BPs and ALL Brococks and Daystates and Benjamin Marauder Field and Targets and Fortitudes (just leak issues) and Umarex Gauntlets and ATI Nova Libertys (haven't shot them much though but stored 4 years then first shots ok dead on believe it or not) and no issues with first shot duds with HUMA after the fact Marauders and P-Rods and HUMA After the fact Daystate Renegades that didnt even need regulators didn't make them more accurate anyway stupid me I guess introducing a foreign cancer that will turn malignant one day at the least welcomed and Unexpected moment. Regs do require servicing sooner or later.

What is a regulated gun?

It is an unregulated one that you operate at the same pressure over and over.

Well...almost.

Ideally the regulator always outputs the exact same pressure. Realistically it produces a narrow range of pressures. What that means is, if you have your regulated gun tuned well, it will function like an unregulated gun operating in the sweet spot of its bell curve. The sweet spot being where the rifle produces a stable velocity in spite of the fact the pressure swings several hundred PSI.

Regulator creep isn’t a disease so much as it is your gun saying show me the same love you showed that other rifle. 

What is a regulated gun?

It is an unregulated one that you operate at the same pressure over and over.

Well...almost.

Ideally the regulator always outputs the exact same pressure. Realistically it produces a narrow range of pressures. What that means is, if you have your regulated gun tuned well, it will function like an unregulated gun operating in the sweet spot of its bell curve. The sweet spot being where the rifle produces a stable velocity in spite of the fact the pressure swings several hundred PSI.

Regulator creep isn’t a disease so much as it is your gun saying show me the same love you showed that other rifle.

Click to expand...

100% agree and very doable with a little extra fine tuning. No need to blow off shots with a little extra effort. Tried explaining the the same thing a couple days ago. But apparently its voodoo and your supposed to live with it.

https://www.airgunnation.com/topic/did-anybody-install-a-huma-regulator-in-there-air-arm-s400-mpr-ft/?referrer=1

For a target gun, blowing off a few shots is not a big deal, but for a pesting gun where I never know when the next shot is going to be, this is unacceptable. I also had this issue a few months ago and a few people did tell me that blowing off the first few shots is no big deal. I learned and really took my time tuning my gun and it now shoots correctly no matter how long the gun has sat unused. So far, the longest I've left the gun unused is a day over a month. Picked it up, shot it over the chrono and it was less than 10 FPS above average and was still right on target. Slight regulator creep is normal and I think most guns has it but proper tuning will definitely help the gun deal with it better as not to change the point of impact regardless of how long the gun has sat unused.