Umarex Notos first shot is off

[The BB Bandito]

I have my Notos zeroed for 25yds. The max I can shoot in my yard. My problem is the first few shots are way off in the mornings or after the gun has sat for a while. Usually to the right, with no change to elevation. I was thinking a slight leak on the regulator but the elevation doesn’t shift. After a few shots it groups back up nice and tight. What is the problem here? I put a picture of the group below with a corn kernel from my squirrel feeder death trap for reference.

 

[Cantona256]

Cold bore… this is a common term with firearms as well. Metal contracts and expands with temperature changes. The times you mentioned very much indicate that the gun is “cold.” If you can let the gun warm up in the sun before shooting that usually helps. I live in the mountains so I’ll set my gun on a tripod in front of the heater vent and let it warm up that way if I’m going for an early morning hunt…. If you’re trying to get the drop on some critters maybe set up a spot in your garage or something and fire 2-3 rounds to warm the bore up before approaching live targets.

 

[nervoustrig]

In the world of airguns, cold bore is a blanket term frequently used to encapsulate a variety of subtle factors having little to nothing to do with the actual temperature of the bore.

N/A - What's this about "cold barrels?"

I posted this question in response to a few people talking about the first shot out of a cold barrel, seeming to imply that the POI would shift as the barrel warmed up. Or am I missing the point? (I often do......) " Kinda new to all of this, but I do have a question. Considering that we are...

www.airgunnation.com

How much is the lateral shift at 25 yards? Differential material expansion rates resulting from modest temperature changes won’t usually translate to a meaningful difference at 25 yards. However, even it were a contributing factor, tracking it down can be quite tedious.

My advice would be to start by putting the first few shots over a chronograph to ascertain whether it is or is not a potential cause. The absence of a perceptible vertical shift at 25 yards may be misleading, but harmonics resulting from the valve being knocked open less forcefully as a result of pressure creep can produce unpredictable POI shifts.

The other thing that comes to mind, is there any play whatsoever in the barrel, or the way it is supported/kept centered in the shroud, or play in the shroud itself? Likewise, are there any O-rings involved in keeping any of the aforementioned parts aligned?

 

[Vetmx]

What nervoustrig said and you should clean your barrel. I’ve noticed the slight wondering around then spot on issue over the years with several guns. And the velocity wasn’t the problem. But you’ll want to check it anyway. But at 25 yards you have a pretty wide velocity range to work with and still land a pellet on the money.

 

[The BB Bandito]

The POI shift is pretty substantial for 25yds. Anywhere from 6-8” after 1-2 shots it’s back in business. Even with firearms and huge temperature differentials I have never seen a POI shift that big @25yds. I don’t have a chrono yet so I can’t pull data on the first and second shot. I have a sneaky suspicion you might be right. I was thinking a pressure change was the culprit, but I was wrong in thinking that the vertical shift would be a key tell for the pressure change.
I did like your theory on the harmonics and how that valve behaves during the assumed lower pressure shots. I could see how that may cause a lateral shift.

 

[The BB Bandito]

What nervoustrig said and you should clean your barrel. I’ve noticed the slight wondering around then spot on issue over the years with several guns. And the velocity wasn’t the problem. But you’ll want to check it anyway. But at 25 yards you have a pretty wide velocity range to work with and still land a pellet on the money.

I had the barrel cleaning cross my mind but with it shooting so consistently after the first few shots. I don’t think that would be the culprit. This is just the 1st shot and maybe the second shot at most. If it was a dirty barrel wouldn’t it be consistently inconsistent.

 

[The BB Bandito]

Cold bore… this is a common term with firearms as well. Metal contracts and expands with temperature changes. The times you mentioned very much indicate that the gun is “cold.” If you can let the gun warm up in the sun before shooting that usually helps. I live in the mountains so I’ll set my gun on a tripod in front of the heater vent and let it warm up that way if I’m going for an early morning hunt…. If you’re trying to get the drop on some critters maybe set up a spot in your garage or something and fire 2-3 rounds to warm the bore up before approaching live targets.

I’ve just never had a temp differential throw the POI 6-8” @25yds before. All of the environmentals are pretty much the same as when I made that group. Not ruling it out completely though.

 

[nervoustrig]

The POI shift is pretty substantial for 25yds. Anywhere from 6-8” after 1-2 shots it’s back in business.

Oh wow, my assumption was we are talking a nuisance shift of a half inch or inch tops. Pretty safe to say 6 to 8 inches is not due to differential material expansion rates or even harmonics. Can’t say that I’ve ever encountered something that severe but the good news is it should make it easier to troubleshoot because a slight change should quickly produce an observable difference. Just spitballing, I would investigate the aforementioned areas of possible play in the barrel or shroud, or movement in the scope rail or rings, and try a different scope and rings. For example, a bad erector spring in the scope tube could conceivably produce a symptom like that.

 

[The BB Bandito]

Oh wow, my assumption was we are talking a nuisance shift of a half inch or inch tops. Pretty safe to say 6 to 8 inches is not due to differential material expansion rates or even harmonics. Can’t say that I’ve ever encountered something that severe but the good news is it should make it easier to troubleshoot because a slight change should quickly produce an observable change. Just spitballing, I would investigate the aforementioned areas of possible play in the barrel or shroud, or movement in the scope rail or rings, and try a different scope and rings. For example, a bad erector spring in the scope tube could conceivably produce a symptom like that.

I’m going to look things over. I experimented and if I dry fire it a few times before I shoot then it’s shooting lights out again. I’m not sure what it is? It’s a laser after I dry fire it though. Any ideas? I’m gonna start trying to move stuff or checking for play. I did a check of the rail and rings. My scope mounting is fairly particular. I don’t think it’s any of that moving, otherwise it would be inconsistent all the time. After those two dry fires I can shoot a dried corn kernel at 25yds and hit 2 out of 3 times. I’m clueless right now.

 

[nervoustrig]

Hmm, yeah that’s interesting. It seems to point away from potential movement of the barrel or shroud or scope. Unfortunately I don’t have a theory as to how dry firing avoids an initial lateral shift of such a huge magnitude. I’ll definitely keep an eye on the thread for developments or details that will help narrow in on it.

 

[The BB Bandito]

Hmm, yeah that’s interesting. It seems to point away from potential movement of the barrel or shroud or scope. Unfortunately I don’t have a theory as to how dry firing avoids an initial lateral shift of such a huge magnitude. I’ll definitely keep an eye on the thread for developments or details that will help narrow in on it.

Thanks I appreciate it, definitely has me scratching my head.

 

[Cantona256]

Oh wow, my assumption was we are talking a nuisance shift of a half inch or inch tops. Pretty safe to say 6 to 8 inches is not due to differential material expansion rates or even harmonics. Can’t say that I’ve ever encountered something that severe but the good news is it should make it easier to troubleshoot because a slight change should quickly produce an observable difference. Just spitballing, I would investigate the aforementioned areas of possible play in the barrel or shroud, or movement in the scope rail or rings, and try a different scope and rings. For example, a bad erector spring in the scope tube could conceivably produce a symptom like that.

Yeah I agree with this too. I didn’t realizing your shift was that bad.. wow.

 

[JimD]

I've never seen anything that big but my SPA guns seem to not like being 5% under peak velocity for the regulator setting. When I do that, my first shot does not go where subsequent shots go. Or where it was shooting when I put it away. My new-to-me Bullshark is doing that right now and it is tuned about 5% under. When this has happened previously a small tweak to the hammer spring has solved it. So like 3% under peak instead of 5%. On the bullshark my velocity on the first shot may be 5-10 fps low but not enough to explain the POI. It's really close to being in the range of the rest of the shot string just a little on the low side.

 

[Vetmx]

Definitely check you first three or four cold shot velocities. If it’s a short barrel gun, like pistol short, maybe it being a blast cannon the first couple shots is really disruptive to your pellet.

 

[The BB Bandito]

I've never seen anything that big but my SPA guns seem to not like being 5% under peak velocity for the regulator setting. When I do that, my first shot does not go where subsequent shots go. Or where it was shooting when I put it away. My new-to-me Bullshark is doing that right now and it is tuned about 5% under. When this has happened previously a small tweak to the hammer spring has solved it. So like 3% under peak instead of 5%. On the bullshark my velocity on the first shot may be 5-10 fps low but not enough to explain the POI. It's really close to being in the range of the rest of the shot string just a little on the low side.

I called umarex and they said to adjusting the hammer spring might solve it.

 

[The BB Bandito]

Definitely check you first three or four cold shot velocities. If it’s a short barrel gun, like pistol short, maybe it being a blast cannon the first couple shots is really disruptive to your pellet.

Yeah as soon as I find a chrono I will.

 

[JimD]

I used to have and use a conventional chronograph but I shot it one too many times. Now I use one of my cheap chinese chronographs. The clamp on is completely dependable and the cheapest. But on some guns it shifts the point of impact so I usually use a tripod mount. As long as I am fairly centered in it's window it is also completely reliable but if I get to the edge of it's window it sometimes misses shots. Amazon has at least the clamp on model. Should cost about $30.

 

[The BB Bandito]

I used to have and use a conventional chronograph but I shot it one too many times. Now I use one of my cheap chinese chronographs. The clamp on is completely dependable and the cheapest. But on some guns it shifts the point of impact so I usually use a tripod mount. As long as I am fairly centered in it's window it is also completely reliable but if I get to the edge of it's window it sometimes misses shots. Amazon has at least the clamp on model. Should cost about $30.

Oh I didn’t realize they were that cheap
EDIT: It will be here Sunday thanks

 

[Gerry52]

Are you filling gun to MAX pressure? With some guns I've experience with I noticed that if filled to MAX (250 bar) the 1st couple or 3 shots would be off, although not as drastically as yours. Once pressure got under the MAX things leveled out. So, I stopped filling to maximum pressure & they're spot on from the 1st shot. I'm not the only one who's experienced this. The problem MIGHT be as simple as that.

 

[The BB Bandito]

Are you filling gun to MAX pressure? With some guns I've experience with I noticed that if filled to MAX (250 bar) the 1st couple or 3 shots would be off, although not as drastically as yours. Once pressure got under the MAX things leveled out. So, I stopped filling to maximum pressure & they're spot on from the 1st shot. I'm not the only one who's experienced this. The problem MIGHT be as simple as that.

Unfortunately this can happen throughout the tanks charge ( whether it’s full or not). I can fill immediately after shooting a few times and it’s dead on. I can not shoot it for a while and it will throw the POI. Shoot a few times and it’s back in business.