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Gamo Gamo Swarm Magnum velocity drop off

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Sawney Bean

Sawney Bean

Member
Oct 21, 2023
761
878
Tacoma, Washington, USA
First post here,, but I've been an airgunner for decades.

I was in Bass Pro the other day and saw that they had the Gamo Swarm Magnum 3i in .22 for $300, so I picked one up.

I've been playing with it off and on for the past few days and for the most part I've been impressed. I haven't really wrung it out for accuracy, but just shooting off my knee at 10 yards I was getting dime sized groups. The trigger was somewhat heavy and "sproingy", kind of like a Glock, but I didn't find it hard to shoot with. It's not good, but it doesn't really suck either. I didn't find it to be particularly hold sensitive at all, which for a relatively light, magnum springer was impressive to me. It's light, very powerful, reasonably accurate and cheap. I'm planning on making it my truck gun.

Now for what I did find concerning. The velocity was all over the place. I've put around 200 shots through it and the dieseling seems to be over. It took me a little while to discern the pattern, but with each magazine the first three shots will be around 815-830 fps. The next few will be around 795-810, then by the last shot or two it will drop way down to around 750 or so. This is with 18.1 JSBs.

It seems like the gas ram is heating up with use and the velocity is dropping as it does. I'm sure that if I waited a minute or so between shots that it would be more consistent and that without a magazine it wouldn't be noticeable. What I'm wondering is whether this is a problem or not. I can live with waiting a few seconds between shots, but if it's a failing gas ram then I want to return it to Bass Pro. Just wondering if anyone here has any experience with this. I haven't found anything when I search.
 
Just keep shooting it. It can take a tin or two to settle in. You'll either burn off the excess lube or it'll get worse and you'll find you have a torn piston seal allowing lube to slip by. The second part is what I found to be true on my BSA which is all Gamo guts.

If it was a failing gas ram your velocity would be steadily dropping as it lost pressure
 
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You are correct regarding heat buildup being the culprit. Increased friction is a result of
heat expansion. Whenever I shoot 10 shots over my chronograph with both my R7 and
Feinwerkbau 124D the last shots average a little lower than the first shots. Although
my extreme spreads aren't nearly as high as yours which looks like 70-80 fps. Which is
a little on the high side. Even at 750 fps with a 18gr pellets that's a potent shooter you
have.
 
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If it was due to dieseling however, then I should have been seeing abnormally high velocities. By most accounts these are supposed to be 26-28 fpe guns and with velocities in the low 800's that's what it's producing. If those velocities are ultimately going to stabilize in the low 700s then I'm dealing with a 20-23 fpe gun, which isn't particularly appealing considering its cocking effort.

I'm guessing you're probably on the right track about it being a torn piston seal.

I'm going to go ahead and put another 200 rounds or so through it, but I suspect that come Monday I'll be taking it back to Bass Pro.

I'm also somewhat suspicious that this might have been a refurb. The trigger seems suspiciously good, almost like someone already tried to adjust it and the scope came already perfectly centered in its one piece mount. Inside the box everything was wrapped in new plastic, but I'm a little suspicious.
 
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Piston guns generally put out LESS energy as the pellets start to get too heavy. My Swarm Magnum put out ~25fpe once settled in with the JSB 15.89gr. I can't recall what it put out with the 18s though.

As a side note, store the gun barrel up. It sounds like lube is slipping past the seal as it sits. You burn it off in the first few shots and then it settles in after 5 or 10. You may notice a pretty distinct smell to go along with it.
 
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GoldenStateAIRGUNer said:
You are correct regarding heat buildup being the culprit. Increased friction is a result of
heat expansion. Whenever I shoot 10 shots over my chronograph with both my R7 and
Feinwerkbau 124D the last shots average a little lower than the first shots. Although
my extreme spreads aren't nearly as high as yours which looks like 70-80 fps. Which is
a little on the high side. Even at 750 fps with a 18gr pellets that's a potent shooter you
have.
Click to expand...

It's actually worse than 70-80 fps. That's more like an average drop off. The strings with the worst variance were over 100 fps.

The thing that makes me wonder if it might not be a defect however is the magazine. Most springers simply don't have one and that forces us to slow down and allow the gun time to cool. With a magazine though you can fire every couple of seconds and as I was chronographing it and noticing discrepancies, well that's what I was doing. I usually don't chronograph hundreds of shots from a cheap spring gun, but in this case I was trying to figure out what was going on.

I'll be sure and give it 1 minute intervals to cool between shots today and see what effect it has on it.
 
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Sqwirl57 said:
Piston guns generally put out LESS energy as the pellets start to get too heavy. My Swarm Magnum put out ~25fpe once settled in with the JSB 15.89gr. I can't recall what it put out with the 18s though.

As a side note, store the gun barrel up. It sounds like lube is slipping past the seal as it sits. You burn it off in the first few shots and then it settles in after 5 or 10. You may notice a pretty distinct smell to go along with it.
Click to expand...
I tried 14.3 JSBs as well but it didn't seem to like those. Energy varied from 25 fpe to 18 fpe, (891 fps to 756 fps).
 
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Sawney Bean said:
It's actually worse than 70-80 fps. That's more like an average drop off. The strings with the worst variance were over 100 fps.

The thing that makes me wonder if it might not be a defect however is the magazine. Most springers simply don't have one and that forces us to slow down and allow the gun time to cool. With a magazine though you can fire every couple of seconds and as I was chronographing it and noticing discrepancies, well that's what I was doing. I usually don't chronograph hundreds of shots from a cheap spring gun, but in this case I was trying to figure out what was going on.

I'll be sure and give it 1 minute intervals to cool between shots today and see what effect it has on it.
Click to expand...
Extreme spreads of 100 fps are a issue. Try the tissue test to check if your
breech seal is good. As mentioned, it could be a piston seal.
 
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Sqwirl57 said:
I'm going to put my money on a bad piston seal. Exchange it if possible. If not possible you'll have to send it into Gamo to have it fixed. They won't sell you the parts. There is a company in Australia that sells 33mm Gamo seals though but you will want a compressor to replace it yourself
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I just bought it on Thursday and I still have the packaging and receipt, so I doubt a return will be a problem.
 
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Sawney Bean said:
I just bought it on Thursday and I still have the packaging and receipt, so I doubt a return will be a problem.
Click to expand...
Any reason in particular why you bought that gun specifically? For an extra $150 you could get a Diana 350 Magnum in .22 and it is without question $150 better. MUCH better trigger, better barrel, better support, and to top it off, replacement parts are readily available. Not only are they readily available but they'll still be available in 30yrs.

As an alternative, slightly less powerful gun, the HW80SL can be had for $200 more. I actually prefer this gun over my 350 Magnum to each his own.

EDIT: You can get a 350 Magnum from AoA for $399 and they don't charge sales tax. 22 cal is OOS but I'm sure a phone call to them will tell you when they'll be available again.
 
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18 grain pellet is still good weight to think your going to be a speed demon..lol.

Also Gamo support is fast and the first year of warranty they pay all the cost / shipping. Just hook up with probably amber at gamo. Set up the rma print the shipping thing and apply it to the box.

They probably get it back to you in like a few days .( Time to ship it , a day or 2 to look it over , and shipping time back) .

That's if you want to keep the gun .. a lot of places won't take a return and it's a send it to gsmo thing in the end anyway..

My whisper fusion took for ever to settle in almost to the point I was giving up on it . Then out of the blue one day it was on and never looked back.. she'll lay the smack down with cphp all day long now..
 
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Sqwirl57 said:
Any reason in particular why you bought that gun specifically? For an extra $150 you could get a Diana 350 Magnum in .22 and it is without question $150 better. MUCH better trigger, better barrel, better support, and to top it off, replacement parts are readily available. Not only are they readily available but they'll still be available in 30yrs.

As an alternative, slightly less powerful gun, the HW80SL can be had for $200 more. I actually prefer this gun over my 350 Magnum to each his own.

EDIT: You can get a 350 Magnum from AoA for $399 and they don't charge sales tax. 22 cal is OOS but I'm sure a phone call to them will tell you when they'll be available again.
Click to expand...
I just have a fixation on super-magnum springers. I like plinking with them and watching when the targets go flying. I've got a few nice guns already so it's not like I'm constrained by a tight budget or a newbie obsession with power. In this particular case I wanted to see how the magazine feed works and see how it compared power wise with the Hatsan 135, (the Hatsan has more thump, but is heavier and with a super loopy trajectory).

The next quality gun I intend on getting is an HW95. I like the precision of PCPs, but 80% of the time I end up shooting springers just because I find them more interesting.
 
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Sawney Bean said:
I just have a fixation on super-magnum springers. I like plinking with them and watching when the targets go flying. I've got a few nice guns already so it's not like I'm constrained by a tight budget or a newbie obsession with power. In this particular case I wanted to see how the magazine feed works and see how it compared power wise with the Hatsan 135, (the Hatsan has more thump, but is heavier and with a super loopy trajectory).

The next quality gun I intend on getting is an HW95. I like the precision of PCPs, but 80% of the time I end up shooting springers just because I find them more interesting.
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That's more than reasonable. An HW95 is an excellent choice as well. Have one in .20 cal and that gun doesn't even remotely know what the word "miss" means.
 
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Another thing to look at is if the loader is deforming/ damaging them pellets..

I guess you can try 2 loading single shot by hand to see .. it's a long shot with the newer 3i loader, but ya never know .. maybe bending a skirt and not getting a good seal when fired ?

According to what that gsmo girl said was with there rams if one was to be bad it goes bad quick like well under a 1000 shots .

Sadly I never shoot them heavy pellets in any springer . I stay below 9 in .177 and below 16 in .22. I shoot cphp 99.9789% of the time so it's 7.9 and 14.3 grain.

Though I did figure a strong gas ram slugs should be a go vs spring .lol

Ol' Gamo there having you stuck on any self fix .. as in they seem to do there best to prevent that.. near a send it to them or the trash can cause your not just buying a part . Look how hard it is just to get that 33mm piston seal.. Australia..lol
 
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Hateful McNasty said:
Another thing to look at is if the loader is deforming/ damaging them pellets..

I guess you can try 2 loading single shot by hand to see .. it's a long shot with the newer 3i loader, but ya never know .. maybe bending a skirt and not getting a good seal when fired ?

According to what that gsmo girl said was with there rams if one was to be bad it goes bad quick like well under a 1000 shots .

Sadly I never shoot them heavy pellets in any springer . I stay below 9 in .177 and below 16 in .22. I shoot cphp 99.9789% of the time so it's 7.9 and 14.3 grain.

Though I did figure a strong gas ram slugs should be a go vs spring .lol

Ol' Gamo there having you stuck on any self fix .. as in they seem to do there best to prevent that.. near a send it to them or the trash can cause your not just buying a part . Look how hard it is just to get that 33mm piston seal.. Australia..lol
Click to expand...
Gamos buisness model is pretty straightforward. Make your name widely known and use big numbers and fancy, yet borderline meaningless specs, and colorful boxes to get sales. From there make replacement parts and self repair as hard as possible to get. Its the same game companies like John Deere and Apple use to boost sales.

Gamo wants to sell high mark up guns. When something breaks after a few years they want you to just go buy another one. We live in a throw away and replace society.
 
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Hateful McNasty said:
Another thing to look at is if the loader is deforming/ damaging them pellets..

I guess you can try 2 loading single shot by hand to see .. it's a long shot with the newer 3i loader, but ya never know .. maybe bending a skirt and not getting a good seal when fired ?
Click to expand...
I’m pretty sure now that this is the case. I fired
A string of 10 allowing a 1 minute break between shots and observed a very similar change in velocities from the first shot to the tenth.

I wanted to test it adding one shot at a time to the magazine, but two shots into that string my battery died.

What I did do though was review my different strings and they all followed the same pattern. So the only good explanation that I can see is that it is clipping pellets as it goes.
 
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Well, I tried to return it to Bass Pro, but they refused to take it back on the grounds that it was a firearm. I asked them why they committed felonies and sold me a firearm without filling out an Alphabet org form or running a background check on me, but they continued to insist that despite not doing the things they would have been required to do if it were a firearm that it was a firearm and that they could not accept returns.

So I went out and shot it some more. The velocity drop off is definitely caused by the magazine and so long as I shoot pellets from the first three holes of the magazine it holds a reasonably steady velocity. I’ve got a couple of extra mags on order and I’ll see if that fixes things.

I also did a bit of shooting at longer distances and was rather pleased with the accuracy. I was shooting these groups off of wood blocks and not trying all that hard to be precise. For a springer at this price point, power level and weight, I think it did extremely well.

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