Do these numbers sound right?

[fishinwrench]

I'm trying to use the Chrono Connect app to get the velocity readings from a Gamo Swarm .22
I have all the setup measurements entered accurately and am using the suggested BC values, and here is what I'm getting....

JSB JUMBO HEAVY 18.10gr shows 608fps

JSB JUMBO 15.89gr shows only 629fps

Crosman Prem HP 14.3gr shows 750fps

Seems like too much of a drop between the 14.3 and the 15.9 

On an earlier test (a few weeks ago) I got a 635 on the 18.10 JSB's which seemed about right. Is this CC app just total bullpoop....or what?

I was expecting somewhere in the neighborhood of 690fps with the Jumbo 15.9gr. pellets.

 

[Jadocs]

Temp variation perhaps? Are Gamos known to loose pressure at all?

 

[JeffDodge]

My .22 Swarm shoots the following and I've cleaned the barrel extensively, added a drop of RWS silicone lubricant to the chamber and shot about 1000 rounds through it at least;

Crossman HP 14.3: 730FPS
H&N Feild Target Trophy 14.66 5.4mm head: 704FPS
H&N Feild Target Trophy 14.66 5.3mm head: 710FPS
JSB Exact 15.89: 657FPS
Predator GTO 11.75: 825FPS
Gamo Red Fire 15.9: 665FPS

my gun feels a little slow...

 

[John "spysir" Blount]

Jeff, good info. At first I was thin king pellet hardness might be at play here but perhaps they do like a larger dia. ?

I personally tend to stay with the 14.3g range with most .22 springers.


John

 

[fishinwrench]

Ok so I calculated my ballistics backwards by measuring POI at 15, 25, 35, 40 yards and it looks like I am 650ish with the 15.89gr. which is pretty much inline with what Jeff is getting from his Gamo Swarm so I bet that's as accurate of a calculation as I'm likely to get.

Spysir, I like the CP 14.3gr. also, and they shoot well through my gun, but according to chairgun the energy really starts to fall off after 25 yards with them. So on squirrels at 20 yards I get a blow-thru, and on 35-40 yard shots it doesn't hit hard enough to suit me. Great for plinking but lacks in the woods. Most of my shots in the woodlot behind my house are 30-35 with the occasional 40.
The jumbo Heavy 18.1gr. does the job of killing tree rats very well.... but my goal was to get a slightly flatter trajectory and hit a happy medium with the 15.89gr. Jumbo's.

Here's the thing that's bugging me now though.... Why if I am sighted in at 30 yards with the Jumbo Heavy does the Jumbo hit 1/2 low at that range? Shouldn't it shoot a tad higher? You'd expect that a switch to a lighter pellet would result in a higher POI wouldn't you?

 

[fishinwrench]

One other thing. Has anyone ever actually weighed a Crosman Premier HP .22 ???
Because I have a sneaky suspicion that they are lighter than 14.3gr.
Those suckers just move too damn fast for their alleged weight, doesn't it seem?

 

[crittahitta]

Its not always the weight which increases or decreases speed. It is the diameter of the pellet and how well it seals in the barrel. A loose pellet will go slow as will a tight fitting pellet, but a correct fit will sizzle.

 

[Jadocs]

Fishinwrench, do the same test at 50 yards and see if you get the same results. It could be that the Jumbo is still on its way up at 30, but it’s just a guess. 

 

[fishinwrench]

"Jadocs"Fishinwrench, do the same test at 50 yards and see if you get the same results. It could be that the Jumbo is still on its way up at 30, but it’s just a guess.

I don't think so. The trajectory curves peak at 18 and 21 yards, for the two projectiles.

 

[fishinwrench]

"crittahitta"Its not always the weight which increases or decreases speed. It is the diameter of the pellet and how well it seals in the barrel. A loose pellet will go slow as will a tight fitting pellet, but a correct fit will sizzle.

So out come the calipers.

I'm gonna drive myself crazy trying to figure all this out. Oh well, that's what winter's are for.

 

[JeffDodge]

I think the Gamo barrels like the 5.50 size pellets. Below is a chart I made comparing pellets which shows the information I could dig up on the internet but I'm not sure how accurate the head/skirt sizes are. Fishinwrench - the ballistic coefficient is key for a medium power air gun like the Swarm if you want to go out to 40yds, I've been LOVING the Sniper Magnums through my Gamo Magnum and would love to try the Sniper Lights through the Swarm, maybe consider those in your next order. Also, both my Gamos shoot faster after the barrels are dirty so clean it very well if you haven't since you got it but then let it build up a little.

 

[davidsng]

I just got the Gamo Swarm and ran some quick chronograph numbers with the Barracuda Match, GTO, H&N FTT Copper, and a few others. The numbers seem correct to me. The gun was initially shooting hot because of the dieseling. It lasted a longs time before it burnt off. There was a lot of oil in that gun. I shot it over 500 times before the numbers became predictable.

 

[JeffDodge]

"davidsng"I just got the Gamo Swarm and ran some quick chronograph numbers with the Barracuda Match, GTO, H&N FTT Copper, and a few others. The numbers seem correct to me. The gun was initially shooting hot because of the dieseling. It lasted a longs time before it burnt off. There was a lot of oil in that gun. I shot it over 500 times before the numbers became predictable.

Can you post some numbers? What do you like?