Accuracy with a GAMO Viper...

[Shane Tuttle]

I bought a GAMO Viper today chambered for .177 pellets. It has a mil-dot illuminated recticle scope and claims to have the capabilities to shoot 1000-1200 fps.

http://www.sportsmansguide.com/net/cb/cb.aspx?a=444236

When I got home, I set up shop and made the attempt to sight it in. I used GAMO's targets with their bullseye's appearing to be about the size of a quarter. I shot from 45 feet. Here's what I used for pellets:

1. GAMO Rocket Ballistic Tip-Lead with what appears to be a BB for its center. Claimed velocity is 1000fps.
2. GAMO Raptor Power Pellets-18k gold plated, PBA. Claimed velocity is 1250fps.

I started with the Rockets and they seemed to be OK. The case seemed to be that they either shot extremely well (touching) or they had a spread of about 1/2 inch. They were hitting at the 5 O'clock of the 9 ring for the most part.

I then tried out the Raptors. They appeared to shoot more consistently. A penny would easily cover up most of the shots. However, the pattern was about 1.5" high and 1" to the right of the bullseye.

I am an experienced yet very average rifleman at best. My questions are:

1. Is the spread I'm getting about average for accuracy at 50ft?
2. Is the claimed velocity on each of these pellets the reason why they hit differently on target?
3. I'm using this mainly for shooting rabbits/raccons. Would you think this spread is good enough to provide quick kills on them aiming at the head at said sight in range or is it best to aim for the lungs?
4.I think I'm going to tweak the sights just a bit more for the Rockets and leave well enough alone. If I need to shoot farther than that I'll use the Raptors. Is this a good way to go?

 

[stephen426]

I seriously doubt that the extra 200 fps from the Raptors will make the difference in shooting high. At 50 feet, (ignoring wind resistance), it would take a pellet travelling at 1000 fps .05 seconds to reach the target versus .0416 second at 1200 fps. Its been a long time since high school physics, but .0084 seconds is not a lot of additional time toresult in a 1 inch drop at 50 feet.

My best guess is that it might have something to do with how the alloy reacts to the rifling. Different bullets react to different twist rates. It has been a while since I shot my AR-15, but I remember that the lighter bullets would need a higher twist rate to stabilize and that firing a heavy bullet out of a high twist rate barrel could cause the bullet to tumble. Don't quote me on that since it has been a long time. I suggest you check with some hand loaders who develop different loads for hunting.

I suggest you go for head shots since the kill zone on the critters you are talking about is pretty small. Besides, pellets are really light and lack penetration. Head shots are probably the most effective since there is much less tissue to penetrate.

 

[zoomie]

but I remember that the lighter bullets would need a higher twist rate to stabilize and that firing a heavy bullet out of a high twist
rate barrel could cause the bullet to tumble.

Backwards. Lighter bullets require a slower twist rate and can come apart if it's too fast. Heavier (longer) bullets need a faster twist rate to stabilize. (1:8 is faster than 1:12.) A lower number = faster twist. Maybe that inverse relationship is where we're missing. Maybe you meant "higher" as in "slower" twist rate.

 

[Shane Tuttle]

My best guess is that it might have something to do with how the alloy reacts to the rifling. Different bullets react to different twist rates.

I forgot to add that the GAMO does have rifling. Maybe the Raptors respond better to it compared to the lead?

They're both the same size pellets...

P.S. I took your advice on the X2 from Sportsman's Guide but they were already sold out....

 

[stephen426]

Backwards. Lighter bullets require a slower twist rate and can come apart if it's too fast. Heavier (longer) bullets need a faster twist rate to stabilize. (1:8 is faster than 1:12.) A lower number = faster twist. Maybe that inverse relationship is where we're missing. Maybe you meant "higher" as in "slower" twist rate.

Thanks. That is what I was thinking of. That is why I mentioned not to quote me on it. Haven't shot high power matches in a heck of a long time. Maybe time to shake the rust out of the barrel and give it a whirl!

 

[AK103K]

I have one of the Gamo combo guns, I think it was a "hunter". It came with a scope, light, laser, and an assortment of fancy pellets. Ditched the light, laser, and fancy pellets. It likes the big, el cheapo box of Crossmans from Wally World.

Trigger sucks, but you can still consistently hit beer cans at 50 yards across the back yard, and the 1" holes in the burn barrel are pretty easy at about 35 yards. If they dont go through they are close.

I got mine for a plinker and maybe a rabbit in the garden gun, but I soon got a .17HMR, so now I'm blowin up....I mean, huntin' rabbits.

 

[hogdogs]

Avid Gamo guy here...
I find that the crossman pellets "premier hollow point" from walmart are great.

As far as killzone... I shoot for the head often but also find that the vital zone is a larger % of overall size and as long as you hit forward of half way they are DRT or nearly so. I have shot rats all night at 50 feet and headshots were out as they don't sit still long enuff to set up that shot.

For different pellets at 40-50 feet the difference in POI is not very noticeable. Much beyond that it is crucial to verify POI.
The gamo rifles are VERY adequate for small game out to 60 yards.
Feel free to visit boartuff outdoors for a decent air rifle section.
http://www.boartuffoutdoors.com/cgi-bin/yabb/YaBB.pl?board=air_rifles;action=messageindex;start=

This was at 45 feet...
Brent

 

[JohnKSa]

Remember that this is a spring piston rifle which means that it will have recoil. What's more, spring piston recoil is complicated with recoil forces directed both forward and backwards depending on where you are in the recoil cycle.

If you change the pellet velocity, it will be in the barrel for a different amount of time and therefore the gun will be at a different point in the recoil cycle when the pellet exits. That will likely cause the pellet to impact on the target at a different point. Because of the complexity of the recoil cycle, it's going to be hard to predict whether it will be high or low based purely on pellet velocity.

 

[hogdogs]

To add one point to John's post... you also have an imparted twist in the recoil as the spring unloads.
It takes a very firm grip and shoulder plant. Or the pellets will be all over the page...
Brent

 

[Shane Tuttle]

Thanks, hogdogs and John.

That really answered a lot of my questions. I think that answers a lot about why my spreads were off-base. Some of the time when sighting in, I wasn't placing the stock very firmly in my shoulder and wasn't holding onto the forend. I had the rifle placed on our patio furniture padding and just zeroed it in from there.

I guess the amount of time the pellets are in the barrel really lend to different POI.

As far as killzone... I shoot for the head often but also find that the vital zone is a larger % of overall size and as long as you hit forward of half way they are DRT or nearly so.

I'm sorry, hogdogs. Are you saying the percentage of effective killzone is higher shooting at the head? What do you mean by "forward of half way" and DRT?

 

[hogdogs]

Sorry... it sounded clear to me...
I mean forward half of torso length. I also should point out that in scale the pellet is equal to like a 1 inch bullet on a squirrel or a 16 inch bullet on a rat or bird. What I mean by this is size of pellet compared to square inches of target area. The pellet is literally nearly the size of the "vitals area". Plus the hydrodynamic shock is incredible... I have literally blown the insides out of the rat and they were carried thru the hole made in the wooden fence board. I have a few kill pics if you want me to post them. Also not just the time pellet to pellet but also the rate of acceleration... a bullet gets sent out when the powder lights off. The pellet won't move in the first milli/micro/nano seconds until air pressure picks up than it is accelerating the whole way out. Loose pellets are weaker, slower and very inaccurate. If you don't have to press them in the breech throw 'em away. I have had so called premium brands fall out when closing the barrel. Good luck and happy hunting.
Brent

 

[thebaldguy]

In my Gamo Big Cat 1200, I find the lightweight non lead pellets shoot about one inch higher than the lead pellets. They also make the air rifle sound about as loud as a .22!