Benjamin Fun With A Benjamin Kratos

[JackHughs]

Taking a break from my Impact and Panthera, I recently bought a refurbished .22 Kratos from Airgun Revisions. I've always liked the looks of these rifles and saw this as an opportunity to try out a well-reviewed, unregulated rifle at a very attractive price.

I did a full power test of several different brands and configurations of 25.39 grain slugs and two brands of slugs. The test was conducted with 6 shot groups within 3 chronograph sessions. MV was recorded for each shot and ME (muzzle energy) was calculated for each shot. MaxV, MinV, ES, SD, and group size on-target was recorded for each 6 shot group. Te shroud was removed for this test.

Total energy produced, total energy expended, and efficiency was calculated for for Session188 and for the combination of sessions 189 and 190.

Test results are attached. The most remarkable result is how flat the MV remains from a full bottle at 3,000 psi down to about 2,200 psi. However, even though the MV remains constant, the SD of the individual groups increases as bottle pressure decreases. Some pellets performed quite well. Both slugs performed poorly. The overall efficiency was in the mid 70% level. I guess that a portion of the lost energy results from hammer bounce.

 

[Hammer]

I'm assuming you are going for maximum power, but shortening the hammer spring really wakes these Craftsman Series guns up, as far as consistency, and shot count. AR also has a tune kit which includes a nifty hammer spring adjuster.

The choked barrel makes them questionable for slugs, although some guys have reported good results.

Carbon bottle reportedly saves a full pound too.

I am very happy with my refurb Akela.

 

[JackHughs]

I'm assuming you are going for maximum power, but shortening the hammer spring really wakes these Craftsman Series guns up, as far as consistency, and shot count. AR also has a tune kit which includes a nifty hammer spring adjuster.

The choked barrel makes them questionable for slugs, although some guys have reported good results.

Carbon bottle reportedly saves a full pound too.

I am very happy with my refurb Akela.

HI,

Thanks for the info. Yes. I was going for maximum power - but not by choice. The only .22 pellets on hand are the 25.39's. I have some lighter pellets on order for future testing.

One of the most interesting discoveries is that the Craftsman Series are "regulated" rifles. Not in the normal sense of pressure regulated but instead these rifles are airflow regulated. When I bought the rifle, AR told me that I would not see the bell shaped curve of muzzle velocity normally associated with unregulated airguns. Well, testing shows that to be true and it took a bit of head scratching to discover why.

The Kratos bottle is rated for 3,000 psi. The following is an estimate but it appears that the transfer port is sized for maximum airflow at 2,400 to 2,500 psi. Therefore, bottle pressures exceeding 2,500 psi will not result in increased airflow though the transfer port and muzzle velocities will be very consistent from 3,000 psi down to 2,500 psi. MV's will then drop as the bottle pressure drops below 2,500 psi.

The above also applies to the "power control" built into the rifle. The power control is nothing more than a mechanical valve in the transfer system that is used to further restrict airflow through the transfer system.

At my age, I really enjoy learning new things. So far, the Kratos has been a real treat.

JackHughs

 

[Hammer]

I believe the tune kit from AR would shift your "sweet spot" down considerably. It includes a hammer spring, and a valve spring. If you use pellets over 16g, he says to omit the valve spring, which makes it a 10 minute install. 80 shots at 880fps with 14.3 Premiers!

Shortening the stock hammer spring can also give good results. It did wonders for my Akela.

Akela, Kratos, Cayden tune kit

Tune kit allows for greater shot count over factory. Recommended for .177 and .22 only and 16g and under ammo.

www.airgunrevisions.com