Pellet ballistics?

[DMS1]

So, I'm not an airgun guy. I'm in the process of choosing a couple high powered air guns for my twin boys. On the fence on a couple X25s tuned from flyin dragon air rifles in the states, since my inlaws are in Michigan, I can import physically myself without issue, and there are no Itar restrictions for air rifles.

My question is, since my kids have their hunting license and could use it for rabbits and squirrels, .177 seem basically out of the question, definitely .22 is called for to put more energy on target. My question is, .22 pellets seem to be shaped like a brick. Are there any longer .177 pellets that are longer to make the same weight and possibly have a higher ballistic coefficient to translate to higher FPE? Is the base diameter of the pellet required to be larger for more surface area x pressure? Would more hollow, longer pellets increase this area?

Thanks in advance!

 

[Barfman]

I'm assuming that you mean that .22s tend to be shorter relative to a .177, and you are wondering how to get a better ballistic coefficient, and in the end, better FPE at the muzzle and over distances.

There was an interesting video from Ted Bier recently where he explained his reasoning on why he chose .25 over .30 in the most recent Extreme Benchrest competition which he won. Generally, ballistic coefficients increase as you go to larger pellets. However, heavy class pellets a size down tend to match or exceed the BC of the larger pellet. Here's a chart with some relevant info:

http://www.photosbykev.com/wordpress/userfiles/pelletdata.htm

You'll notice that the JSB Heavy 10.5gr in .177 has the same BC as the JSB Jumbo in .22. These days, they are making extremely heavy pellets in larger and larger sizes, such as these monstrosities:

http://airgunsource.com/jsb-match-beast-diabolo-177-cal-1620gr/dp/2292

16.2gr .177 pellets will pack quite the punch. However, it depends on what kind of rifle you have. Springers tend not to shoot the extremely heavy stuff very well as those are generally designed to be used in tuned up PCPs.

The larger the diameter of the pellet, the better it will accelerate to a point. The drag once you pass .25cal starts to get worse which is shown in PCPs where the FPE per air volume used goes down. With the same amount of cocking effort, you are almost always going to get better FPE out of .22 over a .177. Having a longer more hollow pellet would only increase drag in a .177 and cause the pellet to slow down. It is still the pressure in the air chamber / barrel that is moving your pellet forward, and it only applies force to the overall diameter of the pellet rather than contact area. As soon as the skirt expands in the barrel to full contact at the base it is then moving forward as efficiently as possible, and you actually want to minimize the amount of contact to the barrel to reduce drag.

Overall, I would recommend going .22 over .177 for those Flying Dragon springers. They will definitely give you higher FPE. The type of pellets you choose should be based on what shoots best. I personally love the JSB .22 Jumbo Heavies in 18.1gr. It seems rare to me to find a rifle that doesn't shoot those well, and they tend to give very good FPE. If you can get those shooting at 700 fps with a springer, that's putting out a very respectable 20 FPE. In comparison, you would need to shoot a 10.5gr .177 heavy at 920 fps to get the same power and that's not going to happen in the same rifle with a different barrel.

 

[DMS1]

Thanks for the insight. If I bought a nitro piston rifle in .177, do they like the heavy pellets any more than regular springers?

 

[Barfman]

There is very little difference between nitro pistons and springers in functionality. I would say that it more depends on your rifle's barrel than anything in that case. Generally you would want to be on the heavier side, but definitely not super heavy (<11gr in .177, <20gr in .22).

 

[GerardSamija]

The action of a nitro-piston rifle is much the same as a spring-piston. The biggest difference is in the lack of twang, it's a quieter action. The expansion of the nitrogen is quite similar to that of a coiled spring so it's really a matter of testing various pellets in an individual rifle at range to find what groups best. There can be no general statements about what works best with nitro-piston rifles.

That said, in my experience with spring-pistons it seems mid-weight pellets seem to be the most efficient in terms of FPE and providing consistent placement. But I've only used a relatively low powered rifle, a QB57 which puts 13.43gr JSB RS pellets over the chrony at about 545fps. RWS Hobby 11.9gr go faster, but with lower FPE. 18.13gr JSB Heavy pellets go slower and also with lower FPE. So finding just the right weight seems key, through testing for both velocity as it relates to mass and for group size at yourn intended target range. For my QB57 with a 14" barrel, the JSB RS groups very nicely as well as delivering the best power. A longer barrel might help on a more powerful piston rifle. With mine velocity was only about 10fps higher with the factory length barrel.