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diipii · Member

Thanks for the info.
I think my question hinges round the position of 2 pellets of the same weight, the smaller of the 2 must be ballistically more efficient.
I think I have seen an H&N rabbit shooting pellet in .177 at 15 grains. Here in the UK it carried an advisory note that it was for FAC guns only while .22 pellets had no note attached. Also here there doesn't seem to be much science in the airgunning world and a lot of pet theories and supposition...me included. So I must put up or shut up and as soon as Combro get production going again on their super little chrono I will get testing.

rsterne · Moderator

I tried the 25 gr. H&N Rabbit Magnums in .22 cal and they wouldn't hit the broad side of a barn door from the inside in any of my guns.... I have talked to others with similar results.... I have some of the .177s but have not tested them yet.... They would likely be a poor choice in a Springer.... the small base area and heavy pellet would combine to produce a lot of pressure in the air chamber.... which some claim can increase the chance of dieseling and damage....

You don't state whether or not you are looking at an FAC gun or not.... If not, at 15 gr. the pellet would have to be under 600 fps to be under 12 FPE.... You also don't state what type of gun you are looking at.... but if it's a "medium" Springer, you would be lucky to even get that velocity with such a heavy pellet.... In .177, most 12 FPE rifles prefer normal weight pellets (7.9 - 8.4 gr) at ~800 fps.... the 15 gr. pellet will never make up the lower velocity, no matter how good the BC is.... Even a 10 gr. pellet would be considered "heavy" in a 12 FPE rifle and only deliver ~725 fps....

In .22 cal, staying under 12 FPE.... you will indeed have less velocity.... A standard 14.3 gr. pellet will only be going ~610 fps.... However, if you took a gun tuned for that and swapped it over to a .177 barrel I'd bet money that it wouldn't fire the same weight pellet at over 600 fps.... The .22 has a 50% bigger base for the air to push on to accelerate that weight pellet.... It is this factor that makes almost all guns more efficient in .22 cal than in .177.... ie more FPE from the same platform....

What I'm saying is that your original assumption, from what I understand, is that you could swap barrels and keep the same energy output from the same gun.... I think that very unlikely, although most guns could be tuned to the same output (12 FPE or whatever).... If you are talking about a non-FAC rifle.... my understanding of the English law is that if the gun is ever tested, it had better be under 12 FPE with ANY pellet the law decide to feed it.... (Alstone, please correct me if I'm wrong).... If that is the case, you couldn't build a 12 FPE rifle set up just for 15 gr. pellets if it shot stronger than that with lighter pellets.... which I think likely, especially if it's a Springer....

More information is needed for me to assist further.... however, this statement is correct, provided the shape is similar:

rsterne · Moderator

More information for you.... I got out those H&N Rabbit Magnum pellets, weighed them, and put the over the Chrony.... VERY disappointing results in my .177 cal Diana 34.... They only averaged 500 fps (9.1 FPE).... Shocked

First of all, they were a VERY tight fit in the breech.... I could only get them in maybe 3/4 of the way with my fingers.... I have a pellet seating tool, and I literally had to thump the end of it with my fist to get them deep enough to close the breech.... Normally, pellets fit just fine in this gun.... Rolling Eyes

I tested several other weights of pellets, with the following results:

6.9 - 7.1 gr averaged 930 fps (13.4 FPE)
7.8 - 8.4 gr averaged 860 fps (13.3 FPE)
10.3 - 10.6 gr averaged 750 fps (13.1 FPE)
16.4 gr H&N Rab. Mag. was 500 fps (9.1 FPE)

As you can see.... there is very little difference in the energy over the normal range of pellet weights (7.0 - 10.5 gr).... This gun is well settled in, with 3-4,000 pellets through it.... I would NOT recommend the H&N Rabbit Magnum pellets in either .177 or .22 cal based on my experience with them....

Bob

AirGunEric · Site Admin

Maybe threads could be kept together and not split apart so context is lost and the information will be at best overlooked by people in the future, at worst it will just serve as confusing and time wasting?