New rifle, trying to decide between .22 and .25 for slug use

First off, my usage is about 70% ground squirrel hunting / 30% target shooting. Most shots are from 50-90Y but I occasionally will go out to 125-145Y on calm days.

Have been shooting .25 Edguns the last couple years, first an R3, then an R3M, and now an R5M. Used to use 25.4gr .25 JSBs with the R3 & R3M and am now using 34gr 25 JSBs with the R5M. I'm running the 34s at 875 fps / 60 ft-lb-- they're accurate, hit the squirrels hard, and do OK in the wind. Switching to the 34gr pellets meant I gave up about 20 shots per fill compared to the 25.4gr pellets which means more trips back to the car to refill.

Considering a new rifle to play with slugs, possibly an Impact M3, and really want to make slugs work for the higher BC for the long shots... but also want a decent shot count on a fill. The matter of air use has me considering going with a .22 this time to keep the velocity with the slugs in the 950-975fps range but also keep muzzle energy at a more reasonable 55-65 ft-lb range for a decent amount of shots per fill. A .25 running heavier slugs in the same 950-975fps range will be more muzzle energy and more air use for less shots per fill.

Looking at .22 slugs in the 21-30gr range and a target velocity of 975fps or so would put them around 50-65 ft-lbs muzzle energy, comparable to what I'm running the 34gr JSB's at now. The higher BC of the slugs compared to my current 34gr JSB pellets means more retained energy downrange and less drop and wind drift than the .25 34gr JSB's I'm shooting now, but not having played with .22 slugs I don't know how they'll transfer energy to the squirrels... I know they'll be dead, but I'm hoping they'll hit as hard as the 34gr JSB's I'm using now... that "thwap" is very satisfying to hear.

If I went with .25 on the new rifle and ran slugs, I'd either have to run very light for caliber .25 slugs at around 950fps to keep the muzzle energy and air use down (they'll still have a better BC than the 34gr JSBs I'm shooting now though), or run heavier .25 slugs at lower velocities / energy to save on air-- and they might not stabilize and be accurate at the lower velocities.

Another area of thought... right now I'm sitting on a good stockpile of .25 34gr JSB pellets. If I bought the new rifle in .22 and the slugs don't pan out, that means having to pick up new .22 pellets for it, which probably won't perform as well for hunting use as the .25 34gr JSB's I already have. Either that or spending money on a .25 caliber conversion kit so I can use the 34gr JSB pellets I already have. If I buy the new rifle in .25 and the slugs don't pan out or I'm not happy with the air usage with the heavier .25 slugs, I'm only out the cost of slugs I bought to test and can simply shoot up the pile of .25 34gr pellets I already have.

Thoughts?
 
Sounds like you convinced yourself on the .25 in your last paragraph. 

.25 is my favorite all around caliber. When it comes down to it, you can fit 38.9gr .25 slugs with high bcs in the impact mag vs .22 slugs around the same weight and those may not fit well. 

You will have lighter weight .22 slugs avail vs .25, but what's the fun in that at the distances you're wanting to be able to reach.

Plus, all the .25 pellets you're sitting on...sounds like .25 to me!
 
Good point on the mag length... What is the max length an FX sideshot mag will handle?

And contrary to my last paragraph, even though I put in a preorder for a .25 I'm actually leaning towards changing it to a .22... I really like the numbers from .22 slugs around 30gr-- very similar energy to the .25 34gr JSBs I'm shooting now but with less drop and wind drift... Provided I can get the rifle to shoot them accurately. I *know* I can get the .25 34gr JSB pellets to shoot with minimal effort, while slugs are a bit of a science experiment that don't always succeed.
 
Kenny, perfect info-- especially since you're using them on the same central valley ground squirrels that I am. 

Terminal performance on the meat targets looks quite good, also good to hear the .22 slugs leave them dead right there.

Strongly leaning towards changing my order to a .22 and picking up some Nielsen's from 23-31gr and H&N from 23-30gr for testing. Will also be picking up a superior heavy liner, but the rifle is still probably 3+ months out... 

What size bottle do you have on your rifle, and approximately how many shots per fill are you getting with your current tune?

Thanks!
 
I shot up all my JSB branded genuine Mk1 34gr king heavies quite a while ago... My current stash is all Edgun branded 34gr JSBs, and while they're supposedly from dedicated dies, based on the skirt thickness they appear to be Mk2's.

Just changed my preorder to a .22, now need to order an assortment of Nielson .22s and preorder .22 H&Ns & JSBs so I have them for testing when everything arrives... Who knows how long that will be. I was warned it could be up to a 6 month wait for the M3, but it *should* be sooner than that.

In the meantime I'll keep feeding the squirrels 34gr .25 JSBs with my R5M.