.25 caliber slug testing

[stoti]

I plan on buying one of the .25 slug liners for my FX Crown in the near future. Obviously, I don't have the liner but do have some different .25 caliber slugs and decided to shoot some groups today out of my stock Crown to get velocities and check how each of the slugs group with a standard barrel.

The slugs I tested are: #1.AONCO 25.4 gr. It has a massive hollow point and the base is concave with a huge chuck out of the back. #2.Wicked Monster 25.5 gr. It is a hollow point with a concave base, almost flat, it's barely dished. #3.Rat Sniper Slug 31.3 gr. Another hollow point, again with a slightly concave base, slightly dished. #4.Wicked Monster 32 gr. Hollow point with a rebated boat tail. #5.Regular JSB 25.4gr. pellets as a base group. These and the 33.95 JSB pellets are both super accurate out of my gun.

I attached pictures to show the results instead of explaining each of the groups. A picture is worth 1000 words! All groups were shot at 40 yds. using a bipod in the front and a bag in the rear. It was absolutely dead calm outside. I shot at 40yds because I can shoot that distance in my yard. I figured if they didn't perform at 40yds., they wouldn't perform at 100yds or farther.

The reason I am writing this post and showing these pictures is to find out what it is that makes slugs shoot so poorly out of the standard FX barrel. I've been told the heavy weight of the slugs keeps them from stabilizing out of the Smooth Twist X barrel, but the JSB heavies at 33.95 gr. are heavier than any of these slugs. I've been told the shape of the slugs, but as you can see the Rat Sniper 31.3gr. slug, although not a super group like the JSB's, is still respectable. And, the shape of the slugs are far more aerodynamic than a standard pellet. I would like to hear from someone knowledgeable in this area and find out exactly what it is that makes slugs shoot notoriously poorly out of the standard Smooth Twist X barrels? The standard pellet design has remained basically unchanged for decades. I think the slugs designed more like bullets, with higher Ballistic Coefficients and therefore the possibility to shoot extremely long ranges accurately will be the next frontier in PCP shooting. I can't wait to get my slug liner and see what these things will be capable of at ranges of 100, 150 and 200 yards. Thanks, Stoti

 

[2D1C]

Wonder if those groups are bad due to a choked barrel?

 

[PerkyVal]

The twist rate has to be faster for slugs.

The diabolo pellets are dragged stabilized, so they work better out the the smooth twist & smooth twist x with less spin.

Matt Dubber explains this well in his ballistics 101 vids

 

[stoti]

2D1C, I think you're on the right track. I don't know if it's the choke but that is one of the things I've heard suggested many times on different forums. The slug barrels are not choked, so it makes sense but what else is involved in making an accurate slug barrel, or is that it, solely a lack of a choke? What is it about the choke that makes some shoot well and others so poorly if the slugs are all the same diameter? That's exactly why I'm so intrigued! It's kind of strange that the slugs that shot the best seemed to be the hardest. If poor accuracy was because of the choke, I would think the hardest pellets would get thrown off the most, not shoot the best. Maybe I'm looking at it backwards, the harder pellets are less deformed or effected? Are the slug barrels made so the slug fits more tightly in the barrel so it doesn't need a choke, like a rifle?

So, if you're right and it is the choke, and I suspect you're correct, my initial question still stands. Why do some slugs shoot so poorly and others pretty well? Is it just luck of the draw with a choked barrel and the slug design, weigh, length, hardness of the lead or is there more to it? Thanks, Stoti

 

[bdzjlz]

I purchased some Nielson 36 grain slugs and tried them from my Air Arms S510. At 18 yards they grouped well. At 50 they did not do well at all. They were 2” plus and no core existed. The 33.95 King II were nice and tight in the same atmospheric conditions.

In my .22 with the .217 21 grain slug. , they performed on par with the JSB 18.13, but no better and with considerably more drop. 

It was a fun experiment but no more slugs for me.

 

[stoti]

I understand the twist rate has to be faster to stabilize slugs but my question remains...why do some shoot well and others terrible? Is it just a combination of design, density, weight, and other factors? The 31.3gr. slugs shot a respectable group, none of the others are anywhere near good? I'll check out Dubber's video and see what I can learn. Thank you, Stoti

 

[Cpt.Cannon]

+1 to PerkyVal for pointing you in the right direction. I thought that the smooth twist x barrel is twisted the entire length of the barrel and thats what was different from the first version? My guess about the difference is how and how much the slugs interact with the barrel. Since the new slug liners are designed with a single brand pellet in mind they will have the twist rate down to a pretty consistent science. I would be interested to see results for different fps rates for the same type of slug. I bet that would vary group size wildly also, even within the same slug. Perhaps theres a goldilocks fps for each brand slug even without the slug liner? This really is an exciting time for PCP's

 

[2D1C]

I don't have the answers either Stoti but it sure as hell will be fun to experiment!

 

[ViperDude]

I do think it's the combination of the 2 ideas mentioned, and I'm wondering what the diameter of the slug that performed ok vs the one that performed the worse.

 

[stoti]

All the slugs were .250". I understand external ballistics well, I've been shooting long range since before it was cool. Pellets vs. slugs and PCP barrels, not so much! I really do appreciate all of the imput so far.

I guess my question in it's simplest form is this... JSB pellets aside, just looking at slugs, why do some stabilize and shoot well out of my gun and others not? Whether it's got to do with twist rates, choked barrels or any of that shouldn't matter in this instance because those factors are the same for all of the slugs I tested. 

I think with your help I figured it out... I'm over thinking it! Just like some guns like JSB pellets and others like H&N, my gun likes and will shoot 31.3gr. slugs okay and others like crap. I think it's just the subtleties of the slugs themselves and their interaction with the barrel, it has to be, all other parameters are the same.

Pertaining to slugs in general, I agree that it has to do with twist rates, choked vs. non-choked barrels that are designed especially for slugs, and how slugs of different weights and designs interact with those barrels. That makes perfect sense.

I'm going to buy a slug liner, so it really doesn't matter other than I want to know. Maybe it's just a lot more simple than I thought? Thanks for your help everyone! Stoti

 

[Loren]

Have you slugged your barrel to see what the groove diameter is on the barrel?

 

[stoti]

No, that's a little above and beyond since I'm just trying to satisfy my curiosity. I was hoping someone would have a definitive answer but if not, no big deal. I'll do whatever necessary to find the right slug when I get a slug barrel. Stoti

 

[schoofsbock]

Im also struggling with my Huben K1 and the amunition. Last Sunday I was testing some hours the H&N Piledrivers and others, with no positve results. The H&N Piledrivers are absolutely NOT useable for the Huben. Also the JSB Straton Jumbo Monsters and the H&N Rabbit Magnum II. Only the JSB Monster redesigned and the JSB Beast are performing well with the newest Huben. The Special slugs for the Huben Ive not tested, because I can`t get it.

However, why the more typical pellets shape from JSB performs better than the more slug shaped amunition in the same weight category ???

I don`t understand this

 

[Dairyboy]

Well twist rate is definitely a big one. The twist rates for pellet barrels are usually slower than slugs like. There's alot of different things to shooting slugs vs pellets. I think weight, length, outside diameter, speed of bullet, and the twist and what the barrels inside diameter is all tie in together to get slugs to work. 

You should contact Nick at Nielsen Specialty Ammo. He makes slugs for PCPs and he knows alot of info on this.

 

[Spray1Mark]

What is important is RPM, twist rate and velocity are simply the two factors that influence it. If your twist rate is too slow then if possible you can increase the velocity which if fast enough can bring you back to the same RPM as a faster twist with lower velocity.

Downsides to this of course are increased leading of the barrel, perhaps more important is the design of the slug and CG/CM etc.

Interesting point about the choke, which is probably only the last couple of inches so you could just shorten the barrel and remove it!