Opinions on low friction good BC slug designs

[Gman57]

Greetings, I am just starting to tinker with designing a low drag slug for my new slug barrel that will be coming in a couple of months. Has anyone done any testing with a non choked barrel with different slug design with regards to smooth like NSA and drive band like Mr. Hollow point? Wondering how each will perform from a barrel friction and barrel seal stand point. My thinking would be lower friction from the drive band type, but I could way off base here and would like to get some expertise on the matter. 
Thanks

 

[steve123]

There is an affect with drive bands/drag bands at supersonic speeds but I'm not sure how much affect there is at subsonic speeds. Though in the barrel you might gain a little more speed vs no drive bands and the same weight projectile. Maybe it'll be a ballistic wash, more speed due to less barrel friction but more drag in the air?????

I have no expertise to offer but this is what I have read - to point out that the slug must be slightly larger than groove diameter by .0005 -.001, the twist rate of the barrel must be optimal for the length of projectile, and the CG and design must work well in flight which is kind of a mystery as to why some very similar projectiles seem to work well while others don't????

If you plan on more of a long range target application instead of hunting I would not put a hollow point in the projectile because these also cause drag and lower the BC potential.

A friend and I spent a bunch of money on swaging equipment years ago and designed our own slug for our FT guns but the experiment became a flop because we didn't have the know how. Basically we would have had to spend thousands more on barrels and more dies before we had any success so we scrapped the idea altogether. Just letting you know that experiments don't always work out unless one is fully committed financially, etc. 

A guy I know showed me a small plastic container with dies and sizers in it and asked how much I thought $ in worth was in there. I declined to guess so he said $8000 and that was only a part of his investment into bullet design and all that comes with having real success.

 

[Centercut]

The only slugs I've tried that have a BC significantly greater than 0.105 are the boat tail designs from ZAN. Although the .25 caliber 46 grain Round Nose has a BC of approx. 0.150, the slugs weren't as accurate as the NSA 43.5 grain Hollow Points in my .25 Impact with Slug A liner at approx. 920 FPS. The BTs do have less drag in the barrel due to less surface area (friction). Since accuracy trumps all other factors, I am sticking with the NSA 43.5 grain slugs, plus they are about 1/2 the price of the ZANs.

 

[qball]

I won’t be surprised a ton of people are working on better slugs for air guns. As of right now we are still at the beginning of airgun slugs so can’t wait to see what people would come up next. For now a choke is still some what necessary for the barrel to shoot more than 1 slug and shoot pellets ok. The challenge is PCP doesn’t have the explosive power of chemical energy so can’t push slugs a certain way so it’ll be interesting to see how to address that. FX’s answer is the new 800mm barrel and maybe even more aggressive twist rate down the road. maybe one day AirForce will add a mag on their guns. L2 already has the ability of super high reg pressure and add a long barrel. Either way a higher reg pressure than 150 bars and longer barrel will be needed due to physical limitation of PCP and then they can work with barrel and slug makers to find that magic combo. Just wasting time hypothesizing on my throne.



edit: to get better BC or something like VLD bullets you need higher sectional density, which means more mass per cross section area but that means more energy per cross section area is needed to accelerate the additional mass then add the additional friction from increased contact area. There are ways in PB world to help with some of the friction challenge hut requires very precise tolerances(barrel and bullets) but more energy per cross section area is where PCP has a physical limitation. But we do have some very smart people out there so I’m hopeful. 

 

[CyberDyneSystems]

Ive got a question that might be OT, but I think it's germaine



Does anyone know if there is there a reason we have not seen a discarding sabot slug for the big bores? I would have assumed that a soft plasticy sabot for "seal" to trap air vs. lead skirt, could that not help with the "lower friction?" Add to the benefits of higher velocity from discarded sabot vs. full caliber, seems it would be a natural fit for an air rifle. Am I missing something? Is it impractical from ballistics POV or cost?



I've got some sabot .50 made for a muzzle loader I was going to try in the Dragonclaw at some point. Haven't had the weather or space to try that yet.

 

[Gman57]

I agree qball. I have an adjustable reg on my Prophet. It can be adjusted up to 225 bar with a fill of 300 bar. Right now, stock length choked pellet barrel I can shoot a 25.39 grain JSB Redesigned at 1030fps at 180 bar with extreme accuracy. So with a longer barrel and a bump up in reg pressure it might do well as long as all the stars align so to speak, (drag, design, bc, weight , twist and barrel length). One of the LW barrels that is coming is a couple inches longer than the stock LW pellet barrel that is in the rifle now. Pellet barrel has a 32” twist and the longer new barrel has a 17.7 twist. I also have a second LW barrel coming with a 16 twist. One of my concerns is barrel drag as both unchoked LW barrels that are coming are 12 groove with a groove diameter of .221 and a bore of .215. To me, maybe I’m way off, it seems like the rifling is cutting really deep and a solid full length slug might create too much drag to try and stay transonic. 

 

[Redtick12]

I have wondered about slugs that narrowed just a bit in the middle. So like pellets they contacted the bore at the front and a the back and narrowed in the middle, but didn’t narrow near as much as a pellet and the transition was smoother than a pellet I think I would call it a hybrid slug . I would be surprised though if pellet and slug manufacturers had not already thought of and tried this, and I would guess then that it didn’t provide any advantages.

 

[Redtick12]

Either way a higher reg pressure than 150 bars and longer barrel will be needed due to physical limitation of PCP and then they can work with barrel and slug makers to find that magic combo. Just wasting time hypothesizing on my throne.

I believe there is another way of accomplishing this without out higher reg pressure, in fact even reduced reg pressure. It’s very simple I just need to make a nuclear fusion device. Then I can create a basically unlimited and free supply of helium to power our guns. It would have the small added benefit of solving in the entire world’s energy needs. I guess becoming a billionaire from my invention might also be considered an advantage. The idea of creating such a nuclear fusion device seems like such a simple one I wonder why no one else has thought of it. 

 

[qball]

@redtick12: you are a genius!!! You need to patent it and IPO, that will make you billions overnight!