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Joerg's 15 mm Steel Balls

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Joerg's 15 mm Steel Balls

Unread postAuthor: boyntonstu » Mon Aug 24, 2009 6:14 am

I suggest that we all use the same 15mm steel ball as the standard projectile for our slingshot ballistic tests.

Perhaps the same projectile for other guns as well.


Every test will be comparable if we all use the same projectile.

15mm steel ball source Joerg?

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Unread postAuthor: inonickname » Mon Aug 24, 2009 7:11 am

other guns


Co-ax is about 9.5mm bore, aint gonna fit.

I think conformist ammo is important for competition etc but not for basic comparison over a forum, unless for scientific reasons..
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Unread postAuthor: boyntonstu » Mon Aug 24, 2009 7:30 am

inonickname wrote:
other guns


Co-ax is about 9.5mm bore, aint gonna fit.

I think conformist ammo is important for competition etc but not for basic comparison over a forum, unless for scientific reasons..


I agree with you that we could use the most universal size that is readily available for scientific evaluation.


When it comes slingshots, a heavy projectile is always preferred.

Perhaps a lead 9.55 mm?

What is the weight of a lead 9.5 mm?

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Unread postAuthor: Biopyro » Mon Aug 24, 2009 8:11 am

Using a uniform ammo isn't such a problem in slingshots, but in an airgun with a barrel, unless the ammo is a tight fit you lose power, and if it's too big, it just won't fit!
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Unread postAuthor: POLAND_SPUD » Mon Aug 24, 2009 8:22 am

9.65mm BB seem to be quite cheap and available almost everywhere.... while I am not planning to build a sling shot it might be a good idea to find one caliber used as a reference point for different launchers

9.65mm steel BBs are roughly 3.5g each... lead is about 1.4 times denser than steel so 9.65mm lead projectiles should weight almost exactly 5 g
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Unread postAuthor: c11man » Mon Aug 24, 2009 9:40 am

i think that a standard size would work for slingshots of the same size (handheld) but for spud guns its just a bad idea. becuae if i was supposed to do a ballistics test with PLAGUE with a 3inch barel and a 15mm steel ball i dont think it would work to well. it would certenly go fast but it wouldnt show the power than 3inches of porting and 2000cubic inches of 100psi
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Unread postAuthor: john bunsenburner » Mon Aug 24, 2009 9:55 am

I am acctually planning on buying 1000 or so 9.5mm steel bearings, the above idea has been considered however 15mm is a pretty crappy dimention, stuck to 8mm or 9.5 which are the most common and easy available, seeing as they are coresponsing to imperial sizes(lots available in the US, in England and Germany over ebay in those sizes which really covers 90% of this forums needs, be warned shipping is a [female doggy] from Germany!)
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Unread postAuthor: qwerty » Mon Aug 24, 2009 11:05 am

Were do you get your 15mm ball bearings because they would be good use to us in the UK?
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Unread postAuthor: Biopyro » Mon Aug 24, 2009 11:24 am

Don't forget qwerty that 15mm pipe needs 14.5mm ammo!
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Unread postAuthor: john bunsenburner » Mon Aug 24, 2009 11:42 am

Really i ecomend 9.5 or 8mm ammo of ebay or look around, especially for pneu's i wouldn't use huge ammo, then again i have a fetish for tight holes(proven by the fact i do cave diving, am a small caliber guy and enjoy...).
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Unread postAuthor: qwerty » Mon Aug 24, 2009 12:04 pm

Don't forget qwerty that 15mm pipe needs 14.5mm ammo!

it depends is it 15mm ID or OD because it could fit absolutely perfecly or it could be slight to big.
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Unread postAuthor: Ragnarok » Mon Aug 24, 2009 12:14 pm

UK metric copper gives the external diameter. 22mm copper has an average* internal diameter of 20.3mm

*You need to work with minimum internal diameter, so really, it's limited to 20mm projectiles.

Biopyro wrote:Don't forget qwerty that 15mm pipe needs 14.5mm ammo!

13.5mm ammo would be pushing it.
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Unread postAuthor: jonnyboy » Mon Aug 24, 2009 12:25 pm

I remember a post where rag had done some fancy math to compare cannons of lesser size to larger cannons so even D_Halls Vera (massive hybrid) can be compared to a keychain gun. I can't find the post right now but I think the formula is in there so everyone could just use that and put it in there cannon/slingshot specs.
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Unread postAuthor: POLAND_SPUD » Mon Aug 24, 2009 1:02 pm

due to the effect that SOS has on launchers there isn't one ideal projectile for all guns.... 15mm might be good for slingshots because rubber bands are even more limited in terms of velocity than pneumatic guns (so 15mm BBs might be ideal for a slingshot)

As john has mentioned, 9.65mm BBS are, in fact, 3/8" BBs that's why they are commonly used for many applications... as a consequence of this they are rather cheap...

and yeah... 3/8" BBs are no good for larger guns... but they should be good for marble calibre guns and smaller ones as well (16mm marbles are 5g and so are lead 3/8" BBs...)

The problem with BBs is that the price increases more than their mass... so in other words - one 16mm steel BB might cost as much as ten 3/8" BBs... what is more, rare sizes (such as 15.5mm) are usually much more expensive than more commonly sizes (3/8", 1/2", 5.56mm, etc.)
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Unread postAuthor: Ragnarok » Mon Aug 24, 2009 1:08 pm

@jonnyboy: It's simply dividing kinetic energy by barrel volume - hardly fancy maths. It basically gives you an idea of how powerful a cannon is for its size, but it's not really a number of a huge amount of worth.

To tell the truth, VERA would rank pretty low, because its power comes from size, not pressure. As a general rule, because pressure tends to go up as cannon size goes down, you'd find that smaller cannons rank as more powerful for their size. It's also hard (although not impossible) to enter slingshots into.

So because of that pressure/size relationship, cannons are hard to compare independent of their size.
There is a more advanced version of the formula which I sometimes use which irons out that (and other issues), so that version can do the job. The results are interesting.

Amongst other things, with enough decent figures (which I am lacking in), it could tell you what each X from a hybrid is equivalent to in pneumatic terms.
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