Metal detector for finding archery arrows

[Mothough]

Hi,

I'm looking for a metal detector to find shallow shot archery arrows which hide just below sward. They completely slide below the grass making them impossible to see by just looking. Only with the help of a rake one might get lucky and hook onto it, however, this becomes very tedious when the location is unclear and the potential search area larger.

The arrows have stainless steel heads which are 4 - 5mm (150 - 200 thou) in diameter, 3 - 5cm (1 - 2 inches) long and have a weight of 5 - 8 grams (0.2 - 0.3 ounces) (see image below).


Looking through the forum I found that there are many different types of metal detectors. I'm not sure which type would fit this use case best and would be grateful for any feedback.
A detection distance of about 10 - 15cm (4 - 6 inches) would already be sufficient (of course more = better) to even find arrows shot into undergrowth without knocking everything down.

I have no idea if stainless makes it hard to detect or if those targets are small or large at this distance. However, I'm very familiar with electronics and would also be capable of soldering a metal detector kit myself.
I would gladly learn more about metal detector technology as another hobby besides archery. I'm also open to buy a commercial one in the 50 - 100 Euro range if that's anything suitable. A lost arrow is about 5 - 10 Euro so 10 recovered arrows would compensate such an expense easy.

Hope someone can point me in the right direction.

[waltr]

I do find old shot arrows when detecting wooded sites. These were hunting broad heads.

SS is harder to detect but since they will not be deep and a fairly largish size almost any detector would find them.
Since you will have a large area to scan go for a larger coil to cover more area per sweep.
Also wouldn't need discrimination so a PI detector would be fine.

Since I only DIY detector I don't have suggestion on a commercial detector.

It will help us if you state what country you live (Europe but which country) in since this will affect what detects are available.

[Skippy]

SS is a hard metal to detect, it's a poor conductor of electricity, and as a result is easier to find with a higher operating frequency detector. Think 15-25 kHz, not 5 -8kHz. It will also read very low down the 'conductivity scale' used on many popular detectors, to the extent it could well be ignored in the regular 'motion mode' , and will only show itself clearly in 'Pinpoint mode' ( or other similar modes that some machines have ).
I've just done a quick test with a 25mm long M5 bolt of A2 grade stainless steel, on my Minelab Equinox. Pinpoint mode gets it fine. In single-freq mode, 15KHz was mediocre, giving poor identification. Multi-freq mode was the best, but the ID numbers were really low. So not a great result.

Many detectors hold their value quite well. If you can buy a second-hand one, there's a good chance you could re-sell it for 80-90% of purchase price, if it turns out to not be as useful as you hoped. Avoid those cheap 100 Euro machines, they are usually poor or very poor performers.

Do you have any idea about the specific alloy the arrow tips are made from ? Some high-strength stainless steels, eg. kitchen knives, are actually low chromium, and are quite magnetic. This may make them easier to detect.

[green]

Charted PI decay for a SS bolt. Not same size, maybe close enough?

Not magnetic

[Skippy]

Interesting, Mr. Green. 2.8 microsecs equates to a corner-frequency of 57 kHz. Backing up my suggestion that a higher freq VLF machine would be a better choice.
For the benefit of Mr.Mo , it helps detection if the detector operating frequency vaguely matches the corner-frequency of the target. So the popular entry-level Garrett ACE250 at 6.6 kHz isn't an ideal choice, but the ( more upmarket ) Fisher GoldBugPro at 19 kHz [ or it's cousins the F19, and Teknetics G2 ] would be a better choice.

[surfdetector]

This is a very interesting video that illustrates the need for quite high frequencies (>700Khz) in order to detect SS. In this case a test bead of 316 SS.
https://www.packworld.com/machinery/...g_food_2019Jan

[Skippy]

From experiments Mr, Green, myself and other have done, the length of long thin items , like wire, and these arrow tips, has virtually no effect on their corner frequency. Only the signal strength increases with the length of the item, corner-freq is almost entirely determined by diameter of the target.

[Mothough]

Thanks for all the great input so far.

It will help us if you state what country you live (Europe but which country) in since this will affect what detects are available.

Germany

Avoid those cheap 100 Euro machines, they are usually poor or very poor performers.

That's what I expected.

Do you have any idea about the specific alloy the arrow tips are made from?

Looking up a few manufactures it seems to be 303 stainless.

Some high-strength stainless steels, eg. kitchen knives, are actually low chromium, and are quite magnetic. This may make them easier to detect

Using a neodymium magnet a M6 50mm long A2 bolt will stick to the magnet whereas the arrowheads show only the slightest interaction with the magnet.

Charted PI decay for a SS bolt. Not same size, maybe close enough?

That's over my head.

[green]

Charted PI decay for a SS bolt. Not same size, maybe close enough?

Not magnetic

Been trying to figure if bolt is close to heads. Maybe heads TC is 1/2 the bolt or 1.4us?

[green]

That's over my head. 2.8 microsecs equates to a corner-frequency of 57 kHz. Skippy's reply#5 (corner frequency=1/2pi/TC)

[Mothough]

Got it.

An A2 bolt in similar size should be a close approximation though. A2 bolts are typically 304 stainless which is very similar in composition to 303 stainless.

303 stainless:

303 is a free-machining grade of 304 stainless steel that contains added sulfur or selenium. The addition of sulfur or selenium increases the machinability. Its composition contains at minimum 17% Chromium, 8% nickel, and 0.15% Sulfur/Selenium.

304 stainless:

304 stainless steel contains a minimum of 18% chromium and 8% nickel which gives its alternate name 18/8 stainless steel. 304 stainless steel contains chromium-nickel content and low carbon.

[green]

Can't find the formula but think TC for point=.3us(point diameter/2.05mm)^2. Corner frequency=.1592/TC

[Skippy]

Buying a commercial detector is a reasonable choice if you are confident you can find a decent quantity of arrows over a few years; you are interested in also using it for hobby/pleasure purposes - this could include anything from finding spendable coins in a park to uncovering ancient items from Roman times or earlier. Many serious detecting hobbyists find their machine 'pays for itself' in a few years ... spendable coins, lost jewellery, older silver coins, ancient coins and artefacts, plus the fun/challenge/sense of exploration that comes with it.
One very capable new machine that I think is good value is the Minelab Vanquish 440, which sell for about 330 Euro in your country. This will certainly find your arrows, as it has pinpoint mode, plus the multiple operating frequencies it uses include 18.2 and 39kHz, so it's good on difficult targets. And it works everywhere from the wet saltwater beach to ploughed (US: plowed) fields and manicured parks.
An example listing on EBAY Germany:
https://www.ebay.de/itm/Minelab-Vanq...d/174175453924

Obviously other machines could be equally suitable.

[kt315]

Skippy gets 10% of price for the manifest of ML --- LOL!

try seek oldie C-Scope 4PI or 6PI. i think they are good issue for your task.

[Ferric Toes]

Skippy gets 10% of price for the manifest of ML --- LOL!

try seek oldie C-Scope 4PI or 6PI. i think they are good issue for your task.

A CS6PI will detect a M8 x 25mm A2 stainless steel bolt weighing 12gm at 2 -3 inches. A Vallon VMH3CS mine detector will give a good signal on same bolt at 6 -7 inches. Also has ground balance if the soil is mineralised while the CS6PI doesn't. Ex military Vallon detectors are readily available on ebay and are made in Eningen unter Achalm, Germany. Super rugged and totally weatherproof. There is a long thread on them if you scroll down on page 2 of this Tech Forum.

Eric.