Minimum Tin for Airgun Bullets

[rsterne]

I have done a limited amount of casting for my air rifles, from .257 to .357 cal.... and I started with pure lead from RotoMetals.... I was told to add 1% tin to get better filling, and indeed that worked well.... I want to maintain the softest possible bullet because of the limited pressure available for propulsion, and the velocity, which is always under 1000 fps.... I need to purchase more lead soon, and I see that I can get 1:40 Alloy from RotoMetals (2.5% tin) which has a BHN of 8.5....

My first question is, what would be the BHN of pure lead, and of my 1% alloy I currently use?.... My second question is, what is the optimum tin content for my purpose to get the best filling while maintaining the softest possible bullet?.... This is my first thread here, so please be gentle!.... :lol:

Bob

[mikeym1a]

I hate getting old. I was reading this just a couple days ago, and can't remember the title of the thread. Anyway a little search on line and I found that pure lead has a BHN of 5-8, and the 1:40 alloy 8-9. (http://www.calguns.net/calgunforum/archive/index.php/t-393042.html) If you are happy with your 1% alloy, if finances permit, why not just mix an equal amount of pure lead with the 1:40? Unless I don't understand the mix ratio, I would think that that would bring the tin content down to 1.3? Hope I'm right, and that this helps a little.

[Marlin Junky]

First of all, I'd be interested in seeing what you are casting in 25 caliber and what airgun you are casting those pellets[?] for.

I would imagine that BHN 8.5 would be too hard for your purposes. The BHN of pure lead is supposed to be 5, according to Lyman. Perhaps you could double the volume of the RotoMetals 1:40 with pure Pb to obtain a 1.25% tin alloy. To get the precise BHN of your 1% alloy, you would need to measure it; however, I would assume it's approximately 6.

In your case, I would ask around regarding the most accurate tools for measuring BHN. I have a Lee hardness tester and there's no way I can measure more accurately than +/- 1/2 BHN value... and that with much practice and technique.

P.S. I'm under the impression that Pb free pellets are 100% tin, but they are all skirted, correct?

[detox]

My most accurate 22 cal pallets are made from Stannum...thats tin to me and you. Less deformation when fired. They are labled as non toxic.

Dynamic Non-Toxic Sn2
www.airgunpellets.com

[303Guy]

Stannum - that's where the Sn for tin comes from. Pure tin you say? Interesting. Anyway, a cheap source of tin is pewter ware from the metal recyclers. Got me a lifetime supply and not too expensive either. Pewter is something like 97% tin. It's a bit harder than pure tin but that could be corrected with a small amount of lead, I should think.

[Marlin Junky]

Stannum - that's where the Sn for tin comes from. Pure tin you say? Interesting. Anyway, a cheap source of tin is pewter ware from the metal recyclers. Got me a lifetime supply and not too expensive either. Pewter is something like 97% tin. It's a bit harder than pure tin but that could be corrected with a small amount of lead, I should think.

All the pewter I've seen has been way harder than necessary for use in an air rifle and more than likely had copper and antimony content. Granted, all the pewter I've seen has been in the form of nick-nacks and other miscellaneous **** women like. :bigsmyl2: I'm not old enough to have played with tin solders.

Where the heck did that air gun caster go!?

MJ

[GaryN]

If you look at the Rotometals webpage and go to the bottom of the page, they have a small equation that might help you. It says 1% tin adds 0.3BHN
http://www.rotometals.com/Bullet-Casting-Alloys-s/5.htm

[rsterne]

Sorry, just got back to this thread now.... First of all, only the "non-lead" airgun pellets are tin, and the ones I have used are typically very innacurate.... The most accurate tend to be pure lead or nearly so.... Typical airgun pellets have a hollow skirt that obturates when fired to seal well with little bore drag.... What I'm doing is NOT typical for 90% or airguns, but is primarily what the "big bore" airgunners use.... ie cast boolits.... Once you go bigger than .25 cal (which in airguns is 0.250", not 0.257") until recently there were virtually no "pellets" available, you had to purchase or cast your own boolits.... I have a DAQ .308 Exile, which is a typical example, I cast some Lee 113 gr. FN and 120 gr. RN, and that gun shoots them at about 835 fps (180-185 FPE).... It operates from 3000 psi down to 2000, and delivers 5-6 shots within 5% muzzle velocity over that pressure range....

I recently built four different versions of my scratch built "Hayabusa" PCP (pre-charged pneumatic) in .224, .257, .308, and .357 calibers.... Here is what it looks like....

http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa224_zpsc6671fce.jpg (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa224_zpsc6671fce.jpg.html)

The .224 version (above) uses a .22 Hornet barrel and swaged 41.5 gr. bullets from Holland and duplicates the performance of a .22LR target load.... The .257 version uses a 25-20 liner, and shoots from 65-85 gr. bullets at about 130 FPE.... The .308 has performance similar to the DAQ, and the .357 I have only tested so far with 132 gr. bullets, and it will produce 10 shots at 200-210 FPE in that caliber.... I will be casting some 160 gr. for it soon.... Anyway, that will give you an idea of what I'm casting for at present.... I will eventually add a .457 cal and a .410 shotgun to the Hayabusa test program....

I guess my primary question is, would I notice any difference in mold filling (particularly in the .25 cal) between my 1% tin alloy and the 2.5% (40:1) mix?.... If not, I will stick with the 1%, which I did find worked better than pure lead.... Just in case you might be interested, here are some tests I did with the .257, shooting into "melt and pour" soap (point blank)....

http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/IMG_3133_zps68d4ee7d.jpg (http://s378.photobucket.com/user/rsterne/media/Ballistics/IMG_3133_zps68d4ee7d.jpg.html)

On the left is an as cast solid, in the middle a recovered solid, and on the right a recovered hollow point version.... Top row is a 65 gr. Lyman at ~900 fps, bottom row is an 85 gr. RCBS at ~820 fps, with the hollowpoints being about 40 fps faster, of course.... All were at ~130 FPE energy....

Bob

[williamwaco]

I am a little late to the party but I did an experiment with and without tin.

Unfortunately my "with tin" alloy was 2.5% +/-

You can see the results here:

http://www.reloadingtips.com/pages/exp_110818a_tin_in_alloy.htm

2.5% tin increased the BNH from 7.2 to 8.2. That is .4 BNH per percent tin. Good agreement with the above comment of .3 BNH per percent tin.

How hard is pure lead? I wish I knew. The "sources" mostly agree on 5 to 5.5.
Most "pure lead scrap " I see measures around 6 to 6.5.
I have measured some .38 factory wad cutter bullets that measure around 5.5.
Most stick on wheel weights measure around 5.5.

That said, I have also seen "pure" lead measure as low as 4.6 to 4.8.

I wonder of there is an ingredient that could soften pure lead from 5 to 4.6. I have no idea.

I might one day repeat this with 1% tin but I doubt it.
I find that adding tin to clip on wheel weights does not help fill out. I am told they contain around 1% tin.

[Marlin Junky]

rsterne,

Thanks for the post. So you started with a 25 caliber Marauder and increased the power 2.5 times. Looks like all you retained of the Marauder was part of the stock and the trigger.

What kind of groups are you getting at 75 yards with RCBS 25-85-CM?

With respect to small game hunting, how would you rate the results of your project against a quality 22LR shooting CCI hollow points?

I would stick with 1-2% tin and increase the casting temperature conditions a bit. Preheat your mold until the cavities and shinny hardware (e.g., the sprue pivot) turn dark blue and set your melt temp at about 650F. If the boolits come out frosted, cast slowly, giving the mold a chance to cool slightly. If the fill-out is not quite right, try closer to 700F in your pot. You do own a casting thermometer and an electric hot plate, correct?

MJ

P.S. On second thought and considering the small size of the 25-85-CM boolit, you might need to start at 700F in the furnace... sorry I can't be more precise... I don't own that mold. I certainly would get that mold preheated to about 475-500F before dumping alloy into it, though.

[Marlin Junky]

That said, I have also seen "pure" lead measure as low as 4.6 to 4.8.

Don't you think that could be due to measuring technique and/or tester quality/calibration?

MJ

[R.M.]

I seem to remember reading someplace that pure lead's BHN is actually below 5. What it was I can't remember. 5 is probably close enough for our purposes though.

[rsterne]

Actually, I scratch built everything but the stock, trigger, barrel, tank, and the fasteners.... The MRod just happened to have a good trigger and the stock was already inletted to fit it and large enough for my 1" CrMoly maintube.... I haven't had an opportunity to test at longer ranges yet, hopefully very soon.... I do have a thermometer, I'll try increased temperature, thank you for that suggestion....

This gun is similar in performance to a .22LR.... at significantly more cost.... If you don't understand why, I can't explain it.... kind of like climbing Mt. Everest, I just did it "because I can"....

Bob

[Marlin Junky]

This gun is similar in performance to a .22LR.... at significantly more cost.... If you don't understand why, I can't explain it.... kind of like climbing Mt. Everest, I just did it "because I can"....Bob

That's good... in addition, I would imagine you can take small game w/o primers, powder, or brass. What does the rig weigh?

If possible, it would be nice to eventually see some 50-100 yard targets.

MJ

[rsterne]

It's around 8 lbs.... I also have two regulated (1900 psi) versions, in .22 and .25 cal using Lothar Walther barrels, that are repeaters using an MRod magazine in my own breech.... The .25 cal delivers 45 shots at 52 FPE (950 fps with 25.4 gr. JSB Kings) and were deadly on gophers and rockchucks.... Those were so successful it prompted me into the cast boolit (unregulated) versions....

Bob

[Buzz64]

Really interesting work! How do you charge the system?

[rsterne]

I fill from a SCUBA tank, which I fill from a "ShoeBox" compressor.... I top up the tank when it drops about 500 psi, and that takes about 3 hours.... You can use a hand pump, but let's just say it's a good aerobic workout, especially to 3000 psi with a large tank like I have (22CI)....

Bob

[williamwaco]

Don't you think that could be due to measuring technique and/or tester quality/calibration?

MJ

Yes, it could be.


.

[detox]

Crosman/Benjamin Marauder PCP air rifles are avaliable in calibers .17,.22,.25,.357 and are sound supressed. My Marauder .22 cal rifle is very quiet and powerful. My Marauder PCP .22 cal. pistol with shoulder stock is my favorite...very deadly on squirrels. You fill these to slightly under 3000psi using scuba tank or hand pump

http://www.crosman.com/airguns/rifles/pcp

[MT Chambers]

I have a Daystate Wolverine in .303, a Daystate Huntsman in .22, and an Air Arms S510 in .25, I'm playing around with different sizes of cast bullets, but can't even chamber bullets that are not plain lead. I don't want any hard bullets stuck halfway down the barrel. The Wolverine is a monster but I believe that it and the .25 could benefit downrange from heavier cast bullets, I'd like to share info with folks that have the same interest in making this work!!!! From what I can tell so far the .303 is actually .300", the .25 is .251" and the .22 is .220", and I'll prolly need molds that drop at those sizes.

[rsterne]

The .30 cal FX and Daystate are indeed 0.300", most .25 cals are 0.250", and most .22 cals are 0.217" (groove diameters in each case).... and the head diameter of the pellets matches that.... I have found that to chamber a cast boolit, even one in pure lead, you need a longer chamber than found in the typical airgun, so that the boolit can slide forward so that only the nose or forward driving band starts to engage the leade of the rifling.... If the chamber is too short, you can literally break off the bolt handle trying to chamber a boolit, even if the boolit is the correct diameter to match the groove size of the barrel.... The 52 gr. cast boolit for a .25 Auto will work in most airgun barrels if the chamber is long enough.... Once you go up to 65-85 gr. boolits, they are 0.257", and you need a 25-20 barrel (14" twist) to match them.... For even heavier bullets, you need a 25-35 or .257 Roberts barrel (10" twist), all of those in .257 cal....

Bob

[melloairman]

If you go to LBT bullet molds Veral will make you any 25 caliber diameter mold in about any weight you want . I have a .250 and a .252 Spitzer that he has made . They cast about a 60 grain bullet . I believe Mr. Hollow point has a .251 55 grain in a Spitzer from him . Mine are MOA accurate bullets . And my barrels are a 1- 16 and a 1-14 twist Also If you are running a choked barrel a pure lead bullet will tend to lead the muzzle after a few shots and accuracy will go away . Marvin
http://i301.photobucket.com/albums/nn55/melloroadman/IMG_7359AA_zps82862b45.jpg (http://s301.photobucket.com/user/melloroadman/media/IMG_7359AA_zps82862b45.jpg.html)
http://i301.photobucket.com/albums/nn55/melloroadman/IMG_7357-Copy_zps77ba82ac.jpg (http://s301.photobucket.com/user/melloroadman/media/IMG_7357-Copy_zps77ba82ac.jpg.html)
http://i301.photobucket.com/albums/nn55/melloroadman/IMG_7356-Copy_zps688a401d.jpg (http://s301.photobucket.com/user/melloroadman/media/IMG_7356-Copy_zps688a401d.jpg.html)

[MT Chambers]

I gonna try swaging in a hollow base to the Lyman .25 acp bullet, and any other cast bullet for airguns, as the bullet "as cast" is not close to the accuracy of JSBs.