Polymer selection for unique gun magazine

[kdoske]

We have a gun magazine that is a little unique and we need help on making polymer selections. I can't post pictures but I will give the best description I can.

The gun magazine contains a follower that is pushed by a spring. The follower has two guide rails on the front and rear. There are guide rail channels on the forward and the rear of the magazine that the follower is obviously guided up and down. Whats unique is the front and rear edge of the followers guide rails will make continuous sliding contact during the entire path of the magazine. The follower is under the tension of the spring and the weight of the ammunition so there will be some very obvious slide wear involved. If the followers guide rail wears to much the magazine will fail to function. We are looking at getting at least 500-1000 up and down cycles before failure. The more the better obviously. Are we asking too much from polymers or have they advanced this much? So far the selections we have made for polymers are below.

Main Housing
Key points that we would like:
[ol 1]
[li]Strength[/li]
[li]Wear Resistance[/li]
[li]Impact Resistance[/li]
[li]Chemical Resistance[/li]
[/ol]

Polymers we have Considered: (our ceiling is $10.00 a pound)
[ul]
[li]Nylon 6 - Fiber Filed[/li]
[li]Polyphthalamide - Fiber Filed[/li]
[li]Rigid Polyurethane - Fiber Filed **<-- Recommended by RTP [URL unfurl="true"]http://www.rtpcompany.com/info/guide/descriptions/2300.htm[/url][/li]
[/ul]
**The Rigid Polyurethane we were not sure about. RTP recommended us to it and said that it was already being used by another weapons manufacturer for a gun magazine.​

Follower
Key points that we would like:
[ol 1]
[li]Wear Resistance[/li]
[li]Strength[/li]
[li]Impact Resistance[/li]
[li]Chemical Resistance[/li]
[/ol]

Polymers we have Considered: (our ceiling is $30.00 a pound)
[ul]
[li]Polyester - Unsure of best additive for wear (something like the brand name Ertalyte-TX by Quandrant Plastics [URL unfurl="true"]http://www.quadrantplastics.com/na-en/products/machinable-plastics/engineering-175-325-f/ertalyte-R-pet-p.html[/url][/li]
[li]Peek - Unsure of best additive for wear (expensive overboard maybe?)[/li]
[/ul]​

Other Concerns:
Our other concern is how are these polymers going to wear against each other and will the main housing have a huge sliding wear rate regardless of what polymer we choose for the follower. RTP suggested adding Teflon as and additive to the Rigid Polyurethane but we are not sure how that would effect its other characteristics. They didn't seem to know either.


I really appreciate any suggestions you guys can make. I have really been racking my brain over this being as I am definitely not a polymer guy.

 

[cloa]

Chemical resistance to what (explosive gases)? These criteria are a bit vague- you define the strength needed and how much wear is too much. Which fiber is used to fill- I assume glass- which glass?

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[curtiscollar]

Have you looked at Lubricated polymers? Delrin or Nylon filled with PTFE are the classic products in wear applications.

Since your application requires a very rigid polymer you may want to look at siloxane lubrication where you can use less, allowing the polymer to be highly filled with fiber or glass as required. I beleive the trade name for these is Everglide.

 

[Pud]

I guess you are in the USA?

Have a look at nylon 610 - good chemical resistance, abrasion, wear, etc. It's the European version of PA12, thanks to to Du Pont. Your price target is way out - more like $10 per pound.

(Although any moulder could reach your target!)

What calibre are you looking at? .22LR has nasty ground glass in the primer? Dirty stuff.

H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[kdoske]

Cloa: well as I said I am not a Polymer guy. I appreciate you need for such specific things but I just don't know the answers.

There are many many residual compounds that are left from the ammunition when fired. To name a few...

Propellants:
Nitrocellulose, an energetic component of most smokeless propellants[21]
Nitroglycerin, an energetic component of double-base and triple-base formulations[21]
Nitroguanidine, a component of triple-base formulations[21]
D1NA (bis-nitroxyethylnitramine)[22]
Fivonite (tetramethylolcyclopentanone)[22]
DGN (di-ethylene glycol dinitrate)[23]
Acetyl cellulose[24]
Deterrents, (or moderants), to slow the burning rate
Centralites (symmetrical diphenyl urea—primarily diethyl or dimethyl)[25][26]
Dibutyl phthalate[21][26]
Dinitrotoluene (toxic, carcinogenic, and obsolete)[21][27]
Akardite (asymmetrical diphenyl urea)[23]
ortho-tolyl urethane[28]
Polyester adipate
Camphor (obsolete)[26]
Stabilizers, to prevent or slow down self-decomposition[29]
Diphenylamine[30]
Petroleum jelly[31]
Calcium carbonate[21]
Magnesium oxide[23]
Sodium bicarbonate[24]
beta-naphthol methyl ether[28]
Amyl alcohol (obsolete)[32]
Aniline (obsolete)[33]
Decoppering additives, to hinder the buildup of copper residues from the gun barrel rifling
Tin metal and compounds (e.g., tin dioxide)[21][34]
Bismuth metal and compounds (e.g., bismuth trioxide, bismuth subcarbonate, bismuth nitrate, bismuth antimonide); the bismuth compounds are favored as copper dissolves in molten bismuth, forming brittle and easily removable alloy
Lead foil and lead compounds, phased out due to toxicity[22]
Flash reducers, to reduce the brightness of the muzzle flash (all have a disadvantage: the production of smoke)[35]
Potassium chloride[36]
Potassium nitrate
Potassium sulfate[21][34]
Potassium hydrogen tartarate (a byproduct of wine production formerly used by French artillery)[36]
Wear reduction additives, to lower the wear of the gun barrel liners[37]
Wax
Talc
Titanium dioxide
Polyurethane jackets over the powder bags, in large guns
Other additives
Ethyl acetate, a solvent for manufacture of spherical powder[31]
Rosin, a surfactant to hold the grain shape of spherical powder
Graphite, a lubricant to cover the grains and prevent them from sticking together, and to dissipate static electricity[20]

 

[kdoske]

Pud: its actually a detachable shotgun shell magazine.

After the nylon suggestions we looked it up more and it does look like nylon has more wear resistance then Polyester. So I guess its back to Nylon. On Quadrants website we found Nylatron® NSM but it doesn't appear to be structurally reinforced. I think we are just going to contact a company like quandrant and see if they are willing to work with us. This is obviously out of our knowledge base.

 

[Pud]

Sorry, Nylon 610 is the US version of Nylon 12...
H

www.tynevalleyplastics.co.uk

It's ok to soar like an eagle, but weasels don't get sucked into jet engines.

 

[rickfischer51]

It might make sense to go to MidwayUSA or Cheaper Than Dirt and buy a Magpul magazine for an AR15 and send it out for some FT-IR and TGA. Magpul has been in the business for a long time and supplies the Feds (or at least they did). Why reinvent the wheel?

 

[Demon3]

I would try PA6 or PA6,6 with GF then use an additive to give excellent lubricity and wear.

Also agree to analyze an extant product. FTIR will tell yo what it is and TGA will tell you the filler level,

Chris DeArmitt

Expert consulting & training

http://www.phantomplastics.com