40mm Barrel Dimensions

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[ARCHIVED THREAD] - 40mm Barrel Dimensions

Posted: 5/9/2020 8:32:50 PM EDT

Hello,
I'm almost positive this information is on here somewhere, so I'm sorry.

A few months ago I bought a 40mm barrel for my 203 after I got my stamp back. The barrel has no markings, but was a good deal.

I'm finally getting some rounds to start using it, so I'm doing some final, pre-shoot inspections. Everything looks solid and in working order, but I'm not sure about the barrel ID. It measures 1.602 inches (40.7mm) between the rifling lands and 1.622 inches (41.2mm) for overall bore diameter. Anyone else have some insight or bore measurements?

Also, shooting M781 chalk rounds, looks like the zinc pusher is the widest part of the projectile. Will these actually engage the rifling? Is Zinc not harder than Aluminum? Just thinking about the long term of the barrel rifling.

Thanks for any input.

Attached File

Posted: 5/9/2020 8:56:54 PM EDT

[#1]

Seems entirely correct to me. Very little of any 40mm projectile - aside from the driving band - touches the rifling.

Posted: 5/9/2020 10:59:53 PM EDT

[#2]

I'm not sure about the hardness of zinc Vs aluminum. But the key here is that the aluminum barrel is hard anodized. This process leaves a much harder surface than bare aluminum. And it's also why you can use projectiles with aluminum driving bands (HE, Flares, etc)

Many people, including Scot Pace of Reloadableshells.com, think it's best to use a plastic for the driving band to be on the safe side. Which I agree with as well since we don't have the barrel replacement budget of the US military. So you'll see that his projectiles all use a replaceable driving band ring

Posted: 5/10/2020 7:56:12 AM EDT

[#3]

Projectile rotating bands measure 1.620 OD. The aluminum, when used, is lubricated on the paras and HE. The bands and bodies appear goldish in color. That is the lube. I have some in my shop for making HEDP reproductions. It requires the bodies be slightly heated before applied. GROG

Posted: 5/10/2020 8:53:36 AM EDT

[#4]

Interesting! Any detail on what the lube actually is? I wonder if it's something that is in commercial use and can be sourced elsewhere - or if it's military "secret sauce".

This thread brings to mind a fact a lot of people gloss over about 40mm barrels. They're disposable. I've had to sleeve launchers other than the M203 and of course the M203 itself has to have the barrel replaced as needed. With care it seems like it takes plenty of rounds to get to that point.

Posted: 5/10/2020 3:00:03 PM EDT

[#5]

Alodine 1132. It's not cheap, and hazmat shipping... GROG

Posted: 5/10/2020 3:08:49 PM EDT

[#6]

Hazmat shipping is a way of life in the DD world isn't it.

Thanks for letting me know what I'm looking for. I've wanted to turn some projectiles to play with but I hate to scrap barrels any faster than needed.

ETA: It's a Henkel product - no wonder it costs so much. At least what they sell generally works well for the stated purposes.

Posted: 5/10/2020 4:49:03 PM EDT

[#7]

Heat the projectile bodies before applying it. I do a few seconds with a propane torch, just to raise the metal temp, and use a lathe to turn them while I'm doing it. Then keep the lathe running very slow and apply the lube (if you are using the pen like I do). It will go on wet and clear and dry gold. If it turns brownish, your metal was too hot, but it will still work. With reproductions, I go for finish color... GROG

Posted: 5/10/2020 5:31:19 PM EDT

[#8]

Prior to heating do you do the whole degrease and scotchbrite procedure as recommended in the instructions?

Posted: 5/10/2020 5:48:52 PM EDT

[#9]

The projectiles I use are freshly lathe turned, and sanded lightly. No other prep is needed if you are working with freshly cut aluminum. GROG

Posted: 5/10/2020 7:15:00 PM EDT

[#10]

Just curious. Are we certain this is a lubricant? Or is it just a cpc to keep abrasive aluminum oxide from forming on the aluminum?

Seems like it'd be a perfect corrosion preventative for this application as it does not add any discernible weight or increase the diameter at all.

Posted: 5/10/2020 7:49:21 PM EDT

[#11]

It's a chromate conversion yes. Not really meant to increase lubricity from the documentation I've read but just as you thought - to prevent abrasive AlO from forming.

Posted: 5/10/2020 9:33:51 PM EDT

[#12]

Yes, used as corrosion resistance, as opposed to anodizing, which alters the aluminum. If you are making aluminum projectiles, I recommend using it... GROG

Posted: 5/11/2020 10:42:52 AM EDT

[#13]

The name changed to Bonderite a while ago. I'm not sure if the composition changed too

I bought a jug of it and the acid prep solution at an aircraft supply store to treat boat parts. Didn't know they had it in pen form, that would be handy

Posted: 5/11/2020 1:18:50 PM EDT

[#14]

I think I'll practice on the lathe more before I commit 100 bucks to a magical sharpie

Posted: 5/11/2020 4:32:28 PM EDT

[#15]

I turned some pushers out of 6061 and have had no issues with the barrel.
I checked the hardness of both before testing.
GROG, if I remember right the barrels are 7075 so much harder than zinc or 6061.

Posted: 5/12/2020 11:47:54 AM EDT

[#16]

Quote History

Quoted:
I think I'll practice on the lathe more before I commit 100 bucks to a magical sharpie

View Quote

The liquid is only $35/quart:

BONDERITE M-CR 1201 AERO (FORMERLY ALODINE 1201)

I don't know the difference in composition between the pen and the stuff in the jug. The directions for the pen say that the part doesn't need to be rinsed with water, the stuff in the jug does

The color that the stuff in the jug leaves varies with the material that it's applied to. Sometimes yellow/gold, sometimes more brown. I don't use it enough to know which metals produce what color

I can dunk a zinc pusher in it and see what it does. It will be different than AL though

Posted: 5/12/2020 12:17:14 PM EDT

[#17]

I got the Alodine as it is what they use on real M433s and doing reproductions, I try to stay true to the actual products used in most cases. I also use the same ink when marking them as the original. Either way, regardless of what product you use, it's best to use something that will keep your projectiles from corroding, and not effect the hardness of the aluminum. Especially if you are storing your stuff for long periods. GROG

[ARCHIVED THREAD] - 40mm Barrel Dimensions

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