SpudFiles

Moonbogg wrote:Why is this being sleeved anyway?

coupla reasons;

1. the DOM is pretty much dead straight, the copper isn't perfectly true.

2. the DOM is extremely rigid for 56", the copper, even being type k, is flexible enough that the barrel sags slightly, and after watching some video of some shots, has some pretty nasty barrel whip.

3. THe DOM is heavy, decimater is designed as a mounted gun, and the extra weight will help quell recoil(currently ,when firing, it stands the 30lb tripod on its hind leg with the front 2 legs a foot in the air even with me leaning into it, when you pull the trigger, you'd better be ready<count so far; 4 people on their @$$'s, and 1 with 4 stitches in his face when the gun came back and hit him>)

4. accesorie mounting, I can drill and tap the steel to accept sight/scopes/etc.

my goal is to be below 3MOA with bearings, a flexi-barrell won't do that...might not be possible at all, but a pneumatic smooth bore grouping less than 10" at 300yds will be one to write home about...And may even exceed that...We'll see...


D_hall, consider the steel is 1.124" inside and the copper is 1.25" out side I'm guessing the gap will actually be larger, since you used .5" as an example......

jeepkahn wrote:1. the DOM is pretty much dead straight, the copper isn't perfectly true.

It's going to take serious effort to get the two together. You've only got a tiny space between the two (about a tenth of a millimetre, unless I've cocked up the maths) and the copper is going to heat up fast.

I personally reckon that if you don't get them together within a few seconds at the absolute outside, they'll jam and be pretty much permanently stuck.
Getting together 140 cm of pipe with that little diameter difference in the instant you've got... I do not fancy trying such a thing myself.

You might buy yourself time by using some kind of thermally insulating grease between the two layers, as well as some ease in fitting the two together - but that may well cause you problems later.

My goal is to be below 3MOA with bearings, a flexi-barrell won't do that...might not be possible at all, but a pneumatic smooth bore grouping less than 10" at 300yds will be one to write home about...

Sounds overoptimistic. 3 MOA is a challenge with a rifled projectile (or one that's somehow otherwise stabilised). I can't see it happening with a smooth-bore firing unstablised bearings.

For one thing, the ballistic inefficiency of spheres will almost certainly mean that they'll lose enough velocity to make them require an impractically curved trajectory to any range like that.
Also, if you are genuinely firing them in the transonic range, then that'll cause some stability issues.

That said, I've made little secret of the fact I want to go MOA myself (ideally at 400 metres). But I'm not going to be using bearings.

jeepkahn wrote:D_hall, consider the steel is 1.124" inside and the copper is 1.25" out side I'm guessing the gap will actually be larger, since you used .5" as an example......

Sorry, in the OP you mention the pipe being ".5x.188 wall" and I assumed the .5 was the ID. Upon rereading, I'm guessing that a 1 got left out of that number.

In any event, yeah, use 1.124 in the prior calculations. Gap will be about 2.25 times as large as those listed.

Ragnarok wrote:It's going to take serious effort to get the two together. You've only got a tiny space between the two (about a tenth of a millimetre, unless I've cocked up the maths) and the copper is going to heat up fast.

I personally reckon that if you don't get them together within a few seconds at the absolute outside, they'll jam and be pretty much permanently stuck.

Rag put it better than I did.

I'll say it again... You're MUCH more likely to have success in this venture by chilling the copper to cryogenic temps (ie, run LN2 through it) than you are by heating the steel. And again, if it gets stuck, chilling it again will loosen the copper and give you another chance. By contrast, once those two pieces are together, heating it up will only make the fit tighter (so reheating the steel is the LAST thing you want to do!).

ooops... I edited the OP, I didn't realized that i missed the "1"... it should've been 1.5"x.188"wall.... I think I'm definitely gonna see if I can use the cryo method, and if I remember correctly,cryotreated will increase the resistance to wear as well... Getting ready to call around tosee if I can find a cryolab nearby...

Sorryto DP, but this info is worthy of bumping...

I called a gas/liquid gas supply company a mile from whereI work..

I told them what i was doing and asked if they had any customers that dealt in shrink fitting with liquid nitrogen, his response was,"Not sure, but i can sell you the LN." my response,"Well out of curiousity, how much is it?", reply, "$2.oo a litre"... I'm going ,here in about 2 hours, to get a coupla litres... he even said that if I don't have a dewar, that I can cap one end of the copper, and they'll fill it directly into the barrel, and after I sleeve the steel over it we can just pour it out... the copper tube handbook says that 56" of 1" type k will hold roughly 1/5 of a gallon, or a little less than a litre...

jeepkahn wrote:ooops... I edited the OP, I didn't realized that i missed the "1"... it should've been 1.5"x.188"wall.... I think I'm definitely gonna see if I can use the cryo method, and if I remember correctly,cryotreated will increase the resistance to wear as well... Getting ready to call around tosee if I can find a cryolab nearby...

My new barrel is 72" x 1.75 od x 1.246 id DOM. Two days ago I bored it out to 1.251 id. It's easy and fairly quick to do. If you give up on the sleave and need an alternative, contact me and I'll tell you how to do it.

I'm actually oversleeving for more strength, not under sleeving for tighter fit... but I'd love more info on your boring method for barrels, could come in handy for a project thats on the back burner...

yes, please share. And I would suggest that you take both pipes and sleeve them in the parking lot, since the LN will evaporate very quickly. I mean, if you are hauling one pipe of a given length somewhere, hauling a second is no big deal (assuming reasonable diameters).

jeepkahn wrote:Sorryto DP, but this info is worthy of bumping...

I called a gas/liquid gas supply company a mile from whereI work..

I told them what i was doing and asked if they had any customers that dealt in shrink fitting with liquid nitrogen, his response was,"Not sure, but i can sell you the LN." my response,"Well out of curiousity, how much is it?", reply, "$2.oo a litre"... I'm going ,here in about 2 hours, to get a coupla litres... he even said that if I don't have a dewar, that I can cap one end of the copper, and they'll fill it directly into the barrel, and after I sleeve the steel over it we can just pour it out... the copper tube handbook says that 56" of 1" type k will hold roughly 1/5 of a gallon, or a little less than a litre...

A large stainless steel thermos is a dewar. Never ever put in the tight cork in the dewar. It will behave like a co2 pop bottle bomb on steroids. If you have a pickup truck with an open bed and a short travel distance a Styrofoam cooler (not the rough duty ones, the cheap easily broken one) can be used to transport some, but it has much poorer insulation than a dewar, but holds more.

Don't under estimate the volume. It boils rapidly on contact with superheated metal and will vent nitrogen out at high speed. When we fill portable dewars at work, the amount used veries widely depending on if it was empty and warmed up. Our dewars are listed for consumption for an initial fill and cold refill. A cold fill takes a little less than twice as much as a cold refill. To chill a long pipe exposed to air that will condense components from the air such as water and oxygen on contact, large amounts of LN2 will boil off. You will not be able to cool a length of pipe capped on one end. The boiling LN2 will make it impossible much like trying to fill a hot coffeemaker by dribbling water in the tube the hot water comes out of.

Your best bet is to find a funnel slightly larger than the pipe, attach it to a piece of pipe a foot or two long, then to an elbow into the horizontal pipe you wish to cool with the far end open. Pour in LN2 so the vertical section provides pressure to overcome the high rate of boiling in the horizontal section. The horizontal section will slowly cool as the cold gas cools the section ahead of the liquid. When you get mostly liquid out of the pipe then the full length is cold and ready for assembly. Assemble very quickly. Your best bet is to see if you can rent a 5 or 10 liter hand dewar for the day or weekend. Wear safety goggle and work outdoors. You will dilute the air so the local O2 level will drop some. Try to work above the cloud that forms. The cloud is moisture from cooled air. The cloud has oxygen, but is diluted. The very cold tends to make the area above the cloud full strength regular air unless confined indoors where it maybe recirculated and warmed. Safety first.

FYI, I do work with the stuff in my job.

Just a thought: would moisture frozen to the outside of the copper tube interfere with the sleeving?

Have you considered sanding the male pipe down just enough to make a snug fit and then JB welding the crap out of the whole thing?

Update... My measured interference was a lot more than what spec's said,(specs being nominal numbers), measured id on the steel is 1.121", and the outside of the copper meaured 1.127", which means even with LN2 the copper would only shrink to 1.1235" and thats still not small enough, so I've been sanding the copper(mounted on a drum sanding mandrel, spinning the copper while hold the sand paper, and I've got the copper down to 1.124"ish... So, If I keep the steel warm 75+f, and I LN2 the copper, it might not slide on, but at least I should be able to use a dead blow to drive it on... If anyone reads this(tech/rag/dhall) in the next 15minutes, and you have any suggestions... We tried this morning and we were able to fill the copper by having a vent near the bottom that we capped once liquid started coming out, but after the steel went on 1.5" the steel shrank enough to halt progress(which tells me my digital micrometer is fallible, because after calculating it shouldn't have gone on at all)...

as I said before, do the whole operation in the parking lot of the gas supplier. Watch for condensation on the copper barrel.

ramses wrote:as I said before, do the whole operation in the parking lot of the gas supplier. Watch for condensation on the copper barrel.

Condensation at that temperature is not too much of a problem. There will be some frost, but after the pipe is very cold, the moisture in the air will freeze before contacting the pipe so a solid build up of ice doesn't happen. It will snow near the pipe. frost on the pipe will be light like standing snowflakes. Ask to see one of their cryo evaporators in operation, there is often a snowbank under them even in the summer.

An operating evaporator often looks like this.


This picture shows the high boiling rate you should expect when trying to pour nitrogen into a very hot (room temperature) pipe. You will need to use gravity and have the far end of the pipe open to let out the boiled gas. This photo is showing filling a portable dewar with LN2. Initial fill takes about 1.5 dewars full of LN2 because of the amount that boils off.