Very tight Mega Monolithic Upper ???

[WillD]

I'm using this Mega upper for my Satern Spartan barrel and it's every bit if not tighter than the Mega upper I used on my first build. The problem is the monolithic design makes it harder to fit the barrel.

Mega suggest heating the upper with a hair dryer. I've used a torch before on cases and put bearings in the freezer for this type fit in the past. Since the only hair dryer I use is terry cloth I was wondering if anyone has done this before.

How long with the hair dryer and do you think chilling the barrel will be a benefit?

TIA, Will

[DangerClose]

I have heard this many times about Mega being a tight fit. It is the finish they use on their recievers. Since it is a mono, you cant sand the barrel connection area on the reciever.

So, the hair dryer and freezer trick. It does work, to an extent. Get the barrel as cold as you can. A deep freezer will work the best. Then, bring a hair dryer by your freezer. Start to apply heat to the lug area. This may be hard with that mono, but it is the only way to do it. After some light heating, take the barrel out and try to fit. If it doesnt, then add more heat while the barrel stays in the ice box. Try again.....and again......and again.

If the upper starts getting too hot, id email Mega about doing it for you. They have great customer service. That way, if they mess up, then they replace the upper. If you mess up, you are SOL and out hundreds if you have to replace.

The key is keeping your barrel safe and the temper of the upper intact. Make sure you barrel has no moisture in it. Simple science, freezing water expands. This, inside a barrel groove, will expand your zero exponentially. So, swab the barrel well. As far as the temper, just dont use a heat gun or a torch.

All of this info is based on you building a tack driver and trying to save your accuracy (post is minus the science and physics behind it all). If its a truck gun, try the heat gun and dont worry about moisture in your barrel

Hope it helps,
DCO/Ben

[StoneTower]

You have to be careful with the heating freezing technique. I have used this method to put bearings on a shaft for a rotisserie that was for cooking 3 whole pigs/lambs at a time. Once the temperatures equalize, there is no way to remove the bearings. You may never be able to remove your barrel. You cannot heat or cool the completed part because they will both move in the same direction.

[kamrr4437]

There have also been instances where the upper actually cracks after using this procedure. I would use caution doing that.

[DangerClose]

Yeah, I have heard about that. Its why I suggest to only using a hair dryer. Having the upper to warm and then trying to mate the frozen barrel can be like hot water on a wintertime windshield.

Just use CAUTION, like Kamrr4437 said

[StoneTower]

The cracking has nothing to do with the temperature. The cracking is caused by the same reason a glass jar cracks when you fill it to the top with water and put the lid on and put it in the freezer. If there is too much of a difference in size, something is going to have to give. You can temporarily reduce the size if the barrel and temporarily increase the size of the upper, but when they return to roof temperature, the upper is going to be too small and the barrel is going to be too big to fit together, The thin aluminum receiver is the weaker of the two and it either going to have to remain stretched or if it shrinks too much, it will crack. I would make Mega fix the undersized upper and I would not let them sand or turn you barrel extension to fit their non-standard part.

[kamrr4437]

So essentially it has everything to do with the temperature. That post is exactly what im talking about. The barrel shrinks from cold goes into the hot expanded receiver when they are fitted the barrel swells and receiver shrinks hence crack. So yes temperature has everything to do with it cracking. Hence why i said use caution lol.

[leopard6.5]

WillD: Is it just a matter of the coating thickness causing the problem?

I had this problem with a gasblock once where it was so tight I couldn't get it to slip on.

I bought a long piece of wooden dowel( 3 feet because that's the only length they had, Lowes) in the correct diameter( 3/4" in this case) and worked it into the hole and got it to eventually rotate. The wood dowel worked off just enough of the coating so I could then work the gasblock on.

Hopefully this gives you another idea.

Of course, after this I didn't need to worry about any gas leaks because it still fit really tight.

Good luck with your build.

Lee

[WillD]

Stonetower and kammr4437 I appreciate your input. I have seen cases break after using this method and too large a bearing.

Lee I'm pretty sure it's only the coating thickness. That's what I removed from my Mega HD upper and got a nice snug barrel fit. I do have a dowel and a supply of emory cloth. The design of the monolithic upper makes it difficult to measure with the tools I have available and difficult to see to be sure everything remains in alignment.

I'm still hobbling in my cast and I can't drive so I'll have to round up a ride to a friends machine shop to better assess the course of action.

Thanks guys

[DangerClose]

Mega has that reputation for a thick coating

[StoneTower]

So essentially it has everything to do with the temperature. That post is exactly what im talking about. The barrel shrinks from cold goes into the hot expanded receiver when they are fitted the barrel swells and receiver shrinks hence crack. So yes temperature has everything to do with it cracking. Hence why i said use caution lol.

You can believe what you want but the receiver is not as elastic at room temperature as it is when it is heated. The molecules are farther apart when it is heated. When the upper shrinks it is essentially the same a driving a peg that is too large into a hole that is too small. If the hole cannot stretch enough to accommodate the peg, the material that the hole is drilled into will fracture. This is different than heating a bottle in a campfire and then dripping cold water on it. When the cold water hits the bottle, it cools only part of the bottle and the uneven cooling is what causes the bottle to fracture. When you use the heating and cooling technique to get to parts together as long as the larger part does not over stress the smaller part, you have a nice tight (almost permanent) fit. The problem is getting the two parts apart if you ever want to change the barrel. The cooling of the parts is even unlike the glass bottle example.

If you have an old barrel (with an old barrel extension attached), you could remove the index pin and turn the extension down slightly. You could then use jeweler's rough to lap the coating off the upper until you get a tight but proper fit.

Take care,

David

[Wally Bear]

The simplest way to fix it, is to use emery cloth and hand fit the barrel to the receiver.

[WillD]

I really like my Mega uppers but man are they tight, I expect to allow for a range of tolerances on barrel extensions. My first HD billet upper provided a excellent fit after much fitting. A gunsmith buddy even commented about it when I asked him to check my work before torquing the barrel nut.

This last Mega Monolithic is a really nice piece but it caused a bit of teeth gnashing mostly because of the difficulty reaching the area that needed attention. I solved my problem with judicious use of a brake cylinder hone. A few spins of the drill, rinse with contact cleaner, and attempt barrel fitment; several times. Final fit still required a few taps with a rubber mallet.

An 8 1/4" hone inserted from the rear of the receiver was just right. With the upper clamped upside down in a vise care should be taken not to allow the hone to expand on the threads for the barrel nut. The drill chuck looks to be about 7/8" which was easy to keep centered while using about 1/2" stroke on the stones which were 1 1/4" in length.

Thanks for everyone's suggestion, pictures soon!

-Will-

[Wally Bear]

Well played sir.

[ctrmass]

I have toe opposite problem with my upper/extension fitment..