Dave;
Looks like you've got a lot of good advice on tracks.
As for the barrels, I like to use the aftermarket turned aluminum or brass ones. If you can't, don't want to, or just want to have the fun of building up the plastic halves:
1- clean the barrel halves of flash, mold parting lines, sprue attachment points, etc.
2- tape or hold the barrel halves together
3- slide a single edge razor blade between the barrel halves on one side.
4- using liquid styrene cement, touch the brush on the razor blade near the barrel halves. Capilary action will draw the cement from the razor blade and into the joint. Try to get enough glue on so that as the plastic softens, a little of it "guishes" (another technical term) out of the seam, but not too much to be messy. Be careful not to let anything touch the soft plastic.
5- move the razor blade down the length of the barrel a bit and apply more glue.
6- keep doing this until you've worked your way around the barrel and have glue through the whole joint.
7- align the barrel halves so they are in alignment and round for the whole barrel.
8- carefully clamp it and check the alignment again.
9- Let the glue set hard.
10- unclamp the barrel, scrape, then sand and polish the joint all the way around carefully to not get flat spots (flex-i-files are supposed to be fantastic for this).
Doing it this way, you shouldn't have to use any filler, and it's really easy to scrape the excess plastic from the joint.
Good luck
Bill
Bill
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DML M4A2 Red Army
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-- There is a fine line between "hobby" and "mental illness". (Author unknown)