I'm finishing an MPI semi-inlet stock and removed too much of the foam in the barrel channel. It will take more epoxy to fill back up than I want - even wrapping a lot of bedding tape around the barrel (the channel is not barrel shaped, more U shaped.

Option 1 is to mix Acraglass with 50/50 volume with micro balloons. I've done 1/3 volume ratio before of micro balloons. It was lighter than straight epoxy but not as light as foam. Do you think 50/50 will be light enough? Can I go higher? 2/3 micro balloons by volume?

Option 2 is to build the foam back up in the channel. This is what I think would be best, but not sure the best way to go about this. My plan was to sufficiently wrap the barrel with bedding tape to give me enough room for a final epoxy coat to seal the foam and room to float the barrel. Since the action is already bedded I could tape the barrel to the stock at several places along the stock and use some sort of expanding foam to fill the gap. This would prevent the foam from pushing the barrel out. Thought about the foam used for door and windows which has minimal to little bowing. The other option is using a pourable urethane foam. Any suggestions on either of these ideas?

Any thoughts would be appreciated!

Thanks!

That self-expanding door and window foam might work structurally but when you trim it back flush and finish the channel it’s going to be full of tiny air pockets, like a sponge. You’d have to skim coat it with something solid before paint for it to look right

quote:

Originally posted by kala_azar:
That self-expanding door and window foam might work structurally but when you trim it back flush and finish the channel it’s going to be full of tiny air pockets, like a sponge. You’d have to skim coat it with something solid before paint for it to look right

Yes, I planned to heavily tape the barrel and then remove half the tape and do a skim coat bed with epoxy.

Put a wrap of fiberglass cloth on the outside of your barrel tape wrap. That way it will stick to the foam and you could smooth a layer of epoxy on the cloth afterwards and add a bit of strength. This is just an idea...I've never tried it!

what's the max % of microballons that I can mix with acraglass? I calculated if I used 2:1 microballoons to AG that the fill will weigh around 1 oz. Around 1.5 oz if I do 50/50.

quote:

Originally posted by Austin Hunter:
what's the max % of microballons that I can mix with acraglass? I calculated if I used 2:1 microballoons to AG that the fill will weigh around 1 oz. Around 1.5 oz if I do 50/50.

You're worried about .5 ozs ?

dry micro ? and flock?

Clean up the sides and front of the forend and then leave the bottom as open air space?

quote:

Originally posted by Mike Scott:
Clean up the sides and front of the forend and then leave the bottom as open air space?

I mixed up some 2:1 MB to AG ratio as a test and am waiting to see the results.

On the deepest areas I thought about just gluing some thin pieces of foam I have and just covering them.

I be real careful with the house hold stuff my brother was sealing a crack some leaked inside and touched a barrel.

left a very nasty pit and spot.

Do not use Acraglss, it already has a lot of fillers. Get plain epoxy and mix in micro balloons until it is a thick putty.

The spray foam is no good for anything but filling cracks, it has near no strength and does not cure in a thick cross section. The two part urethane foam is good. Comes in many densities.
I do composite work building large model rockets. Www.tripoli.org

M

This stuff looks pretty easy to use and Amazon carries it.

https://www.smooth-on.com/products/foam-it-3/

i wouldn't use expanding foam .. well, i might would, but the cost to acquire from new makes it a hassle .. fact is, you could fit in some styrofoam, shape it, and skip with AG .. or get REAL cotton balls, tear into tufts, mix with AG in a DRY mix, ... etc etc etc ...

There are light weight two-part fiberglass repair compounds that are pre-mixed with fibers for strength. A place like West Marine or Amazon would be a good start.

route it square and cut a piece of balsawood re-inlet and glass bed.

quote:

Originally posted by richj:
route it square and cut a piece of balsawood re-inlet and glass bed.

Balsawood is an excellent idea!

I have some sheets of thin foam - the type that you see in boxes of custom ammo that protect the tips. I think I will layer this. Just need to experiment with an adhesive to hold it in place and together without melting the stuff. Might just use acraglas to hold in place.

3M makes a spray adhesive formulated just for foam. I have used it to laminate the stuff used for Army sleeping mats. I have also laminated the blue sheet foam used in new home construction. My application was building up a base for scenery in a model diorama, but it held up just fine while shaping it with this thing:

thanks for the 3M lead!

It's this stuff.



Want me to drop off a can with Mark Pharr?

I decided just to go with 50/50 Microballoons and AG. It only added .66 ounces.

I've used that 3M stuff to attach felt/cotton to foamcore poster board for a fitted rifle case.

Yeah I thought of it when I saw a fiberglass benchrest stock for sale recently. Wrong barrel channel, but wow, what a paint job. I may try it next time that kind of thing comes up.

Some years ago bsing with a house builder putting on tyvex insulation I asked if he knew the difference between Tyvex and Tovex.

He didn't. IF you don't, check it out sometime just for laughs.

George