Acraglass at 110 degrees F

R

RickD

Moderator
I just got my Savage 10FP back from SharpShooterSupply. I decided to spend a small chunk of change (about $50) to have them true up the action, barrel, boltface, and install a machined recoil lug.

The diagram they gave me showed that the rifle was pretty close to tolerances. The receiver/barrel area was out just 3-thousandths of an inch, and the rest of the measurements such as boltface squareness and lug contact area were much better than that. He told me that he sees all sorts of rifles that are 15 thousandths or worse out of whack, including newer Remingtons, Savages and the rest. My brother had a rifle that was 15-thousandths out of spec. When he got it back from SSS, the point of impact changed 13 inches. That's a lot of scope adjustment.

So, I decided today to glass bed my action. To make a short story even shorter, the directions said that I would have about 10 minutes after doing the 4-minute mixing routine to apply the resin. Of course, that time frame is when the temperature is 70 degrees F. My Phoenix garage was toasting at about 110 F.

I had just applied the resin to the pillars and recoil lug junction about 2 minutes after the final mixing stir when my wife said, "Why is that black gunk in your paper cup steaming." I told her that it was supposed to get very hot. Then I noticed what appeared to be a hard shell forming in the cup.

Oh, hell. The resin on the stock was evidently not as hot as the resin in my cup, so I quickly slapped in the barreled action to the stock and torqued down the screws.

Tomorrow morning will tell if I hosed this thing as much as I think I did. A good chisel will be needed to redo this, I suspect. ;)

Live and learn.

Rick
 
I de-stocked the barreled action this morning. The pillars appear to be nicely glassed. The recoil lug area, as I suspected, will have to be re-applied, but that was likely to happen anyway.

After I get the stock bedded, I am going to bend the forearm down (pre-load) and apply JB Weld there to stiffen it up. It will look hacked by it will function.

Rick
 
If you want vertical preload on the barrel, why not use rubber or plastic spacer? Can change spacer thickness to vary the preload.

Or a threaded bushing and screw with a saddle of plastic to bear against the barrel.

Sam......thinking hurts sometimes.
 
One of the things that Brownell's fails to tell folks about Acraglass is that you must mix SMALL quantities of it. No more than 10 CCs at a time.

All epoxies are exothermic, and Acraglass is notorious for undergoing "uncontrolled polymerization with subsequent violent exothermic reaction" when there is too much reacting thermal mass in the cup. The additional mass accelerates the problem.
The added heat in the garage futher compounded the problem by increasing the latent heat in the components prior to mixing.
one way to reduce this problem is to refrigerate the components before mixing. Don't allow them to freeze, but get them down to about 50 F, then mix. Pot life is increased a bit, and the exotherm is retarded until you can get the stuff distributed in the bond/bed areas.

Epoxies that have undergone too sharp an increase in temperature during curing are prone to cracking and other problems due to their reduced density (because of excessive thermal expansion that can not shrink back prior to cure) and broken (heat sheared) DGEBA rings in the resulting polymer.
 
Or I coulda just placed the Dixie cup in a water bath.

I only mixed one-half ounce of the resin. Far less than their directions suggested (for those lining the stock as well.

When I mixed up a small quantity of resin to redo my recoil lug area I had no such problem. The garage was a little cooler, maybe 103F. But the mixture that remains in the cup, after six hours is not yet hardened (did I use enough hardner?). It is now about the consistancy of a hot-glue stick and, I hope, getting harder. I don't want to have to remove that stuff and do it again, but I will.

I found the measurements to my Savage, prior to them truing it that SharpShooterSupply sent with my gun. In inches:

Receiver Face Squareness: 0.003 T.I.R.
Barrel Locknut Squareness: 0.004 T.I.R.

Recoil Lug Flatness:
Top 0.1915 Bottom 0.1965

Bolt Face Concentricity:
In back: 0.0005
In front: 0.001

Bolt Face Flatness:
-0.0015 in center
 
I don't understand why people use acraglass when they can use a better epoxy like Marine-Tex (get it at your local boating supply for a LOT less). M-T is easier to use, can be machined easily, and is stronger. Won't crystalize/break down easily, so it lasts longer in the stock. Working time with liquid hardener is longer, paste hardener is shorter. Less shrinkage than most others, too.
 
It's not used by gunnies because it is sold in boat shops, not gun shops. Of course, I'm gonna JB Weld my stock for stiffness and got it at the autoshop, but that's a more common area. Maybe I shoulda used JB for the pillar beds as well?
 
Third time is a charm

My second attempt at glassing the action still didn't cover the recoil lug adequately. The third time did it.

After I get done with this week's Freedom Summit www.freedomsummit.com I will JB Weld the forearm to give it some rigidity and extra clearance from my barrel. Then it's off to the reloading room and the range to see how things *really* went.

Rick
 
JB Weld Results

I put the 10FP in a vise with the barreled action torqued down to the stock. I nailed a 2x4 to the workbench to act as a fulcrum. I used kevlar string (cuz that's what I have) to crank the stock down from the front swivel to create a gap between forearm and barrel.

I then removed the barreled action from the stock and mixed up a rather large couple of batches of JB-Weld. I had planned to put something stiff in the forearm slot like a fiberglass arrowshaft or the pushrod from a Ford 289 V8, but I decided not to.

I glopped the goop in there and let it set for about 24 hours.

I came back after work the next day and plopped the barreled action in the stock and cranked it down.

Yep, the forearm was stiffer, but not much stiffer. And I did have a nice gap between the barrel and stock.

And then after about an hour or so, I noticed the gap becoming smaller and smaller. It now is about the same gap as when I started.

Oh well.

Time to mount the scope and go shootin' next Sunday.

Rick
 
Here's a "Rookie" type question!
What's wrong with "Bondo"?
I know it shrinks some, but other than
that what's wrong with it?
You can find that stuff everywhere!
TF
 
My favorite remains Acraglas (tm) GEL. Wish their dye came in a reclosable container. I've also used regular and fast-set JB with similar results, though now I don't really trust JB because it has proven so brittle in other applications.

Any sources for powdered stainless steel or other additives to improve the epoxy? I'm quite interested even in fiberglass or maybe shor-fiber nylon to improve the impact resistance.

As my tool kit has grown over the years, I'm toying with the idea of doing more "glass" bedding in a few months...
 
If you like Brownells Acraglass. They have a version with powdered steel - called Acrasteel I think.

didn't know about Marine Tex. Thanks for the rec.
 
Those chemical compounds can be dangerous...
I used an off the shelf radiator repair kit that contained a two part packet of resin and activator. The label says: (in a nutshell)
You break the seal between the two sides and mix. When you start to feel some warmth, its ready to use.
Okay...
Mixing, mixing... okay its warm... cut open with scissors... gettign warmer... I apply a portion and work on the mesh... apply the covering coat...
OUCH! SHEARING BURNING PAIN!
That packet turned in just a matter of seconds into a hard little lump of burning coal! WARM MY BUTT! I had BLISTERS!
It fixed that leak sure... but welded my wifes new scissors too!
I had to ditch them into the dumpster. "Honey, Where are my new scissors?" Uh... think fast George... "Did you check the draw in the hall closet?" She went back in and I made a fast run to the scissor store. It all turned out okay... that lump... was still hot an hour later.
 
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