I am guessing the problem is that you need more "meat" for the mounting screws to grab. I'd drill out what you have to insert some 3/4" length hardwood dowels. The only question would be the diameter, but that depends a little on what screw size you are using now. I  am guessing 1/8 or 3/16 diameter dowel.

The gear is pretty "springy", so I am not sure what else you can do, except to try to slow down a bit more. If you are on grass I think you are stuck since 1/2a size gear is pretty inadequate on all but the very low cut grass field.

Hey Alan and Larry, thanks for the suggestions.  Actually I like what both of you suggested and I may try and combine them.  Lately I've been flying at a local softball field.  I've been taking off from the sand and worn down grass between the basis and flying over the outfield.  Usually the grass I fly over is two tall for a really clean landing and two short to provide much cushion from a hard landing.  As a kid, my brother and I often flew in a hay meadow--never a good landing but never much if any damage.  Later a friend and I flew often over a paved parking lot--lots of nice landings with an occasional disasterous crash.

Similar to Larry's advice.

Put a groove in the firewall to neatly contain the LG wire.
Put 2/56 blind nuts behind the firewall before attaching to the fuselage.
Use fibreglass cloth or silk to beef up the firewall attachment.
Put a thin aluminum plate between the engine and LG.

Remove the landing gear and hand launch.

This is a typical design problem with Scientific, Blackhawk,, Enterprise, Cavacraft, or any Hollow Log fuselage with "V" landing gear attached to it. You have this (relatively) huge mass of an engine and LG assembly up front, compared to a very light (airframe) mass behind. The larger mass just wants to do what it has to, which is to conform with Newtonian laws of physics, and break away when a sudden stop occurs.

Definitely go with 2-56 blind mounting nuts, as mentioned.

A lot of times, the firewall wants to come off, too. I run a wood screw, countersunk, right through the middle of the firewall, into the front of the Hollow Log. Make sure you leave a lot of beef  in the Log front. Epoxy the screw in, since you are not going to remove it.

The groove in the firewall is stamped in all of the Scientific Musciano designs where the LG lies against it, but it often is indistinct, and doesn't really cover up the music wire. This gooove needs to be enhanced if you are building from a kit, or put into any scratch model. You can do this with a Zona saw or thin hacksaw blade.

If cementing the firewall to the Log, make sure you double glue. Better still would be epoxy, the long curing type. In either event, take the Zona saw or fine hacksaw blade, and cut very thin grooves into the surface of both the Log front and the firewall back. Let the grooves in one be about 90 degrees to the grooves in the other.  This will give the adhesive of your choice more "tooth", and not simply leave it up to shear strengh to pull them apart.

Hey, they fly better without gear! (But you need a launcher, the landings aren't much to speak of, you scratch things if on pavement, etc).

Currell

When I first built my first Scientific plane I held the LG in that groove with the engine in place. After landings pried the engine off a couple of times I cut the groove deeper with my tusty X-Acto and cemented it on with gauze to hold it in place. By extending the gauze around the firewall and back about 1/2 inch, it held the firewall on better too. At that time, firewall sides were the same width as the fuselage.

Somewhere along the way, firewalls started extending past the fuselage. Not sure if the firewalls were made wider or the fuselages narrower, but they stick out.

Currell, I could not have used that screw on my first ones because I was using a Space Bug Jr.    The intake hole was in the center.

George

I believe the "oversize" firewalls in some Scientic kits were designed to fit the vacuum-former cowls (which were seldom used in flight).    When smaller stock was used for the "logs", the firewalls remained oversize.   The fix, (obvious) sand the firewall to fit the fuse and use fibreglass or gauze to hold the front end on.

...At one Musciano Meet, I talked to the son of Mr Frisoli, founder and owner of Scientific. The way Scientific saved $ was fiddling with the wings, not the fuses.  As time moved on, the newer models had 1/8" sections, not the 3/16+" ones the 50s designs had. Also, the newer models usually had 18" spans, not the larger ones often used in the 50s, such as the Bullet, Cyclone, the larger F-51, Piper Cub, Stinson Voyager, etc. And, some models had their spans reduced over time. Examples include the Thunderbird, Little Bipe, F-51 again.
 
Currell

I can understand that. Mine were all pre-seventies. They all had the nice thick airfoiled wing. All you had to do was sand the mill marks off and you had a decent airfoil. 'Course the first few were built with such haste that some (most?) of the mill marks were still visible. Couple coats of clear, couple coats of color...off to the field.

I think most of the Scientifics I built "back in the day" had "Little" in the name: Little Mustang, Little Bipe, Little Devil, etc.

George