In order to press the receiver onto the barrel we need to have at least one fixture that will time the barrel to the receiver. This will ensure that the gas block and the sights are properly aligned. The second fixture is needed to provide some place to press on.
The rear of the receiver has a ~6.1 degree taper on the rear. Which concerns me, I want to press the receiver onto the barrel as straight as possible. Pressing against a slanted surface may make it difficult to get a smooth straight press. The purpose of this fixture is to offer a square surface to press against.
As with the barrel blocks, I may have over complicated this. I already know if I was to do this again I would have done it differently. The concept I think is good but the construction, I could have done better.
I made this out of aluminum flat stock. I tried my hand at using aluminum soldering. The hardest part was clamping the part in such a way to get a good heat sink. Since aluminum is an excellent heat conductor it wasn’t hard to heat one side up only to have the newly soldered part to come loose.
I did not take very many pictures of the actual construction as I had my hands full. Here is the completed result.
When clamped to the receiver two things become obvious. The gap, and the lack of support under the gap.
After giving it some thought I figured the easiest way to fill the gap, and provide more support was to use JB Weld. It’s an epoxy that is supposed to be pretty tough. I’ve used it a couple time in other projects, and it seems to do well enough. Since the primary force will be compression think it will hold up ok to the job. This would not be the approach I’d take if I was making a jig for production, but for a one off build, I think it’s fine.
Do do this I applied some electrical tape to masked of the receiver. I placed a small piece of aluminum in the crevice to fill some of the space so that not all of the wedge was made up of aluminum.
JB Weld takes about 24 hrs to set up. Once I filled the gap I set the piece aside. I also applied the JB Weld around joints that I had Aluminum Soldered in place. Honestly I wasn’t real confident in the solder joints.
The fixture is now complete. It definitely is not pretty, and I am skeptical it will hold together for more then one or two uses. This is a one off build so as long as it holds together for one build then I’ll stick with it. There are things that I would do differently.
The stringers don’t need to be long. Just enough to hold it in place with a C-Clamp. By notching the plate and slipping the stringers into the notch, the joint becomes far stronger. In order to accommodate this the plate dimensionally is changed from a 1.50×1.50 piece to 1.50×1.75. Pretty simple, this is one of the many instances where you get to benefit from my mistakes.