I am attempting to lighten the ejector & extractor springs in a couple of
AR-15 based target rifles. My wife and I shoot in a league in May, and
it's all standing (offhand), one shot at a time. I would prefer A) not
to bounce hot brass off adjacent competitors, and B) not have to hunt for
brass flung all over the place.
One guy on our team has gone so far as to remove his ejector completely.
He ends up having to fish hot brass out of his action, which I view as a
good way to cook your trigger finger.
I have about 6 different brands of extractor springs to compare. These
are a bit special, and are conical & have to fit properly. The ejector
spring is a simple straight compression spring. I measured one, and it
is 0.103" in diameter, and just under an inch long. It's is very stiff.
For the extractor, I was thinking of comparing their strength by stacking
two of them on an 2-56 screw with a washer in between. I can use a nut
to provide some arbitrary amount of compression, and then compare how
much each one compressed. This should give me some sort of relative
strength numbers. I'm mostly interested in finding the feeblest one, but
it would nice to be a bit more quantitative.
The big problem is the ejector spring. 0.103" appears to be an odd
diameter for a spring, and it only gets compressed about a 10th of an
inch, so shortening it doesn't do much. I really need to get a softer
spring. It's awfully long & skinny to try to wind my own. Assuming I
can find someplace that will sell me small quantities in the right
diameter, I need to specify a spring constant, i.e. pounds per inch.
Does anyone have any neat tricks for measuring spring constants, and/or
suggestions for comparing the strength of small springs? I'd also like
suggestions for spring vendors who sell small quantities. I've checked
McMaster Carr, and they don't have anything that small. Brownells has
0.088" diameter, and I'm a bit concerned that is small enough to kink in
the hole. Alternatively, how can I wind a spring that small?
"Doug White" wrote: (clip) For the extractor, I was thinking of comparing
their strength by stacking
That method should work, to give you comparative values. If you want real
spring constants, you could measure their length with a pair of calipers
while hanging a weight from one end. The spring constant should be the same
for extension as compression.
To get a spring that does the job, you could rotate it lightly against a
belt sander to reduce the cross section of the wire, and measure your
progress with the "Doug White Screw Compression Method. Having a spring "in
series" with it that remains unaltered, and which is compressed the same
amount every time will enable you to see how the spring changes as you
lightly sand off metal.
I don't have the articles handy, but if someone else from the group
can check the May and July 1987 issues of the Home Shop Machinist,
there was a detailed article on coil spring making. I would not be
surprised if there was a section on measuring the results, but I don't
have the articles readily at hand to check.
I did something a whole lot simpler: I cobbled up two chopsticks, one
fixed, one (above the other) hinged. I put one spring between the sticks
at a marked point and hung a little weight off the end, and measured the
deflection. Then I put the other spring in and did the same thing. I
never measured the spring constant, but I knew for sure which spring
Ned Simm> >
It can be easy to measure spring constant with a weight measuring scale
and a distance measuring ruler. You could probably get good enough
accuracy of the "weight needed" to compress your springs some "given
distance" by placing the spring on a postage scale of the appropriate
sensitivity and push down on the spring . First, force the spring to move
some small distance and record a weight and a length reading. Then add
some force to compress the spring a little more. Those force and length
numbers provide all the data needed to identify "Pounds per Inch" of each
"Jerry" wrote: (clip) You could probably get good enough
Theoretically. What will actuaqlly happen is that there will be too much
vibration. Both the length and the force will be bouncing around so much
you won't get good readings.
On Sat, 12 Jan 2008 08:19:08 GMT, with neither quill nor qualm, "Leo
Lichtman" quickly quoth:
You'd get bounce on a balance scale, but not on a digital,
pressure-sensing type. Use ACME/SAE screw holddowns vs. your hand for
providing the down-pressure and it'll be clean. Whooee, ah
Chaos, panic, and disorder--my work here is done.
I was thinking about this, but in one case the spring is too short to
work with easily, and in the other, it's too long and flexible to keep
straight. I like the idea of adding a weight & measuring extension if I
can figure out a good way to hang on to each end.
Thanks to everyone for all the good ideas!
I thought about that, and there are aftermarket gas tubes with valves
built in. That would require a fair amount of disassembly to retrofit.
I've also heard that the gas tube valves can get clogged up & are a
royal pian to clean. I figured I'd fuss with the springs first & see how
it works out. It only takes a couple minutes to pull the bolt &
disassemble it completely so it's an easy thing to do.
Both rifles are flat tops, and have side cocking handles that will
probably require a custom deflector design. The side cocker is needed
because the adjustable butt stock has a raised cheek piece that
interferes with the standard charging handle:
I've already started thinking about how to build a deflector. Even if I
get the springs nice & light, a deflector will tend to bounce the brass
forward, which is an OK direction as long as they don't go too far. The
range is built on a swamp, and the firing line is a raised berm.
Bouncing the brass more than a few feet forward gets them in the tall
grass at the edge of the swamp. My hope is to come up with a soft
deflector that will drop them neatly on my shooting stool. if I can get
them into a cartridge box, I'll be really set...