M14 Forum

art7

I can get access to the camera if you want me to test things, but a quick math model might be easier.

The total spring energy is constant.

The energy in the hammer will be = 1/2*I*o^2, where I is the polar moment, and o is the radial velocity of the hammer (in radians/sec).
The energy in the plunger will be = 1/2*m*v^2, where the v can be calculated as a cosine function of the o of the hammer.
If you want to get really precise, you can add the mass of the spring as = 1/4*m*v^2.

This will give you a ratio of how the total energy is distributed. By changing the plunger mass in the equation, you will change the ratios slightly, and for the same total energy input, you can figure out how much faster the hammer will be.

You should be able to set this up in a spreadsheet, so you can just change the plunger mass and see hammer locktime pop out.

As stated, in my gut, the benefit will be almost negligible.

Thanks for the lead on the 762mmfirearms, I have contacted them to see if they can make me some custom hammers.

art7

Triggers are shipping now, and so are the first test batch of hammers if you want to try. $220 for the set. The only issue with the hammers is that they have not been thoroughly tested, so I don't know if e.g. the rough surface from the EDM might be a source of crack initiation with repeated shock. I am offering a money back guarantee for the $60 hammer in case there is an issue.

Art
shootingsight@nuvox.net

jmoore

Eh, miniscule change or not, with a couple of 5/32" dia. side scallops just behind the nose contact area, the spring plunger weights are now:

#1 66gr
#2 58.4gr (Which mades it a little better than 1/2 original weight!)
#3 63gr

Non-winged (early M1 Garand type) plungers seem to range from 118 to 121grs.

Easy and pretty quick mod.

Now back to hammers.

Bamban

Could I send you one to mod?

Nez

jmoore

Sure.

But it might be a while before there's opportunity to do the operations. Gotta have opening on the machine (which is not one I regularly run- not near big enough!) AND a light workload to fit it in (and permission from the suprervisor...). My friend's lathe isn't capable, otherwise scheduling would be no problem.

ETA: Or, if you want to take a chance with the commercial spring plunger that's already done, I could send it your way- consider it a "hostage swap", and would allow me to hollow out yours without time constraints. Had intended using the "commercial" plunger for testing with art7's equipment, but that won't happen immediately. (BTW, this little project had been ready to go for over a month before the opportunity arose to make chips!)

ETA1.5: It's possible that turned "commercial" plunger is Winchester mfg. Didn't occur to me until just a little while ago.

On the hammer front, a test burn with the modified electrode was started. Good enough for review purposes and decision making on the Mk.III electrode. That poor old hammer's been through the wringer! And more to come. Left side is all that's being worked so far. Right side- no tests yet! But that is a far easier cavity to generate correctly- uh, huh...suuure... The intent is a very thin web that's more on centerline to minimize torque loads.

jmoore

Whilst off on a minor tangent, here's photos:


1st attempt







Couldn't cut the oddball used plunger- too wierd! It seems to have been either machined off center, the plunger was cold headed like a nail, or the head was never turned. Regardless, it seemed to have been used quite a bit.

jmoore

A couple of unrelated but interesting things noted from watching your video.

1) Trigger overtravel to the stop is extremely fast! The sear stops moving in just a few frames. A longer overtravel could produce some degree of jarring to the system if the velocity is great enough to be noticed here.

2) The stock hammer overtravel into the trigger housing seems to distort the forward structure a fair amount. Yikes! Enough to drive the entire bolt and case forward, if the bolt has fore and aft play- which would be increased by bolt lug lapping. Makes for potentially shorter case life due to increased web stretching. So maybe the lighter hammer will help reloaders too...

jmoore

My day to hog the thread:

art7's hammer came in. (and JyWolfe's package as well)

So...:










The hammer plunger seat will need serious help before it's servicable, so some delay there. Polishing of the bolt contact surfaces won't be a big deal. It is a cheap cast hammer, but that was known. If it survives testing, then "good" hammers ought not have dramas.

ETA: No weight yet. It'll be reduced, so the first entry will be "baseline".

jmoore

Some hard numbers, now that all the players are at hand:

USGI (-2 SA) hammer: 769 grains/ 1.8oz. 100%
USGI D5546008 hammer with one sear leg missing: 747gn/ 1.7oz. 97%
art7 Mk.I hammer: 520gn/ 1.2oz. ~68%
art7 Mk.I hammer mod. 1: 490gn/ 1.1oz. ~64%
jmoore Mk.I hammer: 485gn/ 1.1oz. 63%

Just now a'fixin' to whittle on Art's Mk.I hammer. Shouldn't be too hard to shave off some meat. Just remember, I expect to "abuse" the concept until something fails!

ETA,BTW: Either the -2 hammer is lighter than a cast SAI hammer, or my math/memory is off! 881gn starting point seems heavy- need to find the old notes on the jmoore Mk.I!

ETA2:

Yet more photos! art7's Mk.I hammer after a morning's piddling "aboot".




Some off the top. Having installed it, the front scallop is too conservative.


Milled the spring plunger seat. Very hard surface! No polishing done, that's just a 1/8" carbide cutter's work.

jmoore

The first trial burn of the corrected Mk.I left hand electrode for the "jm Mk.II hammer" just emailed in.



Yee ha! Visible progress...

jmoore

399 grains, folks!



52% of the original weight.

Going to go get it right now.

May be a while before photos.

Bamban

While chasing Bambi's boyfriend in the middle of the week the hammer arrived, installed it when I got home last night, but have not done any live fire testing with it yet. Tomorrow, with Boss' permission, I should make it to the range and do some standing training.

Installing the hammer requires that the trigger adjustment screws to be backed off and re-adjusted again. And locktited again for insurance.

Initial impression on the speed hammer. I grabbed another M1A with a standard hammer and tried the triggers alternately dry firing tonight I could notice the difference.

art7

Very interesting hammer there Mr. Moore.

In your example, you will need to do multiple setups to get at both sides. I suspect the way to do this economically (assuming the market supports it) is to make an investment casting using tool steel, leaving the sear surfaces slightly fat. Then fixture it once and come in and EDM the sear surfaces and the plunger pivot seat, then heat treat.... or maybe heat treat then EDM.

This will keep a well machines sear, yet drop your part cost way down. Your tooling cost for the wax injection mold will be several thousand though, so that is why you have to be sure the volume is there.

Art

casebro

Couldn't billet CNC avoid the set up costs?

Or use stainless- soft enough to mill, tough enough to avoid heat treat costs?

But I think you two have more up to date machining experience then I do.

art7

The issue is that the time it takes a person to handle the part is a large portion of the final cost.

If you have to get it in the machine and clamp it from one side, then have the operator remove it, flip it over, and re-clamp it to machine on the other side, that will cost more.

Using a tombstone can reduce costs, if you are doing lots of parts, but it usually requires lots of parts to justify the cost of setting up the tombstone. At the 50-100 number we are talking at this point, we're not there.

At this stage, the EDM process I am using is very expensive, but since it requires very low setup cost, it is justified for the 10-20 parts I am making.

Heat treat cost is negligible. My guy has an $80 lot charge for small lots, so if you do 20+ parts, it's only a few dollars per part.

Art

Art