PDF of Army testing of G3 and early 93 rifles

[holescreek]

Hopefully the forum will allow a PDF of this size, Someone just posted this on another forum. Very interesting reading for us DRLB geeks. Great test info!

Click here to download (http://www.militaryfirearm.com/Forum/Tanker/USAhktest.pdf)

[M1 Tanker]

Holes, if you email it to me m1tanker(at)militaryfirearm.com I'll post it.

[holescreek]

Thanks! It is on it's way.

[M1 Tanker]

File uploaded!

[hunter_la5]

Awesome stuff, thanks for posting this y'all! :rockon:

[hansellhd]

Good Stuff, thanks again.
HDH.

[FiremanFrank]

Thanks for posting.

[Patria Povo]

Wow, what a find! Thanks for sharing that with us.

[shibbykins]

that was a good read

[HKILLER]

yup that was interesting.

[Perro Del Diablo]

excellant!!
now i have the formula for the force required to overcome the bolt locking lever and spring

but they missed something completely, or maybe in my fast skim i missed it (will have to reread this several times)

who here is super uber duber smart at math that can help me take there formula for bolt locking lever and factor in the amount of preload on the Bolt Locking Lever caused by different gap??


there formula of the force required to overcome the bolt locking lever and spring is

F2 tan a must be larger than Fs (or the strength of the bolt locking lever spring) and a is the angle on the bolt locking lever and bolt shoulder
how do i calculate how much delay is reduced by preloading the bolt locking lever higher towards the top of the bolt shoulder??
knowing this will prove how much bolt gap affects delay

[Perro Del Diablo]

after rereading i noticed a few things that jumped out at me.

1. they did not put lead in the carriers of the production 33s, they used Tungsten.
(these are prototype guns for testing of course, and we know that the HK33 doesnt have a bolt hold open either ) they used tungsten to weight there bolts, not lead - tungsten is heavier than lead by 1.7 times


2. they talk about putting a shim in between the bolt head and bolt carrier to ease unlocking, and to further increase the bounce of the bolt carrier upon impact.
#1, adding a shim in between the bolt head and bolt carrier does not increase the ease of the bolt system to open. When pressure is put on the bolt head the rollers force the carrier away from the bolt head at a 1:3 ratio and the pressure is not being put on the shim at all, the pressure is on the rollers, locking piece, trunnion, and forward walls of the bolt head roller window.

they go on to say that the shim was .018 inches thick and it only increased the rate of fire 10-50 shots per minute
BUT there factory NEW example had only .014 inches gap to begin with which means there shim would have held the carrier open by .004 inches
there used example had .008 inches gap which means the washer would have held the carrier open by .010 inches
the reason for the increase in the rate of fire is because the washer was preloading the bolt locking lever more which decreases delay or the amount of time the carrier stays shut - this is why the rate of fire changed from 10 shots per minute (most likely on the newer bolt set) to 50 shots per minute (most likely on the well used bolt set)

the shim is also keeping the bolt system from being completely locked 100% like it should be. The carrier is being held from pushing the locking piece forward, and the shim is preventing the locking piece from shoving the rollers tight into the trunnion and bolt head forward wall.


more as i reread this great study!!

[holescreek]

I only read the first 32 pages at a fairly fast clip but some of the things I read didn't add up. I will also have to re-read it several times in it's entirety. Somewhere around page 28 IIRC where they showed their math they talk about the angles of the LP's all being 60 degrees. At first glance I thought that the x51 should have been 50 degrees, then I remembered that based on what we've seen in the type study, it very well could've been 60 degrees. The big thing I was looking for was what they found the trunnion angle to be and I don't think they knew as it wasn't stated but rather eluded to.

This came up on another board (AKFiles) because someone wanted to know how to check their bolt gap on a 33. The correct info was given as to how, but the gap info given was wrong. The poster used this report as proof that the gap should measure between .010-.014". Frankly, I was just glad to have snagged the report.

[Flesh Thorn]

there formula of the force required to overcome the bolt locking lever and spring is

F2 tan a must be larger than Fs (or the strength of the bolt locking lever spring) and a is the angle on the bolt locking lever and bolt shoulder
how do i calculate how much delay is reduced by preloading the bolt locking lever higher towards the top of the bolt shoulder??
knowing this will prove how much bolt gap affects delay

Wouldn't positioning the lever higher on the bevel (preload)compress the spring and increase Fs ? Just looking at the the data in the PDF, a worn locking spring and lever bevel edge requires less F2. A lower F2 allows earlier unlocking and increases the velocity of the bolt group. Just bear with me. I think I understand where you are wanting to go with this, but I may be missing something. I don't think we need to actually calculate anything as long as we can grasp what is occurring.

[Flesh Thorn]

Aaaahhhh.....I think I follow you now.

Lets say it takes Fs to compress the spring enough to unlock.

Fs< Fpl + F2 tan α : Fpl being the pre-load applied by positing the lever higher on the bevel. In effect, we are decreasing the F2 required to overcome Fs.

Force (Fpl) = k(DStanding - DDeflected)

Fs< k(DStanding - DDeflected)+ F2 tan α


k = Spring constant determined by experiment or calculation.

We could probably calculate the amount of deflection with respect to the position on the bevel edge. We probably don't need to actual have a value for k to explain the relationship. Of course I may be all wrong.

[Perro Del Diablo]

In effect, we are decreasing the F2 required to overcome Fs.

yes, the more bolt gap you have, and the higher the bolt locking lever sits on the bolt shoulder = the less force required to unlock

also the less distance required for the bolt carrier to travel rearwards before the BLL is clear of the bolt shoulder which also decreases time the bolt stays locked.

im no math wizard so give me a bit of time to digest your formula, and any examples would be beneficial to me!!
i use trig at work, but im only good with my particular application of bending conduit

[weasel_master]

Flesh, I follow you. I'll have to read the report for the formulas. Give me a little time but between the math needed for my EE degree and my math degree, I should be able to get it.

[bladeworks123]

Very enlightening, I think there was some conjecture in here like Perro says, but for the most part it makes some pretty good sense, and closes up some holes in some of my questions too. I'm glad we have some geometry folks here.

Anyway, thanks for sharing this one....

[Flesh Thorn]

I think I now understand why some who have PTRs that will not perform with tar sealed ammo have had luck swapping out the locking lever spring. It speeds up the extraction a bit plus not as much force is required to cycle. I have such a PTR and I am tempted to try a slightly weaker spring to see if it has any effect.