1968 report on XM177E2 ballistics

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[ARCHIVED THREAD] - 1968 report on XM177E2 ballistics

Posted: 9/10/2010 7:28:08 PM EDT

Came across this while trying to find a .pdf of the XM177E2 manual:

LAUNCH CHARACTERISTICS OF THE M-193 (BALL) AND M-196 (TRACER) PROJECTILES FROM THE XM177E2 SUBMACHINE GUN

Things I learned:

Moderator-induced POI shift — Unsurprisingly, build-up of crap inside those baffled moderators seems to have resulted in a significant change in point-of-impact over time. "The shift from no suppressor to the [suppressor with 9200 rounds fired through it] appeared to be about 60 centimeters at 73 meters from the muzzle (approximately 9 mils)." Another good reason to abandon the baffled moderator for a regular flash hider / 14.5" barrel on later carbine models.

Dispersion — Without moderator, the XM177E2 firing ball ammo averaged very similarly to the M16A1 rifle tested, at about .31 mils or 1.05 MOA. But with a moderator used for 1000 rounds, it averaged .57 mils (1.92 MOA), and accuracy grew progressively worse with longer-used moderators (0.85 mils / 2.87 MOA after 9200 rounds). This was with changing just the moderator, not using a barrel that had 9200 rounds through it, so barrel wear would not be a factor.

Muzzle Velocity — "The muzzle velocity, although not yet well known, appears to be on the order of 865 m/s (2838 ft/s) for both M-193 and M-196 projectiles."

All in all, it makes me happy about my non-NFA clone with fake moderator by Brick.

Anyway, anyone know where I can get good .pdf copies of retro manuals like I was originally looking for?

Posted: 9/11/2010 7:51:44 AM EDT

[#1]

Great info., thanks for sharing!

Posted: 9/11/2010 8:07:29 AM EDT

[#2]

Although I like the Viet Nam era "shorty" models from a historic perspective, they are the worst of both worlds with muzzle blast and loss of velocity.

The later 14.5" carbines are a much more efficient use of real estate on the front end.

Posted: 9/11/2010 11:46:55 AM EDT

[#3]

clean the moderator

Posted: 9/11/2010 12:19:13 PM EDT

[#4]

Quoted:
clean the moderator

You couldn't- they were a two part affair that was welded closed when manufactured, there was no way to take it apart to clean the baffles. It may look cool but it was a really poor design in size, effectiveness, and maintainability.

Posted: 9/12/2010 2:28:16 AM EDT

[#5]

Now I am curious if Brick's moderator clones have this problem if you let them get filthy. I assume you can readily clean his since there's no baffles.

Posted: 9/12/2010 5:35:10 AM EDT

[#6]

Quoted:
Now I am curious if Brick's moderator clones have this problem if you let them get filthy. I assume you can readily clean his since there's no baffles.

His do not have baffles so cleaning is not an issue.

Somewhere around here there is a picture of a cutaway original moderator, and it is easy to see why it gets clogged up so bad- lots of little channels and such running through it.

Posted: 9/12/2010 6:36:47 AM EDT

[#7]

Quoted:

Quoted:
Now I am curious if Brick's moderator clones have this problem if you let them get filthy. I assume you can readily clean his since there's no baffles.

His do not have baffles so cleaning is not an issue.

Somewhere around here there is a picture of a cutaway original moderator, and it is easy to see why it gets clogged up so bad- lots of little channels and such running through it.

+1 for ^^^^^ And Bricks moderator inside hole diameter is just a tad larger then the barrel inside diameter,so you can get real clean using a chamber brush if you feel the need.But as said above,there are no baffles to deal with so it's just like cleaning the rest of the barrel. Beautifully made item he makes!!!!!

[ARCHIVED THREAD] - 1968 report on XM177E2 ballistics

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