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Armor/AFV: Modern - USA
Modern Armor, AFVs, and Support vehicles.
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Barrel length of M256 120mm
MikeyBugs95
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Posted: Tuesday, March 14, 2017 - 07:09 AM UTC
I know that the length of the barrel is 17.3 feet long but measuring up to where? Is it from the end of the breech? Or where the barrel first exits from the turret? Can anyone mark it on this diagram?
jon_a_its
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Posted: Tuesday, March 14, 2017 - 03:34 PM UTC
Traditionally, the gun barrel length is measured in multiples of the calibre, excluding the breech assembly, here to the right of the trunnion ring, but exactly where isn't apparent on this diagram
GTDeath13
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Posted: Tuesday, March 14, 2017 - 08:04 PM UTC
Do these pics help?



MikeyBugs95
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Posted: Tuesday, March 14, 2017 - 08:33 PM UTC
Yup! The helps! Thank you!
MikeyBugs95
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Posted: Friday, March 24, 2017 - 04:30 AM UTC
Does anyone know what the shape of the bore evacuator is? Is it circular or oval-ish?
HeavyArty
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Posted: Friday, March 24, 2017 - 05:15 AM UTC

Quoted Text

Does anyone know what the shape of the bore evacuator is? Is it circular or oval-ish?



Yes. It is both. At either end, it is circular. On the center, bulged part, it is oval.
seanmcandrews
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Posted: Friday, March 24, 2017 - 05:21 AM UTC
Looks to me like the center section's not oval but simply offset from the front and back diameters.

Sean
HeavyArty
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Posted: Friday, March 24, 2017 - 05:26 AM UTC
I guess the center is more of an oblong circle. It is not fully circular, and not treuly oval. These shows it well.

majjanelson
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Posted: Friday, March 24, 2017 - 06:02 AM UTC
To me, the larger "bulge" of the fume extractor appears to be circular, but it's center line is offset from the center line of the bore of the M256.





MikeyBugs95
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Posted: Friday, March 24, 2017 - 06:37 AM UTC
Thanks for all your help on this topic guys. I'm also airing on the side of circular. Now onto the muzzle reference sensor. I'll keep this thread updated for a short time with questions when I have them.

New question: What is the angle of the muzzle reference sensor in relation to the center line of the barrel?
Vodnik
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Posted: Friday, March 24, 2017 - 10:44 AM UTC

Quoted Text

it is oval.


No, it is circular.
Vodnik
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Posted: Friday, March 24, 2017 - 10:46 AM UTC

Quoted Text


New question: What is the angle of the muzzle reference sensor in relation to the center line of the barrel?


I don't remember the exact angle, but it is easy to determine - the angle must be such that the sensor mirror points directly to the doghouse (gunner's main sight housing).
MikeyBugs95
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Posted: Friday, March 24, 2017 - 11:35 AM UTC

Quoted Text


Quoted Text

it is oval.


No, it is circular.



Ok, good. I modeled it correctly then. Which lense in the doghouse? Or does it really matter in this scale as long as it's pointed towards the doghouse?
Vodnik
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Posted: Friday, March 24, 2017 - 02:10 PM UTC

Quoted Text


Quoted Text


Quoted Text

it is oval.


No, it is circular.



Ok, good. I modeled it correctly then. Which lense in the doghouse? Or does it really matter in this scale as long as it's pointed towards the doghouse?


I think it was the one closer to the tank centerline, but it probably doesn't matter much in this scale
MikeyBugs95
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Posted: Saturday, March 25, 2017 - 03:19 AM UTC
Ok, thank you. I will shortly have some renders to send over to you to inspect if that's fine with you, Pawel.
MikeyBugs95
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Posted: Friday, March 31, 2017 - 02:33 AM UTC
If anyone wants to inspect the drawing I have of the barrel I recently finished up, please say so. Shoot me a PM or tell me here and I'll get a drawing over to you. I need to know how accurate the barrel is before I put it up in the shapeways shop.

Pawel "Vodnik," could you send me a PM? I sent over the drawings to your PM but haven't heard back from you.
dtniedert
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Posted: Friday, March 31, 2017 - 04:01 AM UTC

Quoted Text

Thanks for all your help on this topic guys. I'm also airing on the side of circular albeit mounted non-concentrically to not cause damage during larger depression angles. Now onto the muzzle reference sensor. I'll keep this thread updated for a short time with questions when I have them.

New question: What is the angle of the muzzle reference sensor in relation to the center line of the barrel?



I believe the bore evacuator is essentially a circle within a larger circle. To be honest I never really thought too much on it though. It is non-concentric so that it will not be damaged against the tank itself while traversing at lower angles.

The MRS on the 120mm is definitely canted to which angle I do not know. I believe the 105mm was much less if not parallel to the barrel and mounted differently to boot. Also you will notice in the pic of the MRS posted by Gino P. Quintiliani the MRS is the battery powered version and not the earlier radioactive one.

ETA: The doghouse (the thing in front of the .50 cal) houses both the gunners primary sight on left and the thermal sight on the right as viewed by turret orientation not viewing angle.
MikeyBugs95
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Posted: Friday, March 31, 2017 - 04:27 AM UTC
Yeah I got everything modeled. I just need someone to check it and make sure the accuracy is within acceptable limits and then give feedback.
dtniedert
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Posted: Friday, March 31, 2017 - 04:45 AM UTC

Quoted Text

Do these pics help?






I'd actually move the barrel further back. Right about where the breech begins to angle downward and maybe a bit more even. The barrel begins where the red vertical line is in this image. http://www.inetres.com/gp/military/cv/weapon/M256/M256_M1A1_00.jpg
MikeyBugs95
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Posted: Friday, March 31, 2017 - 06:35 AM UTC
Well I would hope not. That means that the model is significantly underscale. Can we get a second (or third... Or fourth) opinion in here?

Another question... Is the Meng barrel short a few mm's?
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