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Milsurp OAL vs SAAMI OAL

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Sawbones View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sawbones Quote  Post ReplyReply Direct Link To This Post Posted: May 22 2022 at 9:55am
SAAMI rationale for OAL of 1.680?  Any ideas?  Could it have something to do w/ the lands?  Some sort of pressure deal?
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Matt_X View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matt_X Quote  Post ReplyReply Direct Link To This Post Posted: May 22 2022 at 2:07pm
Originally posted by Matt_X Matt_X wrote:

  Some place I recently read an explanation of why the military velocities WW2 era were much further out. 


Answer:
The early digital ballistic chronographs were built with vacuum tube logic for counting a crystal time base. The crystals were ultimately traceable to the old Bureau of Standards. I don't know the details of the proximity sensing coil system that was developed between the wars for use in place of breakwires as part of a portable system. I only know that, like the electromechanical devices from the 19th century, its response was slow. Without digital logic, the analog instruments need to make a big enough trace or meter movement to resolve small bits of time. That's why the first screen (wire or coil) was at 6 feet and the second was way out at 150 feet, for an average of 78 feet. That's where the military 78 foot rifle velocity measuring distance came from.
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Nick

We see velocity discussed in documents related to the cartridge development and changes.  This is probably velocity at 78 feet from muzzle.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: May 22 2022 at 6:32pm
Originally posted by Sawbones Sawbones wrote:

SAAMI rationale for OAL of 1.680?  Any ideas?  Could it have something to do w/ the lands?  Some sort of pressure deal?

Must also consider the longest round that would fit and feed from the magazine. I guess it depends from which end they designed for, the action length or the cartridge length. If they went from action length, one has to consider the oal of the round that will fit the magazine. They could have easily made the chamber longer than 33mm, but the action would have to fit the oal.
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Dan Pinto, Photo Editor

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Post Options Post Options   Thanks (0) Thanks(0)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: May 23 2022 at 1:55pm
@Sawbones, What carbine and serial range are you using?
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Sawbones View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sawbones Quote  Post ReplyReply Direct Link To This Post Posted: May 25 2022 at 3:48pm
So sorry for the late response.  For reason unknown the Forum is not alerting me of replies.
Quality Hardware 1,583,8XX
I think this one was a Closet Queen.  Obviously sat in a closet somewhere since 1943 birth. Stock is beautiful walnut w/ few handling marks and all working parts show little wear.
The best thing about this group of candidates is only one of them can win. Will Rogers
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Dan Pinto, Photo Editor

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Post Options Post Options   Thanks (0) Thanks(0)   Quote New2brass Quote  Post ReplyReply Direct Link To This Post Posted: May 26 2022 at 3:09pm
So your carbine was made early to mid 1943.
In the links below we discussed that the barrel chamber was changed in June of 1943. Basically from that point on all ammunition on hand was reserved for stateside and the new profile ammunition went to the theaters of operation.
The new ammo worked in early and late barrels, but the old ammunition may have problems in the new barrels.

In reality any new made ammunition should be to the latest standards, but if not held to the standard it is possible that there may be an issue in an early barrel.




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Matt_X View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matt_X Quote  Post ReplyReply Direct Link To This Post Posted: Jul 09 2022 at 12:59pm
Originally posted by Sawbones Sawbones wrote:

...the milsurp stuff, namely  Evansville Cartridge Company 1944 and Lake City 1952 all measured 1.665 +/- 0.002"


I bought an unopened box of M13 Dummy cartridges made by Winchester Repeating Arms Co. lot 22038.   Opening the box they are all stamped WRA * 44.

Overall length 1.675" + .001" /- .002"
Measured with vernier caliper.
Sample size of 10
Standard deviation .0011"

So far the military contract ammo is all within the drawing specs of 1.660 to 1.680"

Case length measurements average 1.285"  with std dev of .00158"
Measuring the case length with the bullet installed probably reduces the consistance of my masurements using a caliper.

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Matt_X View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matt_X Quote  Post ReplyReply Direct Link To This Post Posted: Jul 27 2022 at 1:14pm
1971 Lake City  50-205   From an original box that was a bit beat up.

Overall length 1.676" + .004" /- .003"
Measured with vernier caliper.
Sample size of 10
Standard deviation .0024"

Average case length 1.283"


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