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Timing Analysis of Unlocking Cycle for M1 and M14

This is a discussion on Timing Analysis of Unlocking Cycle for M1 and M14 within the Reference forums, part of the M14 M1A Forum category; Timing Analysis of Unlocking Cycle for the M1 and M14 Rifles The unlocking cycle of the M1 Garand and M14 rifles was tested in 1957 ...


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Old December 31st, 2009, 04:24 PM   #1
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Timing Analysis of Unlocking Cycle for M1 and M14

Timing Analysis of Unlocking Cycle for the M1 and M14 Rifles

The unlocking cycle of the M1 Garand and M14 rifles was tested in 1957 by Springfield Armory. The purpose of the test was to determine the average time (in milliseconds) from firing pin contact to:

a. Bullet passing the gas port
b. Bullet exit
c. Initiation of operating rod recoil
d. End of operating rod dwell
e. Completion of bolt unlocking
f. Position of bullet at initiation of operating rod recoil
g. Position of bullet at end of operating rod dwell
h. Position of bullet at completion of bolt unlocking

Three single rounds were fired from each of three M1 and three M14 (T44E4) rifles. The ammunition used was M2 AP for the M1 rifles and armor piercing (T93E1 or T93E2) cartridges for the M14 rifles. Each rifle was fully loaded for each series of three shots. High speed motion picture cameras (operating at 6,000 to 7,000 frames per second) and flash strobes were used to record hammer fall, bullet exit, operating rod movement and bolt unlocking during each firing sequence. Lumiline screens were used to record average bullet velocity at a distance of 53 feet forward of the muzzle. The film was analyzed to obtain the data below. Average values were computed from the high speed film as follows:

Data Item M1 Rifle M14 Rifle
Type of gas system gas impingement gas cut-off and expansion
Location of gas port from muzzle 1.5 “ 8.0 “
Gas port diameter 0.0793 “ 0.0768 “
Barrel length 24 “ 22 “
End of hammer fall 0 milliseconds 0 milliseconds
Bullet passes gas port 1.31 milliseconds 1.01 milliseconds
Bullet clears muzzle 1.36 milliseconds 1.25 milliseconds
Initiation of operating rod recoil 1.58 milliseconds 1.53 milliseconds
End of operating rod dwell 2.89 milliseconds 3.57 milliseconds
Completion of bolt unlocking 4.07 milliseconds 5.00 milliseconds
Amount of bullet travel at start of op rod recoil 7.2 “ past the muzzle 9.2 “ past the muzzle
Position of bullet at end of op rod dwell 50.2 “ past the muzzle 76.1 “ past the muzzle
Position of bullet at completion of bolt unlocking 88.9 “ past the muzzle 123.0 “ past the muzzle
Average bullet velocity 2735 feet per second 2733 feet per second

Reference: Springfield Armory Technical Note SA-TN11-1094 dated 16 Dec 1957

Thanks from 2336USMC, CNelson, jmoore and 4 others
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Old January 1st, 2010, 11:41 AM   #2
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Thanks Different

So doesn't this eliminate the movement of the the gas system from the accuracy questions? The bullet has left the barrel before the op rod or piston moves? Lee did you get this from the book "The M1 Grand to the M14" by Stevens? I thought I read it in there. Also Lee are you going to the Shot show again in Vegas? Anyways Happy New Year to all and may it be a peaceful and prosperous year.

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Old January 1st, 2010, 12:01 PM   #3
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Quote:
Originally Posted by Full Auto M-14 View Post
So doesn't this eliminate the movement of the the gas system from the accuracy questions? The bullet has left the barrel before the op rod or piston moves? Lee did you get this from the book "The M1 Grand to the M14" by Stevens? I thought I read it in there. Also Lee are you going to the Shot show again in Vegas?
1. No, changes to the gas system can affect accuracy because of how they affect travel time of the bullet inside the barrel. Though small, changing gas pistons or modifying the geometry of parts will change the gas volume. Change the gas volume and you change the gas pressure. Change the gas pressure and you change the amount of time it takes the bullet to leave the muzzle. These changes are on the order of hundredths or thousandths of a millisecond but they result in increasing or decreasing POI dispersion, e.g., swapping out gas pistons with no other changes made. I refer the reader to the links below.
2. Yes
3. No, you read Technical Report SA-TR11-2610 which was a 1954 comparsion of the two gas systems being considered for the T44 (Stevens pages 183 - 186). The 1957 SA-TN11-1094 test was a more exacting analysis of the unlocking cycle of the two types of gas systems using the M1 and the T44E4 rifles.
4. Yes


Last edited by Different; January 3rd, 2010 at 03:55 PM.
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Old January 1st, 2010, 02:35 PM   #4
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Thanks for posting this Different. Great info, I have copied it into my permanent stash of info.

Fascinating that the M14 bolt fully rotates and unlocks in 1.4 msec. That's fast.

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Old January 1st, 2010, 03:00 PM   #5
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Great data, Lee! This should be a sticky.

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Old January 1st, 2010, 03:58 PM   #6
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1. No, changes to the gas system can affect accuracy because of how they affect barrel vibration.
Lee, have you read any of these studies/theories about barrel vibration??

http://www.the-long-family.com/OBT_paper.htm

http://www.the-long-family.com/OBT%20tool.xls

http://www.the-long-family.com/OBT%20Table.pdf

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Old January 1st, 2010, 04:15 PM   #7
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tjh121, no, I have not. Thanks for the links. I'll read them. If it's appropriate for me to respond in this thread, I will. Thanks again.

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Old January 3rd, 2010, 05:01 AM   #8
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Lee thanks this is great info and it is on a subject I never was able to get a good answer on.

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Old January 3rd, 2010, 06:02 AM   #9
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nice find thanks for posting it.

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Old January 3rd, 2010, 03:47 PM   #10
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tjh121, I read the links. I agree with Chris Long's Shock Wave Theory. I have modified my answer to question # 1 posed by Full Auto M-14.

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Old January 6th, 2010, 03:48 PM   #11
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Lee, IF you reload, is there a chance of getting your results with various powders/charge weights? I'm guessing that being in Nevada right now is better in terms of "range time" than being in Nebraska (the low temps within the next 48-to-60 hours are predicted to go into the MINUS 20 degree range)?

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Old January 8th, 2010, 06:56 AM   #12
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Sorry, I don't reload ammunition, just magazines.

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Old January 25th, 2015, 08:05 PM   #13
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Good reference info that needs a bump!

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Old March 15th, 2017, 09:01 AM   #14
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Originally Posted by Different View Post
1. No, changes to the gas system can affect accuracy because of how they affect travel time of the bullet inside the barrel. Though small, changing gas pistons or modifying the geometry of parts will change the gas volume. Change the gas volume and you change the gas pressure. Change the gas pressure and you change the amount of time it takes the bullet to leave the muzzle. These changes are on the order of hundredths or thousandths of a millisecond but they result in increasing or decreasing POI dispersion, e.g., swapping out gas pistons with no other changes made. I refer the reader to the links below.
2. Yes
3. No, you read Technical Report SA-TR11-2610 which was a 1954 comparsion of the two gas systems being considered for the T44 (Stevens pages 183 - 186). The 1957 SA-TN11-1094 test was a more exacting analysis of the unlocking cycle of the two types of gas systems using the M1 and the T44E4 rifles.
4. Yes
Wait a second, if all the gas is trapped behind and driving the projectile prior to escaping through the gas port in the barrel, the only way to affect that pressure would be with more powder behind the round, wouldnt it?

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Old March 15th, 2017, 09:30 AM   #15
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I missed this one, I knew there was a reason I like shootingsights speed hammer! Thx for the bump

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