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How thick is an M1 helmet? How thick is the liner?


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I was reading this rather interesting (if blurry) test on M1 helmets and how well they could hold up to .45 caliber rounds: http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA954941

 

(Strange test, since basically never was a US troop getting shot by a .45 but OK)

 

There's a range of helmet thickness given, though - .032 to .038. Was there ever a standard thickness, or was this kind of variance to be expected at the time?

 

Also, how thick and hefty were the liners? They sound like pretty light construction, but I've never had or held one to check.

 

Thanks,

 

M.

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At long range an M1 will stop rifle rounds... Just saying...

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"The battle belonged that morning to the thin wet line of khaki that dragged itself ashore on the channel coast of France." - General Omar Bradley.

 

 

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Liners (high pressure liners specifically) were made of material similar to fiberglass and we're not thick at all. I don't think they stood a chance if the steel shell itself failed. Of course there was the cases where the steel slowed the bullet enough that the bullet then "rode the liner" which actually saved a few lives

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I was reading this rather interesting (if blurry) test on M1 helmets and how well they could hold up to .45 caliber rounds: http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA954941

 

(Strange test, since basically never was a US troop getting shot by a .45 but OK)

 

The test was not set up to measure the affect of a .45 caliber round against the armor defense of the helmet. The ballistics test was established to discern if a helmet could adequately deflect an impact from a projectile originating from a specified distance traveling at a velocity of 725 ft/sec. The testing criteria were standardize so all test results could be measured the same. The .45 was just the instrument chosen for testing the helmets ability to deflect ballistic impacts.

 

 

There's a range of helmet thickness given, though - .032 to .038. Was there ever a standard thickness, or was this kind of variance to be expected at the time?

 

No, there was no single measurable standard thickness as this was not achievable under the conditions of the manufacturing process or the variance in helmet steel supplied although, I would agree with aef1917 that the middle of the variance would be the ideal. The range was provided due to the requirement for the 7 inch deep draw necessary to make the helmet. The M1 was required to be made in a single draw the result of which was a helmet thinner at the crown than at the rim and this is what lead to the variance you have listed above. Helmets pulled for various testing were first measured for thickness and those with the thinnest variance within the sampling were the ones that were sent to the ballistics test.

 

Also, how thick and hefty were the liners? They sound like pretty light construction, but I've never had or held one to check.

 

Assuming you mean the final version of the liner or the "high pressure" liner, it was approximately 1/16" thick. It was made of two layers of phenolic resin impregnated duck cloth and a crown reinforcement patch. When formed under high pressure the liner became rigid yet flexible and complete weighed about 10 ounces. The liner was tested by dropping an 8 pound steel ball from about 3 feet onto the crown. The measurement of success was an indention or deflection of less than 1 1/4" from the impact.

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I was reading this rather interesting (if blurry) test on M1 helmets and how well they could hold up to .45 caliber rounds: http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA954941

 

(Strange test, since basically never was a US troop getting shot by a .45 but OK)

 

The test was not set up to measure the affect of a .45 caliber round against the armor defense of the helmet. The ballistics test was established to discern if a helmet could adequately deflect an impact from a projectile originating from a specified distance traveling at a velocity of 725 ft/sec. The testing criteria were standardize so all test results could be measured the same. The .45 was just the instrument chosen for testing the helmets ability to deflect ballistic impacts.

 

 

There's a range of helmet thickness given, though - .032 to .038. Was there ever a standard thickness, or was this kind of variance to be expected at the time?

 

No, there was no single measurable standard thickness as this was not achievable under the conditions of the manufacturing process or the variance in helmet steel supplied although, I would agree with aef1917 that the middle of the variance would be the ideal. The range was provided due to the requirement for the 7 inch deep draw necessary to make the helmet. The M1 was required to be made in a single draw the result of which was a helmet thinner at the crown than at the rim and this is what lead to the variance you have listed above. Helmets pulled for various testing were first measured for thickness and those with the thinnest variance within the sampling were the ones that were sent to the ballistics test.

 

Also, how thick and hefty were the liners? They sound like pretty light construction, but I've never had or held one to check.

 

Assuming you mean the final version of the liner or the "high pressure" liner, it was approximately 1/16" thick. It was made of two layers of phenolic resin impregnated duck cloth and a crown reinforcement patch. When formed under high pressure the liner became rigid yet flexible and complete weighed about 10 ounces. The liner was tested by dropping an 8 pound steel ball from about 3 feet onto the crown. The measurement of success was an indention or deflection of less than 1 1/4" from the impact.

 

Thanks for that one! Looking at the liner, wouldn't 1.25" deformation put it in your dome anyways?

 

M.

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Thanks for that one! Looking at the liner, wouldn't 1.25" deformation put it in your dome anyways?

 

 

Apparently yes you are correct, it looks like they calculated the position of your head within the liner based on how the suspension cradle was supposed to be adjusted to prevent serious injury. If the liner cracked, splintered or flexed upon the impact test down to the 1 1/4" limit it was rejected.

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