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1928A1 Grip Mounts


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I finally found a ‘fore grip reinforcing band' to add to my collection, together with some assorted Thompson springs to put into my Gordon Herigstad spare parts container.

My intention was to add the 'fore grip reinforcing band' to my deactivated Auto Ordnance M1A1, but I decided to look at the grip mount on my deactivated Savage M1 too. Both grip mounts were identical, so I looked at my deactivated late production Savage 1928A1, smooth barrel and ‘L’ sight. The 1928A1 grip mount was different, so I dug out my copy of the Ultimate Thompson book and referred to page 357 . To my surprise, Tracie Hills book identified both the M1 & M1A1 grip mounts as the earlier one piece version, but the 1928A1’s grip mount is a late WW2 with riveted grip mount.

I therefore decided to check the grip mounts on my other deactivated 1928A1’s, both of those have one piece grip mounts. So the only example I have of a riveted grip mount is on the late production 1928A1. Has anyone come across riveted grip mounts being attached to a late production 1928A1’s or is mine an anomaly?

​Stay safe

​Richard

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So far I have only seen the riveted grip mounts on the demilled late M1s I've come across. I've never heard of them on a 28a1, although anything is possible with a field repairs.

 

Andrew

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Andrew /Jim,

The fact that my 1928A1 had the riveted grip mount surprised me, but as you say, anything is possible with field repairs.

 

May have to fit the 'fore grip reinforcing band' to my 1928A1 :happy:

 

Stay safe

 

Richard

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I have to say - I got a band for my M1A1.

 

Once that reinforcing band is put on the gun and tightened properly, that grip is going nowhere.

 

Whatever flaws the riveted mount has are 100% cured by the band, it's a giant improvement.

 

 

From an engineering standpoint,

 

The grip as supported by just the riveted mount is called a "cantilever beam", and it carries the load by the bending force in the riveted mount.

 

Once you put the band on, it becomes a "propped cantilever beam" and the bending forces in the riveted mount drop by 75%.

 

So if you were wondering how much better off the riveted mount is when the band is put on, it's bending load is reduced by 75%.

 

The shear (sideways) force on the riveted mount is reduced by 37.5% when the band is put on.

Edited by buzz
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I have to say - I got a band for my M1A1.

 

Once that reinforcing band is put on the gun and tightened properly, that grip is going nowhere.

 

Whatever flaws the riveted mount has are 100% cured by the band, it's a giant improvement.

 

 

From an engineering standpoint,

 

The grip as supported by just the riveted mount is called a "cantilever beam", and it carries the load by the bending force in the riveted mount.

 

Once you put the band on, it becomes a "propped cantilever beam" and the bending forces in the riveted mount drop by 75%.

 

So if you were wondering how much better off the riveted mount is when the band is put on, it's bending load is reduced by 75%.

 

The shear (sideways) force on the riveted mount is reduced by 37.5% when the band is put on.

 

 

But, did the band change the point of impact at max range?

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RBPCPS, I have seen at least one WW2 era photo that shows a soldier with a 1928A1 with reinforcing band on the forward horizontal grip. I would assume that although the ordnance cats had directives for the application towards the M1A1's, some thought it would be helpful on the 28's as well. Of course we know these guns received incredible abuse, even the solid grip hanger on a 28 at some point can succumb to extreme or unintentional forces, cheaper to apply the band than depot the gun. I will try and find that photo. If anyone finds it first please post. JB

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RBPCPS, I have seen at least one WW2 era photo that shows a soldier with a 1928A1 with reinforcing band on the forward horizontal grip. I would assume that although the ordnance cats had directives for the application towards the M1A1's, some thought it would be helpful on the 28's as well. Of course we know these guns received incredible abuse, even the solid grip hanger on a 28 at some point can succumb to extreme or unintentional forces, cheaper to apply the band than depot the gun. I will try and find that photo. If anyone finds it first please post. JB

 

JB,

If you can find that photo, I'd be grateful.

 

Stay safe

Richard

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Field Service Modification Work Order A32-W3 included M1928A1 Models for Foregrip Reinforcing Band Upgrades.

 

War Manufacturing sometimes creates an interesting dilemma. The manufacturing changes taken on The M1A1 Grip Mount in an effort to reduce costs, created a requirement for a separate part to be manufactured to correct an issue that didnt previously exist. Definitely growing pains involved with the design of an Econo Thompson.

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Field Service Modification Work Order A32-W3 included M1928A1 Models for Foregrip Reinforcing Band Upgrades.

 

War Manufacturing sometimes creates an interesting dilemma. The manufacturing changes taken on The M1A1 Grip Mount in an effort to reduce costs, created a requirement for a separate part to be manufactured to correct an issue that didnt previously exist. Definitely growing pains involved with the design of an Econo Thompson.

 

Indeed, this is a classic case of a penny saving modification costing dollars to fix.

 

​Stay safe

 

​Richard

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. Buzz - I think your calculator ran away with you. Once the grip mount

is held to the barrel by the band it won't bend because it is defacto now

part of the barrel. It won't bend unless the barrel bends with it, or unless

the barrel band is loaded to the point where it stretches/deforms. The only

way to apply the bending force to the grip mount is by loading the swivel

which would rip out of the wood long before anything would bend, or by

pulling on the wooden forend which would also splinter and break before

any bending of the barrel/grip mount/band would occur.

Maybe if you constructed a special machine in which you clamped

the gun with additional devices to mechanically pull the grip mount

away from the barrel your calculations. - if they are correct - would come

into play. Your cantilever theory may look good on paper but practically speaking

the forces cannot be applied to the gun.

I agree that the best grip mount is the one piece. Not all later grip mounts

bend. Putting on the band should be a last resort because it crushes the forend

and scars the barrel. Of course in wartime and combat this is not relevant but

75 years later the guns are no longer tools to be used and discarded but valuable

collectors pieces.

 

Bob

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Reconbob,

 

I'm too lazy to type out a wall of text to explain my engineering stuff. And nobody would want to read it anyway.

 

If I could stand in front of a chalkboard and talk about this topic for a half hour, you would a.) stop thinking that I'm a calculator jockey and b.) understand my meaning exactly.

 

Engineering calculations don't replace reality, they reflect a simplified version of reality.

 

The closer that the actual object is to the idealized version, the closer the calculated values are to the real world values.

 

If I have a static 1000 lb load hanging from a single beam made from elastic material, the calculated internal forces in the beam are going to be within 1% of the actual forces.

 

But if I tried to calculate the loads in the 100s of 2x4s in your balloon framed house, I would be lucky if I had a 25% error.

 

There's a name for engineers that don't understand the relationship between calculations and reality, they're called "dumb asses".

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So anyway,

 

The original grip and mount is a determinate beam called a "cantilever beam".

 

If you put your M1 in a vice and hung a 100 lb weight from the center of the grip (about 4" away from the mount), you would get a bending force in the mount of

 

Mx = F x d = 100 lbs force x 4" arm = 400 lb inches.

 

If you put strain gauges on the actual gun, the real load on the mount would be like 391 lb inches, match the calculations almost exactly because it's a very simple mechanism.

 

Now, if you add the barrel band on, the forces in the grip become very complicated and full of imponderables.

 

In order to get a feel for how much the band is helping, you can pretend that the band is an idealized simple support and pretend that the grip is an idealized determinate beam called a "propped cantilever". And according to the perfect idealized elastic behavior, the bending in the mount drops from 400 lb inches to 100 lb inches.

 

HOWEVER, the 100 lb inches number depends on the band acting like a very simple support, a point load.

 

In reality, the band is not an idealized point load, it presses the mount tightly against the barrel and makes the whole assembly very rigid.

 

So in real life, as Bob pointed out, you would expect the actual bending load to be far lower than the idealized calculated value, maybe 25 lb in instead of 100 lb in.

 

As an engineer, I'm aware of the discrepancy, but I can still use the calc as a tool, because I'm actually interested in the upper bound, the highest possible load.

 

Like if I was designing a $500,000 version of this gizmo out of rolled steel beams to support some pipeline on an oil rig, I would use the idealized version to design it, and it would work fine because it would be a conservative design but still reasonably economical.

 

I would have a finished product that was guaranteed to be stronger than the applied load and would be reasonably efficient.

 

If you were doing something similar to design a part for the space shuttle, where weight is critical, the crude idealized design method would be too heavy and you'd have to get out the computers and strain gauges and start refining the crap out of the calculation.

 

So anyway, the barrel band does one heck of job reducing the load on the mount, as a MINIMUM it reduces the load by 75%.

Edited by buzz
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There are lunar landers standing on the moon and it's the result of a very happy marriage between the slide rule guys, the testing lab guys, and the craftsmen that machined it.

 

Those things are all part of one big process, not exclusive of each other.

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Be careful - Theres one other thing the band does - it scratches hell out of the barrel and wears a groove in the forend over time. I wouldnt put one on a gun thats now a 20K collector piece.

So, the barrel does flex while firing and technically the "POI " does change, even with it strapped to the handguard. Thank you 21A, that cleared up some info for me.

 

But, why is the Band wearing away the metal of the barrel and not the wood of the handguard?.

Edited by Paladin601
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Be careful - Theres one other thing the band does - it scratches hell out of the barrel and wears a groove in the forend over time. I wouldnt put one on a gun thats now a 20K collector piece.

So, the barrel does flex while firing and technically the "POI " does change, even with it strapped to the handguard. Thank you 21A, that cleared up some info for me.

 

But, why is the Band wearing away the metal of the barrel and not the wood of the handguard?.

The band usually does not clamp tight to the barrel, but it does clamp tight to the wood and has two small dimples that dig in.

 

Ron

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But Buzz - once you clamp on the band the grip mount is no longer

a cantilever because now its supported at both ends. And your 100 lb.

or whatever weight hanging from the middle of the grip mount is now no

longer trying to pull the end of the grip mount away from the barrel. It is

trying to bend the grip mount in the middle since at one end its supported

by the receiver and at the other end by the band.

When the weight is big enough to cause the band to fail by stretching,

yielding, and breaking, now you have returned to a cantilever.

But these forces are so many times greater than those that exist

in the normal handling of the gun that you empirical calculations

don't really come into play.

 

Bob

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Be careful - Theres one other thing the band does - it scratches hell out of the barrel and wears a groove in the forend over time. I wouldnt put one on a gun thats now a 20K collector piece.

So, the barrel does flex while firing and technically the "POI " does change, even with it strapped to the handguard. Thank you 21A, that cleared up some info for me.

 

But, why is the Band wearing away the metal of the barrel and not the wood of the handguard?.

The band usually does not clamp tight to the barrel, but it does clamp tight to the wood and has two small dimples that dig in.

 

Ron

so, a "mis bent" could remove the small amount of clearance between the barrel and band causing a wear in finish and possibly a barrel change?

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Bob, I understand exactly what you're saying.

 

I need a chalkboard and a half hour of talking to make myself understood, typing a dozen sentences into the internet is futile.

 

In a half hour in person I can say about 3500 words and draw 10 pictures.

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  • 3 years later...

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