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  #1  
Old 07-26-2010, 04:37 PM
VMFn542bob VMFn542bob is offline
 
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Default MANN ACCURACY DEVICE - Chamber Test -

A comprehensive test of the MANN Accuracy Device chamber using STANDARD and SMALL BASE case sizing.
Some time past, a thread on the MANN Accuracy Device said that a gunsmith determined that the head space on the MANN Accuracy Device he was given was too tight.
The gunsmith then recommended and was given permission to remove and re-headspace the barrel.
I found it difficult to believe that any of the expertly handcrafted MANN Accuracy Devices would need to be headspaced again.
I have two of them so I decided to perform a basic test.

THE TEST:
Twenty, once fired, polished and de-capped .308 WIN cases of mixed manufacturer and dates were randomly selected.
The body and neck of these 20 cases were full length sized and the necks then expanded using two different dies.
The cases length were not trimmed before or after sizing.
Ten cases were sized with a RCBS STANDARD full length .308 WIN die.
Ten cases were sized with a LYMAN SMALL BASE full length .308 WIN die.
All 20 cases were then tested by inserting them into the chamber of a MANN Accuracy Device and then closing the bolt.
All 10 cases sized with the STANDARD die chambered easily but the bolt would not close on any of them to full battery locked position.
All 10 cases sized with the SMALL BASE die chambered easily and the bolt closed easily on all of them to full battery locked position.

The .308 WIN cartridge head spaces on the case shoulder but it can also head space on the mouth of the case if the COL is too long.
The specified maximum Case Overall Length (COL) of the 7.62x51mm NATO / 308 Winchester cartridge is 2.0150 inches.

The Shortest COL case, sized with the STANDARD.308 die, AFTER sizing was 2.006 inches. The bolt would not closed in full battery position on this case or any of the other 9 cases..
The Longest COL case, sized with the SMALL BASE .308 die, AFTER sizing was 2.033 inches. The bolt easily closed to full locked battery position on this case and the other 9 cases.

This information is provided by RCBS for their SMALL BASE 308 WIN die: "These dies size the body of cases somewhat smaller and set the shoulder back slightly more than a regular full-length sizer die in order to ensure proper functioning in semi-automatic, pump action and lever action rifles."

My Conclusion: The MANN Accuracy Device was designed to eliminate the gun to the greatest extent possible in the performance of the ammunition being tested. It has a tight head space by design, not by accident.

Last edited by VMFn542bob; 07-31-2010 at 06:31 PM.
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  #2  
Old 07-30-2010, 08:08 PM
pwrshifter pwrshifter is offline
 
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Default bare with me this is my first post

i bought my mann accuracy about a 1 1/2-2 years ago as a abandon project and ive been reading and watching this thread for years.(whatever happened to the mail match?) when i first got the device it would not chamber a new tz 80 brass(isreali 7.62x51)nor a 308 in any shape or form and if it did it was tight going into battery, so i took the device to my friend lou from LRB(http://lrbarms.com) and he allowed me to use his headspace guages, the first one we put in was the minimal match headspace gauge and found that the bolt wouldnt close easy. rite then and there i knew i had a problem cause i was told by the person i bought it from that he had headspaced it and gave me the spec's and his spec was off by .001-.0015. 1.630 would almost close right that told me it was a little on the tight minimal size, so to rereaming the chambering it i was a little scared about doing that cause g-d only knows what reamer was used(and to me it was all experimental back then and they didnt have smallbase dies back then either) and the way i saw it the chamber was off by .001-.0015 to being a match chamber, and of cause knowing that the barrel had no ramp or extractor cut, well that kinda made it a little easier to deal with and timing was no issue, so i proceeded to make a barrel shim out of a coca- cola can, it took some time but i did managed to make a perfect shim(coke can is about .0015-.002)and of cause made my own wtness mark for before and after. i then chambered the new brass tz-80(isreali 7.62x51 nato) and closed with ease i even put a piece of scotch-tape on the back which is about .0015 thick and it wouldnt close that easy, so that kinda told me that my chamber is NOW between 1.631-1.632 match(proberly more like 1.6315) and chambers everything that i put into it. it might be a little unorthadox but it works and the device or should i call it sniper system is a tac-driver.
the next hurdle i had to make was when i put the action and barrel assembly into the stock, i bought it with, the gentleman never set it rite in the stock he said it shot just fine, hmmm chamber problem, barrel not floated and pressing on the forearm of the stock cant see how it shot well with that much pressure on the barrel. so i proceeded to fit the action and barrel into the stock and fully floated the barrel in the channel, and i also got the smithless scope mount from s&k with the deal also along with the stock. (I WILL NEVER DRILL ANOTHER 1903A3 RECIEVER again 6 hours drilling and tapping no heat didnt want to loose the integrety of the metal, i did that on my first biuld which was a suto 1903A4 from scratch, thats my hunting rifle, i put that together from parts and did the headspace myself and reamed it) after getting all this done so i then i mounted a 8x32x56 30mm tube scope on top, and i had to use the high scope rings on it cause the front scope bell wouldve hit the barrel and with that i didnt even have to worry about the original bolt clearing the scope. my first outing with the rifle i was kinda disappointed cause i was using the tz-80 7.62x51 nato, it got me on paper BUT not the results i was looking for so i took 1 apart to find that it had a 143gn head with 45.1gn of ball powder(dam what junk!)note on history:isreal did not have a rifle that used 7.62x51 ammo those years and if so it was a sniper rifle and it wasnt using 143 head bullets they were using this stuff in there converted browning machine guns, i stopped using my isreali fal i built years ago cause of it.so i pulled down all of that ammo i had. and loaded my own. and biult up a great load. ive heard alot of guys said they couldnt get them to shoot well with heavy grain heads. keep in mind what these devices were made for, the 7.62 garands and the m14's(m1a's), 1-10 twist same as the mann device. so i biult up a load using 168gn sierra hpbt match heads with 4064 imr behind the head. 2640 ftps w/ standard deviation +/- 10. so hence bob i am kinda with you on this DONT rechamber or reream the chamber small base dies but then your really working the brass very hard, or go my way and measure and then shim, which some or alot of people might not agree on, but it does work!
thank you for reading and listening,
neal aka pwrshifter
G-D bless our troops everywhere and all theaters
and our vets, my dad a ww2 marine who was in the 2nd battlalon in the pacific and my great uncle who was in the army air corp who started from north africa
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  #3  
Old 07-31-2010, 12:41 AM
VMFn542bob VMFn542bob is offline
 
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pwrshifter - Thanks for your interesting post.
I was amazed at how well you handled the head space problem.
I don't plan to make any modifications to either of my two MANN Devices.
I don't even plan to replace the sawed off stock.
There are very few of these Devices existing and to me it represents an important piece of history that I am privileged to own.
I will support the barrel with a fabricated piece attached at the collar (breech end).
That piece will also have a forward support extension under the barrel for a bi-pod and another over the breach and receiver for a Picatinny rail mounted scope.
It will also have a third extension going under and around the sawed off pistol grip to a small shoulder stock.
It won't be pretty but it leaves the barrel floating essentially the same as if it was being fired in a machine rest.
That stock was sawed off because it was in the way.
A stock cannot support the weight of the barrel by the breach end alone.
I have not found any information to support the following conclusions but I am certain the engineering in this generation MANN Accuracy Device intended the barrel to be supported by a machine rest at that collar.
The early MANN Devices did not have collars. Two Precision ground steel donut bearings were attached with set screws at the breech and muzzle ends.
The assembly was then placed up-side down in a precision ground steel "V" way which was secured to a stable platform.
Supported by the two bearings in the "V" Way guaranteed that after each firing the Device would be returned to the same exact point of aim.
There was no need for gun sights on this device. They were testing ammunition, not the gun.
By the time the 7,62x51 NATO cartridge was perfected, or sometime before, I suspect testing had left the field and gone indoors. Soon after that I suspect the collars were added.
In all likelihood the new firing range was through a large diameter pipe where total control over the environment could be maintained.
This would further ensure that the ammunition alone was responsible for the results of the testing.
I also suspect that these MANN Accuracy Devices would not have been turned over the the CMP if the Army did not already have a even better means of testing ammunition.
One final observation. Both of my barrels have steps in the diameter. I do not believe this is an accident either.
It is well known that changing the diameter of the barrel in steps at strategic locations will disrupt harmonic waves in the barrel.
I do not intend to remove the steps or polish the barrel. I would rather have the ultimate shooter than have a handsome one.
A lot of the information posted on the CMP forum regarding work being done on the MANN Accuracy Devices was lost when the new forum was put on line and the old one finally died.
But there are two threads that remain on this new forum. If you have not already found them, here are the links.
You will get a better understanding of what I plan to do by a drawing I posted there.
I do not yet have any unfired 7,62x51 NATO (+) head stamped cartridges to test the chambers of my barrels.
Of this I am certain: The Army would not make up special 7,62x51 ammunition for use only in these devices to prove the performance of the 7,62x51 NATO ammunition that would be issued to our troops.
Therefore, when I do get some American made 7,62x51 NATO ammo I expect it will chamber with a snug fit, eliminating all possible influence the device has on the outcome of the ammo testing.

How To's - Mann Accuracy Device (This thread also contains a link to what remains of an older thread)
http://www.thecmp.org/forums/showthread.php?t=6338&highlight=MANN

Last edited by VMFn542bob; 07-31-2010 at 12:47 AM.
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  #4  
Old 07-31-2010, 08:32 AM
gpw9552 gpw9552 is offline
 
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VMFn542bob

Drop me a PM. I have M118 and special ball (lake city).

I'm in Mesa.
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  #5  
Old 07-31-2010, 12:11 PM
VMFn542bob VMFn542bob is offline
 
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gpw9552 - PM sent.
One more observation and some more speculation about the MANN Accuracy Device barrel and the receiver used.
Even though the MANN barrel is fitted with a 5-round 1903-A3 receiver, the device was not intended to be used as a repeating rifle.
It is not a rifle at all. It is a test barrel. The 1903-A3 receiver was selected because it was readily available and had a long history of reliability and strength.
The MANN Device is a single shot testing machine and I suspect the bore was cleaned after each shot or group of shots was fired.
There is no feed ramp built into the mouth of the MANN Device chamber. The cartridge must be placed directly into the chamber and the bolt closed.
Cartridges will not feed properly into the unaltered MANN chamber from the 1903-A3 magazine.
The MANN device does not have a sloppy, forgiving chamber like the GLOCK has. The case is fully supported and the head space is purposely tight.
For those that say that a small base die shortens the life of the brass I can only reply, that is not likely in this instance.
Once the brass has been fire formed in the tight chamber of an unaltered MANN barrel it should have a long life.
Future reloading should only require neck sizing to reload it for that same chamber.
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  #6  
Old 08-03-2010, 04:29 PM
pwrshifter pwrshifter is offline
 
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also bob to keep in mind that the 308 brass IS larger then the 7.62x51 brass, after messaging on the board i did chamber a NEW winchester.308 brass and though it did chamber and go into battery it was a very little drag on close but still with ease. i wonder how that will do on yours even after using the smallbase dies. and also beware of high pressure signs at the base of the brass and i my self i use a crono when working up loads cause im looking for more accuracy and consistancy. i havent used the rifle that much this year so far cause ive been heavily involved with shooting service rifle high-power matches this year. and about keep it original i agree, truly a piece of history and that why i still have everything to put this back into original form again, by keeping it all simple but very, very accuate. ive seen what some people have done to make them into some very fine but yet very expensive toys that can never be returned back to there true faces ever again, kinda sad but each to there own and the key thing is to enjoy them for they are, truly apart of american firearms history. hopefully ill put a few more down range and post my results.
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Old 08-03-2010, 07:04 PM
watertreatpete watertreatpete is offline
 
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I am not sure if I am correct but the barrels on these look exactly like the ones used on a browning 1919a4 ?
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  #8  
Old 08-03-2010, 09:02 PM
VMFn542bob VMFn542bob is offline
 
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Quote:
Originally Posted by watertreatpete View Post
I am not sure if I am correct but the barrels on these look exactly like the ones used on a browning 1919a4 ?
It's not the same barrel. The 1919A4 has a 24 inch air cooled barrel. The ventilated cooling/support tube around the barrel makes it look fatter than it is. The MANN barrel length is about 2 inches shorter and really is fat, about 1-1/4 inches. It is equipped with a 1903-A3 receiver and only the pistol grip and receiver support portion of a 1903-A3 stock. It weighs about 12 pounds.
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  #9  
Old 08-03-2010, 09:26 PM
VMFn542bob VMFn542bob is offline
 
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Quote:
Originally Posted by pwrshifter View Post
also bob to keep in mind that the 308 brass IS larger then the 7.62x51 brass, after messaging on the board i did chamber a NEW winchester.308 brass and though it did chamber and go into battery it was a very little drag on close but still with ease. i wonder how that will do on yours even after using the smallbase dies. and also beware of high pressure signs at the base of the brass and i my self i use a crono when working up loads cause im looking for more accuracy and consistancy. i havent used the rifle that much this year so far cause ive been heavily involved with shooting service rifle high-power matches this year. and about keep it original i agree, truly a piece of history and that why i still have everything to put this back into original form again, by keeping it all simple but very, very accuate. ive seen what some people have done to make them into some very fine but yet very expensive toys that can never be returned back to there true faces ever again, kinda sad but each to there own and the key thing is to enjoy them for they are, truly apart of american firearms history. hopefully ill put a few more down range and post my results.
YEP! The 308 brass IS larger then the 7.62x51 brass. And the 7.62x51 chamber is larger than the 308 chamber. So it has a lot in common with the Glock: sloppy chamber means fewer problems. BUT the MANN Accuracy Device is neither a 308 nor a 7.62x51. It is a 7.62x51 cartridge testing machine. If the cartridge is too long it fails. If the ammunition is correct it will be a snug fit in the chamber with little head space and will perform as a carefully crafted target rifle. I always go back to what this device was designed for: testing FACTORY 7.62x51 NATO ammunition. Hope to have some soon to try and expect it to chamber as easily as that which I have sized with a small base die.
Incidently I recently received my own standard die (LEE) and small base die (RCBS) and repeated the previous chamber tests with the same results. That is exactly what I expected. No one should need to modify this device to shoot it. It just needs a sighting system, a longer stock and barrel support. Does not even need a sighting system if it can be held in a stationary machine to check grouping.
Flaring/chamferring the mouth of the chamber permits easier loading from the magazine but it also compromises the fully supported case. I will have no problem loading one cartridge at a time. That's what I learned to shoot with when I was 12.
This is what my MANN chamber look like.
308 Small Base NATO Chambered in MANN Accuracy Device


MANN Accuracy Device 308 NATO Chamber Cross Section



Last edited by VMFn542bob; 08-04-2010 at 08:58 AM.
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  #10  
Old 07-11-2012, 12:44 PM
VMFn542bob VMFn542bob is offline
 
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Default DILLON Precision 308 Head Space Case Gage MANN Accuracy Device Chamber Test

This post is being added to an old thread to help clear up some misunderstandings about the head spaceing of the MANN Accuracy Device.
All too often the device has been diagnosed by some "experts" as having a head space problem when ammunition would not chamber in it.
The Army used it to test ammunition so that conclusion makes no sense at all.
The MANN Accuracy Device is created with ZERO head space. That is not a defect and it enhanses the performance of the ammunition.
The Army manufactures their NATO ammunition to precise U.S. standards and the MANN chamber can be thought of as a GO-NO GO case gage.
If the ammunition will not chamber it's not fit for use by the Army.
The photo collage below demonstrates two MANN chamber tests that I once made, one with standard case sizing dies and one with small base sizing dies.
You can draw your own conclusions.
,

Last edited by VMFn542bob; 07-17-2012 at 04:38 PM.
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