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Discussion Starter · #1 ·
Guys, What is the normal booster sizes for all your guns?

BFA's are in the .170" to .199''
308/7.62 is .5"
30'06/ 8mm is .718"
30'06 booster/flash hider A4/A6 guns? some say its bigger?
short barrel 7.62 / 16.5" from what I read its at .80"

Some people talk of speeding up a full auto or lower pressure 7.62 ammo being in the .450" or so?

Anyone have a special one that they have done?
Any you have found that are not in this range?
 

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here,
.308 = .531
. 30/06 = .718
. m6 flashhider = 720 +- .003 usually on the + side
ive measured alot of these and this is what i have found.....:)
 

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Discussion Starter · #3 ·
The ones that I got on most of my kits are .5 or .51.

Is there a difference in the rebuilds that the kits have, or any of the others new made?
 

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Discussion Starter · #4 ·
Just looked at a picture that showes the booster.....

13.5 and sure as crap its .531"
Now to go back and look at mine, I know a few were .5" maybe there is dents or something in there or my mic is wrong.
 

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More than you want to know

.718 is the correct dimension for Cal.30.

Booster plugs/front barrel bearings are somewhat confusing because Ordnance experimented with several different openings in the plugs.

M2 Ball has openings from .617 and a different driving spring, a 1938 attempt to increase the rate of fire to 600RPM somewhere along the line this was increased to .625 then to .718.
Still trying to nail all that down.

As far as I can tell from the drawings I have the one piece booster bearings were .718 +.005 and there were two different interior designs and two different exterior designs The so called A5 one piece style with the tapered exterior was just an early version, the taper was dropped from the drawings and the two piece style was also dropped 8-22-42 when all the drawings were combined, however there were likely LOTS of the older two piece style in the system as they are still common and the 1947 SNL shows all of them including the plug with stock numbers..

M1 Ball plugs have been .870, .876 and .920.

Early plugs were marked M1 or M2 and later .718 and finally, no marking at all
There is at least one with the part number imprinted on it in a private NFA collection although that was not required.

M1 Ball featured a 173 GN ? projectile giving much better long range performance (just like today's Match ammo), however Ordnance had difficulty making this cartridge work reliably in the M1 rifle apparently because of higher port pressure.

M2 Ball is nearly the same cartridge as the US Caliber .30 Model of 1906 the original .30'06 i.e. 150GN +/- flat base spitzer projectile.

Ordnance gave up on M1 Ball about 1939 because they didn't want the logistics nigntmare of trying to supply both types, and they were committed to the M1 rifle.

The end result was we ended up with less effective ammo for machine gun use.
 

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I have read...

...a different reason in several books. I heard M1 was to replace the old round for better performace in MGs , our round found lacking in compairison to others. Lots of old stock left from WW1 , so none realy made for years. When M1 started to enter the system , the garand had to be modified to work with it ( it was done) , but that the ammo was too long range for most of the existing firing ranges and it would cost big bucks to expand them ( when posible) , that money would have to be spent to re-fit all the rifles/BARs / MGs with new sight leaves , the ammo was harder on the guns ( more money for new ones) , and that the orig. reason for adopting it did not seem as important to the people now in charge as the fad of using MGs as artillery was falling out of style.
Prob'ly comes down to the between-wars budget.
Chris
 

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30'06 booster/flash hider A4/A6 guns? some say its bigger?
you can trust me, the A6 booster is much larger than a standard a4 by about an 1/8 of an inch
id have to get the calipers out but if i recall correctly the A6 booster is .820 inch where the a4 booster is .718


Anyone have a special one that they have done?
i have removed the israeli plug on one of my caps to run the gun slower. i believe it was real close to the .820 after the plug was removed


when i get around to it ill get you exact measurements - calipers are elsewhere at the moment



 

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you can trust me, the A6 booster is much larger than a standard a4 by about an 1/8 of an inch
id have to get the calipers out but if i recall correctly the A6 booster is .820 inch where the a4 booster is .718


i have removed the israeli plug on one of my caps to run the gun slower. i believe it was real close to the .820 after the plug was removed


when i get around to it ill get you exact measurements - calipers are elsewhere at the moment




The cap style booster plug drawing for the A6 B7160461 which appeared March 21, 1944 shows a hole diameter of .812 (+005).

The original one piece ArmaSteel A6 bearing drawing B261109 from Oct 1942 had a bored thru hole of 1.254 without any plug. It looks like the end of the barrel protruded out the end of the bearing. This no boost arrangement likely brought about by the lighter A6 barrel might explain the "insufficient recoil" problems experienced early on and the development of the B7160543 and B7162160 bearing for the cap style booster.
 

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i broke my calipers out and measured the a6 booster above and its reading .820 inch with mitutoyo dial calipers that have been tested on various plug gauges and are the most accurate set ive ever had.

my particular a6 cap may be out of spec, or my calipers may be wrong, but it measures .820 and coupled with a GI A6 barrel it runs quite a bit faster than a GI a4 barrel and a Gi .718 06 booster, and could stand to be opened up quite a bit still.

i also measured my custom a4 cap that i removed the pressed in israeli reducing plug from and it measures at .832 with the same calipers and will cycle a full weight a4 barrel in my gun perfectly - not sure if it would make a difference, but my gun is full auto, not semi auto, and i think each gun is a bit different, so your results may vary
 

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It is what it is

i broke my calipers out and measured the a6 booster above and its reading .820 inch with mitutoyo dial calipers that have been tested on various plug gauges and are the most accurate set ive ever had.

my particular a6 cap may be out of spec, or my calipers may be wrong, but it measures .820 and coupled with a GI A6 barrel it runs quite a bit faster than a GI a4 barrel and a Gi .718 06 booster, and could stand to be opened up quite a bit still.

i also measured my custom a4 cap that i removed the pressed in israeli reducing plug from and it measures at .832 with the same calipers and will cycle a full weight a4 barrel in my gun perfectly - not sure if it would make a difference, but my gun is full auto, not semi auto, and i think each gun is a bit different, so your results may vary
You can't argue with the actual measurements. I have only one drawing of the Cap style and it's dated 1945 with 2 revisions, maybe one of those changed the opening, so its another one of those things to put on my list of things to be investigated
 
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