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Discussion Starter #1
I built my gun about 12 years ago and last shot it about 10 years ago. Yesterday I got it out to clean it in anticipation of shooting it next week.

I started thinking about the booster orifice diameter. The gun was originally set up as .308 Izzy but when I bought the kit it also came with a 36-06 barrel but one booster plug. I measured it last night and it is .690" and has Israeli markings. I also have an 8mm barrel for it. I know what the different booster diameters are for the different calibers. Is it possible the Izzy booster was opened up to work with both .308 and 30-06, as well as 8mm? Is .690 still too small for 30-06 to not beat up the gun? The gun is semi auto.
 

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PhD in Over-Engineering
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I think that .690 is considered standard for the 8mm conversion. About that, anyway. It was likely, as you surmised, opened up from the normal Izzy .631. I used to run 8mm in the standard .718 USGI booster orifice. But the difference of using 30-06 in your .690 is probably negligible. I wouldn't worry about beating up the gun over a .028 difference. Gun might not even run perceptively faster, but in a semi you almost certainly won't even notice it. The military played with orifice and cyclic rates extensively, but they were more concerned with efficient use of ammunition than the wear to the gun. You can get new made .718 booster plugs from greaser/Ravenna Armory, I believe, if you feel the need.
 

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Discussion Starter #3
I think that .690 is considered standard for the 8mm conversion. About that, anyway. It was likely, as you surmised, opened up from the normal Izzy .631. I used to run 8mm in the standard .718 USGI booster orifice. But the difference of using 30-06 in your .690 is probably negligible. I wouldn't worry about beating up the gun over a .028 difference. Gun might not even run perceptively faster, but in a semi you almost certainly won't even notice it. The military played with orifice and cyclic rates extensively, but they were more concerned with efficient use of ammunition than the wear to the gun. You can get new made .718 booster plugs from greaser/Ravenna Armory, I believe, if you feel the need.
I think that .690 is considered standard for the 8mm conversion. About that, anyway. It was likely, as you surmised, opened up from the normal Izzy .631. I used to run 8mm in the standard .718 USGI booster orifice. But the difference of using 30-06 in your .690 is probably negligible. I wouldn't worry about beating up the gun over a .028 difference. Gun might not even run perceptively faster, but in a semi you almost certainly won't even notice it. The military played with orifice and cyclic rates extensively, but they were more concerned with efficient use of ammunition than the wear to the gun. You can get new made .718 booster plugs from greaser/Ravenna Armory, I believe, if you feel the need.
Thanks. That the kind of information I was looking for.
 

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I always ran the 8mm with the -06 booster and it worked wonderfully. 8mm with the 308 booster seemed to be a little rough on things. I was thinking the 30 boosters were near .630" diameter and the 06 was .813". I was running a full auto gun too so that could affect things. In the semi I would run the largest diameter booster orifice that would reliably cycle the gun. Any more is just beating things.

Frank
 

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I've run the -06 booster on my 7.62 semi with no problems. I don't think the semi-auto guns are as particular as the full auto guns.
 

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Discussion Starter #6
I ran all 3 calibers today and the gun ran fine.
The only problem is an old one. More of a nuisance than anything: during rapid fire the trigger will sometimes go dead and not reset. I always thought it was the booster orifice being too large and the gun not recoiling enough, (short stroking).

What I think I found today is that it may have been a weak sear spring. The gun recoiled enough to pick up and chamber the next round so it wasn't short stroking. After replacing the spring I ran 15 rounds fast and the trigger reset every time. I'll run it again soon to be sure.
 
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