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1919 Bearing / Booster Diameter

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The two 1919A4s that I have were ex-film guns and had BFAs in the front of the bearing.

They were tapped out to 16mm (5/8") thread and the BFA put in from the inside.

The centre of that thread is only about .555" diameter, so much smaller than the .718" I see quoted.

With modern commercial 30-06 will I be over boosting ?

If so what are the tell-tale signs?

I don't like to remove metal unless it's really necessary, so I'm resisting boring out to .718".

Any advice welcome


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In my experience...yes, you'll over-boost the gun with a 0.555" oriface while running 30-06. The symptoms my gun experienced was a very choppy, inconsistent cycle...the bolt really hammers the back-plate.

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Boosters are relatively cheap and easy to install. Get one for .30-06 and put the modified one aside for possible use with blanks in the future or for sale to someone who needs it. Get a .308 one while you're at it.

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