Bleed off Gas Blocks and Pressure

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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ReadyAimDuck
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Bleed off Gas Blocks and Pressure

Post by ReadyAimDuck »

I've been noticing that my most accurate loads are at or slightly above max loads listed in certain published load data. And a good amount of load data for 300 blackout seems to be a bit conservative for the powder that I am using primarily (H110). I don't normally like to load max loads and especially not above max loads. But I began wondering if the pressure is actually reduced by using a bleed off adjustable gas block. I certainly can feel less recoil. So I am wondering if this means that there is less chamber pressure. Does using a bleed off block allow you to load to higher pressures? Is it safe for the rifle? Does the brass still feel the effects of the higher pressure?
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dellet
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Re: Bleed off Gas Blocks and Pressure

Post by dellet »

Short answer is, no, peak pressure will not be changed. That pressure is reached long before the bullet passes the gas port and is often less than 10,000 psi at the port, when peak was well over 60,000 psi.

Muzzle pressure will drop, and velocity. Same way that shutting off the gas block will increase velocity. Not really enough to notice on target. But measurable. Less muzzle pressure=less recoil.

Dropping muzzle pressure, drops the amount of pressure that is holding the case in the chamber when extraction starts, this will help brass life and show up as less swipes on the case head. So you can’t really load to higher pressures because of the bleed off, you just hide one of the signs people look for. The thing is a swipe isn’t a sign of high pressure, it’s a sign of over gassing. It just shows up often with high pressure.

Less gas in the face because it went out the side of the barrel instead of the ejection port.

Hope that helps
300 Blackout, not just for sub-sonics.
ReadyAimDuck
Silent But Deadly
Posts: 174
Joined: Tue Jul 14, 2020 11:08 am

Re: Bleed off Gas Blocks and Pressure

Post by ReadyAimDuck »

Very good. That is exactly the info I was looking for and more. I appreciate it.
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