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thoughts on blow back
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  kberk50

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Posted: February 16 2017 at 11:09am | IP Logged Quote kberk50

I would like to hear thoughts about using blow back with out the use of a gas system, but having a ported barrel to vent enough of the initial gas pressure until a suitable level is obtained to use a light enough bolt. There has been much debate and info here about using blowback as its an easy to do system for lighter pistol calibers. I have my reason for asking. I would like to use a 300 black out as I load a wisper round that can function on a blow back bolt 5 grains of unique with a 230 grain bullet. The weight vs powder load is about the same result of a 45acp however if you would shoot a full 300 loaded shell by accident then a big problem would happen for sure. I also have a tapered bolt face that is a tight fit to close against the barrel instead of the locking lugs that can also act as a delay to keep the bolt forward a bit longer. Its an idea that id welcome feed back on and try out keeping safety in mind. I have also seen some adjustable gas systems in use that pretty much do the same thing just in reverse to allow light loads to function when there is not enough gas to operate a full gas system. So any thoughts would be appreciated Thanks
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  backbencher

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Posted: February 16 2017 at 12:18pm | IP Logged Quote backbencher

That's a VERY clever idea.  Maybe 16" bbl, w/ ports most of the way down, shrouded by a full length suppressor?  Blow back will give up some suppression, however.  That way you have a 1 stamp gun, and given enough ports, all ammo might be subsonic.

Same way you do a single stamp Ruger 10/22, & vent enough gas to keep cheap bulk pack subsonic.  Similar problem.

And given you have a .30" barrel, if you do drop a .223" in there, it'll just go rattling down the bore - but w/o baffle strikes.
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  kberk50

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Posted: February 17 2017 at 9:59am | IP Logged Quote kberk50

thanks for the response. I thought to start with a small hole and work up and with a given known load that works to keep things in check. I was also thinking to vent the extra gases through a tube like one used as to hold a gas piston and vent it ahead of the bullet and into the blast chamber of a suppressor or faux tube and back in to the end of the barrel at exit. I know with a full load I will loose velocity but with the ability to shoot full loads and sub loads with out a gas system I can build a more compact and some what lighter weapon. any other thoughts are appreciated thanks.
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  backbencher

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Posted: February 17 2017 at 12:02pm | IP Logged Quote backbencher

kberk, I rather think you'll end up w/ a simpler, but heavier weapon than a gas-operated locked breech gun b/c of the needed mass of reciprocating parts.
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  justin22885

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Posted: April 15 2017 at 11:34am | IP Logged Quote justin22885

at 200 yards a 230 grain 45acp and 220 grain .308" bullet leaving the barrel at the same ~1100fps velocity will have minimal differences in impact velocity, energy, drop, TOF, etc.. these rounds both drop off very quickly after that so for the range they are both actually capable of, a 45acp can be used, be fired from a blowback carbine

but also when that 45acp impacts it will have roughly the same energy as being fired from a handgun inside 50 yeards which means if youre using JHPs like XTPs, theyre going to expand and cause massive damage.. when a 220 grain .308" bullet hits at handgun velocities the terminal ballistics are more or less the same as a 32acp

so for all the work and complications of what you want to do with a high likeliness that its not even going to work, consider other calibers to do what youre looking to do
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