PWS piston diameter

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Posted: 9/10/2019 10:04:58 AM EDT

I'm looking at using a PWS short piston for a little project, can someone with a PWS upper tell me what the piston diameter checks with calipers/mics?
I asked PWS but no response yet, only that i can buy them for spares.
Thanks.

Posted: 9/15/2019 1:24:03 PM EDT

[#1]

.375 at the piston head

Posted: 9/16/2019 8:30:42 AM EDT

[#2]

Thanks!

Posted: 9/21/2019 8:59:17 PM EDT

[#3]

What sort of project is this? Custom piston upper?

Posted: 9/21/2019 9:06:27 PM EDT

[#4]

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Quoted:
What sort of project is this? Custom piston upper?

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Yep, 7.5" 300blk, bufferless

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Posted: 9/21/2019 9:11:32 PM EDT

[#5]

Have you gotten it running? If not, what work do you have to do to it? I'm particularly intrigued with how you're modifying the bolt carrier for the shorter travel. I've dabbled in a custom piston gun, but it was a lot more simple than a bufferless gun haha.

Posted: 9/22/2019 10:09:13 PM EDT

[#6]

I've built a few DI bufferless guns in the past in 5.56, 6.8 and .45acp.
Just chopped the carrier and welded up an extended gas key.
This will be my first stab at a bufferless piston gun, will be using a single RFB action spring with a similar setup to a RRA PDS.

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Posted: 9/23/2019 1:12:47 AM EDT

[#7]

Looks neat, keep us posted.

Posted: 9/23/2019 6:58:33 AM EDT

[#8]

Quote History

Quoted:
I've built a few DI bufferless guns in the past in 5.56, 6.8 and .45acp.
Just chopped the carrier and welded up an extended gas key.
This will be my first stab at a bufferless piston gun, will be using a single RFB action spring with a similar setup to a RRA PDS.

https://www.AR15.Com/media/mediaFiles/173511/Attach11443_20190917_221652_jpg-1099843.JPG

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You Sir are destined to engineer firearms, which I hope you take full advantage of.

Posted: 9/23/2019 7:34:48 AM EDT

[#9]

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Quoted:
You Sir are destined to engineer firearms, which I hope you take full advantage of.

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Now may not be the best time to get into the industry, but I use it for myself

I've roughed out the gas block from Ti to save a little weight.
I forgot how nerve-wracking it can be tapping small holes in 6Al4V...
This tap is done, but it made it through. I chased them with a fresh 4-flute.

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Posted: 9/23/2019 12:02:32 PM EDT

[#10]

sounds similar to something I want to try. So I take it this will be long stroke? or is it going to be short stroke with the captured assembly being external from the receiver? Thats the part i'm hung up on.

Also are you going to sleeve the piston bore in that Ti? I would be worried about it galling and seizing the piston once you add in some heat/carbon.

I have always admired your projects. looking forward to see it come along.

oooh one more question. Forward cocking handle no reciprocating? or standard charging?

I'm after the mp5 esq feel on my build. much like your 5.56. Still havent tossed the LR300 gas system idea yet as you've proven it to be reliable....my problem is my barrel length/gas system is notably shorter.

Posted: 9/23/2019 12:11:29 PM EDT

[#11]

Quote History

Quoted:
sounds similar to something I want to try. So I take it this will be long stroke? or is it going to be short stroke with the captured assembly being external from the receiver? Thats the part i'm hung up on.

Also are you going to sleeve the piston bore in that Ti? I would be worried about it galling and seizing the piston once you add in some heat/carbon.

I have always admired your projects. looking forward to see it come along.

oooh one more question. Forward cocking handle no reciprocating? or standard charging?

I'm after the mp5 esq feel on my build. much like your 5.56. Still havent tossed the LR300 gas system idea yet as you've proven it to be reliable....my problem is my barrel length/gas system is notably shorter.

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Long stroke, like the PWS. The piston bore will be a ID/OD nitrided ejector sleeve.
The gas valve and oprod will be as well. It will be functionally similar to a Sig 556, but the action spring will be inside the oprod and extend to the rear of the upper, like the RRA PDS.
And yes, forward/side charging, non-reciprocating.

I couldn't go shorter than Carbine gas with the LR300-based system, so I had to get a little further out there for pistol length barrels. I may still swap the 7.5" for a 6", but I plan to use the dead space in front of the front sight for an integrated weapon light that comes off with the handguard when cleaning the gas block parts.

Posted: 9/24/2019 10:38:36 PM EDT

[#12]

Piston was about 0.002" large, a little time on the lathe with a fine stone took care of that.
Should work perfectly for what I'm doing.

I'm planning for ~3/4" of pressure stroke before the vents, and a ~0.020" oversized bore beyond that to avoid any binding, since the op rod will be the same diameter as the piston.
The ejector sleeves we use have a 1deg lead-in at the transition and it seems to work well.

Posted: 9/28/2019 6:50:10 PM EDT

[#13]

Quote History

Quoted:
Piston was about 0.002" large, a little time on the lathe with a fine stone took care of that.
Should work perfectly for what I'm doing.

I'm planning for ~3/4" of pressure stroke before the vents, and a ~0.020" oversized bore beyond that to avoid any binding, since the op rod will be the same diameter as the piston.
The ejector sleeves we use have a 1deg lead-in at the transition and it seems to work well.

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We?

did you partner up with a company to back your cool projects?

Posted: 9/29/2019 11:44:57 PM EDT

[#14]

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Quoted:
We?

did you partner up with a company to back your cool projects?

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We use ejector sleeves in some of our dies at work...

Posted: 10/9/2019 11:02:36 PM EDT

[#15]

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Quoted:

We use ejector sleeves in some of our dies at work...

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You are officially the suck!

Posted: 1/9/2020 12:08:50 PM EDT

[#16]

Any update on this build?

Posted: 1/9/2020 12:18:02 PM EDT

[#17]

Thought I'd be done long before now, but been busy with family stuff and house projects, but there has been a little progress.
Got the gas key cut out and welded, gas block is almost functional, will whittle it down for weight, going to slot the upper for a sealed charging rod that will extend up the inside of the handguard to the front charging handle.

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