Pump action ar15 pistol. Disabling gas system

[johnsonian09]

Hello, been tinkering with some parts. Got most of the pump worked out.

Curious if anyone else thinks I can plug the gas port by tapping it and fitting a set screw. Just as long as it doesn’t protrude into the barrel I think it would be okay, red lock tight probably.

CT sucks.

Any thoughts?


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[stubshaft]

I don't see a problem with that. If worse comes to worst, you can mill off the top of the gas block, cutting off the tube portion and turn it upside down or sideways to block the port.

[rancher1913]

put an adjustable gas block on and close it down to no gas, easy to switch back later if things dont work out with the pump part.

[johnsonian09]

Because it is a pump, and short barreled I need a near flush to journal port block. As that space is needed to actuate the bcg.

I figured tapping for a set screw would be easy and reversible. Other then that welding it shut and turning down the spot makes me nervous because of the heat. Not sure if it will get hot enough to mess up the heat treat of the barrel or anything like that.

But does anyone think that a set screw will not be able to handle the brief pressure in the barrel during the dwell period before the bullet leaves the barrel?’


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[DDriller]

Should be fine. Not that much pressure goes through the port.

[Mal Paso]

Plugs in plumbing are usually rated at the pressure of the fitting so it should work. The solid portion should be longer than the diameter. Could sacrifice some of the socket. Were you thinking small like #4? How big is the port?

[Gtek]

I have a 300 BO 10.5" almost done here. Made a sleeve that will be press fit matching OD of barrel behind gas block area. Future change of mind or plans, cut, split remove and back to a gas block we go.

[Nobade]

I have drilled and plugged them and it works fine. The sleeve idea works also if you don't have to have that part of the barrel the same size as it was.

I have been saying for years that a pump action AR would be the way to go, especially for us cast boolit shooters. Should be more accurate if done properly and you can run any load through it you want within pressure limits.

[johnsonian09]

https://uploads.tapatalk-cdn.com/20220729/7d59a8c28484a836c2567ff8d660ce7c.jpg
This is my mock up pump assembly in the locked back position. Where the bushing is now is just barely touching the forward edge of the gas port. The gas port is 2mm/ 0.080in



https://uploads.tapatalk-cdn.com/20220729/154895fb13426cfc1c9b74392cd5c35c.jpg
This is the bolt locked forward.


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[Baltimoreed]

I did a forward charger .45acp ar sbr. Ran the op rod through the gas tube hole in the upper. I would love to see your build when done. As the .45 is a blowback I didn’t have your gas port problem.

[johnsonian09]

This is mostly made with spare parts. So the colors don’t match and looks kinda dumb but it works. https://uploads.tapatalk-cdn.com/20220804/96ae34eee3d905f3cc87ed566aa53b5a.jpg
https://uploads.tapatalk-cdn.com/20220804/6e65ffae84ed1055703cff23f201b8ad.jpg

https://uploads.tapatalk-cdn.com/20220804/6e65ffae84ed1055703cff23f201b8ad.jpg


I call it a de-sync pump action. Because you can use it as either a pump action or a straight pull bolt action


I cut a gas block in half to gain clearance for the stroke assembly and turned it 90*

The stroke assembly is 2 Amazon Chinese (I’m assuming at 8$) 5slot pica rail barrel clamps. Discard the non pic half’s of each and ream out the threads on one of the plates.

The bushing is a “3/4 x1x 1 1/2” bronze self lubricating bushing. This slides along the Fore end of the barrel. On and past the gas block journal.

The push rod is 4.5mm stainless steel tubing. Bent to shape and clamped in the assembly
Taper the end of the tube slightly so it self aligns into the gas key.

The grip is a handstop grip kit from magpul attached to the pic rails.

The only permanent modification is I bore the upper receiver so the gas tube inlet to 8mm and fit a self lubing bronze flanged sleeve bearing 4x8x10mm And bore that bearing out to 5mm after I’ve pressed it into the receiver.

If I want to switch back to semi auto I just reinstall the old gas block and tube.

I chose a blast forwarding cone to shield my hand a bit.

If you have 5 inches or more of barrel past your gas block journal, you too can build a pump action ar15.


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[johnsonian09]

https://uploads.tapatalk-cdn.com/20220804/ae1268ef173ec8e3ea58e2cefcf1760a.jpg
This is the out of synch position. But you can hit the bolt catch and resume operation.

Also I set mine up so that when the bolt is locked, I have an 1/8 inch of play with the pump assembly.

In the future I want to build a gas block that locks a guide rod attached to the stroke assembly. That makes it so when you push forward. It latches the stroker in that position. And when you fire, a small amount of gas coming from the port unlocks the guide rod and you can pull it back to unlock the bolt and cycle the action again.


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[popper]

So buffer and spring still used?

[johnsonian09]

Yes, the buffer spring is still used. When I looked at congraf a a ct company that makes a pump action ar15/ar10 upper kit. Uses a similar set up to mine except he uses a modified gas key that has a fixed push rod. And he requires a heavy barrel where the pump assembly rides behind the gas block journal vs mine is after the journal.

I debated fixing the gas key to the pushrod similarly to congrafs and installing a spring and retainer inside the hand guard that would push the assembly forward.

However the only thing that would drive me to delete the rear buffer tube and recoil assembly would be to install a folding brace. The problem I found with that is the rear half of the bcg still needs a place to go as the back of it would protrude out the receiver if there is no tube there.

I suppose if I link the pushrod to the gas key and move the spring into the fore end then I could cut the rear portion of the bcg off. It would look similar to a fightlite bcg without the strut assembly. And I could gain the clearance to delete the rear buffer system. But my goal here was to make something that could be easily convertible.

The only change here to revert to semi is replacing the gas block and gas tube. Vs needing to replace a bcg and recoil assembly.

Also I didn’t want to cut the nickle boron whatever coating bcg up and have to buy another.


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[Gtek]

One observation if I may- Am I the only one that gets a kick out of the number of gun pictures with feets in them?

[Reverend Recoil]

Yes, you are the only one.

[popper]

I just wondered about the legality of it, equivalent of side charger with gas disabled. I do see an advantage for the pistol length. You could find a used carrier and cut it but you need a straight rod then.

[johnsonian09]

There is not a single word of legislation in the USA that restricts manually operated firearms. Even in ct


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[johnsonian09]

All my ct legal ar15s that I have build so far.https://uploads.tapatalk-cdn.com/20220806/7a9047e0c92e51e2122d20f22ed9f71e.jpg
Please forgive the lack of feet

A rimfire rifle, non collapsable unthreaded. Like the mp-22 they still sell here.

A regular “other”

And the pump action pistol.

The only thing that could be made illegal in the future is the atf pistol brace rule. Which isn’t in effect and they moved the rule issue date to 2023 if I understand correctly.
If this happens I might just take the brace off and put on one of those kinda silly foam things.


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[kenton]

There is not a single word of legislation in the USA that restricts manually operated firearms. Even in ct


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That is flat out wrong. If you don't believe me take a hacksaw to a shotgun and show your local friendly ATF agent your new 12in barreled shotgun.

The issue I see is that atf defines a pistol as being intended to be fired with one hand, clearly a pump action is not intended to be fired one handed. They could claim because of that it is a short barreled rifle. One might argue that it falls in the same gray area as the short "shockwave" style firearms since it doesn't fit any definition but I don't want to be the person testing that case law.

That said we are all adults and can do what we think is best for our selves.

[johnsonian09]

That is flat out wrong. If you don't believe me take a hacksaw to a shotgun and show your local friendly ATF agent your new 12in barreled shotgun.

The issue I see is that atf defines a pistol as being intended to be fired with one hand, clearly a pump action is not intended to be fired one handed. They could claim because of that it is a short barreled rifle. One might argue that it falls in the same gray area as the short "shockwave" style firearms since it doesn't fit any definition but I don't want to be the person testing that case law.

That said we are all adults and can do what we think is best for our selves.

I was referring to state AWB. Yes the nfa is a thing. however pistol braced Ar15s with hand stops and angled forward braces have been used for a long time and the atf isn’t chasing them for it.


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[nekshot]

I have done a pump fit to a ar and then took a side discharge upper and put a bolt on kinda like the Swiss army rifles have. The spring in tube made too much noise so I cut a piece of rubber sandal inside of tube against back wall and noise went away. Fun to do when nothing else to do.

[johnsonian09]

With the gas disabled and the pump cycling reliably with all common j-word ammo.

Has anyone had success with getting an ar15 to cycle with round nose ammo similar to a round nose 30-30 type bullet ? Or at least something with a wider frontal area. My feed ramps are the m4-5.56 type despite being chambered in 300blkout.

I may ask a local gunsmith to recut the ramps but I’m unsure what type or dimensions of cut will actually work for a wide nose.

Alternatively are there other magazine follower designs that can offer some assistance in this?

The left ramp feeds almost fine with pmags. The right not well at all.

GI mags not at all


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[Gtek]

There is a mod one can do in the sides near top of PMAGS for the 300 BO, helps a bunch. Removing the sharp edges from feed slots is a good first start, nice smooth radius and try some.

[elmacgyver0]

That is flat out wrong. If you don't believe me take a hacksaw to a shotgun and show your local friendly ATF agent your new 12in barreled shotgun.

The issue I see is that atf defines a pistol as being intended to be fired with one hand, clearly a pump action is not intended to be fired one handed. They could claim because of that it is a short barreled rifle. One might argue that it falls in the same gray area as the short "shockwave" style firearms since it doesn't fit any definition but I don't want to be the person testing that case law.

That said we are all adults and can do what we think is best for our selves.

Kind of comparing apples to oranges with the shotgun comment.
About taking two hands to operate, just about every semi-auto pistol takes two hands to operate, for the first shot anyway.
But then again with the gun laws are, you may be right, perhaps not right now, but maybe next week.

[johnsonian09]

Also, they sell mares leg, lever action pistols here.. that definitely takes 2 hands. So a pump doesn’t seem like it should be a problem.


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