Suppressors Glock 1/2-28 barrels are... metric-y!

[kombayotch]

Got a new Gen5 and decided to give this one an OEM threaded barrel because they were on for a good price. Received it, unthreaded the protective cap and saw this:

Thought that was a bit odd, so I threaded on an AAC piston and it looked like this:

There was the expected gap, but not as large as the secondary shoulder. I could see the piston was going over that shoulder. So, I unscrewed it and looked inside. It had been used on regular 1/2-28 barrels where the piston bottoms on the shoulder, so there was carbon on the inside face. I got a clear ring that showed the piston was bottoming on the muzzle (as is common on M13.5x1LH barrels).

Worked the same with my DA piston and noticed it was the same with their thread protector:

So, it appears Glock's 1/2-28 threaded barrel is designed like an M13.5x1LH barrel and the secondary shoulder is a distal feature intended to keep the suppressor aligned if it starts to unthread.

It doesn't bother me, the pistons bottom on the end of the muzzle on my MPX with it's tapered shoulder and it has never been a problem. Just found this interesting because I've never seen this on an imperial threaded barrel (with enough shoulder meat) before, so I thought I would share.

EDIT:

BTW, they've offset the crown so that it isn't affected:

T

 

[Zak Smith]

I'll say it. That was dumb of them to do.

 

[Yondering]

Be careful with bottoming the muzzle on a "shoulder" inside the piston, for a couple reasons:

1 - Some pistons look like there's an internal shoulder, but if you measure the ID of that shoulder it may be around .465"-.470"+ (nominally about .468"), which is just the internal thread depth for 1/2"-28. In other words, there's not actually a shoulder for the muzzle, it just stops against one spot on the threads and forces misalignment. Some others do have an actual shoulder that can be used, so just make sure you know what you've got and don't just eyeball it.

Also keep in mind the difference between a 9mm bore and 1/2"-28 internal threads is only about .055" per side (I'm approximating a bit, internal thread IDs do vary), so any internal shoulder there will be smaller than that.

2 - The carbon fouling you mentioned. I've found that can force misalignment too, if you use the same parts (either the piston or the barrel) with other components that register on the barrel shoulder and allow fouling buildup inside the piston shoulder and/or on the muzzle.

IMO, an internal shoulder only works well if those components are always paired, or at least always used as an internal shoulder setup and never mixed with a more traditional barrel shoulder register (by using either component on a different barrel or piston).

One solution of course is to have that barrel trimmed back at the muzzle so that it doesn't contact the internal piston shoulder, if there actually is one.

 

[mewillis]

I just looked at my G34 it's the same, I wish they would have stayed with the metric like the legacy Glocks.

 

[kombayotch]

Betting the new G19X they just released is the same.

@Zak Smith, do the 1/2-28 pistons you provide with your cans have a stop surface that will work with these barrels? I have one of your cans on order. Wondering if I need to order another piston for it that's designed specifically for indexing on the muzzle?

 

[carbonbased]

So here is my Rugged 9mm piston. Looks like it has an internal shoulder but it’s just the screw threads. I ran a pick around it and yep, screw threads.

Here is my factory Glock threaded barrel bought after the sale of the pistol. It’s dirty.

Here it is slightly cleaned up.

Threaded on fully and a piece of tape butted up against the end of the piston

Tape shows the piston is butted up against the barrel shoulder…I think.

So…I guess in my case I’m good?

 

[kombayotch]

I would think that Rugger pistons are designed with this in mind. Some pistons may be problematic though. I suspect there is a reason companies like Silencerco and Griffin have special muzzle indexing 1/2-28 pistons in addition to their standard ones. This kind of implies that the standard ones won't index on the muzzle even on something like a threaded G43/48 barrel that doesn't have a shoulder.

Found an interesting post from DA Mike on ARF regarding this. Apparently some of the P320 barrels are designed like this as well:

The Sig 320 factory 1/2-28 barrel threaded muzzle architecture is somewhat unique among 1/2-28 threaded barrels. It kinda looks like what you'd get if a "standard " 1/2-28 barrel and a M13.5 x 1 left hand barrel had a one-nighter that resulted in offspring. Like the left hand metric profile, the 320 barrel has an unthreaded section just behind the muzzle face, and another behind the threads where the "shoulder" would be on other barrels. The diameter of the unthreaded section behind the threads is a relatively tightly held at Ø.510-.511. The barrel behind this section is right at 14mm at Ø.5505. This leaves you with .020" per side for shoulder, with half of that eaten up by a ~.010 radius in the transition between the Ø.510-.511 section and the main barrel diameter of Ø.5505. This clearly sets this barrel up as a muzzle indexing barrel. A lot of 1/2-28 pistons are now set up for muzzle indexing straight from the manufacturer. This feature is in the form of a perpendicular bulkhead in the bottom of the 1/2-28 threaded socket with a hole big enough to pass a 9mm projectile. Tis is particularly necessary if you have a CZ-75 barrel or a Browning Hi-Power barrel, both of which have a main barrel shank diameter right at .500", which precludes any type of shoulder behind the threads. What could prove problematic is the Ø.510-.511 unthreaded section of barrel behind the threads on the 320 barrel. Most 1/2-28 pistons will have an unthreaded counterbore or lead-in at the rear. This lead-in is of course larger than .500", but how much larger is the question. To adequately accommodate the 320 barrel, this counterbore must be larger than Ø.511. Otherwise, the piston/suppressor will thread on and stop, or have an interference, between the Ø.511 diameter and the counterbore in the rear of the piston. When this interference occurs, it may feel like the piston is fully threaded onto the barrel, but it has not fully shouldered on the muzzle face. This tenuous relationship between piston and barrel will most likely be broken within the first few shots, and you're left with a loose suppressor on the barrel. A loose suppressor can lead to all kinds of issues. In response to this, we've opened up the counterbore in the Mojave 9 piston to accept the Ø.511 barrel section so that the muzzle face will index against the bulkhead/stop surface in the bottom of the bottom of the piston.

SilentMike
Dead Air
AAC 1998-2018

 

[Zak Smith]

We have a B model piston for the SIGs that don’t have a shoulder. Not sure if it would work on these or not

 

[kombayotch]

We have a B model piston for the SIGs that don’t have a shoulder. Not sure if it would work on these or not

I'd be happy to check for you!

 

[Yondering]

View attachment 8344332
So here is my Rugged 9mm piston. Looks like it has an internal shoulder but it’s just the screw threads. I ran a pick around it and yep, screw threads.

View attachment 8344333
Here is my factory Glock threaded barrel bought after the sale of the pistol. It’s dirty.

View attachment 8344334
Here it is slightly cleaned up.

View attachment 8344339
Threaded on fully and a piece of tape butted up against the end of the piston

View attachment 8344340
Tape shows the piston is butted up against the barrel shoulder…I think.

View attachment 8344336View attachment 8344337

So…I guess in my case I’m good?

Your piston doesn't have an "internal shoulder", it has a thread relief, which is there specifically to work with barrels like the one you're using.
A more conventional piston thread would reach all the way to the shoulder, which wouldn't work with your barrel of course.

When we talk about indexing on an internal shoulder in the piston, that would be at the other end of the piston threads down inside, where the muzzle would contact it.

 

[carbonbased]

Your piston doesn't have an "internal shoulder", it has a thread relief, which is there specifically to work with barrels like the one you're using.
A more conventional piston thread would reach all the way to the shoulder, which wouldn't work with your barrel of course.

Yeah, in so many words, that’s what I said?

 

[Yondering]

Yeah, in so many words, that’s what I said?

Not really, no. If you tried to say that, the picture you showed with that text said otherwise because it wasn't a picture of the area where an internal shoulder would be. That's a thread relief.

 

[carbonbased]

Not really, no. If you tried to say that, the picture you showed with that text said otherwise because it wasn't a picture of the area where an internal shoulder would be. That's a thread relief.

I think I see where we are miscommunicating.

I was not responding directly to your internal shoulder talk.

Looks like it has an internal shoulder but it’s just the screw threads. I ran a pick around it and yep, screw threads.

I was just saying that with my Rugged piston, there was NO internal shoulder, just screw threads. Obviously there’s thread relief there…didn’t bother to mention it as it’s plain as day.

Then I showed that with my setup, the outside shoulder of the piston seems to hit the main shoulder of the barrel (not the secondary mini shoulder).

I thought my example might be helpful for Rugged piston owners.

You dig?

 

[mewillis]

I dig because I have a rugged piston, it works perfectly on the new G threaded barrel and a Sico Sig TB which is the only 1/2x28 barrels it will be used on but I do see where there might be issues with other mfg. pistons. I do prefer metric but I guess G decided to get away from metric to inch because it's obviously more popular here but Sig is still metric afaik........

 

[Yondering]

I think I see where we are miscommunicating.

I was not responding directly to your internal shoulder talk.


I was just saying that with my Rugged piston, there was NO internal shoulder, just screw threads. Obviously there’s thread relief there…didn’t bother to mention it as it’s plain as day.

Then I showed that with my setup, the outside shoulder of the piston seems to hit the main shoulder of the barrel (not the secondary mini shoulder).

I thought my example might be helpful for Rugged piston owners.

You dig?

I think there's still some misunderstanding here, and my intent was to help provide some clarity on that. I do appreciate the level response though instead of how some people here take offense at little stuff like this.

The part where you mentioned a "secondary mini shoulder" is where part of the issue lies - that's not any kind of a "mini shoulder" at all, even though it may look like it if you don't have a lot of experience threading things. If you put a set of calipers on that, you'll find that it's the same OD as the threads, or within a few thousandths of it - prior to cutting the threads that "mini shoulder" section and the threads were all one straight section of barrel, then when the threads were lathe turned it left that relief cut (the groove) behind the threads leaving what looks like a shoulder but really has no possible way of acting like a shoulder for that thread size.

That's important to understand for other barrels too, like the Glock 43 and CZ 75 series that have ~.500" barrel ODs - when threads are cut in those barrels, they're left with the same relief that you called a "mini shoulder", and I've come across a number of people who think that butting the suppressor piston thread up against that is an adequate stop. It's not; it forces the piston and thread into the maximum amount of misalignment their tolerances allow. That's where an actual internal shoulder inside the piston (at the other end of the threads) is required for the muzzle to register against because there is no external shoulder.

Now back to your parts, you initially said you thought that piston might have had an internal shoulder but then picked at it saw it was not - that's what I was initially responding to, and the fact that if you'd understood the interfaces between this barrel profile and that piston better you would not have thought that was an internal shoulder. That internal relieved section of your piston is intended to be a close fit to the short straight section on the barrel that it slides over (I believe the thought process is that it'll help maintain alignment if the threads back off while shooting). However even if that section of the piston were relieved so much that there was a shoulder inside, it wouldn't do anything because there's nothing for it to stop against on your barrel. Again, understanding the barrel dimensions first is key, specifically the bit that your "mini shoulder" is just thread diameter.

I do see your ultimate conclusion of the piston stopping against the real shoulder is fine, and I have no disagreement with that. Just hoping to clear up the terminology and misunderstandings of the stuff in between.

 

[carbonbased]

I think there's still some misunderstanding here, and my intent was to help provide some clarity on that. I do appreciate the level response though instead of how some people here take offense at little stuff like this.

The part where you mentioned a "secondary mini shoulder" is where part of the issue lies - that's not any kind of a "mini shoulder" at all, even though it may look like it if you don't have a lot of experience threading things. If you put a set of calipers on that, you'll find that it's the same OD as the threads, or within a few thousandths of it - prior to cutting the threads that "mini shoulder" section and the threads were all one straight section of barrel, then when the threads were lathe turned it left that relief cut (the groove) behind the threads leaving what looks like a shoulder but really has no possible way of acting like a shoulder for that thread size.

That's important to understand for other barrels too, like the Glock 43 and CZ 75 series that have ~.500" barrel ODs - when threads are cut in those barrels, they're left with the same relief that you called a "mini shoulder", and I've come across a number of people who think that butting the suppressor piston thread up against that is an adequate stop. It's not; it forces the piston and thread into the maximum amount of misalignment their tolerances allow. That's where an actual internal shoulder inside the piston (at the other end of the threads) is required for the muzzle to register against because there is no external shoulder.

Now back to your parts, you initially said you thought that piston might have had an internal shoulder but then picked at it saw it was not - that's what I was initially responding to, and the fact that if you'd understood the interfaces between this barrel profile and that piston better you would not have thought that was an internal shoulder. That internal relieved section of your piston is intended to be a close fit to the short straight section on the barrel that it slides over (I believe the thought process is that it'll help maintain alignment if the threads back off while shooting). However even if that section of the piston were relieved so much that there was a shoulder inside, it wouldn't do anything because there's nothing for it to stop against on your barrel. Again, understanding the barrel dimensions first is key, specifically the bit that your "mini shoulder" is just thread diameter.

I do see your ultimate conclusion of the piston stopping against the real shoulder is fine, and I have no disagreement with that. Just hoping to clear up the terminology and misunderstandings of the stuff in between.

Ah, I think I see where you’re coming from. The “mini shoulder” not being a shoulder at all, actually having the same diameter as the threads, and that it sort of nests inside the Rugged’s thread relief. I think I get it.

I was so laser-focussed on making sure the piston shouldered up correctly to the barrel that I glossed over some of your finer points.

Thanks!

 

[Yondering]

Ah, I think I see where you’re coming from. The “mini shoulder” not being a shoulder at all, actually having the same diameter as the threads, and that it sort of nests inside the Rugged’s thread relief. I think I get it.

I was so laser-focussed on making sure the piston shouldered up correctly to the barrel that I glossed over some of your finer points.

Thanks!

Exactly.
Excellent, if some small part of that helped illuminate some detail that might be helpful in the future, that's all I'm after.

 

[carbonbased]

Exactly.
Excellent, if some small part of that helped illuminate some detail that might be helpful in the future, that's all I'm after.

Here’s the part where it is mandatory that we call each other idiots, mid-pack, etc lol

Good talking! I learned something today.

 

[kombayotch]

Fly 45 arrived. Got a 1/2-28 model "B" piston with it. It's basically the same as the AAC piston in the way it mounts. Same lock-up on the Glock OEM barrel as above. Mates on the shoulder on my Silencerco G34 barrel. Works on my G43X and G48 barrels as well (which require muzzle indexing).