History of Piston guns and running suppressors

[The_Swede]

Can someone tell me a little bit about the background on how piston AR15 became a thing?

Im specifically thinking about the 416. I have read a lot of different reasonings. Some say DI SBRs at the time of 416 invention were not very reliable and thats why some units saw a need for a piston gun. Others say it was because piston guns run much better when using a suppressor. Can someone clear this up for me?

What specifically is it that makes piston guns run better with suppressors should that statement be true?

If at the time of 416 fielding DI SBR in fact were less reliable then what has since changed in DI SBR configuration? What specifically makes a piston gun better when run with a short barrel?

[LRRPF52]

For the units that were shooting a lot of suppressed carbines, I think they were experiencing more early bolt and extractor failure due to higher cyclic rates and the shear forces of early unlocking on those components.

LMT actually had a great solution for this with the enhanced BCG, where the cam path was elongated like HK did to the AR18 when they made the G36, and one of the AerMet alloys was used for the bolt to increase strength of the tiny lugs and limited lug root, as well as cam pin hole walls.

https://www.m4carbine.net/showthread.php?3379-LMT-Enhanced-Bolt-Question&p=62128#post62128

I was talking with one of the Colt Canada (formerly Diemaco) engineers about all this, and he said they took high-speed camera video of the action comparing suppressed Stoner Internal Expansion and HK416 Op-Rod driven guns, and the regular Stoner gas system was more suppressor friendly as it unlocked later. The 416 immediately begins carrier movement because the gas hits the piston head, which instantaneously starts a rapid movement of the carrier.

On the standard Stoner gas system, there is a bit of a delay, because the gas has to pressure up the tube and expansion chamber inside the carrier to get enough BCG inertia for extraction and ejection.

My suspicion is that the units using the HK416 prefer it suppressed because the bolt is made from a superior alloy, and lasts longer in their high volume sessions. The carbon deposits are also moved to the front of the gun at the gas block and plug, rather than inside of the carrier and upper receiver.

Either way, I think 2 main approaches are more important than the method of operation for the action:

1. Flow-through suppressors that don’t significantly increase cyclic rate
2. Increased strength bolts

The big Army didn’t allow SOCOM to adopt the LMT Enhanced BCG upgrade for the M4A1 PIP because if those BCGs ended up in a RLGS M16, they would short-stroke the guns, so SOCOM responded by initiating an independent program to find their own carbines, hence the SCAR.

Another great solution for the AR15 bolt strength when suppressed is the KAC SR15E3 system, which has more lug root strength for both the bolt and the extension, and more cam pin hole wall thickness by using a smaller diameter cam pin.

[MegademiC]

Wouldn’t a proper gas port fix a lot of the issues? I realize there is a tighter tolerance required with sbrs(I think), so perhaps a reduced gas port for a silenced gun?

[vicious_cb]

@The_Swede

If at the time of 416 fielding DI SBR in fact were less reliable then what has since changed in DI SBR configuration? What specifically makes a piston gun better when run with a short barrel?

A little rubber o-ring, a copper washed extractor spring and a heavier buffer made all the difference. Today’s M4 FOW has evolved into a much more reliable system than even 10 years ago.

It doesnt, not anymore. HKs outlasted Mk18s because they are overbuilt HKs, not because of their piston system. The only thing a piston has over a DI gun is in OTB operations.

[MistWolf]

@MegademiC

Wouldn’t a proper gas port fix a lot of the issues?

Yes. Yes, it does.

[MQ105]

@vicious_cb

…The only thing a piston has over a DI gun is in OTB operations.

I think this is the biggest reason some units chose a piston-gun.

[Renegade]

@The_Swede

Can someone tell me a little bit about the background on how piston AR15 became a thing?

Im specifically thinking about the 416. I have read a lot of different reasonings. Some say DI SBRs at the time of 416 invention were not very reliable and thats why some units saw a need for a piston gun. Others say it was because piston guns run much better when using a suppressor. Can someone clear this up for me?

What specifically is it that makes piston guns run better with suppressors should that statement be true?

If at the time of 416 fielding DI SBR in fact were less reliable then what has since changed in DI SBR configuration? What specifically makes a piston gun better when run with a short barrel?

Well first, piston guns were a thing long before the 416. I would say the commercial market popularized them first. I had used several conversion kits myself long before the 416. Can’t remember them all but the Ares kit was one of them.

I tried it to see how it worked. I was doing a lot of heavy F/A fire, with can. The piston clearly dumped less crud into gun, and less heat. So for me it was an obvious win.