SIG M400 SRP

Had the opportunity to pull apart a SIG M400 SRP - 16" 1/7. Interesting aspects - I was really surprised to see such a small gas port. I dropped gauge pins in the port and it appears to be .059" port.
My .0595" pin would not go in (barely) but the .055 pin dropped right in. I'm guessing a 1.5mm port or .0590. The other interesting aspect was that the barrel extension had two holes machined through the sides. One was at 8 o'clock and the other was 180 deg opposite at 2 o'clock. The 2 o'clock hole was plugged with a pin and the other hole was open.
Thoughts?
I'm guessing it was for tooling that installs the extensions - but that's just a guess.

I test fired it after reassmbly (hand guard / gas block / muzzle device upgrade) and it was a nice soft smooth shooting rifle. (M855) It was fired on a different lower with an H2 buffer and a Springco Blue.
Sweet upper.

FWIWAttachment 33022

Tagged for some good information

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Originally Posted by opsoff1

Had the opportunity to pull apart a SIG M400 SRP - 16" 1/7. Interesting aspects - I was really surprised to see such a small gas port. I dropped gauge pins in the port and it appears to be .059" port.
My .0595" pin would not go in (barely) but the .055 pin dropped right in. I'm guessing a 1.5mm port or .0590. The other interesting aspect was that the barrel extension had two holes machined through the sides. One was at 8 o'clock and the other was 180 deg opposite at 2 o'clock. The 2 o'clock hole was plugged with a pin and the other hole was open.
Thoughts?
I'm guessing it was for tooling that installs the extensions - but that's just a guess.

I test fired it after reassmbly (hand guard / gas block / muzzle device upgrade) and it was a nice soft smooth shooting rifle. (M855) It was fired on a different lower with an H2 buffer and a Springco Blue.
Sweet upper.

FWIWAttachment 33022

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IIRC, that is a feature from their piston rifles that prevents the extractor from jumping off of the case rim during extraction. I'm assuming that that hole in the barrel extension is for the installation of that plug.

Brilliant engineering.
This was on a DI gun - but clearly has applications for either.
Learned something today, thx Buford.

Can you post a pic of the inside of the barrel extension if you took one? I wonder if they've changed the extractor support since we've seen a few complaints of it coming out.

I did - can you see what you were looking for?

Pretty sure thats the way all m400 are,mines like that and its an older model than yours think mines a 2013.
I know a bunch of people that have them,one guy on here had a problem with the extractor support falling out on his,but ive never seen one do it. Ive never seen anyone have a problem with one either.

I think the function of the extractor support is to keep the extractor from flying out and hurting someone in case of an over pressure.ive also been told Hk 416 has the same thing.(not 100% on that one though.)

I put a BCM full auto bolt carrier group in mine,but never had a problem with the stock one,or the rifle itself. Soft shooting,accurate as i can shoot it,nice fit and finish and throws .223 at 4 oclock in a little pile all day long.

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Originally Posted by texasgunhand

I think the function of the extractor support is to keep the extractor from flying out and hurting someone in case of an over pressure.ive also been told Hk 416 has the same thing.(not 100% on that one though.)

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Yup, stolen straight off of a 416. My understanding was that it was for OTB.

There was a thread a while back where something went wrong with the pin (i think?) That Sig puts in the barrel extension, backing out and causing malfunctions. Ill try and find it.

Here:https://www.m4carbine.net/showthread...00-malfunction

I think its pretty random. Khaos is the only one ive seen have problems. They have had the same problem with the hk416. I know many people that shoot alot and have never experienced it. I saw i guy shooting one with such hot reloads , it hurt my ears with plugs in.when he shot a box of cheap ammo next it sounded like a cap gun compared to the reloads

Altho i will say i wish they would have not used them,its just another part that can break. (KISS)
Usually when you have a major kaboom with an m4 the extractor is the least of your problem.

I also dont see many people doing the over the beach thing either. If you want to do that use a piston gun,NO DI gun is gona like it very much..