So what does Mil-Spec mean???

**rob_s** · 01-24-09, 09:13

I like to think of the milspec for M4s like a building code; it is a base set of requirements, and if you deviate from those requirements you better have a good reason, be able to elaborate on and explain your reasons in an intelligent manner, and be able to document why your way is "better" and have an engineer willing to sign off and agree that it's "better".

**C4IGrant** · 01-24-09, 09:16

Originally Posted by rob_s

I like to think of the milspec for M4s like a building code; it is a base set of requirements, and if you deviate from those requirements you better have a good reason, be able to elaborate on and explain your reasons in an intelligent manner, and be able to document why your way is "better" and have an engineer willing to sign off and agree that it's "better".

I agree. The sad part is that VERY few companies can even meet the TDP specs let alone go above it.

C4

**Nathan_Bell** · 01-24-09, 09:24

Originally Posted by rob_s

I like to think of the milspec for M4s like a building code; it is a base set of requirements, and if you deviate from those requirements you better have a good reason, be able to elaborate on and explain your reasons in an intelligent manner, and be able to document why your way is "better" and have an engineer willing to sign off and agree that it's "better".

Yup, but that only works when you are dealing with folks who understand the codes well enough to do so.

We used #8 bar to tie all piers together even though most structures only required #6. The reason we told the inspectors we were doing that was that additional 16%(IIRC) strength of the bar. They were cool with that, as we could state why we were varying from what was set in the OBC.

The real reason was that it allowed us to have to stock one less size of bar and buy enough #8 to offset its increased cost as most of our piers were done in #8. So we could offer a "better" product for the same price as those who were trying to figure out how to get away with the minimum spec all of the time.

Reminds me a bit of a few AR mfgs.

**davemcdonald** · 01-24-09, 09:38

Originally Posted by C4IGrant

You cannot say your gear is Mil-Spec (meaning that you are using the term in order to convince people that it is quality) and then say that a part of what the TDP calls for is utterly useless or not needed!

C4

Testify Brother!

**Rider79** · 01-24-09, 11:13

What are the gas ports like on Stags? Am I ok running the carbine buffer that came in my LMT lowers with my BCM midlengths? And does the lower pressure mean I'm going to have problems running Wolf or PMC bronze in my BCMs?

**stlyns** · 01-24-09, 14:54

some info about gas port hole sizes-
I can't remember where I got this, it was along time ago.

Q: My Rifle has a short-stroking problem - the gunsmith says it may be a gas port problem. What are the correct sizes for the gasport?

A: Courtesy of Rick McDowell of Competition Specialties, NRA Life, USPSA Life, Master ( 105 E. Cass, PO Box 451, Osceola, Iowa 50213 Phone: (800)369-4481 / (641)342-2011 )

I have an Extraction Problem, is this related? How can they be fixed?The below gas port dimensions are the ones that I have accumulated while working on AR's for years. When someone is having problems with short stroking and their gas port is not within the below ranges, that is usually the main problem. On individual rifles I have varied both bigger and smaller with port sizes, but these were definitely exceptions, or there was no other choice due to poor quality parts we were working with.

For example;

11.5" barrel, .750" barrel diameter at the port, 3.850" from muzzle; Port should be approx. .086" to .094" in diameter. The smallest I have seen the port on these short barrels is .081" and it worked with some military ammo but not with some faster burning rate, commercial ammo. With the .086" port the military ammunition worked better but the commercial still wasn't getting enough pressure to work the carrier properly. The .094" port would work with both the high port pressure military ammo and low port pressure PMC ammo. Anything over .094" will cause short stroking/timing problems from too much pressure to the carrier and under .086" might cause short stroking for lack of pressure. To know if the port should be changed or not will depend on a few other things. Is the chamber narrower than it should be? Is the chamber rougher than it should be? Are the rings worn and allowing gas to blow by? Is the carrier key allowing gas to blow by? Etc., etc. Eliminate these variables first! With a smaller diameter barrel at the port, the gas port sizes will usually be a little smaller as well, given the barrel length is still the same.
Barrel Length Barrel Diameter Distance from Muzzle Min Port Size Max Port Size
11.5 .625 3.850 .081 .089
11.5 .750 3.850 .086 .094
14.5 .625 8.375 .063 .078
14.5 .750 8.375 .070 .086
16 .625 8.375 .063 .078
16 .750 8.375 .070 .086
20 .625 6.875 .086 .093
20 .750 6.875 .093 .096
24 .825 N/A .089 .089
These are of my own compiling and may not be 'spec', but I was never able to find this 'spec', so I made a list of my own from known good shooting, reliable rifles. And just as important, from the unreliable rifles that worked fine after the gas port was opened up or made smaller. Don't let a gunsmith drill out a port because of a short stroking problem that you might have! More than likely it needs to go smaller, not larger.

**stlyns** · 01-24-09, 15:05

http://www.everyspec.com/MIL-SPECS/M...).00000385.PDF
http://www.everyspec.com/MIL-SPECS/M...).00000387.PDF http://www.everyspec.com/MIL-SPECS/M...).00000386.PDF

**C4IGrant** · 01-24-09, 16:11

Originally Posted by Rider79

What are the gas ports like on Stags? Am I ok running the carbine buffer that came in my LMT lowers with my BCM midlengths? And does the lower pressure mean I'm going to have problems running Wolf or PMC bronze in my BCMs?

Don't know for certain. Since it is a carbine gas system though, I would run at least and H if not an H2.

On a BCM middy, the most I would run is an H.

You could have issues with under pressured rounds and softer gas system.

C4

**Rider79** · 01-24-09, 22:13

Originally Posted by C4IGrant

Don't know for certain. Since it is a carbine gas system though, I would run at least and H if not an H2.

On a BCM middy, the most I would run is an H.

You could have issues with under pressured rounds and softer gas system.

C4

The prvi is good, pressure-wise, right? I hope so, I got 2k more rounds on the way. Also, for the middy, I read somewhere on here about not using the crane O-ring with it. I'm running LMT F/A BCGs in 2 of my BCM middys, and a BCM BCG in the 3rd one. Anything I need to change?

**C4IGrant** · 01-25-09, 07:20

Originally Posted by Rider79

The prvi is good, pressure-wise, right? I hope so, I got 2k more rounds on the way. Also, for the middy, I read somewhere on here about not using the crane O-ring with it. I'm running LMT F/A BCGs in 2 of my BCM middys, and a BCM BCG in the 3rd one. Anything I need to change?

PRVI is just fine.

If the bolt has a 5 coil spring in it, then no need for the o-ring.

C4