Ar15 gas block dimensions

[d0091sa]

I've wanted to make one for a long time and wanted to see if anyone had a verified "known good" print.

Specifically looking for the gas hole spacing.

I can of course post pics of the whole process if anyone was interested.

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[Carcassonne]

There are M16/M4 prints on the internet.


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[d0091sa]

There are M16/M4 prints on the internet.


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Those don't include the gas block specs unfortunately.

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[Quickdraw559]

What is gas hole spacing? Why don’t you just buy and replicated a gas block that you like?

[d0091sa]

Because that's not the right way to do it lol.

Surely someone has the colt gas block print.

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[Quickdraw559]

Because that's not the right way to do it lol.

Surely someone has the colt gas block print.

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I understand that, I’m just unsure that you even need them.

What is it that you’re looking for? (Other than the prints )

[d0091sa]

Gas port hole location, barrel hole tolerance, gas tube tolerance, and all other hole location distances and tolerances.

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[Quickdraw559]

Gas port hole location, barrel hole tolerance, gas tube tolerance, and all other hole location distances and tolerances.

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Have you gone to google images and searched for ar15 gas block dimensions? Quite a few manufacturers have their drawings up.

[d0091sa]

Have you gone to google images and searched for ar15 gas block dimensions? Quite a few manufacturers have their drawings up.

I have and I've made a few and the dimensions aren't correct in some aspects. Or they work but you just know it's not perfect.

Figure having a colt print would be the way to go.

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[ar15barrels]

I've wanted to make one for a long time and wanted to see if anyone had a verified "known good" print.

Specifically looking for the gas hole spacing.

Surely someone has the colt gas block print.

Gas port hole location, barrel hole tolerance, gas tube tolerance, and all other hole location distances and tolerances.

I have and I've made a few and the dimensions aren't correct in some aspects. Or they work but you just know it's not perfect.

Figure having a colt print would be the way to go.

There is NO milspec colt gas block drawing because there has never been a milspec for an AR type rifle with a gas block that was produced by colt.

Now if you were asking about the front sight, you will find some of the details you are looking for on the barrel drawing since the gas port has to be drilled before the front sight base can be affixed.
However, the fsb is spaced forward by the handguard cap so if you want a gas block to slide all the way back against the barrel shoulder, you have to add material to replace the handguard cap since gas blocks are usually used on freefloat handguard systems.
The location of the gas port in the gas block is not super critical as the gas port is commonly 1/16" to 3/32" smaller than the gas path in the front sight base of gas block so there is LOTS of room for misalignment without causing a problem.

I know all the values you are asking for off the top of my head but I doubt you would believe me because I am not Colt.

You can reverse engineer most parts on an AR type rifle because Stoner and Sullivan made most dimensions in even 16th's.

[d0091sa]

It's not that I don't or won't believe you, I've just had some conflicting info given on tolerances.

For example, the barrel hole being 0.740 -0/.0002 to -0/.001 well which is it lol

Then the gas port hole being between .275 to .310 that's a huge range there and depending on the barrel is acceptable. I believe .295 is the actual distance from the barrel ridge to the port hole?



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[Carcassonne]

It's not that I don't or won't believe you, I've just had some conflicting info given on tolerances.

For example, the barrel hole being 0.740 -0/.0002 to -0/.001 well which is it lol

Then the gas port hole being between .275 to .310 that's a huge range there and depending on the barrel is acceptable. I believe .295 is the actual distance from the barrel ridge to the port hole?



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0.275 to 0.310 is 0.035. That is about the thickness of the hanguard cap.

https://www.scribd.com/document/132913635/M16-Drawing-Set

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[ar15barrels]

It's not that I don't or won't believe you, I've just had some conflicting info given on tolerances.

For example, the barrel hole being 0.740 -0/.0002 to -0/.001 well which is it lol

Then the gas port hole being between .275 to .310 that's a huge range there and depending on the barrel is acceptable. I believe .295 is the actual distance from the barrel ridge to the port hole?

The gas port should be 0.295" from the shoulder on a milspec barrel.
That accounts for 0.275" from the rear face of the front sight base to the centerline of the gas passage and 0.020" of handguard thickness.
Some non-milspec barrels have the shoulder located an extra 0.020" forward because they were intended to be used with a gas block and not a handguard cap and front sight base.
Some non-milspec gas blocks have an extra 0.020" added to the rear face so they can sit on a milspec barrel without a gap.

The real deal colt dimensions are 0.275", 0.020" and 0.295" based on my measuring hundreds of colt barrels and front sight bases.

Barrel diameter at the gas block seat should be 0.7498 to fit the 0.7500 honed hole of the FSB.
I have measured lots of colt front sight bases and they all fell within a 0.7500" -0/+0.0001" dimension so a 0.7500" -0/+0.0002" spec is probably correct on the bore.
Many gas block makers go bigger than 0.7500" but it's not necessary as most QUALITY barrel makers stick to the 0.7498" max barrel diameter.
Crappy barrel makers hold crappy dimensions and it's not uncommon to need to fit a crappy barrel to a gas block.
It's far less common to need to fit a crappy gas block as they run loose far more often than they run tight.

[d0091sa]

Perfect, so would it be safe to say if need to make two sizes for the port locations k to match the .295 and shorter?

Long story short, I've got a customer/friend that's commissioned me to make 4000 gas blocks with no print and I'd like to make it right.

Think holding a -0.000/+0.0008 tolerance on the barrel hole will be good enough or should I tighten it up? I'm trying to get away with high speed reaming all holes instead of bringing out the big Kaiser boring heads.

I've got the cycle time down to 2 min 10 seconds per gas block now with this approach.



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[ar15barrels]

I have an M16 front sight base drawing from the department of the army at rock island arsenal.
It calls out a 0.6249" bore with a +0.0005" tolerance.
They do not call out a negative tolerance so I would call that a -0/+0.0005" tolerance.
Army specs are obviously looser than what Colt works to based on measuring actual parts.