Gas-port regulating gas-block insert install and DIY manufacture.

[MQ105]

You're on to something. I've made my own inserts from a drill bit, but these seem easier in that they are already threaded. I think the alloy steel versions McMaster-Carr has would be better than the SS. The SS are B80 and the alloy are C45 rockwell, which is harder.

[jerrysimons]

You're on to something. I've made my own inserts from a drill bit, but these seem easier in that they are already threaded. I think the alloy steel versions McMaster-Carr has would be better than the SS. The SS are B80 and the alloy are C45 rockwell, which is harder.

Yeah, thanks for bringing that up. I noticed that a few days ago and just finished studying up on the Rockwell hardness scale. That is a significant increase! Though alloy steel is more susceptible to oxidation with its coating removed after machining. I am thinking the 1/4" long alloy-steel, non-vented, cup-point set-screws might be what I use going forward, after I think more on the matter. What do you think?

With either grade of steel I like the deeper regulating hole of the 1/4" screws and the increased machining time to shorten them is not significant since I am only manufacturing these for personal use.

[MQ105]

I used drill bits because I figured the metal was fairly hard and I wanted as much length (depth) for the port in the insert as possible. I made the first few without threading. I turned down the drill bit shaft that I used for stock using a drill for a lathe, and file and sand paper to get a compression fit. I thought threading might be better and quicker to make. Your idea will make it faster yet.
I've made 8-10 inserts so far while trying to dial in a few 10.5-11.5" barrels. I had to make so many because I kept making the port too large. Now, I start quite small and work my way up. For example, in my Sionics 11.5 I am running a .0595" (#53 bit) port and it cycles and locks back with Wolf Gold - without a suppressor. I am going to try .0550 next.

[tom12.7]

I'm all in for a simple solution that adds a secondary fixed orifice in the gas block that compliments gas regulation for a specific gas port size to maintain a cyclic range to help counter erosive wear.
With all of the negatives involved, I would not be inclined to choose the primary orifice in this location. Look at the broader spectrum of what all is involved.
Using a R&D tool that was intended to help determine a fixed size barrel port is not the same as using that said base barrel port in the long term. Too many negatives come up.

[jerrysimons]

I'm all in for a simple solution that adds a secondary fixed orifice in the gas block that compliments gas regulation for a specific gas port size to maintain a cyclic range to help counter erosive wear.
With all of the negatives involved, I would not be inclined to choose the primary orifice in this location. Look at the broader spectrum of what all is involved.
Using a R&D tool that was intended to help determine a fixed size barrel port is not the same as using that said base barrel port in the long term. Too many negatives come up.

Tell me about the negatives.
I am all for properly ported barrels but options are limited. For 12.5" you have CA. For 11.5" you have KAC complete uppers or a Sionics RGP barrel. Maybe V Seven Weapons for a stainless option from some reports.
That's all I know of.

Comparatively I think gas-port regulating gas-block inserts, while less than ideal porting in the barrel itself, are the most simple and most robust method of regulation available, beating out adjustable gas-blocks, adjustable gas-key/bolt carriers, etc.

Now I have learned from you that one of the draw backs of secondary regulation is that the larger gas-port hole in the barrel you are regulating still introduces more internal gas-port erosion than a smaller gas-port would in the same barrel over time. The secondary regulating orifice does nothing to lessen the amount of hot, expanding gases and powder particulate escaping from around the rear of the bullet at the barrel's internal gas-port opening and blasting the muzzle side wall of the gas-port hole. Thus erosion degrades the rifling and increases cyclic rate as erosion increases the hole's size.
I see that you would therefore like to pair a properly sized gas-port in a barrel with a correspondingly sized gas-block insert to maintain cyclic rate over time as the barrel's gas-port erodes internally, which puts the limiting factor in barrel life on the accuracy parameter over the cyclic rate. With that in mind though I am not necessarily starting with huge, gapping gas-port barrels. I'll be putting a .065" insert over a .071" Noveske 12.5" carbine barrel. Even BCM ports their 11.5" carbine barrel at about .076" and nobody is complaining about poor barrel life due to gas-port erosion. I see what you are saying about erosion but if I regulate a BCM 11.5" carbine barrel down to .067" orifice with an insert I have successfully reduced cyclic rate and at worst still have the same internal gas-port erosion an otherwise high quality barrel would have had with a .076" carbine gas-port in the first place. Even with gappingly sized gas-port barrels already owned this insert method still successfully reduces cyclic rate as a stop-gap solution.

Lingering questions I have are: what level of erosion is the insert itself subject to and what kind of round count/firing cycle can be expected before significant degradation of the secondary orifice size? Also how does actual barrel gas-port size correspond to the size of the secondary orifice regulating flow in the gas-block? So far I have just went with the size insert I think the gas-port in the barrel should have been.

In the absence of proper barrel porting from the factory would you prefer to take a factory barrel and have it cut down to length and then potentially also rheam the gas-port open a little instead of using a robust secondary regulating method like gas-block inserts?

As always, thanks for your participation!

[elephantrider]

Re: port erosion. The port erosion will likely be the exact same with or without one of these inserts, so not likely an issue unless the barrel was going to have port erosion issues to begin with (huge oversized port, or really soft steel, accelerated erosion). So assuming a port is only slightly larger than it needs to be to start with, I doubt it'd be a problem. I'd be more concerned with insert erosion.

Also how does actual barrel gas-port size correspond to the size of the secondary orifice regulating flow in the gas-block? So far I have just went with the size insert I think the gas-port in the barrel should have been.

I think (so don't hold me to this) I've seen Clint post that the inserts can be a bit smaller than the "correct" port size because they don't quite regulate the gas down as well as the barrel port. So maybe go down one drill size from your "correct" barrel port size.

[jerrysimons]

Re: port erosion. The port erosion will likely be the exact same with or without one of these inserts, so not likely an issue unless the barrel was going to have port erosion issues to begin with (huge oversized port, or really soft steel, accelerated erosion). So assuming a port is only slightly larger than it needs to be to start with, I doubt it'd be a problem. I'd be more concerned with insert erosion.



I think (so don't hold me to this) I've seen Clint post that the inserts can be a bit smaller than the "correct" port size because they don't quite regulate the gas down as well as the barrel port. So maybe go down one drill size from your "correct" barrel port size.

Yeah those are my impressions too on a barrel's internal gas-port erosion and using inserts. Start with a good barrel which usually are not too badly over gassed and it likely will not be an issue practically.
I am curious about insert erosion aswell but the internal gas-port on the barrel takes the brunt of the powder blast. The insert sees less pressure and less particulate since the gas already turned the corner and the muzzle side wall of the gas-port already served as a blast baffle of sorts. Still I can make an insert out of harder steel with a deeper hole than others, so why not I guess, it can't hurt.

The orifice size being able to be smaller at the insert is interesting, that would jive with the sizes that MQ105 posted above for his 11.5" carbine gas!

[jesuvuah]

I might have to try this. I have a 10.5 chf PSA upper that I am sure was over gasses to begin with. Now that I added a suppressor I need to try something. I have a ffs so this is probably my best option

Sent from my Z797C using Tapatalk

[jerrysimons]

Here we go
Inconel 718 made 10-32 threaded screws...what insert erosion? This is bound to chew up some drill bits and the carbide end mill! Chop saw off the head past threads, then trim to length, drill and grind a flat head slot.

http://www.ebay.com/itm/5x-SPS-Incon...-/291647502770

[elephantrider]

Here we go
Inconel 718 made 10-32 threaded screws...what insert erosion? This is bound to chew up some drill bits and the carbide end mill! Chop saw off the head past threads, then trim to length, drill and grind a flat head slot.

http://www.ebay.com/itm/5x-SPS-Incon...-/291647502770

LOL, you read my mind. Inconel... it's the only way to be sure.