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

[MQ105]

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

I'm interested to know what bit will drill that material.

[elephantrider]

I'm interested to know what bit will drill that material.

Carbide

[jerrysimons]

I'm interested to know what bit will drill that material.

I Need to get ahold of the guy in the eBay store. eBay says he is out on vacation and his shop is on hold. If that is real deal Inconel $15 for 5 is a great deal. I found one site with Inconel 10-32 machine screws $123.00 EACH!

[tom12.7]

If I can not find a base barrel with the porting that I am looking for on a particular combination for that barrel length, then I would first look for longer suitable barrels that may be cut down in length and open the port to what I'm looking for. If that option does not exist for whatever reason, then I would spin my own up out of a blank.
Different combinations erode areas in the barrel in different ways. Some of those will erode the port enough to push the cyclic rate higher than what may be wanted. In those cases, a secondary orifice can potentially extend a lifespan for that product. If a said combination though consumes the throat area in a way that balances out with the base barrel port erosion, maintaining a cyclic rate, then a secondary orifice is not required. Another combination may erode the throat more aggressively, and to maintain that cyclic rate range, you might want the barrels gas port to become less of a restriction, a secondary orifice would not help here.
When you use an orifice as a primary restriction in the gas block, you are applying a large quantity of heat and erosive power to that component. There is a limited amount of heat capacity that the added restriction has in total. This is true for a fixed screw orifice in a gas block, and an adjustable gas block's orifice. When you add the heat energy in, those parts have to deal with it. Normal straight threads and adjustable gas blocks do not really have enough contact area under tension to help transfer that heat well to their higher mass surroundings. I've seen many instances where such items eroded away. Another possibility would be to use taper threads on the fixed outside of the barrel orifice, the added pressure between the orifice and the gas block increases the rate of heat transfer, you could possibly insert an interference fit sleeve as well with good surface finishes for the fit.

[jerrysimons]

If I can not find a base barrel with the porting that I am looking for on a particular combination for that barrel length, then I would first look for longer suitable barrels that may be cut down in length and open the port to what I'm looking for. If that option does not exist for whatever reason, then I would spin my own up out of a blank.
Different combinations erode areas in the barrel in different ways. Some of those will erode the port enough to push the cyclic rate higher than what may be wanted. In those cases, a secondary orifice can potentially extend a lifespan for that product. If a said combination though consumes the throat area in a way that balances out with the base barrel port erosion, maintaining a cyclic rate, then a secondary orifice is not required. Another combination may erode the throat more aggressively, and to maintain that cyclic rate range, you might want the barrels gas port to become less of a restriction, a secondary orifice would not help here.
When you use an orifice as a primary restriction in the gas block, you are applying a large quantity of heat and erosive power to that component. There is a limited amount of heat capacity that the added restriction has in total. This is true for a fixed screw orifice in a gas block, and an adjustable gas block's orifice. When you add the heat energy in, those parts have to deal with it. Normal straight threads and adjustable gas blocks do not really have enough contact area under tension to help transfer that heat well to their higher mass surroundings. I've seen many instances where such items eroded away. Another possibility would be to use taper threads on the fixed outside of the barrel orifice, the added pressure between the orifice and the gas block increases the rate of heat transfer, you could possibly insert an interference fit sleeve as well with good surface finishes for the fit.

That is a great point about threads and their limited ability to transfer heat, the potential for the insert to retain more heat than is necessary due to insufficient heat transfer makes MQ105's use of turned-down drill bits with smooth walls and a friction fit seem like a better design in theory, also one would not have to tap the gas-block gas-admission port. But what I here you saying for threaded inserts is ... Inconel Bring on the heat baby!

How often does gas-port pressure decrease significantly enough to effect cyclic rate as a result of increased internal barrel volume owing to throat erosion? This is, as I understand your post, an instance where you are saying gas-port erosion and what would otherwise be an increase in cyclic rate stemming from a bigger, eroded gas-port hole actually compliments the pressure decrease resulting from the barrel's throat erosion and thus maintains the base cyclic rate. An insert maintaining regulation at the levels of the original port-size would thus be a liability to function in this instance.

Is throat erosion that significant and/or the margin of function in gas-flow that narrow for the above instance to be a common concern for the life of the barrel? I tend to use FN machine gun steel CHF barrels. Also I would tend away from using an insert to run the rifle to the ragged edge of function instead opting for a healthy but conservatively gassed regulation since this method is more fixed and semi-permenant compared to an adjustable gas-block.

[tom12.7]

Sorry if this is short, but I'm short on time right now.
You need to transfer heat well, not doing so only asks for problems. I have not looked into turned down drill bits, but I wouldn't think that it may be appropriate? It has no design intent for this, and I would suspect better alternatives could be used. A smooth surface interference press fit is simpler and transfers more heat that a straight thread, a tapered thread has the potential to do well though.
There's different inconels, they don't all have the same characteristics. The work hardening can make machining difficult. While I have not been exposed to all of them, the ones that seem more appropriate for this have not been easy to machine.
Erosion from the gas ports and chamber throats and cyclic rates. For the most common loadings, the 20" rifle gas maintains this better concerning cyclic rate. The carbine gas length tends erode the port more and bump up the cyclic rate more. Lighter bullets with slower powders tend to wear the port more. Heavier bullets with faster powders tend to erode the chamber more. I can go more into this later, if wanted.
Different combinations may benefit in cyclic rate consistency with usage using a secondary orifice in the gas block to maintain that range. Shorter length gas systems for the 5.56 can benefit, longer ones ammunition dependent.
For a generic response for using the gas block secondary orifice, can a 20" rifle gas improve with this? Not by much, but a carbine gassed 14.5" can see an improvement in a reduced span width of cyclic rate deviation with usage when comparing them to one that does not have a secondary restriction in the gas block.

[jerrysimons]

Inconel 718 Update:

Proof of concept





Got a steal of a deal on the base 10-32 threaded 718 Inconel bolts, $15 for 25 I was worried they may have been falsely advertised until I started to cut on them (took 2 Dremel cut off wheels just to chop off the tip)! Each bolt can make about 3 inserts if you can afford crewing up carbide bits enough to make 75!
http://m.ebay.com/itm/291918559723?_...-1&_mwBanner=1

Process:
Cut bolt
Trim with carbide end mill
Drill/rheam regulating hole
Cut flat head slot

This first one is kind of rough, I wish I had a better way to make the flat head slot. I got a carbide *100 countersink but coming to help index the drill bit. This concept insert was drilled with a cobalt steel bit very slowly (1 time use only), I also have carbide bits and rheamers coming to do this right. It is best to cut off the bolt to near the exact length desired for the insert because cut off wheels are much cheaper than the uncoated carbide end mill I dulled (won't cut Inconel anymore but still cut stainless) trimming to size.

[elephantrider]

Nice, well done. I wonder if I could do the screw slot any cleaner with a mill and a slitting saw? Might also make drilling the hole more on center easier as well? Unless, that was intentional?

[jerrysimons]

Nice, well done. I wonder if I could do the screw slot any cleaner with a mill and a slitting saw? Might also make drilling the hole more on center easier as well? Unless, that was intentional?

Thanks. No the off center hole was not intentional, even if it doesn't really effect function it wasn't what I was going for. The cobalt drill bit walked when I first started the hole, which was expected since I didn't have any kind of indexing for it, just went straight in on the flat surface. After seeing how hard this stuff is to cut using the cut off wheel and carbide end-mill I was surprised how well the cobalt bit did, of coarse one time use only. The walking is why I ordered the carbide countersink bit to make a cone to start the drill bit and to provide a little bit of a beveled gas inlet.
https://www.mcmaster.com/#2944a32/=16vemha

The flat head slot has me thinking, o don't know how best to do it it looks like crap done by hand with the cut off whee (it also walked off center on me). What are you thinking with a mill?

[lysander]

For the Mark II version?