Benevolence

If you’re trying to just remove the ‘black’ aspect of it and make it shiny metal, just use rust remover (naval jelly) carefully. Don’t know why you would want to do that but it’ll make it bare metal-ish

Just my two cents: watch your temps on the nitriding; you could get some distortion or make it brittle (400-580C). I've had some stainless medical devices that rusted after laser engraving as well. Also, nitriding is a surface treatment, not a coating. Would recommend laser engraving followed by DLC. I've had some distortion issues from CrN but DLC is usually quite a bit lower temperature.

In addition to the posts above, I would recommend mosinvirus' videos on youtube. Those in conjunction with the Kunhausen books will help you understand the details. You need to fit the barrel hood, then locking lugs (~0.050" of vertical locking engagement on the hood), then the legs (aka lower lugs) of the barrel to the frame, and finish with some filing of the radius of the lugs to allow for the link pin to pull the barrel down. This is quite an indepth process and requires some 1911 fitting tools that can be found on brownells. It sounds like the radius on the lugs needs some relief to allow for the slide stop pin to clear it.

This may show my ignorance, but I believe too much overtravel on a trigger can let the trigger bar push the sear reset leaf and you end up with a dead trigger or hammer follow?

Earlan357 did some modifications on the disconnector as well as got different springs for the internal FCG (trigger return springs?) and it changed the trigger quite a bit. That’s a bit more involved than just a recoil/striker spring changeout but just to show more can be done. I’m having a hard time finding his thread but it’s out there, maybe on czfirearms.us

If you’ve a good live center method of holding the tap/tap-handle aligned with the drill press chuck and hand turning it in I would do that. Keep the same X,Y location when tapping as drilled (don’t move between steps unless you’ve a good dial/DRO), and back out half a turn (or when you feel the thread chip break off). Pull it all the way out and clean it out every 3 or so full turns. Hopefully you’re working with 6-32 or larger? I never was able to get my 4-40 taps to not snap in 416 stainless.

Not sure what design route you're going for, but I would start with a 80% or junky lower, drill some holes for retaining pins across the magwell to fit your magwell features/prototypes in. Design the prototypes in solidworks and find someone that can 3d print them out of polymer and ship them to you. Shouldn't be expensive and you avoid gunsmiths/FFLs.

If I understand correctly, you’re saying the gas behaves incompressible until it begins expanding in the carrier, and restricting at the gas port only increases the velocity, decreases the delivered mass and doesn’t affect the pressure of the gas. And that the benefits of the gas length are two fold; decreased port (and delivered) gas pressure and velocity into carrier. I suppose the Fat Boy or (perhaps more gimmicky) pig tail gas tubes could be an option. Oh, and I don’t really see how measurements of pressure at the ports and carriers are irrelevant or table talk; I was just trying to present those as they seemed relevant and to demonstrate that there was a pressure decrease in the carrier chamber vs port. I thought it was due to pressure losses along the way and hoping to understand the gas pressure/velocity in relation to the bullet position relative to the gas port and muzzle.

Thanks; I’ve read a fair amount and your posts seem to have some good content so I was hoping to get your thoughts. Also how easy it is to be flat out wrong with over analyzing things without actually trying it and overlooking things that are important. Just trying to understand the recoil from a fundamental perspective. I’ve got a 11.5” carbine (Spikes) JP SCS with white spring and thinking about replacing the steel weights with a Teflon spacer. That, and milling lightening cuts in a F/A carrier and putting in a POF cam pin. Hoping to use the AGB in conjunction with it to get the recoil tuned down. I guess I can math all day but it comes down to actually just trying things out.

Huh, that’s interesting. This mil report (BRLR 1475) seems to show the bolt carrier pressures only hitting about 2.5ksi, which seems like there’s expansion and restriction of that metered gas to a lower pressure than the chamber pressure. I’d think further restriction by a restrictive adjustable gas block would lower that carrier pressure more? From another article showing gas port size (restriction) effects on carrier chamber pressure: Maybe @TonytheTiger has some input on this?

I’m going to nerd out here a bit in order to describe my understanding of the gas operation and but I was hoping to have a discussion about the effects of barrel length on recoil and the methods of reducing recoil. The general consensus as I understand is that a 18” rifle gas length AR is the lowest recoil barrel-gas system combination. It has a 12” port distance, with 6” of dwell length and 0.13ms of dwell time. Pressures are 19.6ksi at the port and 14ksi at the muzzle. I would consider this the ‘working pressure’ range that is used to operate the carrier during the pressure stages when it is accelerating. Generally the carriers have an operating internal gas pressure of 2.2ksi (and an area of ~0.2in^2) and reach a velocity of 15ft/s. So, there’s a significant reduction in gas pressure between the port and carrier chamber even without an adjustable gas block. The rifle I’m trying to reduce recoil on has an 11.5” barrel with 7” carbine gas length, so 4.5” dwell length and 0.13ms dwell time but pressure of 33ksi and 22.6ksi for port and muzzle. As I understand it, the bullet leaves the barrel and gas pressures decrease before any carrier movement really occurs, and you certainly don’t have unlocking; I’m basing this off slow motion video and the relative velocity of the carrier to bullet (~0-15ft/s vs 2500+ft/s). The timing effects of the gas tube length don’t seem important because of how fast the pressure moves, even relative to the bullet speed and certainly the carrier. That acceleration of the carrier has to occur during the dwell length/time of the bullet between the port and muzzle, which for these two barrels are the same. With an adjustable gas block to act as a restrictor and decrease the gas pressure to the carrier, and similar dwell times, I don’t see how the gun would behave any different between a carbine 11.5” and a rifle 18”. The extra gas pressure at the muzzle certainly could contribute to recoil, however the bullet is also going slower; furthermore, more gas pressure helps operate a muzzle device (like 9mm minor vs major with a compensator). Then you can further do all the standard tuning to reduce the parasitic loss of energy from friction (carrier, bolt, feed lips and feed ramp polishing), followed by moving mass/spring ratio/gas block adjusting) to have the bolt hold open on last round but not have the buffer bottom out on the extension tube. With all of this done, why would the recoil be any more (if anything, less) than an 18”? I had a suppressed 10.3” that was harsh on recoil but was obviously overgassed. This link (https://www.ar15.com/forums/ar-15/How-it-Works-The-AR-gas-operation-and-how-everything-works-in-harmony-/66-266108/) has a great explanation of the gas operation but one thing I don’t understand is how the carrier and bolt can already begin to be extracting a round before the bullet leaves the muzzle (in an overgassed situation). The symptoms seem to agree with it but it is surprising; that’d have to move ~1/2” at an average velocity of ~100in/s whereas the bullet has to move 4” while it’s going ~30,000in/s, which is an order of magnitude more time... Thoughts, experiences?

Try forcefully inserting a mag with the slide off, ejector on, but unpinned. Does it lift up the ejector? If so, that’s your problem and where you’ve got to remove material. Also make sure to try it with a fully loaded mag to see if the brass presses it. Just my thoughts, take it for what it’s worth.

I had that issue and it was the magazine over insertion bending the ejector up and out into the slide. The dawson precision mag release seems to have fixed it after I replaced the ejector, but I took some material off the bottom to prevent it from happening again if I really slam a magazine home.

Okay, thanks for the information, I appreciate it. I am returning the cylinder reamer and decided to rent a 460 Rowland reamer and do it right especially with how high pressure of a cartridge this is.

I purchased a Clymer .45 ACP reamer with the intent to ream a barrel out to fit a 460 Rowland (I have the compensator and stiffer recoil spring, and this is in a fnx45T). Unfortunately, in my naivety I got a cylinder and not a barrel reamer so the solid pilot is larger and doesn’t fit (.455 vs .445 I believe). It also appears that the cylinder reamers have a constant diameter throat whereas the barrel reamers have a taper ‘lead-in’? I was thinking of turning down the solid pilot to fit in the rifling and use to ream the extra 0.063” required for the 460Rowland. My question was if the difference in throat (if there truly is) will increase pressures or decrease accuracy drastically. The bullets used for this are hard cast, powder coated lead going at a healthy speed (I suspect gas checked). If I understand it correctly, the jump should be good for lead bullets and perhaps even help decrease pressure relative to tapered?