My solution to a non existent problem

[ericthered]

So i have been quite happy with my 9mm AR pistol. Until I woke up at a to early of an hour today, and went to looking about "bolt bounce" (was intending to look into bolt cant that piston guns get?). Long story short, I found myself quickly dissatisfied with the solid buffer in my pistol. Apparently its only a "thing" with machine guns, but my thought is (my gun is SA) that a solid lock lowers the chances of a out of battery discharge. And it should be more forgiving chambering weak ammo (have never had that issue with this gun).

So my solution was to take a solid buffer I had laying around that I made (see a trend here?) That weighed in at 5.5oz (stainless). I drilled 2" into it. For the sliding weights I just so happened to have a scad of tungsten pieces laying around. I used a 9mm shell that I sharpened with a case reamer to punch out some little plastic circles that I glued to the tungsten chunks. Completed the buffer weighs in at 6.65 oz.
I ran a magazine load of 115gr first with a aero 7.7oz solid buffer, then a mag with the custom buffer. Shooter feel they were so similar that I couldnt tell a difference (probably would have been easier to tell if I had 2 guns side by side). Im confident there probably was a difference, because obviously upgrades are supposed to be better.
I did a slowish motion video of the first three shots with each buffer, looking frame by frame, the 7.7oz solid buffer had a definite bolt bounce on two out of three shots (was 1/4-1/2" judging from the exposed cartridge).
The frame by frame of the custom buffer showed that I did not experience any bolt bounce at all.
I ran a total of 120 shots this morning using the custom buffer without any issues.

Last pic is the buffer and its pills, then just took a couple of pictures of the gun just because I like it. Ah, cant get the file size down far enough on the second gun picture. It is just with the can and handguard removed. It has a 5.5" barrel.

So more of the happy thoughts I tell myself is that my gun will last longer now...

 

[A&S Conversions]

This thread I found entertaining. Unless you can pull the trigger, release the trigger, and release the trigger again at the exact moment as the bolt goes into battery, then bolt bounce makes absolutely no difference at all. Personally I have had much more impact with "amphibian" suggestion using the CMMG rotary delayed blowback 9mm upper with the Kynshot 9mm buffer and Tubbs flat wire spring in a Vltor tube. Thank you for sharing your skills with us. I wish I had those skills.

Scott

 

[ericthered]

I looked into the cmmg stuff when I was putting this together, at the time there was no availability of their stuff. I did end up with a tubb flatwire ar10 spring, the gun doesnt seem to really care what spring I use however.
Hey, all it takes to have skill set is to buy the cheapest mini lathe you can find, and just start chucking up and slicing steel! A expert machinist may notice how I even incorporated "gas checks" into the buffer body. They are those staggered marks going down the entire buffer body. Which, i do not have any carbon buildup in my buffer tube, so I know they work!

 

[A&S Conversions]

As long as the spring has enough strength to strip the top round out of a fully loaded magazine, that is all a semi auto needs. And the heaviest buffer the blowback system needs is enough mass to hold the shell in the chamber during the high pressure phase. If you see the spent shell with the brass bulging near the bottom of the shell, the blowback system needs more mass. If a blowback bolt group is too light, the side of the shell can rupture. If that rupture is facing the ejection port, brass shrapnel could come flying out at the shooter's face. That would be very bad.

Scott

 

[ericthered]

Aye. I had previously had issues with the bulges when I was getting hammer follow previously (have another thread where that was resolved by swapping trigger). I have been referencing the uzi talk bolt page https://uzitalk.com/reference/pages/bolts.htm and using the 14oz micro bolt as what I wouldnt go lower then with my goofing around. As is probably plain to everyone that reads the junk I post, I am one of those yahoos that cant leave a perfectly good gun alone. Which if you think about it, my 5.5" barrel is most likely fine for a light bolt setup, but I would think that a longer barrel would most likely need a larger bolt weight (euphemistically mixing the bolt and buffer to a combined thing) to keep the bolt closed for that little bit until pressures drop to a safe point. So theoretically a 14oz bolt would be great unless using a longer barrel, then would possibly need a heavier mass.

 

[A&S Conversions]

In pondering this thread, I realized that I was incorrect. In the full auto system, the hammer is released by the auto sear a little before the bolt goes completely into battery. The ideal timing is that the auto sear releases the hammer such that the hammer strikes the firing pin at the exact moment that the bolt is in battery. This is very difficult to achieve. So the the factory timing is at or after that exact moment of the bolt (or bolt carrier striking the barrel extension, depending on caliber) strikes the barrel. If the hammer hits the firing pin before the bolt is in battery, the firing pin will not strike the primer with enough force for ignition.

The semi auto fire control can not release the hammer until the trigger is released, releasing the hammer from the disconnector, such that the hammer is held by the sear surface of the trigger. I don't know as the trigger spring could return the trigger such that the disconnector could release the hammer onto the sear surface of the trigger before the bolt group has cycled. Even if the hammer could be released by the disconnector before the bolt group has completely cycled, the hammer must be held long enough for the bolt group completes the cycle so that the hammer has a long enough throw to strike the firing pin with enough force for reliable ignition. So I don't know as a semi auto trigger could actually function fast enough to have bolt bounce effect semi auto ignition function because of the design of the of the semi auto fire control.

For those using the AR 9mm blowback system, I found https://blowback9.wordpress.com/2022/12/06/ultimate-gentle-recoil-9mm-ar/ to be interesting.

Scott

 

[ericthered]

I read that writeup on the link you attached. Very interesting. Which his combined weight for bolt, spacers, and buffer are going to be running pretty close to a full size Uzi. Which I would say that my Uzi is quite soft shooting. An ar15 with that amount of weight would probably feel different then the Uzi just based on how far foreward all of the weight is with the uzi and far back with the ar.
I really liked the buffer spacers he used. Would require a extended tube (which he used) to maintain the same spring rate

 

[Paul Kersey]

I realize I'm an old fart with an Olympic 9MM conversion (no longer made and often criticized), but I just switch uppers on my NFA M16 and insert the magazine adaptor, insert mag, and fire. I do not change anything and it has works perfectly for over 30 years. Within 20 seconds I can switch it back to my .556 upper.

 

[A&S Conversions]

It is great that your kit runs and you are happy with it's performance. Have you ever been interested in slowing the cyclic rate? Do you have any interest in the front sight being more steady during a burst? I have shot an Olympic 9mm kit back when I had a Colt M16. I found that the mags sucked to load and I couldn't find a mag pouch for the Sten mags with the square tubing welded on the back of them.

If the Olympic 9mm kit runs satisfactory for you, I am glad to hear it. I wanted to use my M16 in subgun competitions with family and friends. I found that the Olympic 9mm kit did not work for me. I spent a bunch of money trying to get the Colt blowback system slower and smoother in the Colt gun. I found a deal on a DIAS and put it in a factory Colt 9mm lower. It still wasn't as smooth as my brother's converted 94 with a sear in it. I am interested in trying this new recoil configuration out. I do run the Colt 9mm lower with the drop in and a DOE style upper every once in a while. I hav had better performance with Tubbs BLK OUT spring, Kynshot 9mm buffer, in the Vltor A-5 tube. I am willing to try the configuration above. I just need the longer receiver extensions and the extra weights. Nothing ventured, nothing gained. YMMV.

Scott

ETA, The full size Uzi is a great open bolt subgun. I just don't like the "double bump" of an open bolt. When you pull the trigger and the bolt group jumps forward feels like the recoil pulse. The first time I shot an open bolt gun was a full size Uzi. I could sware that I was shooting doubles, but the owner said singles. I had to put one round in the mag to be sure.

 

[Paul Kersey]

Yea- those STEN mags are a bitch to load without a tool! It is just a fun gun for the range, but as stated I love how easy I can switch back and forth by basically just switching uppers. I did have to sort through my STEN magazines to find the ones that run great.