Who makes the lightest bolt?

Even if it’s titanium, I’ll consider it (within my means that is).

tag for interest. I've only ever seen them in tool steel and stainless steel.

I wonder if it'd be possible to make a 3d-printed subcaliber bolt assembly - maybe with a metal insert for the bolt face to provide durability and proper chamber support?

Actually the reliability kits have weights to make the CMMG bolt heavier. With blowback you do not want too light a bolt it's really the only best way to slow down the bolt (good thing!)

2A Armament used to sell an AR-15 pattern .22LR assembly that featured a titanium bolt.  It also had dual recoil springs and a polymer buffer at the rear.
Below is a photo of what they looked like.  They sold dedicated barrels assemblies and conversion units (pictured). From what I recall, "high power" ammo was recommended (to overcome the recoil spring force?).


MHO, YMMV, etc.  Be powerful, be well.

I’m trying to get a semi auto that’ll cycle the CCI Quiet ammo at 710 FPS (the original stuff).  

I actually don’t care if it’s an AR15 type gun or whatever.  

The light weight bolt for the 10/22 by Volquartsen was junk.  Hence they stopped making it.  

Some feature weights to make the CMMG bolt heavier, and some do not. Every engineering design is a compromise of one sort or another. The Lakeside reliability kits comprised springs - a light hammer spring plus two or three stiffer than typical recoil springs. One would replace the standard hammer spring and then try out one of the stiffer recoil springs with the ammo one intended to use and clip coils one or two at a time till reliable operation was achieved.
Reliable operation generally requires a balance between reciprocating mass and combined spring forces (i.e., recoil spring plus hammer spring); to an extent, is magazine/ammo drag dependent; and in the case of full auto, auto sear trip force dependent.  Too much or too little in either direction of any factor can result in reduced reliability which of course is also ammo dependent.  Another consideration is the potential for breaking the welds that connect the frame rail section and back plate together. especially with regard to excess added reciprocating mass or using excessively lower powered springs.
All of which is to say, there's more than one way to achieve reliable operation, and even more ways to have unreliable operation.

MHO, YMMV, etc.  Be powerful and be well.

ETA: I haven't used CCI Quiet, but I've reliably shot a lot of CCI SV and some Remington SV and some RWS Subsonic in AR dedicated uppers with barrels of 4.5" (non-suppressed and suppressed) and 9" non-suppressed - shooting was done on an AR pistol lower or an M16 lower. In a 16" bbl. AR 5.56 and a 10.5" bbl. M16 5.56 suppressed (both uppers with a conversion unit), I've used the CCI SV and some Remington SV ammo.  I have all milspec parts in the ARs and M16.  The .22LR units are all standard CMMG.  Shooting full auto I use an Atchisson MKII/III pattern, one ounce anti-bounce weight.

I’m looking to make this a dedicated CCI Quiet upper.

Preferable to have the full 16 inch barrel, otherwise the performance drops off considerably.  I don’t mind adding a suppressor for additional noise reduction, will it give me any meaningful back pressure?  

I assume yes, but at 16 inches and only 710 FPS, it’ll be not much.  

2A Arms is completely out of the the 22LR market
I wrote to Lakeside about their spring kit.

FWIW, here's a list of some .22LR rifle bolt weights (or masses) that I assembled awhile back from a number of online sources and own measurements:

Various .22LR firearm bolt weight comparison  (Listed are all dressed bolts incl. extractors, FP, and FP springs, but without charging handles or recoil springs and guide rods.):

Charter Arms AR-7: 157.5 grams. (5.6 oz.)

Marlin Model 60: 151.4 grams. (5.34 oz.)

Ruger (std.) 10/22: 185 grams (6.5+ oz.)

Ciener’s Atchisson MkII/III pattern .22LR AR Conv. 142.8 grams (5.0+ oz.) [i.e., 1.5 oz. or ~43 gr. lighter than std. 10/22]

Own measured CMMG .22LR bolts: approx. 137 gr. (4.8+ oz.)

German 22LR AK Trainer: 184 grams

Aftermarket KIDD 10/22 .22lr bolt - Matte bolts: 6.5 oz. (184.3 g.); Scalloped bolts: 6.4 oz. (181.4 g.)


MHO, YMMV, etc.  Be powerful; be well.

I have a 2A Armament bolt/barrel and it does not cycle the CCI Quiet (710fps).  The bolt is lighter but there is substantial spring pressure.

Why don’t you start by cutting coils off the recoil spring?  My original Spikes dedicated upper had reliability problems years ago and they recommended cutting a link or two at a time until it worked.  I haven’t had a problem since.  Recoil springs are cheap and you could color code the end to know which runs the CCI Quiet.

Where to buy the springs?

If your set up is CMMG or similar, just order from TACCOM- AR22 recoil spring..

I’ve used the Lakeside Spring kit as sold by Black Dog Machine LLC but they show out of stock.   Horseshoe Bend Gun is listed as the source but I got mine from BDM.  I think Compass Lake Engineering sold the same spring kit at one time.


http://blackdogmachinellc.net/ciener-lakeside-spring-kit.aspx


Here is a link to HorseShoe Bend Gun but they don’t seem to show actual inventory.

http://www.lakesideguns.com/home.html

 Here's a link to some folks that make/sell stuff that you may be looking for.
The site also has a forum, so you might get some more info there.

FWIW....I'm sorta looking at doing some tuning for a suppressor on a Spikes ST-22 I recently bought used....so I'm in the same boat.

https://borebuddy.com/product-category/ar22/


Please try to keep updating this thread as you progress with your project.....I'm subscribed.

@IdahoPCCinc
@Steamedliver

Here’s some CMMG I stock at Midway Midway USA CMMG 22 conversion Survival Spring kit
You can use the CMMG springs in the Spikes however, you may have trim a few links to get it to operate smoothly.  One more thing, dry silicone or graphite lube on the slidy parts is superior in every way to wet oil.