You essentially have two choices of regular blowback or delayed blowback.
1. Regular Blowback - Like shooting 22LR 10/22, chambered round is "held" against chamber only by recoil spring tension and weight of bolt/buffer. As soon as sufficient chamber pressure builds, round will start to move back from chamber leaking gas around the case neck.
If you go with regular blowback, hybrid bolt meant to work with Colt/Glock pattern magazine will work.
Since you are shooting competition, your objective would be to keep the front sight flatter with less bouncing around for faster follow up shots. With carbine recoil spring, 19-22 oz combined weight of bolt and buffer produces more comfortable felt recoil and will keep the front sight more steady on the target. (16-18 oz combined weight produces harsher felt recoil and will make front sight dance around more) -
https://www.thehighroad.org/index.php?threads/pistol-caliber-carbine-builds-parts-sales-and-what-parts-did-you-use-and-why.825314/
- H1 buffer weighs 3.8 oz
- H2 buffer weighs 4.6 oz
- H3 buffer weighs 5.4 oz
- H4 buffer weighs 6.8 oz
My PSA hybrid bolt weighs 14.7 oz and PSA buffer weighs 5.3 oz for 20 oz combined weight and produces comfortable felt recoil with various 100/115/124 gr 9mm loads. For longest "in battery" dwell time for more consistent chamber pressures, use heaviest buffer that will reliably cycle the bolt.
Some match shooters have found using heavier H4 buffer with around 22 oz combined bolt/buffer weight "short stroked" bolt cycling (No slamming of buffer against back of tube and less slamming when returning to battery) that improved total run/split times while keeping the front sight flatter with less bouncing around.
If you want to fine tune, I would consider the TACCOM 3 stage adjustable recoil system -
https://taccom3g.com/product/taccom-pcc-adjustable-buffer-system/
- Designed for carbine buffer tube length
- For use in blow back actions only
- Comes with either Enhanced Carbine Spring or flat wire spring*
- 6.2 ounces
- 3 stage action
- Allows for the BHO to function
Here's a video of TACCOM 3 stage recoil system compared to their new air cushion system (with claim of faster reset) and note how flat muzzle stays:
"The current 3 stage system is currently one of the top 3 systems on the market presently for the 9mm straight blow back AR’s.. This system is conventional in that it runs (with the bolt) in the 19 to 22 ounce total mass range, which is typical of any of the current systems out there. The weight in the current systems is the main drawback to felt recoil for 9mm.
The 3 stage adjustable system helps tame the felt recoil by use of a second stage that slows the mass down at the end of the recoil stroke and a third stage that separates the mass of the bolt and buffer upon returning to battery and that cushion also slows down the buffer at the end of that stroke.
The current 3 stage recoil system includes a preload load to adjust the preload weight of the recoil spring and you can use the optional short stroke limiter to shorten the recoil stroke. The 3 stage recoil system with out the use of the short stroke limiter allows for the use of LRBHO. This system and all other systems will send the bolt and buffer back to the rear as soon as the round is fired and while the pressure in the 9mm case is at maximum. An interesting note about this system is that due to the 3rd stage cushion……bolt bounce is almost non existent and functions very well in full auto AR9 rifles."
2. Delayed Blowback
A. TACCOM Delayed Recoil System -
https://taccom3g.com/product/delayed-blowback-9mm-recoil-system/
The TACCOM Delayed blowback recoil system is unlike any other recoil system on the market today. We use Rare Earth Neodymium Magnets to retard the movement of the bolt for a split second, this allows for the pressure in the chamber to drop some before sending the bolt back in the recoil stroke. This allows for the use of a lighter system, yet moving at the same speed as a heavier system…..allowing for less felt recoil and with that, less vertical dot (sight) movement. What this means is that you will have a faster return to target for faster follow up shots.
- Momentarily delays movement of the 9mm bolt
- Provides for less felt recoil, less sight bounce
- Second stage cushion at the end of the recoil stroke
- Works in any carbine buffer tube
- Short stroked system*
- Works with any ‘hollow’ pistol caliber bolt**
- Self contained system, no need for traditional detent pin
https://forums.brianenos.com/topic/...recoil-system/?do=findComment&comment=3077849
"The Delayed Blow Back System, uses rare earth magnets to retard the movement of the bolt and buffer for a split second. This allows the projectile to move down the barrel a little farther than any conventional system, allowing for a significant drop in the chamber pressure before overcoming the magnetic force applied by the opposing magnets in the buffer and guide rod. Imagine for a moment that if you have less pressure sending your current weight system back……it would move slower. Taking that into consideration, we knew that we could lower the overall mass of the bolt/buffer to bring the speed back up (or a little more) and still reduce the measured recoil.
People that shoot the MP5 with the delayed roller or the MPX with the short stroke gas system already know that with a lighter mass going at the same speed, the recoil is much less than the recoil of a conventional AR9. So get back on track…..we were able to reduce the mass by 25% over our current system and are able to increase the speed of the recoil by a little bit over a conventional system. Now, we already know that we are going to hear that the recoil is more than what they currently have……this is only a perception, do not confuse faster with more.
The bottom line is that due to the less mass the recoil is in fact less and more importantly, the sight ‘bounce’ is minimized and return to POA is significantly reduced. Your cadence will need to be adjusted and typically within the timeframe of one practice session, you will see positive results in split times and bullet to bullet distance on paper. What I am saying is that target reacquisition will be faster and almost (if not) as fast as any roller system or gas system presently available today. The delayed blow back system also incorporates a second stage at the end of the recoil stroke to help slow the mass down before bottoming out on the stop. This is why, if there is any drawback…..it will not allow for conventional LRBHO to function.
In the near future, we will be releasing a new 9mm bolt that when used with any short stroked recoil system (ours or conventional) allow the LRBHO to function. While designed to run with factory loaded ammo, we’ve found that this system works well with lower PF ammo, down to the 110PF for steel loads…….we will be offering a reduced buffer weight for people that want to shoot sub 100PF in the near future. This system has been tested with suppressors, but has not been tested with full auto rifles and presently, we do not recommend using this in full auto.
While this may not be a ‘pros and cons’ of one system over the other…….I’ve laid out the facts of each of the 9mm recoil systems we offer and you can decide which system is better for your use."
B. CMMG Radial Delayed Blowback System™ -
https://cmmg.com/barrel-and-bcg-kit-8-4140cm-sbn-9mm
- Radial Delayed Blowback uses a bolt that is forced to rotate and unlock, slowing the BCG.
- This results in a lighter BCG for a lighter rifle, and less felt recoil than a straight blowback system.
- Barrel and Bolt Kits are designed to work exclusively with mil-spec AR-15 upper receivers with a modified ejection port, like our MkG/MkGs upper, and most mil-spec AR15 lowers when used with 9 AR Conversion mags as well as our MkGs Mk17 and Mk9* lowers. Other manufacturers’ receivers may work, but we cannot guarantee function or reliability.
