Swapping a few parts made charging the ASR easier, and recoil more managable, while still maintaining caliber-conversion compatability.
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The Aero Survival Rifle (ASR), not to be confused with the Aero Precision EPC, is an AR-like 9mm PCC made by TNW Firearms that accepts Glock magazines.
A typical 9mm AR is based on the AR-15 receiver set, which is designed for longer rifle cartridges. It has to use retrofit parts to work with the shorter pistol cartridges.
The TNW ASR uses a few parts borrowed from the AR platform, but the receiver was designed for pistol cartridges from the ground up, which helps make it more compact and potentially more reliable. It is designed to be easily caliber-swappable from 9mm to .40 to .45 (and others) by just swapping the bolt head, barrel, and magwell/lower unit (the serial number is on the upper). The barrel can be easily removed for transport and storage. In order to allow easy caliber swaps they use a proprietary bolt and a proprietary “universal” buffer.
One of my readers, Gary, came to me asking for help to make his two ASR’s rack smoothly with less force and still keep them reliable. He has both the 9mm ASR and .45 ASR.
After over a month and dozens of emails, we found that swapping 3 parts for less than $100 will dramatically improve the feel and operation of the gun and still allow the same simple caliber conversion.
Here are some of the measurements Gary took for the ASR. These measurement apply to both the 9mm and .45:
| Description | Weight or Measurement |
| Bolt weight | 16.1oz. |
| Buffer weight | 9.03oz. |
| Charging force | 21-33lbs. |
| Force to open breech | 21lbs. |
| Force to cock hammer | 12lbs. |
| Recoil spring; bolt close | 10.4lbs. |
| Recoil spring; bolt fully rearward | 18.3lbs. |
| Spring length | 7.5″ |
| Buffer length | 3.5″ |
The ASR’s operate with about 25oz. of blowback mass (good!) but their recoil spring is the equivalent of a .308 recoil spring (bad!). Their buffer is a solid hunk of steel without any sliding internal weights (also bad), making it vulnerable to bolt bounce.
Many people in the field of blowback-operated firearms have been hoodwinked into believing that an obnoxiously strong recoil spring is necessary. It isn’t, and it never was. Recoil springs do not significantly delay breech opening (that’s the job of the bolt/buffer mass in a blowback), and do a poor job of preventing bolt bounce. Strong recoil springs just make charging the gun difficult and the recoil feel harsh when the bolt slams into battery.
Since the ASR is loosely based on the AR9, I started looking at ways to use a standard AR-15 carbine recoil spring and buffer.
Even though the ASR uses a standard 7″ AR carbine buffer tube, the ASR bolt, when in battery, sits about 1″ inside the buffer tube. The proprietary buffer is 3.5″ long; 0.25″ longer than a standard AR carbine buffer. There’s no buffer bumper on the end of their proprietary solid buffer, so a separate polymer bumper is inserted into the rear of the recoil spring to act as a cushion at the end of the buffer’s travel.
The “tail” of the buffer that the recoil spring fits around is very short. This only leaves a small space for the spring when the bolt is fully rearward. The spring has fewer coils than a typical carbine recoil spring, presumably to avoid suffering from “coil bind”. As a result, a standard AR recoil spring won’t work as a drop-in replacement.
So first we looked for a way to still use the TNW spring, but reduce its force.
Cutting coils
One Youtube video describes cutting 5 coils from the TNW ASR spring to reduce its force and provide more reliable function. For the person making the video, this apparently worked well.
This is a valid option, and definitely the cheapest way out. Gary tried it with a spare TNW spring and he noticed an improvement in the force required to pull the charging handle, but thought we could do better.
The 9mm (ONLY!) H3 buffer option:
A standard 3.25″ 5.5oz. H3 carbine buffer can work as a drop-in replacement for the buffer in the 9mm ASR, and as a bonus the longer narrow section of the buffer body effectively reduces the TNW spring’s tension without having to cut coils. The H3 buffer is a deadblow buffer and will help to reduce bolt bounce, too.
However, this buffer reduces the blowback mass by 3.5oz., so the blowback mass is now too light for any caliber other than 9mm.
A consideration when using the H3 is the bolt rearward travel. The H3 buffer is just a little shorter than the TNW buffer, which increases the rearward travel of the bolt and charging handle. Too much rearward travel and the charging handle will smash into the back of the charging handle slot. A few US Quarters in the rear of the buffer tube (under the spring bumper) can be used if necessary to reduce the bolt’s rearward travel.
An H3 buffer may be a good option for someone with the 9mm version if they are never going to do any caliber swaps. Gary reported that using the H3 buffer and TNW spring worked just fine, felt good, and was considerably easier to charge. However, he wanted to keep the system caliber-swappable.
Now the challenge was to reduce spring tension and keep the blowback mass appropriate for the .45 ASR.
New tube, more mass, lighter spring, deadblow buffer:
After some experimentation, we found the right combination of parts. We were able to use a standard AR carbine recoil spring, provide proper spacing for bolt travel using a 9mm AR buffer, give sufficient mass for 9mm and .45 (and presumably the other supported calibers as well), and prevent bolt bounce. The new configuration adds about 2oz. to the blowback mass (27oz. total) which should both be safer and reduce felt recoil for all of the calibers.
For anyone concerned, 9mm has no problem cycling 27oz. of mass. 9mm is capable of reliably cycling over 37oz.
For this upgrade, we used a Just Right Carbines (JRC) 8.5″ buffer tube, standard AR carbine spring, a 10oz. KAK 9mm deadblow buffer (actually 11oz. per his scale), the TNW polymer bumper, and 6 US Quarters.
[An A5-length buffer tube (Vltor, BCM, KAK) may also work by excluding the TNW polymer bumper and the quarters, but this hasn’t been tested yet. If anyone tries this, please let me know! A carbine flatwire spring may also help smooth out the action a bit more.]
The 6 Quarters act as a spacer in the back of the tube to reduce bolt rearward travel and keep the charging handle from hitting the back of the charging handle slot in the receiver. The JRC tube is just a little too long, and dropping the Quarters into the back of the tube make up the spacing difference. More or fewer could be used if necessary. Something else could be used as a spacer, but Quarters are convenient and plentiful. Since they are thin, small spacing adjustments can be easily made.
Gary removed the buffer, spring, and buffer tube. Using the JRC buffer tube, he dropped 6 US quarters in the back of the tube, installed the ASR buffer bumper spacer in the back of the AR carbine spring, inserted the spring (bumper first), inserted the KAK buffer, and re-assembled.
The result:
Success! Reduced charging force and reduced felt recoil.
“Just got back from the range with the 9mm, KAK 11oz. buffer, AR spring, and long tube. It ran flawlessly for a 100 rounds. I think I like the heavy buffer and AR spring. Seems smoother overall (racking and firing).”
“More testing is needed on the .45 but I suspect the KAK set-up is the way to go just like the 9mm. The KAK [buffer and AR spring] is easier to rack and smoother for sure. You can feel it. Less sharpness in the recoil.”
Some additional notes on the TNW ASR:
Gary reports that both guns were full of metal chips and shavings when he picked them up brand new, so a very thorough cleaning is necessary before the first range outing:
He’s also having some feeding issues with the .45, but not with the 9mm. The .45 cartridge is getting hung up as it enters the chamber. This is probably because the .45 is a straight-walled cartridge while the 9mm case is tapered. I suspect the sharp edge at the bottom of the .45 chamber needs a bevel/radius and polish to help with feeding.
Future improvements?
In my opinion, TNW missed a big opportunity with the charging handle. They made the ejector swappable from right to left ejection and machined out an ejection port on the left. However, they didn’t make the charging handle swappable from right to left.
It wouldn’t take much more machining to make the charging handle cut on the left side. It looks like there’s already a hole for the firing pin retainer opposite the charging handle, they just need to make the firing pin retainer and charging handle swappable.
Blowback9.com 