Project Fatboy + My Load Data

[TITAN308]

I finally got around to testing some loads the other day and it was a pretty successful day I figured I'd share a bit more details. I started this build at the beginning of 2016 and the suppressor did not get approved till November 10th. It has gone through some variations on parts and I kind of just settled down on a minimalist build. The only thing left I want to replace is the bipod with a Harris or GG&G setup in near future. Other than that, this was built on PSA receivers and it is a "two stamp" gun. I won't bore you with a parts list of some crap you've all seen a million times before, I will simply note the key parts. My loads have zero FTF, FTE, or FTLB on empty magazine. Runs 100% so far.

Keynote: This is a purpose build sub-sonic only gun! (you'll see why below)

1.) AR Stoner 300BO barrel with a pistol gas system that was cut down and re-threaded to a little over 9.615" in length. My goal was to run a "monolithic" type look from the hand guard to the suppressor. A small 1/8" gap is left so heat does not transfer.

2.) Simple non-adjustable low profile gas glock with pistol length gas tube.

3.) JP Silent Captured Spring (Standard Carbine Configuration)

4.) Gemtech MK9K. This is a 9mm suppressor purpose built for fully automatic H&K MP5's. It touts a massive 2" outside diameter (matches my hand guard choice) and is designed in this manner to help with heat and volume. Gemtech verified directly through my inquires on this build as to compatibility before I started. (see keynote above!) I have also included a picture at bottom of post for a size comparison next to a standard 9mm suppressor (in this case an AAC EVO-9).

While I don't have anything fancy to give you dB numbers, I will say, between the Gemtech and JP SCS it gives a deep "thunk" noise with each shot, which is a combination of the actual sub sonic round itself and the BCG reseting to the forward position.

Ok, now load data. I tried out numerous loads and formulas from across the web (some from this very forum) and to keep this short I listed my top 3 loads using common powders;

1.) A1680 (Top Pick)

Bullet: Hornady 208gr Match
COAL: 2.12"
Charge: 10.3gr
Suppresed FPS: 1068, 1069,1063
Unsuppressed FPS: 1100, 1116, 1081

2.) Hodgen Lil'Gun

Bullet: Hornady 208gr Match
COAL: 2.23"
Charge: 8.3gr
Suppresed FPS: 1054, 1066, 1057
Unsuppressed FPS: 1080,1093, 1090

3.) IMR4227

Bullet: Hornady 208gr Match
COAL: 2.23"
Charge: 10.0gr
Suppresed FPS: 1015, 1004,1052 (bizarre fluctuation on this load)
Unsuppressed FPS: 948, 997, 943

These loads are not tested for pin point accuracy, I just wanted something able to engage mansized targets without issue for training classes I take. All rounds were hitting within a fist sized area at around 100 yards. I like reloading for the cost factor and not to feel the need to round count when I go to the range. If I go to the range and I want to shoot off 500 rounds or more so be it. I'll leave the accuracy optimization to those who enjoy it and tweaking every last minor detail of a load.

[steven11b]

That's a different suppressor choice then I have seen, actually I didn't know they made those. How well does it seem to suppress? Cool looking gun and I like the clean and simple look to it.

[TITAN308]

That's a different suppressor choice then I have seen, actually I didn't know they made those. How well does it seem to suppress? Cool looking gun and I like the clean and simple look to it.

Honestly that is exactly why I built it. Never seen it done before and wanted to build something unique.

I can't give you any official dB readings, all I can say is a part from the "thunk" of the round and BCG resetting forward it is definitely hearing safe. For all I know it performs as well as any other .30 caliber can on the market. Supposedly its is the be-all-end-all of 9mm suppressors. So I imagine that translates well to this platform.

https://gemtech.com/mk-9k.html

I don't think Gemtech openly advertises them. As I said, purpose built for fully auto MP5s, so the civilian market gonna be kind of stale on that front. My dealer had trouble locating one for a short time and when he finally did, there was only ONE. On top of that it uses a 1/2 x 36 thread pattern. I wasn't too concerned with that since this was purpose bought for this build and I don't plan on swapping it around. Do I know if push comes to shove I can get a different endcap from Gemtech for a standard 1/2 x 28 or three lug.

I believe the suppressor ran me $650.

[steven11b]

what is the weight on that? Does it make the gun front heavy? It would be interesting to compare the sound on that to a .30cal can on the same gun. Im guessing it would be comparable as it looks like it has a lot of internal space to take up the sound.

[TITAN308]

what is the weight on that? Does it make the gun front heavy? It would be interesting to compare the sound on that to a .30cal can on the same gun. Im guessing it would be comparable as it looks like it has a lot of internal space to take up the sound.

Website says 20oz.

It is beefy, no argument there.

[ncorry]

1.) A1060 (Top Pick)

Bullet: Hornady 208gr Match
COAL: 2.12"
Charge: 10.3gr
Suppresed FPS: 1068, 1069,1063
Unsuppressed FPS: 1100, 1116, 1081



3.) IMR4227

Bullet: Hornady 208gr Match
COAL: 2.23"
Charge: 10.0gr
Suppresed FPS: 1015, 1004,1052 (bizarre fluctuation on this load)
Unsuppressed FPS: 948, 997, 943
Charge: 10.3gr

On the first load, is A1060 a typo? I haven't heard of it. On the IMR4227 load, was it a Charge of 10.0 or 10.3 grains? Like the set up and look of the fat boy. Did you notice a difference in the report of the various powders?

[TITAN308]

On the first load, is A1060 a typo? I haven't heard of it. On the IMR4227 load, was it a Charge of 10.0 or 10.3 grains? Like the set up and look of the fat boy. Did you notice a difference in the report of the various powders?

Sorry, on the IMR4227 I deleted the extra line referring to 10.3gr - the load is for 10.0gr.

On the 10.3gr load I tested I would sometimes get a spike over 1100fps so I dropped that formula and 10.0 was the next lowest on my test.

And that was a typo on A1060, I meant A1680 - as in Accurate 1680.

My personal opinion on tone, I think Lil'gun gave the deepest, but I could be full of shit to be honest. Minimal variance in FPS definitely goes to Accurate 1680 without a doubt however.

[ncorry]

On the first load, is A1060 a typo? I haven't heard of it. On the IMR4227 load, was it a Charge of 10.0 or 10.3 grains? Like the set up and look of the fat boy. Did you notice a difference in the report of the various powders?

Sorry, on the IMR4227 I deleted the extra line referring to 10.3gr - the load is for 10.0gr.

On the 10.3gr load I tested I would sometimes get a spike over 1100fps so I dropped that formula and 10.0 was the next lowest on my test.

And that was a typo on A1060, I meant A1680 - as in Accurate 1680.

My personal opinion on tone, I think Lil'gun gave the deepest, but I could be full of shit to be honest. Minimal variance in FPS definitely goes to Accurate 1680 without a doubt however.

Thank you for the info!

[bangbangping]

Interesting choice. Like the looks.

Are you sure you didn't mix up the suppressed/unsuppressed velocities on the first two loads? I've never known a suppressor to lower velocity.

[TITAN308]

Interesting choice. Like the looks.

Are you sure you didn't mix up the suppressed/unsuppressed velocities on the first two loads? I've never known a suppressor to lower velocity.

Me neither, but that is what happened. I was a bit baffled on that one as well, but since I planned to shoot suppressed only anyhow I shrugged it off.