300 Blackout Suppressor - fixed the bastard...

The inaccuracy of my Blackout with Sub-sonics has been the subject of much head scratching. I built up a load that cycled well and was pushing 240 SMK's at 1020 fps. My suppressor is an over-barrel one built by Goodwin Prototyping and it looked nice enough, and was quiet, but every time I spun it on, and tried it, the POI was low and left, 7:30 on the clock. I initially sent it back to them as I suspected I was getting internal strikes, and to have the rear bushing redone. They sent it back with a note to say there was no evidence of strikes, and a new busing was fitted.

Today I finally got around to debugging it myself, as it was still giving me a very low left POI. I should point out that without it, I coud zero with subs or supers and the groups varied only in elevation, no windage factor.

I fired a group and got a string of hits from the POA on down to the left. I the unscrewed the suppressor half a turn and got two hits high and right... Here's the target. Ignore the .22 stuff.
Attachment 21726

This pretty much convinced me I was getting internal baffle strikes so I decided to pull the suppressor apart. Some heat on either end with the blowtorch took care of the loctite they'd used and I was able to pull and inspect the baffle assembly. Here's what I saw...
Attachment 21727

Quite obvious copper smears in there...

It looked like the bore through the baffles was slightly over 8mm. I ran a 8.5mm drill through from both ends, cleared out the swarf, reassembled and shot and a reasonable group but it was still low and left. At least the group size was encouraging but still being interfered with by the suppressor. I then opened it up with a 9mm and test fired. With no scope adjustments, the POI was immediately back to near centre. A few clicks brought the group up to the aiming point.
Here's the target, the 5 shots about 8" away at 7:30 are after the first rebore. The ones about 1" away at 5:00 are after the 9mm rebore and with no scope adjustment between those groups.

Attachment 21740

Damned thing has been bugging me for ages but I'm happy I've got it sorted now.

Have you considered that maybe your barrel threading is off center and not true to the bore ?


Ken

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Originally Posted by Ground Control

Have you considered that maybe your barrel threading is off center and not true to the bore ?

Ken

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If it was, then I think rotating the suppressor 180 degrees would not have moved the group the way it did. I think the group would have stayed where it was.

Tell me more about your 240 gr. SMK subsonic load.

Hey mate, I've ended up with 10 grains of AR2207 behind the SMK. It pushes them at just over 1000 fps but with the Sierras costing $1.29 per pill, I won't be cutting loose with it...

I have had problems with my gun cycling subsonic loads. I have been using Accurate 1680. I understand that H4198 is the same as AR2207. I think I'll give your recipe a try with H4198. Glad to see you are still out there blowing holes in paper. Josh and I were stretching our skills a bit shooting a 14" steel plate at 975 Yards in really tricky wind conditions. We learned that it only takes a 2 mph wind change to take you off that small a target. We had some success but got more education than satisfaction.

Hmmm, is yours Pistol length or Carbine length gas system? Typically, Pistol length is great for Subs but Carbine length can take some work. Mine is Carbine length and I had to open the gas port a smidgeon and I've taken all the weights out of the buffer.

975 yards is more like it for that RUM of yours Steve. That'll get you doing some math. :thumbsup:

Today I worked up a load for my match AR, 69 grain SMK's at 2900. Not grouping as well as I'd like, I think they're seated too deep but I need them to fit in the mag. It'll do, it's only for the Service Rifle Nationals in 3 weeks...:o

Mine is a carbine length at 16". I think using a lighter buffer spring might work on the subsonic but then the supersonic projectiles probably won,t work as well. I guess you can't have your cake and eat it too. Good luck on the Service Rifle competition. Give us a report. Did you make that trip to Europe yet?

Oh I swap buffers when I go to Supers. Not really a hassle. We head to EU in 4 weeks, looking forward to it :)

I dropped two monkeys out of my Casaurina trees with the Blackout last night. The 240's are nasty, they go straight through. I may have to experiment with non Geneva Convention modifications. I've always fancied burying a live .22 Short backwards in the front of something... :omg:

I dropped two monkeys out of my Casaurina trees .
Mate that sound like fun where are you or how do I get one of those trees at my place.

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Originally Posted by ishoot10s

Oh I swap buffers when I go to Supers. Not really a hassle. We head to EU in 4 weeks, looking forward to it :)

I dropped two monkeys out of my Casaurina trees with the Blackout last night. The 240's are nasty, they go straight through. I may have to experiment with non Geneva Convention modifications. I've always fancied burying a live .22 Short backwards in the front of something... :omg:

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Try 208gr A max if you can find some

I have tried 208 gr A-maxes with numerous powder charges and they just refused to work at all. I tried 220 grain SMK's and have had to boost the charge to supersonic to get them to work with my standard buffer and spring. I have come to the conclusion that I will need an alternate buffer and spring for the subsonic loads to work. My gun loves 125 grains Nosler ballistic tips. I guess they will be my load of choice. I plan on experimenting with some 150 grain SMK's. We were at the range the other day and a couple of young guys were shooting their 556 AR's at a non AR500 steel plate. When they would fire you would here a bang and an immediate "tink" sound. Josh fired my 300 Blackout at the plate and you would here a bang and then a slightly delayed "clunk" sound. One sounded like you were throwing pebbles at the plate, the other sounded like you were beating it with a hammer. I am developing a real fondness for the Blackout.

Wouldn't work how? They're meant to frag at blackout velocities.

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Originally Posted by Beavis

Wouldn't work how? They're meant to frag at blackout velocities.

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Guessing he means failing to cycle? Surely it can be the only thing as its the bastards with black outs chomping up all the 208gr Amaxs due to their awesomeness, pain in the ass you lot.

Nibblet is correct, it's a cycling problem.They work fine in single shot mode. It really is sacrilege to use 208 gr. A-maxs in a blackout with so few around these days. There is hardly any manufactured Blackout ammunition for sale in the US. If you don't reload, you don't get to shoot.

Adjustable gas block? Open it up a bit and or lighter buffer and spring.

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Originally Posted by mutton gun

I dropped two monkeys out of my Casaurina trees .
Mate that sound like fun where are you or how do I get one of those trees at my place.

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Auckland mate. Monkey = Possum and Casaurina = Sheoak