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Posted: 10/27/2013 11:52:47 PM EST
Evening folks,

I thought I would run this question by you guys with the hopes of seeing the flood gates open and sponge up the knowledge. A buddy and I, both, recently built some 300 AAC (Blackouts). Both are very much different builds. They do have a few things in common though, one being that they are both having some mild cycling issues. We both fired them for the first time today. I was getting at most 2-3 shots before getting a failure to feed. I would get a solid ejection each time. I fired a string of 60 rounds over the course of a few hours with plenty of cool down between. Accuracy was great with iron sights at 50 yards. Shooting Remington 220 grains. On a rare occasion, about 3 times, I got a partial feed where the round wedged in the feed ramps and did not fully insert into the chamber of the barrel.

My buddy, pretty close to the same thing. He did not fire that many rounds, but from what I saw if his shots he was getting about 3-4 shots off before getting a poor cycle/failure to feed as well. I did not see any partial feeds though, like I saw on my rig. Accuracy good on his as well. These are the first ARs we have built, and we are building a few others currently as well. /scratches head. So, for the similarities... We both have the same springs and 3 ounce buffers. Both running the same BCG. Both pushing rounds through PMags 30s. Both running the same trigger. His rig is a Seekins billet upper and lower, with a Blackhole barrel. We were firing different rounds though. He was firing a different round. I believe it was a 150 grain poly tipped.

My rig is a S&W MP15 lower and upper. They were pieced together and not bought as one unit. Guts pretty much stock. Some additions, but none that should effect function (IE anti-roll trigger pins, and some ambi-parts.)

So, what gives? I am at a loss and don't know what to look at this point. Any input would be greatly appreciated.

-Jeremy-
Link Posted: 10/28/2013 1:41:07 AM EST
[Last Edit: 10/28/2013 1:52:48 AM EST by Mike_Anthony]
Hi, and welcome to the site. Could you please post specific information regarding the ammo? Did this issue occur with factory Remington ammo only or reloads, or both? If reloads, please list all the info.

ETA: Also, what type of gas block are you using?
Link Posted: 10/28/2013 2:19:58 AM EST
[Last Edit: 10/28/2013 2:23:47 AM EST by BraqueHunter98]
For my rig, using the stock gas block that comes on the MP15 upper (Factory)

No reloads. All of it was the following, shot from my rig....

Remington Ammunition 300 AAC Blackout (7.62x35mm) 220 Grain Subsonic Open-Tip Match (OTM)

Technical Information •Caliber: 300 AAC Blackout (7.62x35mm)
•Bullet Weight: 220 Grains
•Bullet Style: OTM
•Case Type: Brass

Ballistics Information:
•Muzzle Velocity: 1015 fps
•Muzzle Energy: 503 ft. lbs

For my buddy, he is using a Seekins adjustable pressure block with set screws under the bottom, and he was firing the following...

PNW Arms 300 AAC Blackout 125 Grain Hunting BTIP Ballistic Tip Ammo

SPECIFICATIONS:
Mfg Item Number: 300BLKHNT125BTIP20
Category: AMMO CENTERFIRE
Caliber: 300 AAC BLACKOUT
Bullet Type: Nosler Ballistic Tip
Bullet Weight: 125 Grain
Muzzle Energy: 1343 ft lbs
Muzzle Velocity: 2200 fps
Link Posted: 10/28/2013 2:52:21 AM EST
You need to try something other than subsonic ammo, unless you plan on running your rig with a suppressor or by opening up the gas port to tune it. I would not try, however, to tune the port for specific a specific load of ammo unless you are going to use an adjustable gas block. Remington 220 is not the known as the best ammo to begin with.
Link Posted: 10/28/2013 10:21:12 AM EST
I have a DSA 300 BLK upper, never tested with factory subs, made my own 220 grain subs using published data and never had 100% feed reliability. Subs require critical powder charge and COL control.
try supersonics, I have good function with those, all the press about blackout running super and subs with no mods or can is BS, they don't all do it, a good friend and reloader bought the same upper as I did and had a similar experience
read in a gun rag about testing a new 300 BLK upper and it didn't function well with subs either, my upper suffers from poor accuracy also, 2" or larger group at 100 yards
Link Posted: 10/28/2013 3:23:49 PM EST
So let me get this correct, just in the event I have missed something. This could not be fixed with a component swap? Is cycling issues not related to any springs or buffer weights? And, from the two replies this is most likely just an adverse reaction to a subsonic round being fired?

For my last question... if subsonic rounds are so finicky, then why all the hype? Why not more talk and discussion about reliability issues.

-Jeremy-
Link Posted: 10/29/2013 10:50:50 AM EST
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