Subsonic Unsuppressed 300blk from 8.3" Barrel

Moderators: gds, bakerjw, renegade, bamachem

fancygunz
Member
Posts: 26
Joined: Thu Aug 22, 2019 10:38 am

Re: Subsonic Unsuppressed 300blk from 8.3" Barrel

Post by fancygunz » Sat Sep 07, 2019 11:30 pm

After today's trip to the range I am now up to a total of 21 recipe variations with the 220gr Hornady ELD-X....and I am pretty much "fed up" with it. I just recorded the best ES and StDev numbers of my reloading career (five different 5-rd loads all with ES <15 and StDev <10, one load was even ES 8 and StDev 3.5!!) and I'm still shooting 2+ MOA at 50 yards - I'll be shooting 3 rounds all touching, then suddenly round 4 or 5 goes WAY off from the rest of the group as if hurricane Dorian just blew through. Either that or the 5 shots will look like a shotgun pattern. Compressed, void space between powder and bullet, so long the round barely fits in the mag, so short the bullet starts to dent, min load to cycle, subsonic, transonic, supersonic, crimp, no crimp, doesn't matter....What the heck!!! I'm convinced now that my lack of accuracy is not due to the selection of powder or the reloading process, so it has to be something to do with the bullet selection or the rifle itself.
dellet wrote:
Fri Sep 06, 2019 10:25 am
What it has going for it is a ton of gas, so it will cycle anything. That again is a reason not to use it, nobody I know like shooting with a gas mask on and with CFE you need to.
I'm still getting the weird issue where light powder loads (anything ≤10.8gr CFE blk or ≤11.0 SW Blackout with a 220gr bullet) will NOT cycle the bolt but WILL lock back on the last round. I can't find anything rubbing or hitting where it shouldn't - I tried different mags, I tried cycling dummy rounds marked with a sharpie, and I lubed excessively to reduce drag. I'm curious if whatever is causing this issue is also contributing to my accuracy issues but don't know how to figure this out.
rebel wrote:
Fri Sep 06, 2019 8:09 am
You might try a CCI 450 primer to see if it has better ignition - i.e.tighter group. ( as TRshootem mentioned)
Are you bagging this rifle? On a bench or shooting sticks? Bipod?
I read that CCI #41 and CCI 450 are the same except #41 is more resistant to slam-fires in an AR platform. Not sure if this is true, but right now I don't have access to another primer. Next time I order supplies I'll have to purchase some. I'm shooting this off a bench on a rest with rear bag through a 1-6x Primary Arms scope. I am sure it's not my lack of shooting skills or improperly mounted scope or anything like that. Supersonic is shooting OK (<1 MOA) it's only this darn 220gr subsonic load that I can't get a handle on.

Any other bullet suggestions besides 220gr Hornady ELD-X, even if it's a different weight? Maybe my rifle just hates these for some reason. I was hoping not to spend too much for the bullet (I got these as blems for really cheap from Midsouth) since I'm only shooting paper right now. How are the plated Berry's?

BulletFlight for Android
User avatar
rebel
Silent But Deadly
Posts: 7239
Joined: Mon Apr 22, 2013 2:01 pm
Location: Moonshine Country

Re: Subsonic Unsuppressed 300blk from 8.3" Barrel

Post by rebel » Mon Sep 09, 2019 6:53 pm

Any heavy Sierra Match King.
You can't beat the mountain, pilgrim. Mountains got its own way.

User avatar
dellet
Silent But Deadly
Posts: 6353
Joined: Fri Nov 30, 2012 1:25 pm

Re: Subsonic Unsuppressed 300blk from 8.3" Barrel

Post by dellet » Tue Sep 10, 2019 2:35 pm

I would go with a faster powder before I changed bullets.

I wouldn't be surprised if half your problem isn't due to low pressure gas cutting of the bullet. Just one more reason not to like CFE BLK.

Most 308 bullets are designed to work based on normal chamber pressures. CFE can not provide that. it does not have enough pressure for the bullet to expand and seal the bullet to the bore.

This may be the base of all your problems. Your rifle will not cycle loads that thousand's of others can. That's why I say sorting out the cycling problem is a priority over anything else if you want to shoot reliable, accurate subs.

If you can retrieve a few bullets you might find carbon in front of the base, a sure sign of gas blowing by the bullet.

You can try pushing a bullet through the barrel by hand, you might fell a loose spot.

If the problem goes away using a faster powder, it's also a good clue that might be happening and also make sense why supers shoot so well.
300 Blackout, not just for sub-sonics.

TRshootem
Silent But Deadly
Posts: 217
Joined: Fri Dec 26, 2014 1:13 am
Location: Montana

Re: Subsonic Unsuppressed 300blk from 8.3" Barrel

Post by TRshootem » Tue Sep 10, 2019 4:12 pm

A friend had a similar issue with heavies and CFE BLK, lock back on the empty mag but did not generate enough force forward to pick up a second round out of a loaded mag. He switched to 1680, 296 and H110 for a bit more pressure and his problem went away. This was also a brand new build with unknown gas port diameter.

fancygunz
Member
Posts: 26
Joined: Thu Aug 22, 2019 10:38 am

Re: Subsonic Unsuppressed 300blk from 8.3" Barrel

Post by fancygunz » Thu Apr 23, 2020 1:53 pm

Update: I have since solved my cycling issues by 1: slightly increasing powder charges, 2: replacing the buffer spring with a lightweight Sprinco "yellow" version, and 3: completely disassembling, cleaning out the gas port/tube (there was some red loctite in it!).

Post Reply