Timing issue needs help...

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

Moderators: gds, bakerjw, renegade

Ronn
New Member
Posts: 6
Joined: Wed Mar 01, 2017 6:35 pm

Timing issue needs help...

Post by Ronn »

My 10.5" Blackout Pistol with an adjustable gas block shoots 123 gr. hp... The most consecutive fire before an FTE or FTL or combination is 3 rounds. I have changed buffer weights up to 3.5 as well as springs. When I test the upper on an AR15 lower it plays nice. Any ideas are welcome..... Ronn
20X11
Silent But Deadly
Posts: 1560
Joined: Fri Aug 03, 2012 11:43 pm
Location: Aurora, CO

Re: Timing issue needs help...

Post by 20X11 »

An H2 Carbine buffer is 4.6 oz. I believe that was the recommended buffer from AAC originally.
Boolit_Head
Silent But Deadly
Posts: 349
Joined: Tue Aug 23, 2016 7:15 pm

Re: Timing issue needs help...

Post by Boolit_Head »

With a adjustable gas block use a Carbine buffer and standard springs. The H buffers and the adjustable gas block are two ways to do the same thing and they tend to step on each other in combination. With a carbine buffer and standard springs try to readjust your gas block with one round in the mag till it locks back on a empty mag. Then open it a bit more for insurance.

What is the difference between the two lowers you tried it on? Also how many rounds through the upper, it could still be tight try running it fairly wet.
Ronn
New Member
Posts: 6
Joined: Wed Mar 01, 2017 6:35 pm

Re: Timing issue needs help...

Post by Ronn »

The lowers ... one I bought from Rural King on sale it's a Ruger the other from Del-Ton. I don't remember where I got the pistol buffer assembly.
Thanks for the direction, having tried the stock AR15 buffer weight and spring I'll now try the H4. Any thoughts on flat versus round springs and spring length?
thanks again ... Ronn

p.s. The 10.5 has 150 + rounds through it.
20X11
Silent But Deadly
Posts: 1560
Joined: Fri Aug 03, 2012 11:43 pm
Location: Aurora, CO

Re: Timing issue needs help...

Post by 20X11 »

Mine runs great with Standard Carbine spring and H2 buffer. FA BCG as well.
Boolit_Head
Silent But Deadly
Posts: 349
Joined: Tue Aug 23, 2016 7:15 pm

Re: Timing issue needs help...

Post by Boolit_Head »

Ronn wrote:The lowers ... one I bought from Rural King on sale it's a Ruger the other from Del-Ton. I don't remember where I got the pistol buffer assembly.
Thanks for the direction, having tried the stock AR15 buffer weight and spring I'll now try the H4. Any thoughts on flat versus round springs and spring length?
thanks again ... Ronn

p.s. The 10.5 has 150 + rounds through it.
150 rounds should have loosened it up but going to the H4 is the opposite of what you need. You have a issue where you don't have enough force to open the bolt on that pistol lower. Adding weight will make that worse. If things are as you describe them then you either have a misaligned gas block causing marginal gas flow or there is a reason that pistol buffer is taking a lot more force to function.

I am running a carbine buffer and spring with a adjustable gas block on a 7.5 barrel with a pistol length gas system on my SBR without issues. It was a bit tight for the first 100 rounds but running the bolt wet and making sure the spring had some lube cured that.
User avatar
dellet
Silent But Deadly
Posts: 6967
Joined: Fri Nov 30, 2012 1:25 pm

Re: Timing issue needs help...

Post by dellet »

Not enough information to offer anything but a wild guess.

Your upper appears fine since it worked on a different lower.

Without knowing the difference between the two lowers, it's impossible to know how to help.

Standard configuration for the upper you have, would be a standard carbine spring and an H2 buffer 4.6 oz. That's how it was designed to run, start there.

It sounds like you have some unknown springs.

Standard carbine 11.25" 39 coils
Rifle 12.7" 44 coils.

With a 3.5 oz buffer, depending on how you have your gas block adjusted, it could be too much weight, or too little. But with pistol gas and a normal gas port it's too light. If the barrel has a large port, it only gets worse.

You can try starting with the block closed, many adjustable blocks will not shut the gas of completely. If it's closed completely the bolt should not move. If it still ejects a round, buy a decent adjustable block.

What stock is on the upper that will not work? If it's rifle the it opens up more possibilities.
300 Blackout, not just for sub-sonics.
InMyHumbleOpinion
Silent But Deadly
Posts: 225
Joined: Wed Jan 22, 2014 12:59 am
Location: SW MO

Re: Timing issue needs help...

Post by InMyHumbleOpinion »

Just wondering what you inspiration was to go with an adjustable gas block?
Ronn
New Member
Posts: 6
Joined: Wed Mar 01, 2017 6:35 pm

Re: Timing issue needs help...

Post by Ronn »

It was more of a frustration than an inspiration after trying springs from carbines ( even trimming one ) and weights up to 3.8... I just placed an order with Primary arms for a heavier buffer. In adjusting the block I did one round at a time until the bolt stayed open then did 1/4 1/2 turns to get the timing but it never happened. Ill keep the post up-to date when I test the heavier buffer..... Thanks to all for the direction ... Ronn
User avatar
Dolomite_Supafly
Silent But Deadly
Posts: 3017
Joined: Fri Oct 30, 2009 7:03 am
Location: East Tennessee
Contact:

Re: Timing issue needs help...

Post by Dolomite_Supafly »

What size is your gas port? If it is too small an adjustable gas block will not fix the issue. Drill the port out to .100” then adjust the gas down until it cycles fine.
WWW.thegunmilitia.com

Come join the militia!
Post Reply

Who is online

Users browsing this forum: Bing [Bot], Google [Bot] and 127 guests