Short stroking

[Floydieguns]

Hello, new here.

Built ar308. Have 2000 rounds fired. Parts are to correct dimensions. No abnormal wear. Have assembled roughly twelve various ar's.

Was recommended to use the 10oz heavy buffer from slash as rifle primary hosts suppressor.

Functions flawlessly with can.

Without can.. On factory munition can randomly short stroke and never holds bolt back. Using 168 or 175smk off the Dillon versus 150gr box, has no issue with short stroking.

Before I change to a5 tube with h3 buffer and tubbs spring, does muzzle device truly help? Either use thread protector or suppressor. No brake ever. Looking for inputs.

Contemplating RCA adjusting gas key with the h2 or h3 carbine buffer and tubbs spring. With 10oz A2 weight and standard coil spring - rifle runs like a velvet dream while hosting.

 

Already have the gaskey installed. Can pile brass 3ft away with kick similar to my 5.56 builds when suppressed.

Goal is improving non-suppressed function and using adjustable buttpiece. When weather changes, so does ideal L.O.P

Thanks, Floydie

[Floydieguns]

Sorry for doubling.

To clarify, as during a re-read.. my subject is not very collected.

Does anyone feel using a muzzle brake will help correct the potential short stroke and guaranteed fail to hold open? In current configuration.

When hosting my suppressor, there are zero issues.

Directly, my light hearing protection dislikes the brake/comp. For some reason a target crown sans brake has less report for my ears.

I had intent of using a more low-mass buffer and more stiff action spring in combination to the adjusting gas key. Simply due to the weight bias of most collapsing stocks.

What experience do you all have with the ar15 carbine buffer weights in a5 tubes? I was thinking h3 being 5oz with a tubbs spring should be heavy enough, yet not change the overall weight of rifle too much. I am already aware the weight of rifle complete will increase. Yet, I am concerned about using the h1 or even 'taccom' buffers.

Before spending money, would like insight from any others who have walked down this path.

[jtallen83]

6 minutes ago, Floydieguns said:

Does anyone feel using a muzzle brake will help correct the potential short stroke and guaranteed fail to hold open?

No help, a suppressor would add some back pressure but doubt there are any brakes that would enough to matter.

Best to try one change at a time when it comes to springs, adjustable gas, and buffer weights.

[Floydieguns]

The gas is kept completely open. Adjustable key was installed and used while testing the suppressor's recoil reduction capabilities.

Had figured as much, with the brake. Thought was, perhaps it would add enough forward momentum during the "recoil reduction" outgas.. allowing the bcg a more rapid unlock. Seems the 10oz weight causes such a dwell, the pressure has decayed beyond useful range. Enough to feed properly in most instances yet, not enough for hold open to engage. Have not tried, because I hate those obnoxious boom devices. Makes me go from earplugs to over-ear muffs. Which make for a pain with cheekweld. Darn it, why is it such a difficult thing about having cake while eating it too??

Humor aside;

Was guessing the tubbs spring and h3 buffer in a5 tube would give similar results as a standard rifle buffer and tubbs spring. Granted the slightly shorter tube will give a greater amount of spring load at battery(just a bit more compressed than in a2 receiver extension)..

I was more or less hoping to find information from people who are using their rifles suppressed. What is the lowest weight they use, etcetera.

Thank you!

[Robocop1051]

Are you using a direct thread or a QD suppressor?

you can get some back pressure out of a blast can, like the PWS CQB or the Noveske KX3/KX5. 

[jtallen83]

13 minutes ago, Floydieguns said:

I was more or less hoping to find information from people who are using their rifles suppressed. What is the lowest weight they use, etcetera.

I have a 16 inch rifle gas 308 that I run suppressed. SLR gas block, standard carbine buffer with a Tubbs spring. Runs fine with or without the suppressor with the same gas setting. I could turn it down a bit for suppressor use but don't since it doesn't seem to harsh. I run my AR-10 20 inch rifle with a suppressor, only change from factory is a Slash heavy buffer. Run a Sig P716 suppressed, runs like crap with or without no matter what the setting, came from the factory with a flat wire spring, problem child from day one.

[Floydieguns]

Robocop, it is a deadair sandman QD. I only use the brake with the can. For reasons mentioned above.

JT, I am looking at the UBR2. Consideration was given to h1 and tubbs spring. However, concern about too low of resistance is present. Looking to sustain the longest duration in lockup as possible. Suspect that h3 or even the slash heavy buffer for ar15 carbine would help keep things happy. Yet, this again tips scales. Trying to keep total weight under 16lbs with full magazine/suppressor.

This all disclosed.. There is another suppressor in the works, which is intended for a more permanent use on this rifle.

Appreciate the both of you.

Floydie

[98Z5V]

15 hours ago, Floydieguns said:

The gas is kept completely open. Adjustable key was installed and used while testing the suppressor's recoil reduction capabilities.

This is telling me that your gas port in the barrel is too small.

The gas is kept completely open all the time, it functions great with the suppressor (which will add some back pressure), but it doesn't run right without the suppressor - when removing the suppressor takes away it's additional back pressure.  You need more Oompf when the suppressor is off, to properly cycle it, and the gas is already wide open.  Easy fix - drill up the gas port diameter in the barrel.

You need to close down the gas a little to get it to shoot as smooth with the suppressor - but that's the reason for adjustable gas in the first place...

[Floydieguns]

It is using a 10oz weight currently. I would have to do a partial breakdown, though I am guessing the port was larger than .09" - it has been a while since assembly. It was not "abnormal" in any way. At the time, I purchased two 18" hybrid contour barrels from criterion. Both were visually identicle. Also, I am fairly certain the block is not mis-clocked. I use a fine sharpie to denote the centerlines of barrel port and gasblock port in addition to measuring the depth of bore from gasblock outer edge to barrel shoulder.

 

Everything lined out within .005" or so. I went over that a few times. I truly believe it is the heavy buffer plus factory munitions.

Will inspect in a week or two. Busy currently.

Any other inputs or concerns are gratefully welcomed.

Appreciated much.

Floydie

[COBrien]

I'm going to agree with 98Z5V in that you are not getting enough gas to overcome the buffer weight and/or spring tension.

However, I'd be more likely to suggest swapping the buffer and/or spring before hogging out (I know, that sounds more drastic than it is...) your gas port.

I'm in love with Slash's buffer and Armalite spring in my .308, but if it doesn't run, it doesn't run. You have an adjustable gas block to tame things down a bit.

[Floydieguns]

I thank you all again.

It is the adjustable gas key from RCA, a standard .750 melonite gasblock.

I will look into it this weekend.

What is an ideal specification on gas port? Specifically, the "ideal" port diameter in barrel.

I have a 5.5oz dpms rifle buffer that can be used in place. Most certainly will function as intended when changed out.

If I recall, when playing with shortened barrels on FAL.. the larger port meant more volume, less pressure. Smaller port was less volume and greater pressure. Will have to dig through my spec books.. believe that .088" was just a tad small. Ideal was near .096" with sometimes .110" on the very short barrels. Of course, this was crucially affected by the op rod length.

This is a cross comparison, for comparison only. Please understand that. I am only mentioning this for descriptive purposes.

This stated, ideal specifications please? This is a nitrided barrel. Not very keen on running HSS drill bits down the bore just yet. For any less experienced gunsmith, I recommend avoiding carbide. When it snaps.. you are in a world of hurt for removing it.

Let me blueprint everything before wasting bits and swear words.

[98Z5V]

8 minutes ago, Floydieguns said:

What is an ideal specification on gas port? Specifically, the "ideal" port diameter in barrel.

I have a 5.5oz dpms rifle buffer that can be used in place. Most certainly will function as intended when changed out.

 

Try that standard rifle buffer first.  Just check the outcome.  As far as an ideal specification on the gas port diameter, that's all up to configuration.  Running the 10oz buffer changed all that.  If it runs unsuppressed just fine with the off-the-shelf ammo and the lighter buffer, then it's gonna recoil harder (but still run) with the suppressor on there - and you can adjust it down.  The magic will be finding that happy medium, where it runs suppressed and unsuppressed.

[Floydieguns]

Exactly why I went to the 10oz weight. Got adjustable gas key for intent that eventually, will change for 6.5 to 8.5oz buffer and semi-permanently affix different suppressor.

Just looking for various insight. Mostly what has been previously documented. Am pretty confident in which routes to pick.

The 5oz buffer was originally functioning fine.

Edited March 19, 2018 by Floydieguns

[washguy]

Floyd    that's quite a big step up for buffer wight.....check out KAW valley and Kak buffers  n start with plain ol buffer spring and then go from there with springcos yellow and red buffer springs and the yubbs too......   Wash

[Floydieguns]

Ok, so..

0.093" gauge pin drops in all the way to bottom of barrel bore. 0.094" will firmly seat in the top of gas port but does not actually protrude into bore of barrel. The YHM gasblock takes a 0.123" gauge pin in the port. The gas tube is slightly offset and takes a 0.107" gauge pin through everything. Hard to picture that.

Production date is 01/16 per criterion stamp. " 01/16 RA EX09 " is on barrel.

I see a mild amount of carbon stains inside the gasblock. The ~0.750" bore to match barrel. In additions to the carbon shown on the outside of gas tube/block. Pardon the excess loctite that well.. hardened.

Now, I have 0.237" from edge of gasblock that adjoins barrel shoulder to the 0.107" gauge pin. I measure 0.251" from edge of barrel shoulder to 0.093" gauge pin in gas port.

Seems to be an issue of stackup.

You can see the carbon buildup around the gasblock/gas tube junction.

Now - with math.. I am close, so long as the clocking is spot on even with this stackup. However.. ideas?

[Floydieguns]

Another picture. Ran out of space

[98Z5V]

18" rifle gas barrel?  I just looked through this thread again, and there's no mention of the barrel info.

[Floydieguns]

Yes, rifle length. Thought I covered that. My mistake. I am wondering how much bleed-off is occuring due to ill-fit.

[98Z5V]

12 minutes ago, Floydieguns said:

Yes, rifle length. Thought I covered that. My mistake. I am wondering how much bleed-off is occuring due to ill-fit.

After 2000 rounds, none.  Carbon has sealed that system up. 

Did all this start occurring after the addition of the 10oz buffer?

[Floydieguns]

Pretty much, yup. When using the JP SCS (I forgot that is what my other ar308 had. Thought it was traditional dpms 5oz a2 length. Getting older.. is rough) it ran fine.

Rifle was relegated to suppressor use and saw a change of parts. This has all been a quick decision of, 'do I want to sell this and fund another toy?' That found me in a quick scramble of 'I have time to make adjustments this weekend'. Haha..

In additions, a friend came over and tickled my memory on things. I could pull the carbine stock and buffer off a third ar308.. but, eh..

I am going to grab my numbered bits and ream the gas tube out for being more near to 0.120" and line everything off again.

Dug through my spare parts surplus.. found a slr heavy duty gas block. That thing takes five set screws. Why I ended up with it.. ?? Funny how things get thrown in a drawer and forgotten.

Will report back a few days/weeks later. Baby is almost here. Daughter due in four weeks. Maybe less. Trying to get this year rolling with backlog.

Edited March 23, 2018 by Floydieguns
Do to = to

[98Z5V]

Two choices, as I see it.  Keep the 10oz buffer and take that port size up to 0.100", or switch back to the 5oz buffer.  I doubt you'd have to go over 0.100", but you do have adjustable gas.  0.125" is the max you can go.

[Floydieguns]

I knocked the gas tube out to .125" matching the block. The port is still at 0.093". Spun the adjustable gas key setscrew pretty far out. Going to see how it does in a short while. Will have to dig through my endmills, I may have a 0.100" cutter. Really trying to not ream out barrel port to the 7/64 drill bit I have. However..

Appreciated. Report back later. 

[Floydieguns]

So, just by correcting the gas tube port to be 0.125" as the gas block itself was able to get rifle functioning with 10oz buffer weight.

Hold open works. Turned the adjustable gas key screw in until it failed to lock. Using some 150fmj perfecta. Will be able to reduce gas even more, for the 175smk batch load I run.

Hope this helps someone else. It was very difficult, focusing pictures of the gasblock vs gastube alignment when everything was pined together. Which is why no picture.

Will have to play with everything on a later date. Not had a chance to spin the dillon much lately. Report back on the recoil reduction am able to accomplish with 10oz weight, suppressor, 175smk handloads and cutting gas back even more.

Appreciated, kinds sirs.

[Robocop1051]

So we’re good now? Then we can start making “short stroking” jokes now… Or is it still too soon?

Seriously… I’ve been fighting the urge all week!

[Matt.Cross]

22 minutes ago, Robocop1051 said:

So we’re good now? Then we can start making “short stroking” jokes now…

Go ahead, rub one out!