Issue with short stroking

[trophyhusband]

My AR-15 recently started short stroking. I've been using just the carbine upper on the rifle lower that I built for a 6.5 Grendel that I've ordered.

Could this be the cause of the short stroking?

I'm working on developing an accurate hand load for this and I really think using this lower gives me a more solid base to shoot from than the collapsable stock that that goes with that upper. If the A2 buffer is the culprit, is it ok to still shoot it that way temporarily? I'm ok with checking that a round chambered between each shot while doing load development as long as it is safe and won't damage anything.

Once I get the load worked out (and I think I'm close), I'll be putting my 4x scope and carbine lower back on it.

Also, if it makes a difference, most accurate load so far has been the lightest load I've made so my future tests will be even lighter loads. (Short stroking has been happening with two different brands of factory ammo along with my hand loads.)

 

[c_bass16]

Yes, you're most likely short stroking, because with the carbine gas system, you probably don't have enough juice to move your rifle length buffer and spring all the way to the rear of your tube.

It won't cause any damage, It's just a hassle.

 

[trophyhusband]

I don't mind dealing with the hassle temporarily as long as it's safe. Hopefully tomorrow I'll get a chance to go shoot using my carbine stock and see if there are any problems.

 

[ICANHITHIMMAN]

I don't mind dealing with the hassle temporarily as long as it's safe. Hopefully tomorrow I'll get a chance to go shoot using my carbine stock and see if there are any problems.

It's not safe in my opinion! The ar family of weapons operates with a "floating firing pin" you need to run the correct spring and buffer for your barrel length and stock. If your not generating enough force to close the bolt, you run the risk of an " out of battery explosion". By, by rifle. Not to mention the fact that your doing load work ups with one spring and buffer that is generating one pis speed and then switch back to the other spring and buffer generating another IPA speed, that's not good and will most likely make all for load work up for s--t!

 

[Lefty7mmstw]

It's not safe in my opinion! The ar family of weapons operates with a "floating firing pin" you need to run the correct spring and buffer for your barrel length and stock. If your not generating enough force to close the bolt, you run the risk of an " out of battery explosion". By, by rifle. Not to mention the fact that your doing load work ups with one spring and buffer that is generating one pis speed and then switch back to the other spring and buffer generating another IPA speed, that's not good and will most likely make all for load work up for s--t!

+1

Yep, you are risking your pipe here, bad cycling is to be avoided in floating firing pin rifles. I don't see the load changing much with the ar's lockup but why risk crappy cycling and the possibility of either bad load development or a damaged rifle??

 

[msalm]

Get a Bob Sled and work up your loads in single shot fashion. If you are short-stroking, generally the bolt isn't picking up the next round and there isn't really a safety concern other than stove-piping and jacking up your rounds. You could swap out the carbine buffer spring (NOT the buffer itself) and see if that allows the full cycle. Don't switch out the buffers as the carrier key will impact the receiver rather than the buffer taking up the rear impact.

 

[ncwg2boatguy]

My AR-15 recently started short stroking. I've been using just the carbine upper on the rifle lower that I built for a 6.5 Grendel that I've ordered.

Could this be the cause of the short stroking?

I'm working on developing an accurate hand load for this and I really think using this lower gives me a more solid base to shoot from than the collapsable stock that that goes with that upper. If the A2 buffer is the culprit, is it ok to still shoot it that way temporarily? I'm ok with checking that a round chambered between each shot while doing load development as long as it is safe and won't damage anything.

Once I get the load worked out (and I think I'm close), I'll be putting my 4x scope and carbine lower back on it.

Also, if it makes a difference, most accurate load so far has been the lightest load I've made so my future tests will be even lighter loads. (Short stroking has been happening with two different brands of factory ammo along with my hand loads.)

Shouldnt really make a diffrence with DGI gas system. Try the Carbine buffer and see if it cycles better. Less gas pressure from 5.56 than 6.5.

 

[msalm]

DO NOT swap the buffer itself, you'll beat the carrier key into the lower receiver at the end of the travel. As I stated before, you can just try the carbine buffer spring with the rifle length buffer and it may cycle better.

 

[trophyhusband]

I just put the carbine lower back on it to test some rounds and didn't have a single short stroke, although my groups got bigger. I assume there are two reasons for this, the first would be the stock AR trigger versus the Timney trigger that's in my other lower. The other is I think due to using a shooting pillow under the collapsable stock versus the Atlas monopod on the PRS stock.

I've done this trigger mod before:

15 Minute Practical Trigger Job for the AR-15

While it made a noticeable difference in the trigger pull, I was also getting a lot of failures to fire due to, what I think, is the firing pin not striking the primer hard enough. I've since went back to the stock trigger and I'm reluctant to try the mod again.

 

[ICANHITHIMMAN]

I just put the carbine lower back on it to test some rounds and didn't have a single short stroke, although my groups got bigger. I assume there are two reasons for this, the first would be the stock AR trigger versus the Timney trigger that's in my other lower. The other is I think due to using a shooting pillow under the collapsable stock versus the Atlas monopod on the PRS stock.

I've done this trigger mod before:

15 Minute Practical Trigger Job for the AR-15

While it made a noticeable difference in the trigger pull, I was also getting a lot of failures to fire due to, what I think, is the firing pin not striking the primer hard enough. I've since went back to the stock trigger and I'm reluctant to try the mod again.

Well no, the issue is ips speed, your bolt is not closing consistently with the other buffer and spring, which has other implications as well, the rounds are not stripped off your mag with the same force every time.

 

[trophyhusband]

Well no, the issue is ips speed, your bolt is not closing consistently with the other buffer and spring, which has other implications as well, the rounds are not stripped off your mag with the same force every time.

I'm not following. How does the bolt closing effect accuracy?

 

[ICANHITHIMMAN]

I'm not following. How does the bolt closing effect accuracy?

it affects accuracy with its headspace and machine tolerances. They are held to a certain spec "chamber spc", with it being a DD upper and bcg, I'm sure they both are. However if your not operating the system within its intended design parameters, then your bolt is not "locking up" or fully seating in to battery, which varies your head space, from shot to shot based on how closely the manufacture of your ammunition held to sami spec, how you hold the weapon, how you pull the trigger, barrel length, gas system length, gas port diameter, buffer weight, spring length all effect ips speed and have bearing on the system as a whole.

Bolts bounce, if your spring and buffer don't have enough *** to stop it, your missing out!

 

[trophyhusband]

What is a "DD upper"?

Would pushing the forward assist button between shots ensure the bolt is locking up the same every time?

The gun is an off the shelf carbine with a 16 inch barrel chambered in .223/5.56.

The brass is LC once fired in this rifle, all trimmed to the same length.

Every powder charge is weighed on a balance scale.

The first pic is what I shot using the lower receiver with the rifle buffer and Timney trigger. There are only seven hole because 3 of the ten rounds I loaded got jammed and dented. Some of those seven rounds were chambered by pulling the charging handle and letting it go. Some rounds chambered as a result of the gun cycling properly, and there were a couple at the end of the string that cycled properly but I pulled the charge handle back just a little just to make sure a round chambered and then used the forward assist button.

The second pic is what I shot today using the lower with a carbine buffer and stock trigger. Everything cycled normally. Every shot felt good and even though the trigger pull was much harder, it didn't seem like that was throwing me off.

As you can see, there's a huge difference between the two.

 

[ICANHITHIMMAN]

Disregard the DD I confused another thread on that detail, however that now leads me into a few more questions. Who made this rifle, who made the bcg, is you buffer stamped? I don't know what the propped spring length is for a 6.5 Grenada but bill Alexander sure will.