CRASH! What went wrong?

survivalshop · April 11, 2015

It would solve the issue of the the BCG going too far back . A heavier Buffer would slow the reciprocating action of the BCG down & may actually help . Its not only weight of the Buffer & the resistance of the Buffer spring to slow or Buffer the speed , but a timing thing also . The weight of the Buffer & the Buffer spring resistance , that slows the action down so the system functions as it should . As you pointed out the other factor is the Gas Volume & Pressure & they all contribute to the timing of the action , they have to work in unison to stop the Buffer from hitting the end of the Receiver Extension .

Too little gas , of course , will effect it the opposite , BCG , Buffer/spring will not go back far enough to function properly . Have you measured the Gas Port in the Barrel ?

ironmonster · April 11, 2015

Nope I haven't. It is a Rainer Select barrel and they dont list the spec's on there site either.

98Z5V · April 11, 2015

The PWS tube is 1/8" longer than another random buffer tube I grabbed (7" vs 6-7/8"). So that plastic spacer should do restrict it.

I'm wondering if the PWS tube is too long - and how individuals measure. 7"internal depth is the AR-15 standard, and what you need to have for your setup. It's odd that you say another receiver extension is 6 7/8". That's the difference right there, and shows that no two people measure the same, unless both know "precision measurement." No offense - but i don't know of ANY receiver extension out there that has a 6 7/8" internal depth.

I think this PWS super-tube is off.

However it still means that buffer is slamming into the back of the tube every round fired.

That's the operating system, and how it's supposed to work, and why there's a bumper on the end of the buffer. It slams into the back of the receiver extension, by design. It slams into the back of the receiver extension on a 308AR REALLY HARD when your gas system is all fucked up.

I think it's normal to touch but considering the damage done the carrier is still going full tilt at the back of the cycle.

Too much internal depth is causing that.

With the spacer the bolt locks on the catch and will move about a 1/4" back from there before everything bottoms.

Too much distance. 1/4" over-travel of the BCG is way too much. That's what breaks bolt stops/bolt catches. Reduce it. Stack quarters, or machine another thing that you machined - but longer. If you stack quarters, you can measure the thickness of a quarter, count those quarters, and add that thickness to your spacer that you machined. People might laugh at my suggestion, but it works. $1.75 is the magic number on a 9mm AR. Done. Didn't machine $hit, and lost $1.75 into the receiver extension. And they cycle.

I ordered the Tubbs cws but I think as far as lenght goes it hurts not helps, it adds lenght to the carrier, I need the carrier to be shorter. Maybe the weight would be enough to slow it before it bottoms but it seems to me that an adjustable gas block is a better solution.

You don't need the carrier to be shorter - that's a standard, even when there's "no standard for 308ARs" - that is a standard. You don't need a shorter carrier - you need less internal depth on your receiver extension, to prevent your carrier from slamming into your lower.

You're not fucking listening to the information that's being presented to you. It's time to start listening...

survivalshop · April 11, 2015

I don't believe the Buffer is supposed to bottom out all the time against the Receiver extension . It would put too much stress on the Lower Receive & its Extensions threaded attachment area . I do believe the bumper is there in case it does & it should be sufficiently slowed by the Buffer spring & the Mass of the Buffer to not hit with any damaging authority . Thats a hard Nylon bummer on there , if it were a continuation of the Buffer material , it would not only make a lot of noise , but would probably crack the Receiver Extension , pretty quick .

The back end of the Buffer also acts like a guide for its travel in the spring ( its why it has a taper at the end to it ), keeping the Buffer & spring from wedging its self internally in the Extension . With the spring collapsing from compression , it has to be contained & guided through its travel upon recoil of the action .

If you read my last post , the three things , Buffer , Spring & gas system all work & are supposed to be factored in together to keep the action working to spec's. If you keep all components with in the known working system , there is no problem , its when a manufacturer deviates from those known working components , that there are fitment & function problems , as we have seen here with this Receiver Extension.

Also do not confuse Blow back operated actions with a Gas or Piston Action system . Blow Back systems use a buffering system also , but its just an over travel stop & has no regulated gas system ( Port size ) and they have no Buffer ( Mass ), the Recoil spring or Action Spring is the only thing slowing the action down enough to keep from damaging the Receiver or internal components .

What is the gas system on this Barrel ?

You are right 98 , this high Dollar Receiver Extension is made too deep for normal internal components .

Edited April 11, 2015 by survivalshop

washguy · April 11, 2015

You don't need the carrier to be shorter - that's a standard, even when there's "no standard for 308ARs" - that is a standard. You don't need a shorter carrier - you need less internal depth on your receiver extension, to prevent your carrier from slamming into your lower.

You're not fucking listening to the information that's being presented to you. It's time to start listening...

^^^^^^^^^ :) Wash

blue109 · April 11, 2015

this discussion made me realize I'm ignorant on this aspect of AR operation. is the buffer suppose to "slam" into the rear of the extension? I would think not, and that it would wear out lowers pretty fast. I would also think it would create a much sharper recoil impulse. I always thought it wasn't suppose to hit at all. that the spring and the buffer mass stopped it short and the bumper was just a precaution.

ironmonster · April 11, 2015

I'm wondering if the PWS tube is too long - and how individuals measure. 7"internal depth is the AR-15 standard, and what you need to have for your setup. It's odd that you say another receiver extension is 6 7/8". That's the difference right there, and shows that no two people measure the same, unless both know "precision measurement." No offense - but i don't know of ANY receiver extension out there that has a 6 7/8" internal depth.

I think this PWS super-tube is off.

That's the operating system, and how it's supposed to work, and why there's a bumper on the end of the buffer. It slams into the back of the receiver extension, by design. It slams into the back of the receiver extension on a 308AR REALLY HARD when your gas system is all fucked up.

Too much internal depth is causing that.

Too much distance. 1/4" over-travel of the BCG is way too much. That's what breaks bolt stops/bolt catches. Reduce it. Stack quarters, or machine another thing that you machined - but longer. If you stack quarters, you can measure the thickness of a quarter, count those quarters, and add that thickness to your spacer that you machined. People might laugh at my suggestion, but it works. $1.75 is the magic number on a 9mm AR. Done. Didn't machine $hit, and lost $1.75 into the receiver extension. And they cycle.

You don't need the carrier to be shorter - that's a standard, even when there's "no standard for 308ARs" - that is a standard. You don't need a shorter carrier - you need less internal depth on your receiver extension, to prevent your carrier from slamming into your lower.

You're not fucking listening to the information that's being presented to you. It's time to start listening...

Dude, really? You think anyone would listen too you when you treat them like that? You may be king shyte of turd mountain around here but if you really have the answers giving them like that is a way to make sure no one listen. Being a dick, even if it is warranted (which I cant see that it is) is no way to get your point across.

I have listened to each and every suggestion and implemented and investigated all of them and I am not an idiot. I own 17 AR's and built probably 40, I am not completely clueless. I own a fab/blacksmith shop and have a basic machine shop. I know how to run a fucking tape measure. The PWS tube is dead nuts 7" inside, the other tube is 6 7/8".

I understand I need less internal depth, That is why I made a spacer. I understand the buffer weight, length and spring tension/length affect how the carrier cycles which is why I bought a heavier buffer and the recommended spring.

When I said I need the carrier to be shorter, that was a poor choice of words and something that I did not think through, which is why i immediately posted a follow up statement saying I understood that was wrong. What was going on in my head was that I needed less space in the system between the back of the carrier and the bottom of the buffer tube, and that more space in the system would exacerbate the problem. That came out as "shorter carrier" but thats not really what I meant.

I came looking for suggestions, I am new to the .308 platform, asking questions and verbally thinking through things by posting questions and responses.

Show me one example of information posted here that I have ignored? There is nothing posted here I did not take to heart and consider. The only arguments I have made have been to try and clarify the problem and question weather there was any merit to the idea.

Edited April 11, 2015 by ironmonster

Matt.Cross · April 11, 2015

Fair enough. Do take Tom with a grain of salt though, dealing with his bark is much easier than dealing with his bite. He's just trying to help you, and that means he likes you. Please don't take it personally, that's a mistake.

ironmonster · April 11, 2015

Thanks Matt.

I'm a big boy. Can can take a bit of abuse before gather up my toys and run home crying.

It just struck me out of the blue as I feel like the issue was already worked though and workable solutions proposed, steps taken to rework things and then BamB! I'm a clueless fucking idiot!

ironmonster · April 11, 2015

See, I'm smiling ;-)

unforgiven · April 11, 2015

Don't be so hard on yourself brother.The end result is to have flawless operation of firearm the in between stuff is minor.

washguy · April 11, 2015

ar2.jpg

ironmonster · April 11, 2015

Just out of curiosity I dug out the loose buffer tubes I had laying around in my parts. I came up with 6.

There are two that measure 6 7/8 from inside bottom to end of threaded lip

One that measures 6 15/16, two that measure a dead 7" and one that measures 7 1/32".

All measured to the longest point of the tube lip ( a couple have protruding lips to engage the detent, the longest point always determining the buffer system travel as it is screwed up to the detent

That is a overall variance of .156"

Two quarters stacked up measure .135, three quarters .202

ironmonster · April 11, 2015

Just out of curiosity I dug out the few AR's I have here and measured bolt over travel (using my eyecrometer)

Out of these 13 the distance from the bolt face to the bolt catch varies a lot. The least being an 1/8" or less, the most being a strong 5/16"s (in a factory built Noveske light Recce lo-pro)

I am making the assumption that the carrier/buffer is bottoming before the charging handle runs out of stroke but that may not be the case.

MikedaddyH · April 11, 2015

I still think by adding a Tubb's weights on the back of the bolt carrier will correct both the space problem and with the increased weight will slow down your carrier speed.

Just Sayin'

Edited April 11, 2015 by MikedaddyH

survivalshop · April 12, 2015

Well I took some photo's & also did a little Surgery to one of my old Commercial Carbine Receiver Extensions , No real idea of round count , but well over a thousand rounds , from my 16" 308 . Buffer & Spring are DPMS Carbine 308

The RE measured real close to 7" , Maybe 6 15/16 " ,but close.

With the Buffer/Spring fully compressed , full travel of the Buffer is 4 1/2 " , that only leaves 2 1/2 to the bottom of the RE . Correct ?

With the Buffer/spring collapsed to the 4 1/2 " ( fully compressed till it stops ) , the spring is fully compressed & because of the lip the Buffer Spring sets on , it doesn't go all the way to the end of the Buffer , so no way the Buffer can hit the end of the RE , the Spring is fully compressed & the Buffer end is about 1/2"( close estimate ) from hitting the end.

Just for me , I was wondering , this being a Commercial stock , if the inside of the RE was shaped like the outside , an angle . Well its not , its been milled to be flat , but when I looked at the bottom , the only mark I could see on the bottom was the Buffer Spring seating area , no other marks , like from a Buffers , Nylon Bumper , it should have left some kind of indication it was hitting , not even a scuff on the Finnish . If too long of a Buffer , with this set up, I could see it hitting the bottom .

Here's all the parts & tape measure is for reference only .

You can pretty much figure that Bolt Bounce is not caused by the Buffer hitting the end of the RE , its bottoming out the Buffer Spring . Your Spacer just moved the end of the RE , to make it shorter , keeping the BC from hitting the Lower Receiver & Extension. If you are over gassed , I would think it will force the BCG/Buffer to compress the Buffer Spring fully , which could cause Bolt Bounce .

Seems a balance of components & gas signal , keeps the Buffer spring from fully compressing . It may get close though . Now the Tubb's spring , I have not measured yet , but will in the morning . I'm curious .

ironmonster · April 12, 2015

I still think by adding a Tubb's weights on the back of the bolt carrier will correct both the space problem and with the increased weight will slow down your carrier speed.
Just Sayin'

I ordered one, And I ordered two heavy buffers and corresponding springs. Between the two Im guessing no more crash, I still need to figure out is I am seriously over gassed though. I would not think the Rainer barrel would be anything out of the ordinary for gas port size. Its a 18" mid gas system.

ironmonster · April 12, 2015

Well I took some photo's & also did a little Surgery to one of my old Commercial Carbine Receiver Extensions , No real idea of round count , but well over a thousand rounds , from my 16" 308 . Buffer & Spring are DPMS Carbine 308

The RE measured real close to 7" , Maybe 6 15/16 " ,but close.

DSCN2368.JPG

With the Buffer/Spring fully compressed , full travel of the Buffer is 4 1/2 " , that only leaves 2 1/2 to the bottom of the RE . Correct ?

DSCN2370.JPG

With the Buffer/spring collapsed to the 4 1/2 " ( fully compressed till it stops ) , the spring is fully compressed & because of the lip the Buffer Spring sets on , it doesn't go all the way to the end of the Buffer , so no way the Buffer can hit the end of the RE , the Spring is fully compressed & the Buffer end is about 1/2"( close estimate ) from hitting the end.

DSCN2372.JPG

Just for me , I was wondering , this being a Commercial stock , if the inside of the RE was shaped like the outside , an angle . Well its not , its been milled to be flat , but when I looked at the bottom , the only mark I could see on the bottom was the Buffer Spring seating area , no other marks , like from a Buffers , Nylon Bumper , it should have left some kind of indication it was hitting , not even a scuff on the Finnish . If too long of a Buffer , with this set up, I could see it hitting the bottom .

DSCN2374.JPG

Here's all the parts & tape measure is for reference only .

DSCN2371.JPG

You can pretty much figure that Bolt Bounce is not caused by the Buffer hitting the end of the RE , its bottoming out the Buffer Spring . Your Spacer just moved the end of the RE , to make it shorter , keeping the BC from hitting the Lower Receiver & Extension. If you are over gassed , I would think it will force the BCG/Buffer to compress the Buffer Spring fully , which could cause Bolt Bounce .

Seems a balance of components & gas signal , keeps the Buffer spring from fully compressing . It may get close though . Now the Tubb's spring , I have not measured yet , but will in the morning . I'm curious .

That is outstanding, and really interesting. Tomorrow I'll have to do some comparison . For a .308 I dont have anything but the Tubbs spring, but my assumption is even though its longer it will compress smaller because its nature.

wetncold · April 12, 2015

I would think a compressed spring it will be longer than the buffer. That in itself would prevent the buffer from hitting the rear of the tube extension. If it were me, I would turn the extension out one turn, if it still catches the plunger.

But that's just me.

survivalshop · April 12, 2015

I would think a compressed spring it will be longer than the buffer. That in itself would prevent the buffer from hitting the rear of the tube extension. If it were me, I would turn the extension out one turn, if it still catches the plunger.
But that's just me.

Its not hitting the Plunger , the BCG is hitting the threaded area of the Lower Receiver . There's no doubt the Receiver Extension is too deep for the Buffer/Spring system that would normally work with a std. Carbine RE.

I took a depth measurement with the Tubb's Buffer spring & there is no difference in where it bottoms out , in fact it may be less than the DPMS Buffer 308 Carbine spring. I couldn't take a Photo because my Camera woman was not out of a sound sleep yet , but what I did was drop the DPMS 308 Carbine Buffer in the RE & mark it , so I could see how far or deep the Buffers relationship in the RE was , with the system fully compressed & bottomed out .

The gap between the Spring seat on the Buffer & the Face of the Buffer where the BCG touches , is 0.257" , so about a 1/4 " & from looking at the mark on the RE , the bottom of the Buffer will set off the bottom of the RE ,about half that with the spring bottomed out

CS Tubb's flat wire spring , still measured about 4 1/2 travel to stop & you can see the mark I put on the RE to show the top or face of the Buffer would be if it was touching the bottom of the RE .

Here's the DPMS 308 Carbine Buffer Spring .

I can tell you this , the Tubb's spring is a bear to keep compressed all the way & so was to some extent the DPMS , but the Tubb's was stiffer than the DPMS in almost all of it tracer . Where the DPMS got tight close to the last inch or more of compression .

I will take measurements next of the relationship of the BCG with in the RE , with the BCG set in the RE @ that magic 4 1/2 ".

I think if you keep that spacer or one like it in the bottom of the RE, it should work , to keep the BCG from hitting the Lower Receiver. No idea how your new components will work .

ironmonster · April 12, 2015

Man I really appricate all the effort you put into this. Outstanding, top notch and super cool.

survivalshop · April 13, 2015

Well I stand corrected , in a way . I was not completely satisfied with the measurements , mainly because I knew I had to assemble the RE on the Lower Receiver to be sure nothing changed when all assembled & working on a complete rifle .

As you will be able to see in the Photo's , the Buffer can be pushed back into the RE . far enough , by using the Charging handle , like you were charging the rifle with a loaded Mag. , that the Buffer is barely touching the bottom of the RE., but also note that the spring is fully compressed . The real question is , does it go that far under normal recoil when fired . I can see using high pressure loads , it could go that far every time , but not using normal pressure factory or hand loads .

Having said that , its only an assumption on my part , because I will have to find some way to record normal reciprocation distance of BCG travel , Now that is going to be a challenge.

Using the BCG with the Charging like normal operation , I'm not sure why there is a difference in the compression with a Shotgun cleaning handle & a completed rifle ( well , almost complete , no barrel ) . The only thing I can think of is even though I had the Cleaning rod in the middle of the Buffer , it must have been cocking the Buffer some what , not sure . Could also be the mechanic's of the complete system, all I know is , its different & my first tests with RE , not attached to the Receiver .

Also note that if it is touching the back of the RE . , its not much of a touch , so I still believe that under normal conditions , it will not touch under recoil .

The 4 1/2" mark made on the Bolt Carrier & how far it travels into the RE. & there is no way I can see BCG touching , even with the complete assembled Lower /Upper . Understand that I'm using a great deal of force to hold it there as far as I can get it in the RE. . You can see the 4 1/2" mark on the side of the Bolt Carrier , if you look close .

What I didn't expect was where the Buffer was in the RE, the Buffer had went deeper in the RE by an aprox. 1/8" . If you look at the photo's from my other post , you can see that by using the Cleaning Rod & bottoming out the Buffer assembly , is about 1/8" from the Buffer touching the bottom of the RE.. This photo has the DPMS 308 Carbine spring in .