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Posted: 1/23/2016 8:36:02 PM EDT
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This 308 AR has problems I am sure can be fixed.
Parts: PSA PA10 complete lower (blem) Aero Precision upper DPMS 16" with FSB 308 BCG NiB/QPQ Bolt 308 (8bNQ) 20 rd Brownell mags All standard misc. parts Rifle fits together well. No binding and will discharge 1 round. The problem is it does not cycle properly. The first rd is loaded into the chamber. It fires properly. Then, the extractor pulls the old cartridge out of the chamber. The ejector ejects it into the ejection port but it gets caught when the bolt comes back, grabs the next round and loads it into the chamber. But, the bolt does not lock because the spent cartridge stuck in the ejection port. This is consistent; however, it sometimes initially fires 2 to 3 rds. Then, nada. I have thoroughly clean and inspected, changed ejector, verified gas tube alignment, checked headspace, checked bolt movement, and checked gas rings. That I did before taking the rifle to a gunsmith who does work for the city police and local Air Force community. He had it for 2 months and was not able to fix it. He bored the gas port slightly but was afraid to make it too big for fear of over gassing and ruining my barrel. He also cut off a few rings off the buffer spring. He said the parts and fit are ok. Since, I found that the PSA (Palmetto Stat Armory) buffer tube, buffer, and buffer spring are for AR 15 carbine. I think the only thing left to do is to replace the buffer and buffer spring with a 308 carbine DPMS/SR25 short 2.45" and 3.4oz. AR 10 buffer and buffer spring 27 coils and 11.5". These are recommended for the 16" carbine length upper for DPMS style LR-308 rifle. I will respond to the forum when I get the parts I ordered from Brownells. My last thought is that the FSB (front sight base) might be an issue. I have not seen anything anywhere that addresses the 308 AR carbine with a FSB instead of a gas block. If anyone here has any new ideas for the FTE problem I would be most happy to hear. |
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If you had AR15 carbine buffer and spring, your bolt won't travel far enough back to lock on an empty mag, and stove pipes are very common when trying to shoot with the ar15 buffer setup. Swap those parts, do 3-5 function checks as per the Army manual, then try it again.
The FSB could be an issue of it was pinned out of alignment. But you won't be able to determine that until you solve the buffer issue. ETA: If your order hasn't shipped, I'd highly recommend canceling it and getting the setup from heavybuffers.com, since you don't have an adjustable gas block, and your smith already opened up your gas port, you're most likely going to encounter over gassing problems. You're going to NEED a heavier buffer and spring than the stock stuff dpms sells. The stuff from Slash is substantially more expensive, but will solve many future headaches, especially since you don't have an adjustable gas block. |
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I am using:
Winchester 7.62x51, 147gr FMJ target
Federal 7.62x51, 149gr FMJ Wolf .308 Win 150gr FMJ Steel Case Colt .308 Win 168gr FMJBT Zinc Plated Steel Case I may be getting marginally better luck with Federal but it could be my imagination because there have been very few instances where I do not get FTEs. Thanks |
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I suspect you are right about the buffer length. That's why I am going to try with the shorty (and 11.5"spring). The parts I ordered have not been shipped yet... I will try your suggestion if it isn't too late. One thing though: I don't know about a heavier buffer because I do not think the port has been drilled too much to make a difference. I can't get hold of the gunsmith until later in the week to find out exactly. I remember he said "slightly" because he didn't want to significantly "make a drastic change that would ruin the rifle barrel" and from his experience that probably wasn't the problem. He suggested maybe a longer gas tube but he didn't feel strongly about that either. He said he was out of ideas and that he would not work on another one of these. One thing though, I would have thought, as reputable as he is that he would have thought of the buffer as being part of the problem. Oh well.
One question, there is signs of wear on the lower receiver ring where the bolt contacts the buffer when it comes back as if it might be hitting the receiver. Something I would think might be a result of carrier tilt but on the side not the top or bottom. It is not real noticeable but enough for me to mention it. What do you think? Thanks, JH |
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Is the gas key on the carrier binding at all? Got a pic of the lower receiver ring area you mentioned in your last post? Pics will tell us a lot more than text. The things to check that come to mind are... gas block alignment gas tube alignment (it'd be contacting the carrier key)/barrel nut timing recoil spring/buffer incorrect Normally I'd say check the gas port size to make sure it's correct, but you've already done that. So start looking from the gas port backwards. <ETA> I know there's an issue with a PA10 upper on an Aero lower (the CH will bind) but I don't know if the inverse is true. Might want to verify yoru alignment there is good by removing the buffer tube and looking from the rear while hand cycling the CH/BCG. |
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K1,
Thanks for the response. As I mentioned above, my smith had the rifle for two months and I trust him because he has worked on many of my significant collection of rifles and because of his clientele (Air Force and Police). I checked gas port alignment before taking it to him and he checked it and made sure of the alignment as well. I think the BCG is good and the gas key is tight. The gunsmith said all the components look right and he could not find anything that would cause the problem... except, he did not try a shorter buffer. I believe the buffer spring was an AR15 one but cannot tell for sure because he cut off some coils; however, I do know the buffer tube is AR15 which is not a problem so long as the buffer and spring are the right ones to accommodate the AR15 buffer tube e.g. buffer 2.45" and spring of 11.5" and 29 coils. 
(Picture does not very well show a smaller scratch on left side of ring) |
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Consider ordering a aero 308 buffer kit from scheuyler. Last I knew it was $55 + $7 shipping. At least then you are getting the correct combo of tube, buffer, and spring. As far as the wearing goes I don't see evidence of carrier tilt there nor does it appear like your buffer retainer is getting impacted by the BCG. But I'm on my phone so it's hard to tell. Are there any gouges in the buffer tube? |
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You have the DPMS carbine barrel. It had the ar15 carbine gas system, correct? NOT the mid length?
If this is the case, you will certainly need the heavy buffer. Its expensive, but worth it. Get the CAR10-XH with the spring he sells. Save yourself the headache and frustrating range trips. ETA, the marking on they lower could be from your upper. Maybe it's a contact point, doesn't look like anything could hit in those areas pointed out. I would think that might be from the receivers rubbing together. |
| No gouges in the buffer tube. I haven't spent a lot of time trying to figure out the wear on the receiver ring. After I put in the carbine buffer and spring I will spend more time. I just want to get the cycling fixed first. I am hopeful the shorter buffer will allow the bcg to fully retract. Will post here when parts get here in a couple of days. Thanks. |
| This is a carbine, not mid or rifle length. I have the 2.5" buffer and carbine spring coming from Brownell's. If this does not fix the FTE, I will try a heavy buffer as you suggest but the standard one is not that expensive to try. Range trips aren't a problem because my back yard is a 75 yard range. The local CHL instructors use it for CHL qualification. Thanks for the suggestions, |
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Just a heads up, KAK just announced they're making heavy buffers for the 308 now for 55$. Uses a standard spring, which i don't like.
Heavier buffer usually needs a stiffer spring. The reason i say you'll NEED IT, is the carbine setup for 308s is violently over gassed from the get go. It really should be standard. |
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I would not mix a PSA lower with an Aero upper and expect the gun to work.
Get a matching set. There is no reason to mess with mix and match on $100 receiver sets, especially from competing companies who have variations in the designs that are meant to keep them in house. |
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Quoted:
I would not mix a PSA lower with an Aero upper and expect the gun to work. Get a matching set. There is no reason to mess with mix and match on $100 receiver sets, especially from competing companies who have variations in the designs that are meant to keep them in house. Yup, What he said |
| That's really a good idea... "don't mix and match" But I bought the parts one piece at a time when they were on sale. The lower is a blem. Even though it is all PSA, it cost less than $100. The Aero upper receiver was $129 and the DPMS barrel was $229. Bolt and carrier on Gunbroker was won at $89. I'll throw in $150 for other parts e.g. barrel nut, charging handle, buis, etc. The whole rife cost me $697 and all I have to do is make it work... and I will (with help from all of you great people on this forum). Sure, I could afford to pay twice as much for a sure fire (no pun intended) no worry knock 'em down beauty but what's the fun in that? I have built 5 or 6 AR-15s in .223 and 7.62x39. I put gas piston kits on one of the AR-15s (actually M4) and it worked perfect with 30 minutes to install. I put another kit on one of the 7.62x39s and it took me two weeks (problem basically was AR-15 feed ramps at the lower receiver. I had to file them down and buff them out to what was essentially the M4 ramp all said and done. So you never know. It's all good and everything was done on a dime. I love the challenge and believe me, there is nothing that cannot be fixed! Thanks everybody. |
| I would stop playing around with what you have..........pic up a PSA blemished upper and swap everything over......from what you have and sell the upper receiver that you currently have.............I put together a couple of the Palmetto AR10 type rifles ..... I sold one and kept the other..........both ran great with factory ammo and my reloads............the one rifle I kept has 500 plus rounds through it with only a single hiccup on the third pull of the trigger |
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Quoted:
or, as mentioned above, you pick up a PSA blem upper, AND, you look for an Aero M5 lower on sale (or blem also), and voila, you're on your way to building your 2nd 308 rifle. it's win-win all around. Great idea. No need to mix and match these cheap receivers. They're both very affordable, so why mix and match? Sales happen every week, sometimes you miss them and gotta bite the bullet coughing up 20$ more. |
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Everybody has been really great to respond and offer ideas; however, this project for me is about "making it work", not so much having one that works out of the box. For all of the rifles, well almost all, I have built, the fun is in building them, finding parts, saving money and earning!
This forum is one of the most educational of the ones I read. Sometimes I can even contribute to others who have problems I have solved. Smart people here. I am interested in getting ideas that will make a problem go away without giving up on a project, such as this, and buying something already made or otherwise tried and true. Thanks again for the responses. James H |
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You are not going to be getting two receivers to work that were made with a different datum center of bore.
Where do you re-machine the carrier bore? Inside the upper receiver carrier tunnel? Carrier now bounces around in the bore. Extension tube threads? Now the extension tube will not thread into the lower. You have 2 incompatible critical core components of the rifle, and are trying to make them work, which is a wasted effort. Get a matching upper and be on to your next problem that will show up, especially if you clipped coils on an AR15 carbine spring for a 7.62 NATO carbine. There are a few people here that have been dealing with AR10's and LR-308's for well over a decade, myself being one of them. We're trying to pass on good info to get you up and running, not shoot down your ambitions to pound a square peg into a round hole. |
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AN AR-308 Carbine buffer tube is the same length as a standard AR-15, but requires a shorter, AR-308 Buffer. AN AR-10 Carbine buffer tube is LONGER than an AR-15 Carbine buffer tube, but the Buffer is the Same length as for an AR-15 Carbine. You cannot combine a Short/Long, Long/short Buffer tube/Buffer, or you WILL have problems. I suspect you are running the standard AR-15 carbine buffer tube (short), but you are using a Standard (long) buffer. This means your bolt will not cycle completely back. If you are running the other wrong combo, you will damage your carrier key and upper receiver. Also, you need to be sure you are running the correct spring, or you will also have issues. Some pics: https://i.imgur.com/zMb8y6a.jpg http://i.imgur.com/EPYhwpe.jpg |
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Quoted: He said he's using a 2.45" long (LR-308) buffer. Those are the tiny ones. His problem is mismatched receivers. As to mismatched receivers? The only part of the lower that has anything to do with cycling is the buffer/tube/spring. How would the lower receiver by itself contribute to the OPs issue? Sorry, but that also makes no sense. |
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Quoted:
As to mismatched receivers? The only part of the lower that has anything to do with cycling is the buffer/tube/spring. How would the lower receiver by itself contribute to the OPs issue? Sorry, but that also makes no sense. If the receiver extension is .01" below (or above) the centerline of the upper, you'll get problems.... |
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Quoted: If the receiver extension is .01" below (or above) the centerline of the upper, you'll get problems.... Quoted: Quoted: As to mismatched receivers? The only part of the lower that has anything to do with cycling is the buffer/tube/spring. How would the lower receiver by itself contribute to the OPs issue? Sorry, but that also makes no sense. If the receiver extension is .01" below (or above) the centerline of the upper, you'll get problems.... I suspect his failures to extract are more likely due to a classic cause, or a simple mistake in parts selection. |
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Quoted:
I suspect his failures to extract are more likely due to a classic cause, or a simple mistake in parts selection. Yeah, a mis-matched upper and lower. The lower being .01" higher also means the magazine in .01" higher, the FCG is .01" higher. All of this leads to improper function. Just get a new upper from PSA, or a new lower from Aero.... |
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Receiver mismatch is not a problem. The inside diameters match up perfectly (at least from my imperfect visual inspection) at both ends.
Palmetto State Armory provided the complete lower receiver with a long buffer which would work with rifle length barrel assy or probably even mid length but not a carbine length. DPMS recommends the short buffer and lr-308 carbine length spring with the AR-15 length tube. My tube is an AR-15 carbine length tube with a 11.25 inch AR-15 spring and 39 coils. The buffer is 3.25 inch at 3oz. The buffer spring for the 308 AR variant with an AR-15 carbine length tube should be 11.5 inches with 27 coils. The buffer should be a shorter one, 2.45 inch and heavier at 3.5oz. The fewer coils and shorter buffer should theoretically allow the bolt to cycle all the way back and still provide sufficient power to strip and load the next round in what is probably an over gassed system. An over gassed system overpowers the cycling and causes a situation where the extraction is not complete before the next round is loaded, pinching the spent case between the bcg and ejection port. Failure to eject. Even though the new round is loaded into the chamber, it cannot be fired because the BCG is blocked by the previous spent cartridge that's stuck in the ejection port (between the BCG and the chamber). After that attempt at an explanation, I received the new buffer and spring. In a couple of days I will have an answer as to whether the FTEs are solved. I will post it here. |
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Quoted: After that attempt at an explanation, I received the new buffer and spring. In a couple of days I will have an answer as to whether the FTEs are solved. I will post it here. A quick way for you to check is to pull the bolt back on an empty mag. It should activate your bolt catch, and travel only about 1/4" past to the rear. If it does, you do NOT want a shorter buffer. Can you measure you buffer tube and post the measurement? |
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Okay folks, I put in the AR-308 carbine spring and buffer. I put through two 20 round magazines with 100% success. What DPMS suggests is, and I tried to state it before, the AR 308/SR25 (DPMS LR-308) will work with the AR-15 buffer tube in all configurations carbine, mid, and rifle length. But... if you use the AR-15 carbine length tube you have to use the DPMS spring that has 29 coils and is 11.5 inches uncompressed. You also need to use a shorter buffer that is 2.45 inches long and weight of 3.4 ounces to mitigate overgassing.
After having gone through the entire build for fit and inconsistencies, the only thing left to do was to change out the PA10 (PSA call their SR25 308 a PA10 that could be confused with the Armalite AR10) buffer for the DPMS buffer spring and buffer. I purchased the DPMS OE parts just to be sure. The PSA buffer assy was built for a rifle length system with an AR-15 tube. Had I put a 18 or 20 inch barrel on mine, it might have worked with out changing anything. The AR-308 is definitely not well designed for a 16 inch carbine length barrel due to the short barrel and gas tube that tends to over gas system operation. There are not too many things that give more satisfaction that having a successful build. And it doesn't hurt at all that the total cost was less than $800.00. See you all elsewhere on ar15.com. |
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LRR, I am not sure what you are asking about "...where I machine the carrier bore" or "datum center of bore". Sound like you are talking about GIS mapping or something of that nature. Seriously, I think I know what you are asking but I am not an engineer and what I know and do is "seat of the pants".
As far as alignment is concerned, the BCG has no friction points and the upper receiver aligns internally with the barrel assy as it should. I have had no problems with threading the buffer tube on the receiver even though the outer height of the AP upper receiver is a fraction higher than the outer height of the threaded ring of the lower. With the old spring there was some contact where the back end of the BCG was obviously contacting the inside of the buffer tube but after refitting the tube into the receiver and putting in the new spring and buffer, that issue went away. The charging handle clears nicely and the interior dimensions align correctly. Smart or lucky, I cannot say but I learned a lot about the AR-308 type rifle with this project. I agree, if it were for perfection, I would have purchased a complete rifle. It does not seem that the AR platform is the best one for this caliber. I am really happy with my M1A and its oprod gas system. The only problem with the M14/M1A (and the M1 Garand) is the weight. Otherwise, they are hard to improve on. Hey, thanks for the input. Sorry to be a smart a$$. |
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To close out my topic, I made this thing work.
All who responded to me helped. I am an amateur enthusiast and collector. I have built as many as six ARs as of this date including my AR-308. I make mistakes and probably do not make a lot of sense at times but since I started collecting (C&R and mostly rifles) about five years ago as well as fixing, building, restoring and maintaining guns I can say it is the most enjoyable hobby I have had in my 70 years. There are so many different types of guns one will never run out of things to learn. I was in Information systems for 30 years and owned a retail PC business for about 10 of them. I retired in 2002 and moved to a rural area where, five years ago, I built a firing range where I can shoot whenever I want. CHL instructors use my range for the field demonstration for licensing. The AR platform reminds me of the PCs I used to build in that there are so many configurations and add-ons that keep it interesting. The .308 and 7.62x51 NATO is probably my favorite all around caliber(s). I will probably build another .308 with compatible receivers and at least a 20 inch barrel for long range. See you all next time on this forum. |
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