Magpul PRS on DPMS


April 6, 2011, 11:43 PM
I added on a PRS myself to my AP4 and had a quick question. As I had an adjustable M4 type stock I had to buy an A2 buffer tube that was straight without the 6 position fitments milled into the tube. It is clearly longer than the "stock" stock. The castle nut was not used as the A2 stock only had enought thread to get over the edge of the buffer spring Sliding on the PRS and bolting it on was a cinch. One question though, racking the action now is clearly easier than before. Not rocket science, less compression of the spring yields lower force. (Hookes Law for you Enginerds)

My question...Is this detrimental or concerning to you folks in any way? Should I buy a longer spring? Gunsmiths at the local gunclub thought no but I have to think it should advance the bolt with the same force as before. If I fire my rifle do I get a buffer and the bcg implanted into my shoulder?

Thanks for any advice


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April 7, 2011, 02:05 AM
You need to replace your carbine buffer with a rifle buffer when using the A2 receiver extension.

April 7, 2011, 07:33 AM
Yes, you need a rifle length spring, the ArmaLite AR10 spring is the best choice. Contact this guy, he can fix you up with a quality spring and buffer.

April 7, 2011, 10:12 AM
Looks like you guys have it covered so I've got a question. What makes a buffer like the one listed above worth $125 when you can get others for around $12-20?

April 7, 2011, 10:17 AM
It is nearly twice the weight and stainless steel?

April 7, 2011, 11:15 AM
Yes that was very helpful... I was wondering what performance advantage this is giving me. What will this do that a standard buffer will not?

April 7, 2011, 11:40 AM
Yes that was very helpful
Glad to help. :D

I too am curious, which is why my answer was in the form of a question restating the only things I could gather from their web site.

April 7, 2011, 11:45 AM
Haha roger that! Sorry, thought that was a smart alec obvious answer. We will have to see if anybody else has an answer i guess!

Sam Cade
April 7, 2011, 12:17 PM
The Manual.

To quote:Make sure an M16 Rifle Receiver Extension, Rifle Buffer,
and Rifle Action Spring are installed. If not, replace them with the
correct parts to armorer specification.

April 7, 2011, 01:47 PM
If you guys are still wondering about the benefits of using a heavier buffer, quite frankly, I don't think there will be any when running a rifle length gas system. A heavier buffer will slow the bolt velocity often offsetting the effects of an overgassed rifle and helping to resolve extraction issues; but all of this applies more to carbines than rifles.

I've never NEEDED to run anything more than a standard milspec buffer or spring on any rig that was running a rifle length gas system. Now, running a heavier buffer/spring can and will cause short stroking if you use anything less than full power ammunition. The only way I'd even consider running a heavier buffer in a rifle would be if I'm running a barrel longer than 20" where I'll have a longer dwell time. You MAY see some benefits in this situation.

Don't go adding anything to an AR unless you need to. If it ain't broke, don't fix it.

Generally speaking, as rule of thumb, if your rifle is ejecting the brass at about the 1:00 position, then you'll probably get some benefit from slowing the bolt velocity. If your ejection pattern is between the 2:00 and 4:00 position, don't mess with it, it's running the way it should.

April 10, 2011, 07:23 PM
Thanks to all for the help and advice. I purchased my buffer and spring from Armalite. Thanks again for all of the help.

April 10, 2011, 08:20 PM
You do know Armalite and DPMS 308s are different right? You should have bought the one I linked if you have a DPMS. The Armalite may work but with the 308 ARs there is no parts interchangeability standard.

April 10, 2011, 09:02 PM
Yes, I know there are differences between DPMS and Armalite. I really regretted that when I had a chance to buy a an Armalite SASS upper to combo with my carbine upper for an amazing price but couldnt. The DPMS buffer on both the site you took me to and the DPMS site state they are for AR15. I spoke with a smith at my local shop and he also had the same parts for AR15 but felt it would be a better choice to go with something spec'd for an AR10. The buffers and spring should be compatible. Armalite and DPMS do not interchange anywhere in the upper. Thanks for your help

April 10, 2011, 09:59 PM
I have (4), yes 4 DPMS in 7.62 and not one of them is set up the same. I basically take the LR 308 C's, used to be called the Tac 20, and add all the goodies an turn them into a SASS type rifle. The main reason is because the LR 308 C has a chrome moly 20 inch barrel, which I prefer over stainless steel.
Two of those rifles have over 10,000 rounds down the tube with steel case problems with ejectors, extractor, firing pins or chamber problems

April 10, 2011, 10:55 PM
An AR-15 and AR-308 buffer aren't the same length ... well, mine aren't anyway. I have a MAGPUL PRS on a Bushmaster/DPMS AR-15. I'm using a BM standard rifle buffer that came with the A2 stock. The buffer is 6" long and weighs 5.2 oz. I also have a POF P308 with a MAGPUL PRS and had to buy a AR-308 buffer for it which also weighs 5.2 oz but is 5-1/4" long. This isn't surprising when you consider that the AR-308 BCG is about 1" longer than the AR-15 BCG. It is surprising that both buffers would be the same weight though. I ended up adding weight to the POF buffer taking it to 7-1/4 oz for perfect timing with factory ammunition and my reloads.

As for buffer springs ... I use TUBB CS flat wire springs in all of my ARs and don't see any reason to change. I've had people comment on how soft shooting my POFs are and I put it down to TUBB springs with the correct buffer type, length and weight.

April 10, 2011, 11:27 PM
That's weird I thought I linked the DPMS 308 buffer. Sorry.

April 10, 2011, 11:32 PM
That's weird I thought I linked the DPMS 308 buffer. Sorry.

Your link is for the DPMS AR-15 buffer, but that's what I would (do) use in an AR-15. Why use an AR-308 buffer in an AR-15?

April 10, 2011, 11:35 PM
Oh yeah he was talking about an AR15 in the OP, all the talk about Armalite threw me off. OP you should have used the buffer in the links.

April 11, 2011, 09:28 PM
The rifle I have is a DPMS AP4... It is a 308 carbine rifle and that is why I am using an AR10 buffer and spring.

April 11, 2011, 09:42 PM
Here is a link to it.... When I get all the work done I will get a pic up of it. Thanks for your help.

April 11, 2011, 09:58 PM
The rifle I have is a DPMS AP4... It is a 308 carbine rifle and that is why I am using an AR10 buffer and spring.

OK ... I thought you had a AP4 Carbine but you have an LR-308 AP4 Carbine ... now it all makes sense.

April 12, 2011, 12:00 AM
Sorry, could have been more clear in the original post!!

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