Magpul PRS causing FTF

[Ishallbie O'Cullkillin]

Took me months to figure it out, but there it is. AA 6.5 Grendel, upgraded to a Magpul PRS AR10 stock. Since the upgrade, I have been having frequent failure to feeds and bolt not holding open on the last round. Shortly before the upgrade, I switched to a better handload of 30.4gr of AA2520 under a 123gr Scenar. This, coupled with problems with the 17rd C-mags, had me looking everywhere but at the PRS. As it turns out, the screw that secures the stock to the buffer tube is too long, and prevents the buffer from traveling to it's rearward limit. I backed the screw off about a quarter inch and held the charging handle all the way back, then screwed it back in. I watched the bolt and carrier forced forward about 3/16 of an inch. An easy fix,I just wanted to pass this along and maybe save someone some time and money. Magpul products are awesome.

 

[ORD]

Re: Magpul PRS causing FTF

Magpul ships the PRS from the factory with the specific, shortened, vented buttstock screw. I have seen people fail to use the supplied magpul screw (using the basic A2 buttstock screw instead) and having exactly the same problems you experienced. The protrusion of the longer screw into the buffer tube is just enough to keep the carrier from fully retracting into the buffer tube which causes FTF and LRBHO not to work properly.

Glad you got it sorted out!

 

[Ishallbie O'Cullkillin]

Re: Magpul PRS causing FTF

Yes, the vented Magpul screw was used, and was protruding into the buffer tube space. I just finished grinding it shorter, and am re-assembling the component.

 

[taliv]

Re: Magpul PRS causing FTF

i did the same thing when the PRS first came out, except it was on a KAC SR-25 which had their original plastic buffers. I knew right away because the first shot, the buffer impaled itself on the magpul screw which was sticking out too far, and stayed there.

it was an easy fix, but pretty annoying

 

[Outlaw45]

Re: Magpul PRS causing FTF

Maybe that's my problem. I have a PRS on a custom AR15 I put together. I thought it was short stroking. Hope this is my problem.

 

[steelcomp]

Re: Magpul PRS causing FTF

I can verify this as well. Had the same problem with a new Armalite upper and a PRS and it was the screw supplied with the stock. I could pull the bolt back and it would clear the bolt catch, but not by enough. The other tell-tale was the bolt would not lock open after the last round. Cut about .200" off the end of the screw, and problem solved.

 

[shootist2004]

Re: Magpul PRS causing FTF

tag

 

[sobrbiker883]

Re: Magpul PRS causing FTF

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MattK287</div><div class="ubbcode-body"> but there it is. AA 6.5 Grendel, upgraded to a Magpul PRS AR10 stock. </div></div>

Not to be a dick, but why would you expect a AR10 PRS to work with a small frame AR? Grendels should use the AR15 PRS.

 

[CST]

Re: Magpul PRS causing FTF

they are the same stock except for the position of the cheekpad.

 

[sobrbiker883]

Re: Magpul PRS causing FTF

Then someone put the wrong screw in if its not allowing full travel of the bolt carrier.

I'm not going to get into a debate on it, but I'm pretty sure the carrier travel is different between the two, but I could be wrong.

 

[7.62willdo]

Re: Magpul PRS causing FTF

also remember there are several different lengths of "buffers" out there as well i believe the ar15 buffer is actually longer then the ar10 buffer.

 

[Badshot308]

Re: Magpul PRS causing FTF

Both correct. The AR-10 has a longer carrier travel and the buffer is shorter than the AR-15 buffer. Both the AR-15 and AR-10 rifles use the same length buffer tubes http://cdn.magpul.com/downloads/PRS_Installation.pdf . I took the vented mounting screw out of my AR-10's PRS stock. It measured .598" for the threaded section. This stock is a couple years old and it's screw does not protrude inside of the buffer tube. For you guys with the newer stocks that are having the problems, how long are the current mounting screws?

 

[BERTMAN77MK2]

Re: Magpul PRS causing FTF

hmmm, I didn't know u could interchange the 15 and 10 stocks
interesting

 

[Badshot308]

Re: Magpul PRS causing FTF

If you put the PRS meant for the AR-15 onto an AR-10, it will install just fine. However, if you raise the cheek piece up, you won't be able to pull the charging handle back far enough.