I recently installed a MagPul 308 PRS on my DPMS LR308 AP4. When I took it to the range to sight in my scope I noticed that the bolt catch would not hold the bolt to the rear when the catch was depressed in the down position. If I could get the bolt catch to hold, it would only be for a couple seconds and the bolt would slam home if the charging handle was pushed forward into the stowed position....bolt could not be kept to the rear at all and had to be manually held open in order feed rounds.

I also had difficulty getting the rounds to strip out of the magazine and feed into the chamber...they would miss feed and jam. I was able to manually feed single rounds in order to sight in my rifle and the rifle was shooting like a nail driver as usual but a single shot - hand fed AR is not what I need or want.

Did not have any issues with the bolt catch or magazine feeding before the PRS modification but not sure how it correlates...is the standard spring to strong compared to the carbine spring? I wouldn't think so but hoping one of you experts could help me figure out my major malfunction....thanks.

This post has been edited by HarleyD1259: November 7th 2009 3:31 PM

did you try reverting back to another stock to see if it fixed the issue?

hsracer...no not yet. I broke the AP4 down to look at the bolt catch, and the bolt carrier group components....one thing I never noticed before was a beveled edge on the bottom of the bolt carrier which comes in contact with the bolt catch. The edge is beveled at a horizontal angle which looks like it would not allow the bolt catch to hold the bolt to the rear....

I am going to take a look at my AR15 bolts and also going to look at the DPMS catalog to find pictures of 308 bolts. I will try to post a picture of my bolt carrier with the beveled edge when I get a chance....it seems to me that I haven't had problems with the bolt catch before but I've only fired my .308 AP4 about three times....I never noticed an issue like this before. May resort to changing back to the carbine stock to see if that changes anything

Thanks again.

This post has been edited by HarleyD1259: November 8th 2009 1:07 AM

Are you sure you got the PRS stock that is specifically for the AR-10 and .308 family of rifles? It should have a .308 specific rifle spring and buffer as well as extra cheek-piece clearance for the charging handle.

The .223/5.56 buffer would be too long and cause the bolt to short cycle and not get back far enough for proper engagement of the bolt catch.

definitely make sure you have the right rifle length spring and rifle buffer for your .308/

This post has been edited by SSGN_Doc: November 8th 2009 2:40 AM

+1 I was thinking wrong spring too

SSGN DOC and Warlike, Thanks. I will double check. I did order the parts from a vendor advertising the .MagPul 308 PRS and the MagPul box label had .308. I bought the standard buffer tube, buffer and buffer spring from the same vendor at the same time that I bought the 308 PRS but will call him tomorrow to confirm that they are compatible with the 308 PRS.

So is a buffer and spring is either 5.56 or 308 specific? The standard buffer tube is the same for either one of these calibers isn't it? A commercial tube wouldn't fit in a mil-spec lower receiver like the DPMS LR308 AP4 would it?

I may go ahead and put the collapsible stock back on to see if it fixes the problem and go from there....will call the vendor that I bought the PRS modifcation parts from too. Guess I should have just bought a SASS in the first place and be done with it.....but it's fun to buy and put stuff on the rifle myself...I'm sure you know what I mean.

Thanks again for your inputs. I appreciate it.

HarleyD

I agree with DOc, I would bet money that you have a AR-15 Rifle Buffer and spring when you should have the .308 Rifle spring.

Placing the stock parts back on would be a good idea until you get the right parts in.

Yes,
The buffer tube is the same between 5.56 and 7.62 NATO rounds.

The actual buffer, and spring are differently sized to accomodate the longer bolt carrier of the .308/7.62.

Teh sping is shorter but has heavier coils, and the buffer is shorter as well. An AR-15 spring and buffer will not allow the bolt carrier to travel all the way to the rear extent of it's travel to allow the bolt to actually engage the catch properly. I would think it would also affect loading of the next round in the mag as well.

Here's a link to Fulton Armory's page of .308 specific parts. It should shed some light on some of the items that are unique to 308 carbines and 308 rifles.

FA 308 parts

Thanks gentlemen...I'll check it out....I have an email out to the vendor that I bought the buffer spring and buffer to verify if they are 308 but I doubt it....thanks again for the advice and info...I appreciate it.

I just went to the DPMS website and ordered a "308 buffer spring and 308 buffer" hopefully that will do the trick. I'm only out $14.00 for the wrong buffer and spring...hopefully this will take care of the problem. Thanks again to all that helped.

keep us updated, if that ain't the fix we'll dig deeper

Gents, I received the .308 buffer and spring from DPMS yesterday...and of course that did the trick....the bolt catch does "catch" the bolt face now...amazing what happens when you use the correct parts.

Thanks again for everyones' input and advice. Now it's time to go to the range.

Semper Fi.

TS