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Posted: 9/15/2009 10:24:48 AM EST
Quick question: I just put together my first build. When I brought it to the range today, I shot 55 grain, Tactical TRU, by Federal Premium. The rifle shot a 1” group at 75 yards. That being said, I have a slight problem. When using brand new 30 round P-mags, the bolt fails to remain open on the last shot. I shot four different P-Mags, all with the same problem. So, for shits and giggles, I shot the same ammunition through a couple of regular (metallic) USGI magazine. After the last round, the bolt DID stay open. Any ideas?
My setup is as follows:
Spikes lower w/DPMS LPK installed
Magpul CTR butt stock w/mil spec tube
Spikes 16” M4 complete upper w/7” DD lite rail (free floated)
Magpul MIAD full grip kit
Brand new Magpul 30 round P-Mags

P.S. I am VERY HAPPY SPIKES!!!!!
Link Posted: 9/15/2009 10:27:48 AM EST
Out of spec DPMS bolt catch...
Link Posted: 9/15/2009 10:28:58 AM EST
[Last Edit: 9/15/2009 10:30:50 AM EST by mathecb]
Pull the bolt back, insert an empty p-mag and see if it activates the bolt catch. If it dosn't work with multiple pmags its probably not a magazine issue.
Link Posted: 9/15/2009 11:28:55 AM EST
Originally Posted By 87GN:
Out of spec DPMS bolt catch...


but why then would the problem only occur with pmags and not with the aluminum ones?
Link Posted: 9/15/2009 11:47:16 AM EST
Originally Posted By Captains1911:
Originally Posted By 87GN:
Out of spec DPMS bolt catch...


but why then would the problem only occur with pmags and not with the aluminum ones?


Perhaps PMAGS are built to such awesome standards that PMAGS don't need to work in all AR-15
type rifles. Your gun obviously sucks cause PMAGS are finicky! Just kidding on that last part. I have
1 PMAG and while it is cool looking and works, I won't buy anymore since GI's work perfectly for me.

Checking it revealed that it does not drop free from either of my 2 LMT lowers. They could very well
be out of spec though. Just buy GI's and don't look back.
Link Posted: 9/15/2009 11:48:53 AM EST
Do you have another lower to try them in?
My suggestion would be to replace the bolt catch, detent and spring and see if that fixes it.
Link Posted: 9/15/2009 11:52:23 AM EST
Originally Posted By Captains1911:
Originally Posted By 87GN:
Out of spec DPMS bolt catch...


but why then would the problem only occur with pmags and not with the aluminum ones?


The design of the polymer Pmag is thicker along the backstrap of the magazine than a regular USGI aluminum. This means that a mag catch with a slightly too-short "finger" will not be able to catch the Pmag's follower and activate the BHO.

On one of my older Bushy rifles this results in a hang-up just short of the mag locking in, as the "finger" of the BHO wedges against the back end of the follower.

Tex78
Link Posted: 9/15/2009 12:59:31 PM EST
Originally Posted By mathecb:
Pull the bolt back, insert an empty p-mag and see if it activates the bolt catch. If it dosn't work with multiple pmags its probably not a magazine issue.


I tried this.... The GI Mags hold the bolt back (I tried 3 different ones) I also tried a friends P-mag... It to did not lock the bolt back.
Link Posted: 9/15/2009 1:02:03 PM EST
Originally Posted By Tex78:
Originally Posted By Captains1911:
Originally Posted By 87GN:
Out of spec DPMS bolt catch...


but why then would the problem only occur with pmags and not with the aluminum ones?


The design of the polymer Pmag is thicker along the backstrap of the magazine than a regular USGI aluminum. This means that a mag catch with a slightly too-short "finger" will not be able to catch the Pmag's follower and activate the BHO.

On one of my older Bushy rifles this results in a hang-up just short of the mag locking in, as the "finger" of the BHO wedges against the back end of the follower.

Tex78


I think you are right, because when I take the upper off, then watch carefully as I insert the empty mag, I can see the bolt catch move, just not enough.
Question is.... How do I change this? Is there a different bolt catch?
Thanks for all the input guys
Link Posted: 9/15/2009 1:04:13 PM EST
I doubt it's the DPMS bolt catch. I have this issue with my LMT & Pmags. Pmags work just fine in all of my other lowers. USGI mags work fine in the LMT though. I don't know what the issue is so I just put up with it.
Link Posted: 9/15/2009 1:07:37 PM EST
Originally Posted By warpig8654:
I doubt it's the DPMS bolt catch. I have this issue with my LMT & Pmags. Pmags work just fine in all of my other lowers. USGI mags work fine in the LMT though. I don't know what the issue is so I just put up with it.


Yeah, I agree... The ammo feeds well, no problems there. You just get that ugly "Click" sound ... that lets you know it is empty. I rather that be the problem than to have it not feed.
Link Posted: 9/15/2009 1:31:33 PM EST
I bought my PMAG's about 9 months ago and Magpul told me that they were designed for the Colt and every other AR is a knockoff so there will be some tolerance differences. There were a couple of tabs they showed me to sand down and now my LMT releases it with no problem. It was a known issue with many AR's and that was the fix. I never had the problem with my CMMG lower, so it is different with all AR's. I hope that helps.
Link Posted: 9/15/2009 1:41:14 PM EST
[Last Edit: 9/15/2009 1:42:25 PM EST by Soku]
I have a CMMG LPK in a Spikes lower and the 20 round Pmag I function tested the gun with works fine. Bolt catch works fine with the Pmag. I also have a DPMS LKP in a CMMG lower and it works fine with Pmags.

Can you compare that bolt catch to one in another gun?
Link Posted: 9/15/2009 3:07:56 PM EST
This happened twice with 2 p-mags i bought for my Armalite. It works perfectly with my Thermold mags.

It happened once with my Colt.

Have since gave the p-mags to my brother in-law. He had it happen and gave them to a guy at the range.

Makes me wonder why the p-mags are so bragged about here??
Link Posted: 9/15/2009 3:48:28 PM EST
[Last Edit: 9/15/2009 3:49:22 PM EST by JohnRippert]

Because the rest of us have no problems at all with PMags.


Did anybody who did have this problem contact Magpul and see what they said?
Link Posted: 9/15/2009 4:21:04 PM EST
I have an RRA Entry Tactical with a couple thousand rounds through it.

3 Pmags, 3 USGI, 1 Lancer, all 30 rounds each.

No problems.
Link Posted: 9/15/2009 4:48:33 PM EST
P Mags are not perfect. I had a brand new one that will not stay in the gun. Tried it on my Sig556 and Colt 6721. I have another P Mag that worked in both.
Link Posted: 9/15/2009 5:17:36 PM EST
The rest of us being you and not the other guys posting here with p-mag issues.

To each there own. As stated i use thermolds because they work flawless in my guns. Thermolds may or may not work in your frankengun.

P-mag states there made for Colts?? Maybe..

Link Posted: 9/15/2009 5:27:43 PM EST
Originally Posted By Jeremiah29:
I bought my PMAG's about 9 months ago and Magpul told me that they were designed for the Colt and every other AR is a knockoff so there will be some tolerance differences. There were a couple of tabs they showed me to sand down and now my LMT releases it with no problem. It was a known issue with many AR's and that was the fix. I never had the problem with my CMMG lower, so it is different with all AR's. I hope that helps.


which tabs? I have a brand new LWRC and the pmag's will not drop free. USGI's are fine though. In another forum, I was told that the pmag will eventually "break in" and function after some use. Problem is, I have close to 40 pmags and that's a whole lot of breaking in to do..
Link Posted: 9/16/2009 3:36:25 AM EST
The same thing happens with my rifle tough my LPK is Del-Ton. Magpul sent me some replacement followers which I'm going to try. If that doesn't work, I'm going to swap the bolt catch. Anyone know where you can find a bolt catch assembly w/o buying a full LPK?
Link Posted: 9/16/2009 5:21:20 AM EST
I compared the bolt catch (on my Spikes) to one on a Bushmaster (which the P-mags work fine)... They look the same.

Thanks for all the advise. I will contact Magpul and speak to them about it.
Link Posted: 9/16/2009 6:43:11 AM EST
Looks can be deceiving. A dial caliper is a good tool to have. It only takes a couple hundredths of an inch out of spec to cause problems.
Link Posted: 9/16/2009 7:51:00 AM EST
[Last Edit: 9/16/2009 7:56:30 AM EST by 87GN]
Originally Posted By Hootbro:
Looks can be deceiving. A dial caliper is a good tool to have. It only takes a couple hundredths of an inch out of spec to cause problems.


Exactly.

Here is the thing, if you have a rifle that has both a properly made bolt catch and mag catch, and a good magwell, you will likely have no problems with PMags.

They are slightly larger in certain areas than a standard aluminum mag, so if your parts are just slightly out of spec, you'll find out about it first with PMags. You wouldn't know it with standard mags.

But it is not the PMags fault. Oh, sure, bad stuff slips out. But it's not indicative of a systemic issue with the PMag or any other magazine.
Link Posted: 9/16/2009 7:52:09 AM EST
Originally Posted By Nichonator:
The rest of us being you and not the other guys posting here with p-mag issues.

To each there own. As stated i use thermolds because they work flawless in my guns. Thermolds may or may not work in your frankengun.

P-mag states there made for Colts?? Maybe..



Most people don't use Thermolds because they are made of paper mache. In fact when I was doing destructive mag testing the Thermold I bought was cracked inside the manufacturer's packaging.
Link Posted: 9/16/2009 7:57:41 AM EST
Originally Posted By JohnRippert:

Because the rest of us have no problems at all with PMags.


Did anybody who did have this problem contact Magpul and see what they said?



You and 87GN should meet up and go drink more p-mag coolaid.
Link Posted: 9/16/2009 8:05:19 AM EST
Link Posted: 9/16/2009 8:16:07 AM EST
[Last Edit: 9/16/2009 8:16:18 AM EST by 87GN]
Originally Posted By kavik:


You and 87GN should meet up and go drink more p-mag coolaid.




Link Posted: 9/16/2009 1:48:59 PM EST
Originally Posted By 87GN:
Originally Posted By kavik:


You and 87GN should meet up and go drink more p-mag coolaid.






I also don't blame Pmags, can I get some Koolaid?

However if Pmags won't work for you, just use USGI mags
Link Posted: 9/16/2009 3:32:22 PM EST
Originally Posted By MaxVidd:
Originally Posted By 87GN:
Originally Posted By kavik:


You and 87GN should meet up and go drink more p-mag coolaid.






I also don't blame Pmags, can I get some Koolaid?

However if Pmags won't work for you, just use USGI mags


I have explained in the past that Magpul cannot be held accountable for other manufacturer's specs in regards to their lowers. It is what we in the automotive industry call a "stack up" issue. Parts being at different spectrums of their tolerances stack up and eventually put the end product out of spec. Bottom line is that just because a mag doesn't work in your lower it isn't necessarilly the mag. It could be but isn't always. If GI mags work for you then keep using them and send me all your PMAGs, they work in all my rifles.

P.S. Pass me some Koolaid please.

Olycar15
Link Posted: 9/16/2009 3:40:17 PM EST
I just want some koolaid cause its fucking delicious.

That is all.
Link Posted: 9/16/2009 3:56:17 PM EST
[Last Edit: 9/16/2009 3:59:21 PM EST by ArmedPete]

Originally Posted By F1fanatic:
I have an RRA Entry Tactical with a couple thousand rounds through it.

3 Pmags, 3 USGI, 1 Lancer, all 30 rounds each.

No problems.


glad that your lower that is made by a completely different manufacture than what is being discussed works!
Link Posted: 9/16/2009 4:55:15 PM EST
Originally Posted By Justin-Beard:
Originally Posted By DBLTAPP:
Originally Posted By mathecb:
Pull the bolt back, insert an empty p-mag and see if it activates the bolt catch. If it dosn't work with multiple pmags its probably not a magazine issue.


I tried this.... The GI Mags hold the bolt back (I tried 3 different ones) I also tried a friends P-mag... It to did not lock the bolt back.


Were you able to try your PMAGs in your friends gun (or any other gun) yet?

Originally Posted By Captains1911:
Originally Posted By 87GN:
Out of spec DPMS bolt catch...


but why then would the problem only occur with pmags and not with the aluminum ones?


There could be a number of reasons but occasionally you'll find that some components are simply not compatible with some configurations. It is an unfortunate reality when there are dozens of manufacturers making AR15 components to a loosely defined set of tolerances, hence the reason why we designed our PMAG around the Colt M16. This variability is why we try to provide as much technical information as possible about our products (barring proprietary info of course) and is one of the reasons why we've always offered an excellent return/warranty policy when required.




Link Posted: 9/16/2009 4:57:11 PM EST
Originally Posted By DBLTAPP:
Originally Posted By Justin-Beard:
Originally Posted By DBLTAPP:
Originally Posted By mathecb:
Pull the bolt back, insert an empty p-mag and see if it activates the bolt catch. If it dosn't work with multiple pmags its probably not a magazine issue.


I tried this.... The GI Mags hold the bolt back (I tried 3 different ones) I also tried a friends P-mag... It to did not lock the bolt back.


Were you able to try your PMAGs in your friends gun (or any other gun) yet?

Originally Posted By Captains1911:
Originally Posted By 87GN:
Out of spec DPMS bolt catch...


but why then would the problem only occur with pmags and not with the aluminum ones?


There could be a number of reasons but occasionally you'll find that some components are simply not compatible with some configurations. It is an unfortunate reality when there are dozens of manufacturers making AR15 components to a loosely defined set of tolerances, hence the reason why we designed our PMAG around the Colt M16. This variability is why we try to provide as much technical information as possible about our products (barring proprietary info of course) and is one of the reasons why we've always offered an excellent return/warranty policy when required.





Thanks Justin for returning my call... I got your message. I will call you back tomorrow.
Link Posted: 9/17/2009 2:50:49 PM EST
I have three DPMS lowers with DPMS LPKs (home builds) and I have no issues with my 6 p-mags. Since I have only six of them, they are high rotation mags and I can't complain at all.
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