308 Bolt Catch Problem

[cpmiller22]

Hi all-

I just finished building my DPMS pattern 308 and I noticed that the bolt is not locking open when the magazine is empty. I have a standard 308 lower parts kit and a 10 round DPMS magazine. If I pull back on the charging handle, and press on the bottom of the bolt catch sometimes the bolt will stay open, but closes as soon as I take pressure off of the bolt catch. The magazine has a plastic feed table that seems to sometime sit at an odd angle, so I'm wondering if its just a problem with the magazine?

 

[Engine 22]

Have you tried a different mag?

 

[cpmiller22]

I've been having a hard time finding 10 round mags (since I live in CA) so I only have the one right now.

 

[ORD]

Different mag would be my first suggestion (assuming you have one). I have had "issues" with various DPMS factory LR-308 mags over the years in a variety of platforms, including some with weak mag springs which might account for a lack of force to properly engage the bolt catch and force it up/into position to enable the LRBHO to work properly.

That said, however, you shouldn't have any issues with the bolt catch working without a mag even in the magwell. You should be able to drop the mag completely, pull the CH back and manually engage the bolt catch which should hold without issue. A pic or two of the bolt catch engaging or attempting to engage the bolt (if you can grow a third arm or get someone to snap it for you) might help.

Out of morbid curiosity...what stock, buffer tube, buffer and spring are you using on this build? I only ask because it could also be an issue of the BCG not being able to fully retract and therefore, not properly engaging the bolt catch in the first place. That would explain both the mag-related issue, as well as the failure to operate the catch manually.

 

[LRRPF52]

Out of morbid curiosity...what stock, buffer tube, buffer and spring are you using on this build? I only ask because it could also be an issue of the BCG not being able to fully retract and therefore, not properly engaging the bolt catch in the first place. That would explain both the mag-related issue, as well as the failure to operate the catch manually.

This is one of the biggest mistakes I see in the DIY AR10/DPMS build projects: AR15 rifle buffers used in an AR10 recoil system.

 

[ORD]

This is one of the biggest mistakes I see in the DIY AR10/DPMS build projects: AR15 rifle buffers used in an AR10 recoil system.

Yup...me too!

 

[cpmiller22]

Here is the stock and buffer that I'm using:
http://www.midwayusa.com/product/23...on-collapsible-lr-308-carbine-synthetic-black

I'll post some pics as well.

 

[LRRPF52]

It is simply amazing how guys can bash parts together on 5.56 guns, and they will usually work quite well for a plinker.

Not with the AR10's. Because of the prevalence of AR15 parts, and the 1990's era re-design of the AR10 to be able to use most of the AR15 Fire-Control parts, many enthusiasts new to the AR15/AR10 often end up with AR15 rifle buffers and springs in an AR10. This will prevent you from being able to lock the bolt back, and will also not function as an auto-loader.

I've lost count of how many times I've seen this come up when discussing new AR10 builds.

 

[cpmiller22]

Here are some pics as requested.

 

[LRRPF52]

If using the telescoping stock assembly for a DPMS pattern gun, the buffer should be a ridiculously short little bugger.

 

[cpmiller22]

If using the telescoping stock assembly for a DPMS pattern gun, the buffer should be a ridiculously short little bugger.

Ya, the buffer the short one for the carbine stock.

 

[LRRPF52]

If you used that DPMS telescoping stock assembly with the DPMS .308 carbine buffer, it should be functioning. As ORD asked, can you lock the bolt to the rear manually, without a magazine inserted?

 

[ORD]

View attachment 13719View attachment 13720View attachment 13721

Here are some pics as requested.

Actually...I meant pics from through the ejection port with the upper attached to the lower and the bolt carrier in its rearward-most position with you attempting to engage the bolt catch so that we can see what the catch is actually "catching on" (whether with the mag inserted or manually...or both preferably).

With the stock assembly you linked to above and as LRRPF52 said...you should not have an issue with the bolt catch operating correctly in terms of the carrier retracting back into the receiver extension far enough.

This is what is SHOULD look like if installed and working properly when you depress the catch to hold the BCG back:

 

[BiggHertz]

Where in Cali are you located?

-Jason

 

[cpmiller22]

Thanks ORD for the pick. I can now see that my bolt is not going back far enough.


Any ideas why this would be? Perhaps Midwest shipped me an ar-15 stock assembly?

 

[cpmiller22]

Here is a pic of my stock assembly. It sure seems like its the right size buffer to me.

 

[cpmiller22]

Ok I think I see the issue now. If I put just the buffer and bolt in the buffer tube you can see that it doesn't go back far enough to get behind the bolt catch. I guess this means that they must have sent me the wrong buffer :-(

 

[BiggHertz]

Slash's Heavy Buffers | Products

Order the car 10 from Slash.

 

[cpmiller22]

Where in Cali are you located?

-Jason

Orange County

 

[TitaniumBlue]

308 Carbine buffer should be around 2.5". Just taking a quick look at your picture you clearly have the 223 carbine buffer. The spring may be wrong as well. Otherwise everything else seems to be just fine.

 

[ORD]

It is difficult to tell dimensions from a basic pic, but just "eyeballing it" from your pic of the separate parts and the one with your carrier placed into the receiver extension, I'd say you either have both and AR-15 carbine buffer and spring or one or the other than is preventing the carrier from fully retracting. The longer buffer and/or spring will cause the exact issues you are having. All you need to do is source a correct, SHORT .308 AR carbine buffer (and possibly an LR-308 carbine buffer spring if it turns out yours is not for a .308). The ones from Slash/HeavyBuffers.com are excellent and my personal preference especially for rifles that I shoot suppressed as you can get them in nearly double standard weights which is helpful when shooting suppressed. DPMS and other companies also make shortened buffers that will allow you to run any AR-15 style carbine receiver extension on a .308 AR.

 

[cpmiller22]

308 Carbine buffer should be around 2.5". Just taking a quick look at your picture you clearly have the 223 carbine buffer. The spring may be wrong as well. Otherwise everything else seems to be just fine.

Ya I just measured it and the buffer is 3 1/4" long, not 2 1/2".

Can believe they packaged the wrong buffer in an item clearly labeled as a 308 carbine stock assembly. Ugh...

Thanks everyone for all the help!

 

[DIGITAL X]

How long should a ar10 spring be?

 

[DIGITAL X]

Empty mag engages mine, but wont engage manually without mag, with empty mag and bolt catch engaged, I can still charge back bolt carrier about an inch. I'm using a Odin Works ar 10 buffer and I believe the right spring. Bolt catch moves and returns freely and no binding with with upper and lower united with bolt carrier and charging handle removed.

 

[ShooterwithNoName]

DPMS buffer spring should be 11.5" long...

The 308 is tricky when it comes to building. I actually run a standard AR15 carbine buffer in my 308 but I have an A5 length buffer tube (UBR) it allows me to play with buffer weight easier than with the short 308 buffer.

A check I always make is to look and see that my BCG is locking back on 308 builds. Another thing to keep in mind, if you ever switch to a rifle length buffer tube, (A2) take care to make sure you don't put in a buffer that's too short. If so, your BCG will hammer the back of your receiver extension area every shot and can chew a receiver set up quick.

 

[DIGITAL X]

Your buffer spring should be 11.5" long...

The 308 is tricky when it comes to building. I actually run a standard AR15 carbine buffer in my 308 but I have an A5 length buffer tube (UBR) it allows me to play with buffer weight easier than with the short 308 buffer.

A check I always make is to look and see that my BCG is locking back on 308 builds. Another thing to keep in mind, if you ever switch to a rifle length buffer tube, (A2) take care to make sure you don't put in a buffer that's too short. If so, your BCG will hammer the back of your receiver extension area every shot and can chew a receiver set up quick.

Funny enough, i'm handling her now, the buffer spring is 10.5'', I was at my local ffl and compared the cmmg ar15 (10'' +/-) spring to a ccmg ar10 ( 14'' +/-) got home measured mines and it was 10.5'', so I was happy thinking it was the wrong spring till i read your reply. The seller of the rifle mentioned the spring purchased didn't indicate ar15 or 10 everything else was purchase at Odin works.

 

[DIGITAL X]

Odin Works doesn't sell buffer springs and they only offer 1 lower parts kit, no mention whether for ar15 or10. I'm wondering if bolt catch is wrong one two, although it does engage with empty Pmag.

 

[ShooterwithNoName]

Sorry it was late last night and I didn't pay attention and thought I was answering OP... I fixed my original post.

DIGITAL X, sent you a PM on your set up to try to see what buffer set up you running...

 

[rpoL98]

Expo 5.3oz 308 carbine buffer at Primary Arms

KAK 5.3oz 308 carbine buffer

 

[DIGITAL X]

So heres what i got, the original spring is wrong, 38 coils 10'' long, i got #2 spring from a cheap ar 15 pistol kit laying around 32 coils 11.5" which now allows manual bolt lock with or without mag, making progress. Being a carbine tube on the 6.5 cmm , was told by local ar builder that a 28 coil spring is what I need. What ya think?

 

[drbcolt]

I can't remember the spring I used in my 308/6.5 Creed build but I do run a Magpul UBR stock. I also had to run a adjustable gas block and went with the Superlative! Is the best I have ever used and the gun runs flawlessly. I will try to check the spring tonight and let you know.

 

[DIGITAL X]

So heres what i got, the original spring is wrong, 38 coils 10'' long, i got #2 spring from a cheap ar 15 pistol kit laying around 32 coils 11.5" which now allows manual bolt lock with or without mag, making progress. Being a carbine tube on the 6.5 cmm , was told by local ar builder that a 28 coil spring is what I need. What ya think?

Bought this off of GB recently Like new unfired, Complete upper and Everything else supplied by Odin Works minus buffer spring, which Odin doesn't sell for whatever reason. Seller admitted to ordering spring that didn't specify AR15 OR AR10, he assumed both the same, wrong!

 

[DIGITAL X]

I can't remember the spring I used in my 308/6.5 Creed build but I do run a Magpul UBR stock. I also had to run a adjustable gas block and went with the Superlative! Is the best I have ever used and the gun runs flawlessly. I will try to check the spring tonight and let you know.

A local FFL had a 14.5 long spring available,didn't count the coils, i'm thinking this is for the rifle length tubes like yours ,not carbine length like mines.

 

[DIGITAL X]

I'm thinking I need a 11.5'' 28 coil?

 

[rpoL98]

http://heavybuffers.com/springs.html

308 carbine buffer spring $15. this is what I use with my mil-spec AR-15 M4 carbine buffer tube (7" inside depth) and 2.5" 5.3oz buffer in my Aero M5 308 (and 6.5CM).

 

[bfoosh006]

I think this Tubbs spring will answer your needs ... it being a Flatwire spring, It has worked with every Carbine pattern ( DPMS / short AR15 carbine tubeand Armalite / Vltor length longer carbine tube ) , and works in rifle length buffer tubes.
The Flatwire recoil spring takes up less room when fully compressed.

I run them in all my Large Frame AR's. Never had an issue with them.

Not everyone likes them, since they can be more difficult to remove then a "round wire recoil spring" ... but given the Tubbs life span, I install it and forget about it.

https://www.larue.com/products/tubbs-buffer-spring-ar10-sr-25-buffer-springs/

 

[DIGITAL X]

I think this Tubbs spring will answer your needs ... it being a Flatwire spring, It has worked with every Carbine pattern ( DPMS / short AR15 carbine tubeand Armalite / Vltor length longer carbine tube ) , and works in rifle length buffer tubes.
The Flatwire recoil spring takes up less room when fully compressed.

I run them in all my Large Frame AR's. Never had an issue with them.

Not everyone likes them, since they can be more difficult to remove then a "round wire recoil spring" ... but given the Tubbs life span, I install it and forget about it.

https://www.larue.com/products/tubbs-buffer-spring-ar10-sr-25-buffer-springs/

Do you know how many coils, seller doesn't mention, thanks

 

[DIGITAL X]

http://heavybuffers.com/springs.html

308 carbine buffer spring $15. this is what I use with my mil-spec AR-15 M4 carbine buffer tube (7" inside depth) and 2.5" 5.3oz buffer in my Aero M5 308 (and 6.5CM).

Do you know how many coils, seller doesn't mention, thanks

 

[bfoosh006]

Do you know how many coils, seller doesn't mention, thanks

38ish as far as I can count from the photo , from the link.

FWIW... I have never counted the coils... the Tubbs Flatwire has always worked.

I'd have to count one at home later.... just looked at David Tubbs webpage... and the photo there looks like 42, starting at the end to end.

Remember the flatwire will have a different coil count , since it takes up less room.... and has a different "load"

Again they have always worked perfectly for me... and have a "stiffer " "bolt in battery" load.... ( IMHO a good thing with Large Frame AR's, since it keeps the bolt locked closed milliseconds longer, allowing for extraction at a lower chamber pressure. )

From Tubbs ...
Standard buffer spring load
Bolt in battery: 7.2 lbs
Bolt locked open: 16.5 lbs


Standard buffer spring variation: 7.5 lbs
Tubb Precision Flatwire Buffer Spring
Bolt in battery: 11.1 lbs
Bolt locked open: 15.0 lbs

The above data may be for the AR15 spring... I am not sure... but you can see what I mean about the different load rating.





This photo show AR15 springs compressed by each other... and how much less room a flatwire recoil spring takes up.

 

[bschneiderheinze]

What bolt are you using I had a fail safe that never would lock back except on a mag

 

[drbcolt]

I used the KAK dual ejector bolt group with no issues.