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 How to polish chamber of DPMS .308?
hartzpad  [Member]
8/28/2005 10:02:25 AM EST
I read in this post: www.ar15.com/forums/topic.html?b=3&f=121&t=245174 where Colt45guy says that he polished the chamber of his DPMS AP4 .308 to be able to shoot surplus and reloaded .308. My new AP4 will only shoot factory Winchester so far, it will not shoot quality surplus or even quality factory reloads such as HSM, it has trouble chambering them, at least in semi-auto. I would like to get it to the point where it will shoot surplus .308 as this is not a match barrel from what I've read.

What is the proper way of polishing the chamber? Just use a dremel polishing wheel and some polishing compound? Or do I need something more uniform like a dowel with emery cloth and some polishing compound?

Thanks for any help.
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Randall_Rausch  [Member]
8/28/2005 8:25:40 PM EST
I would get this:
www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=937146

You will also need the flex hone oil:
www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=661733

Lastly, take a hand held drill and go to town.
800 grit is a very mild abrasive and will put a good polish in the chamber.
Remember to keep the drill running as you go into and pull back out of the chamber.
Flush it out really good so you are not firing bullets over honing slurry in the bore.

Randall
Colt45guy  [Team Member]
8/29/2005 7:35:21 AM EST
I used Flitz on a small wool buffing bit....but I think some white rouge--normally used for polishing stainless steel--will work better. I tried using a .45 bore mop, but the paste caused the fibers to get stuck to each other and it wouldn't fit tight after a minute or 2. I wound up buying the Dremel Polishing Kit at Wallyworld to get the right size.
bluewater  [Team Member]
8/29/2005 6:11:19 PM EST
I had problems with my LR-308 chambering rounds when my 20 round magazine was loaded with more than 8 rounds. I called DPMS and they suggested that I return my rifle to them for evaluation and adjustment.

From what I understand, after talking with Shane at DPMS, they changed the angle on the feed ramp. I will receive my DPMS back from them tomorrow after their fix and will let you know what the outcome is. Hopefully it will be better.
hartzpad  [Member]
8/31/2005 7:35:00 AM EST
Colt, what dremel polishing bit did you use and how did you get the dremel tool close enough to the chamber to get in there? Did you use some type of extension? I've already got my dremel polishing bit and polishing compound, but there is no way to get the bit into the chamber without some sort of extension. Thanks.
Randall_Rausch  [Member]
8/31/2005 8:56:36 PM EST
Pull the barrel off the receiver...
The chamber mouth is only 3/4" deep inside the barrel extension.

Randall
hartzpad  [Member]
9/1/2005 4:01:41 AM EST

Originally Posted By Randall_Rausch:
Pull the barrel off the receiver...
The chamber mouth is only 3/4" deep inside the barrel extension.

Randall



I'm new to AR's, are there instructions on how to remove the barrel? Thanks.
Randall_Rausch  [Member]
9/1/2005 9:08:57 PM EST
If you are not already equipped to remove the barrel, then you have come to a decision point in your AR life's path.
Do you want to invest in tools and tinker yourself, or do you want to pay someone else (maybe no charge if DPMS does it) to do the work.

To remove a barrel, you mostly need a barrel nut wrench.
If we are talking about the DPMS 308 rifle, then I recommend this one:
www.superiorweaponssystems.com/ar10DPMSwrench.htm
It works with both DPMS and AR-10.
For one simple tear-down and rebuild, you can probably forego all the other nice tools that would be used for this job.

Do you have a gas block or front sight on your rifle?
In either case, start by removing that.
Gas blocks attach with setscrews from the bottom.
Front sights are usually held on with tapered pins.
Make sure that you hammer on the SMALL end to remove them.
Once you get the gas system clear, you should be able to remove the handguard tube from the barrel nut.
It's a two-piece arrangement that simply threads together.
A strap wrench may be helpful here.
As for holding the rifle, I recommend a padded chair without any arm rests.
Sit on the whole rifle (leave the lower and upper assembled at this point) and let your body weight be the clamp.
With the gas system and handguard tube now removed, remove the barrel nut with your newly aquired barrel nut wrench.
Place rifle on chair, muzzle to the right and sit down.
Insert the wrench into the barrel nut facing forward, away from your body.
Pull UP on the wrench to break the nut loose and then spin it all the way off.
That's all there is to it.
You will need to withdraw the bolt carrier group at least an inch to let the barrel pull free from the upper receiver.

When you put it back together, it's important that the barrel nut is aligned to the same place it came off.
This is to say that the hole (in the barrel nut) for the gas tube needs to be centered over the hole in the upper receiver so that the gas tube goes straight into the center of the receiver.
All other re-assembly is basically the reverse of removal.

Randall
Colt45guy  [Team Member]
9/2/2005 3:29:58 AM EST
what he said, although I prefer a vise and a few blocks of soft pine---I have a bony ass, and the butt-vise method didn't work for me. I bought the AR10/DPMS combo wrench from Art at SWS when I got the railed tube and removed the barrel. When you have the right tools, it only takes a few minutes to disassemble, and only a few more to put it back together
kato01  [Member]
9/6/2005 4:12:23 AM EST
Hatrzpad, I'm in the same situation you are, with my DPMS AP-4 arriving this week. Curious if you've had any luck polishing the chamber or breaking in the rifle so it will accomodate surplus.
hartzpad  [Member]
9/6/2005 4:42:28 AM EST
I haven't had time to try it yet. I'm going to shoot about 100 more rounds of factory .308 this weekend and see if after that it is more broken in to shoot some surplus. I've got some quality Malaysian 7.62 surplus, seems cleaner than South African. I'm debating whether or not to buy that $50 barrel nut wrench to be able to polish the chamber or having a local smith do it. I'm just not sure that I'll get enough use out of the wrench to justify it. We'll see.

I didn't try any surplus ammo this last time I shot it, I shot 20 Federal American Eagle .308 and then shot 3 HSM .308 reloads, the 3rd round got stuck in the chamber and when I forced the bolt back, it ripped a chunk out off of the rim of the case. At least I know the extractor is strong. Didn't have a cleaning rod with me so that ended my day.
kato01  [Member]
9/6/2005 5:04:42 AM EST
Thanks. Let us know how it goes. How many rounds have you put through it so far?
hartzpad  [Member]
9/6/2005 5:19:56 AM EST
I've shot:

10 rounds of Malaysian Surplus, about 7 functioned OK
20 rounds of Federal American Eagle, all functioned perfectly
6 rounds of HSM reloads, almost 100% got stuck in the chamber.
20 Rounds of Winchester White Box .308, 100%, no problems.

I'm going to shoot some more Federal and then try some Malaysian surplus, it could be the surplus will funciton fine while the HSM reloads do not.
Iwantfullauto  [Member]
9/7/2005 5:47:06 PM EST
I just shot my DPMS .308LR today for the first time. I only had 40 rounds with me so I did not shoot it much but it had a malfuntion everytime I shot it:( I shot 20 winchester 150 gn soft points and 20 pmc fmj. It was making one hole in the taget at 50 yards, but it messed up every time. The first 10 rnds would not chamber all of the way and the bolt would get stuck. After that it would chamber, but it would not eject. Then it ejected about 10 rnds but would not strip the next rnd from the mag. The last few shots were not even pulling the case out of the chamber all the way. I am going to take it apart and clean it tonight and try to shoot it again next week. Maybe it just needs to break in. What ammo do yall think would be the best to try? Thanks

James
Randall_Rausch  [Member]
9/8/2005 12:58:43 PM EST
James-

Sounds to me like your gas block was moving on the barrel.
The more it moved, the bigger the problem would get.
Give it a wiggle and see if it's loose.

Randall Rausch
www.ar15barrels.com
Iwantfullauto  [Member]
9/8/2005 6:30:20 PM EST
AAAAAHHHHHHHHH it is loose, and there is black stuff in front of it. How do I fix that. thx ALOT for the help

James
Randall_Rausch  [Member]
9/8/2005 7:56:18 PM EST
Loosen the setscrews on the bottom of the block.
The block should slide around pretty freely.
Now there should be a shoulder on the barrel when you slide the gas block back towards the handguard tube.
Slide it until it stops against the shoulder.
Now, looking at the block from the muzzle end, visually align it so that the gas tube is straight on top of the barrel.
If you have a bipod mounted on the handguard, this is a very convienent way to rest the rifle upright, otherwise something like a shoebox under the magazine well so that the handle can hang down and the rifle should sit upright for you.
Once you have the gas block in the right position, tighten down all the setscrews.
Go test fire again.
If all is well, you will want to get some blue loctite and remove one (1) setscrew at a time, apply loctite and then re-install the setscrew.
Do this for each setscrew.
Make sure at least one of the setscrews is really tight, so it digs into the barrel.
Preferably, it would be the setscrew that opposes the gas port.
This way, you make a nice tight gas seal.

Don't worry about that black stuff on the barrel and gas block, that's just remnants of the gas that was leaking.
It's not going to hurt anything.

Randall Rausch
www.ar15barrels.com
Iwantfullauto  [Member]
9/8/2005 8:09:16 PM EST
thanks I will try it right now. I will be able to test it tomorrow or the next day. thanks again.

James
dpmmn  [Team Member]
9/8/2005 8:11:52 PM EST
I would make DPMS fix it if it doesn't function 100%
Iwantfullauto  [Member]
9/8/2005 8:32:24 PM EST
Ok I got the gas block and tube lined up and it is tight. I guess I will have to wait and see if it works. thanks again.

James

PS If I cant get it to work I will have to get DPMS to do it. I hope I dont have to send it off, It was hard enough to wait the 4 day it took to come in the mail when I bought it. LOL.
Alpha15  [Member]
9/9/2005 6:07:18 PM EST

Originally Posted By hartzpad:
I've shot:

10 rounds of Malaysian Surplus, about 7 functioned OK
20 rounds of Federal American Eagle, all functioned perfectly
6 rounds of HSM reloads, almost 100% got stuck in the chamber.
20 Rounds of Winchester White Box .308, 100%, no problems.

I'm going to shoot some more Federal and then try some Malaysian surplus, it could be the surplus will funciton fine while the HSM reloads do not.



Just an observation.
It seems the rifle functioned just fine with quality ammo. The surplus is of questionable quality to begin with. As far as the handloads go did you use a small base sizing die to resize the brass? If not you will definitly have cycling problems as standard full length dies do not size the brass all the way to the head of the case leaving it slightly over sized, not a problem with a bolt gun but generally a malfunction waiting to happen in any semi auto.
hartzpad  [Member]
9/10/2005 6:32:23 AM EST

Originally Posted By Alpha15:
Just an observation.
It seems the rifle functioned just fine with quality ammo. The surplus is of questionable quality to begin with. As far as the handloads go did you use a small base sizing die to resize the brass? If not you will definitly have cycling problems as standard full length dies do not size the brass all the way to the head of the case leaving it slightly over sized, not a problem with a bolt gun but generally a malfunction waiting to happen in any semi auto.



HSM reloads are supplied to police all over the country. I did not reload them myself. When I compared the Malaysian surplus (which most people agree is quality surplus) with the reloaded HSM .308 and a Federal American Eagle .308, the Federal .308 has a slightly shorter overall length than the other two. Maybe that explains it.
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