Topic: DPMS LR308 bolt locking lugs (Read 639 times)

rhinegarten · « **on:** January 30, 2012, 05:52:41 PM »

Just got my LR308 put together a few weeks ago and have been following the barrel break-in procedure. It's almost complete, with about 120 rounds of surplus US ball and American Eagle run through it.

Yesterday when I was cleaning it I noticed that one rear corner of the all locking lugs on the bolt were slightly rounded, no longer sharp, square cornered as before. It's almost as if the bolt had rotated a degree or two too far upon unlocking and the corners snagged a bit on the adjacent locking lugs of the barrel on opening.

I've had no problems with the rifle - it functions like a Swiss watch. But anything possibly affecting the locking lugs gets me a trifle nervous. The upper was purchased as a factory assembled unit. The lower was assembled myself.

Anyone else seen this? Is it part of normal wear during "break-in" with these? I've assembled three Bushmaster AR-15s and never seen this, even after a couple thousand rounds. Maybe it's something inherent to the .308 version.

planeflyer21 · « **Reply #1 on:** January 31, 2012, 04:01:13 AM »

Photos would be of great assistance.

Jon

Dusty44 · « **Reply #2 on:** January 31, 2012, 12:03:33 PM »

I inspected the bolt on my factory DPMS LR308. This rifle only has a few hundred rounds through it, less rather than more. The blue is worn around the edges on the front and rear faces of the lugs. Some lugs on the face are worn more than others. The top of the extractor face is the most worn. Wear on the rear faces seems mostly uniform. Bare metal is all on edges and corners of the lugs.

I was not concerned. Tight fitting metal rubbing and working while under pressure, even with oil on the surfaces, seems/seemed reasonable to me that metal would wear to match facing surfaces?

There is about four times as much energy in the firing of a .308/7.62 caliber at typical loadings than in a .223/5.56. Would that not result in a lot more stress on the bolt/BCG/chamber locking & support surfaces metal than the smaller caliber rifle?

rhinegarten · « **Reply #3 on:** January 31, 2012, 06:11:49 PM »

I think you're probably right ,Dusty. In looking more closely, even though there's a "ding" on the rear of each locking lug, there still plenty of the original metal. It's not like the bolt is actually weakened. But, if I can figure out how, I'll upload a photo. The lugs appear to measure about .150" in width and appear to measure about .144" at the rounded edge. At the time of the photo the bolt head has a abundance of moly grease on it. I'm beginning to feel like a new doting father. Good suggestion on the photo upload Planeflyer.

survivalshop · « **Reply #4 on:** February 01, 2012, 07:25:18 AM »

Normal break in wear , wait till you get a close look at you cam pin . You will think its cracked , but they will be wear marks on it also .

Nice to see you use grease on the bolt lugs for break in .

rhinegarten · « **Reply #5 on:** February 01, 2012, 06:36:27 PM »

You're right about the cam pin. But I've seen the same thing on my Bushmaster 5.56s. So I was'nt too worried about it. Then I got a good close look at the locking lugs on the 5.56s - pretty much the same thing, just never noticed it.

The 5.56 twins have been going for about 20 years without a problem, so I'm no longer going to worry about the 7.62. Just shoot it and have fun.

Thanks guys for your input!

ron40xc · « **Reply #6 on:** March 17, 2012, 04:33:42 PM »

I would like to see more feedback on this. I also have a 308 bolt that is scrubbing hard enough to create a burr edge on the back side that will reduce headspace. Am using 175 BT with 42.5 gr of IMR 4895. The buffer spring and buffer has been replaced with a setup from Heavy Buffers and that reduced the effect about half. (Had an AR15 buffer and spring) Currently I am filing off the burrs. The burrs will raise enough to need attention after a 50 round HP match.
Opinions, suggestions, feedback, criticism, welcomed. Thanks for your time.
rWd

blue109 · « **Reply #7 on:** March 17, 2012, 07:19:43 PM »

all the corners of my locking lugs on the bolt are nubbed off lol. the gun was so tight when i built it the only way to open the action the first few times was to remove the upper and use a mallet to tap it out. after that i spent a week sitting on my couch working it by hand. had to put the barrel on the floor and my chest on the stock and use both hands on the charging handle at first.
as far as the cam pin...i actually used a needle file to shave one side down a tiny bit. until i did that it seemed like the gun was way too tight and was consistently short stroking. i have a fresh cam pin and maybe after more break-in ill be able to swap it in but as it is it still hangs up and fits pretty tight.
was a painful process and i hate to sound ghetto but it runs like a rolex now. burned 100 rds of 145gr privi stuff the other day in a short time span just to put the scope on paper and get some more break-in and she just sang.

NoFail · « **Reply #8 on:** March 18, 2012, 10:56:23 PM »

Quote from: survivalshop link=topic=2898.msg23482#msg23482 date=1328109918

Nice to see you use grease on the bolt lugs for break in .
[/quote

No kidding all i see is wet grease. I thought you should not get any on the face, I've been told. That must be getting on the face, no?

survivalshop · « **Reply #9 on:** March 19, 2012, 09:34:44 AM »

Quote from: NoFail on March 18, 2012, 10:56:23 PM

[quote author=survivalshop link=topic=2898.msg23482#msg23482 date=1328109918

Nice to see you use grease on the bolt lugs for break in .

No kidding all i see is wet grease. I thought you should not get any on the face, I've been told. That must be getting on the face, no?

The only place I would be worried about getting any lubricant is in the chamber .

You shouldn't pack it like a wheel bearing any way , so a little grease on the locking lugs is your friend , maybe not in all environments or temperature ranges ,but a good thing when breaking in a new rifle .

I've been using Gun Slick grease for a long time & no problems .

rhinegarten · « **Reply #10 on:** March 23, 2012, 09:54:55 PM »

There wasn't any on the bolt face. But Survival Shop is right, it's the chamber that you don't want any kind of lubricant in. It can greatly increase thrust on the bolt face.

Cabinetman · « **Reply #11 on:** March 29, 2012, 05:53:54 AM »

This thread got me to examine my 308b bolt. I've owned this rifle since Oct of 09 and have easily shot 1000 rounds through it, all surplus from different countries; Germany, Port, SA, etc. Nothing commercial or any handloads. I just pulled the bolt and the face and lugs look perfect. The finish on the bolt remains on the exterior surfaces. Most of the sides of the lugs are polished to a mirror where they lock upon the receiver. I've got none of what looks like excessive wear that a few of you fellas have described. There are no bits of metal that I have to attend to at all.

The only lube I use in all my rifles be it a C&R like the Garand or my latest AR15 is Militec 1. I followed the instructions precisely and keep after it after cleanings. The rifle has never ftf, fte, or any other hiccup. It's a lot less messy than grease or conventional oils. There is a lot written about even swabbing the bore with it. Check it out. It’s pretty neat stuff and works perfectly in my rifles and handguns.

I, too, am interested in reading more about this potential issue. Stoner’s first “platform rifle” was the AR-10 for the 762 x 51 caliber. He "scaled down" the technology for the .223. Only about 10,000 AR10s were ever produced so there's not a ton of history available about the wear and tear on their bolts. There are literally millions of AR15s out there, however. With the re-emergence of the "AR-10" style platform and all these different companies making the parts, I wonder if there are wear issues that will begin to surface as we see many more thousands of these large-caliber rifles in the hands of so many shooters. It's probably just a tempest in a teapot but it does bear looking at and forums like this are a good place to discuss and examine them as continue to age.

Rome

mineralman55 · « **Reply #12 on:** March 30, 2012, 11:57:21 AM »

That load you quote is way too much. Sierra lists 41.5 IMR 4895 as the max with their 175BTHP, and in private correspondence their loading experts have told me to max out at one step below their listed max for gas rifles, so that would be 40.3 grains of IMR4895. Back off the charge weight a bit and you should be okay.

Quote from: ron40xc on March 17, 2012, 04:33:42 PM

I would like to see more feedback on this. I also have a 308 bolt that is scrubbing hard enough to create a burr edge on the back side that will reduce headspace. Am using 175 BT with 42.5 gr of IMR 4895. The buffer spring and buffer has been replaced with a setup from Heavy Buffers and that reduced the effect about half. (Had an AR15 buffer and spring) Currently I am filing off the burrs. The burrs will raise enough to need attention after a 50 round HP match.
Opinions, suggestions, feedback, criticism, welcomed. Thanks for your time.
rWd