DPMS type Nickel Boron BCG's available on GB

[planeflyer21]

Strange, if a modern 308 barrel is meant to accept 7.62x51, wouldn't the 308 barrels all fail the 308 no go gauge test?  My guess is that the no go would be at least 1.6355 (go gauge for 7.62x51).

 

Since, I could not turn the bolt with the 308 no go gauge, I guess my barrel/bolt combo does not meet the go gauge for 7.62x51.

 

That's a good question.

 

The SA M1As I had came with cards that stated "This rifle has been headspaced to 1.632", for use with match-grade .308 Winchester ammunition."

 

Here's a fairly good article:  http://www.thegunzone.com/30cal.html

 

Jon

[jrtMA]

That is definately a good question, if anyone can answer it...

If a modern "308" barrel will not accept a .308 no go gauge, which you'd think would be a positive, how would the barrel be able to safely fire a 7.62x51 Nato round? The rainier barrel is a good quality barrel, as are FA barrels like mine, but this headspacing the 7.62 is an odd roadblock to ensure you can confidently fire this round safely.

[BeyondTheShadows]

The lower I used for my build came from Shadow Ops. Its a good piece.

[EasyEJL]

The lower I used for my build came from Shadow Ops. Its a good piece.

I'm waiting on mine to ship from them. that and the bcg are the last 2 parts, the rest is all here

[survivalshop]

I think your reading too much into the head space gages , if you can close on the field gage , you got a problem or just a loose chamber , which can still be servicable , its not writen in stone , unless your a match shooter,bench rest ect. . Other than that ,just shoot what ever you like or better yet ,what the barrel/chamber likes.

 

Head space gage is more for bolt to barrel/chamber/barrel extension fit . 7.62x51 has a longer chamber throat area for a lot of reasons( and none of them for match groups ), the 308 is a higher pressure round. (some what )

 

I have shot both 7.62x51 & .308 in all of my rifles. Of course you may print tighter groups with one or the other( Match .308, of course ) , there is not enough differece in the two to worry about . If your chamber is so tight that it won't chamber & shoot 7.62x51, I would wonder about the barrel/chamber ( DPMS is one I've seen  screwed up chambers )

Edited April 12, 2013 by survivalshop

[512robby]

I'm a newbie to the group.

 

I found this thread on the nickel boron coated BCG from GB and knew immediately many of you had purchased the same BCG I had purchased on GB.

 

I have built 2 AR's but never built an LR308. This was my first attempt at building an upper from scratch.

 

This build includes a DPMS lower with a Timney drop in trigger (new AR10 version) with a fixed A2 stock and Magpul PMags.

 

The upper is also DPMS with a 20" stainless Ranier Arms select barrel and JP Enterprises Bennie Cooley muzzle brake.

 

PRI adjustable gas block and Troy TRX Extreme hand guard\rail.

 

The BCG was the last part on backorder and I finally gave in and purchased the NI-Boron BCG on gunbroker.

 

I was a apprehensive about a trip to the range before I checked headspace, so I took the LR308 to a local DFW gun shop for a go-no go test. The gun shop did not remove the extractor from the bolt before running the test.

 

A long story short- the gun shop ran the go-no go test and dclared the LR308\NI Boron to have a headspace issue.

 

I ordered a Forester single field guage and rand my own no-go test, but I first removed the extractor and the firing pin.

 

The Field Guage did not close. It is a NO GO.

 

I next took a spent, empty Win .308 case and inserted it into the chamber. I closed the bolt and everything closed and locked up. I removed the magazine and used a flashlight to visually confirms the bolt lugs had turned, mated and locked with the barrel extension lugs. Everything looked fine.

 

Do I need to do further testing before I go to the range?

 

To make matters worse...   Today I received a package from Midway. My new DPMS BCG arrived.

 

I quickly traded the nickel boron coated BCG for the black phosphate coated DPMS BCG to do a comparison.

 

The Black DPMS seemed to mate, turn and lock up with the barrel extension lugs much easier-

 

However, the Nickel Boron coating is a definite plus. The NI-B BCG seems slick and slides much easier and with less resistance. I am not saying a well oiled Black Phosphte BCG would not work equally well- But the NI-B BCG was noticeably easier to cycle through the upper receiver.

 

I am considering selling the Black Phosphate DPMS BCG on GB.

 

But, I'm hesitant to do that until I determine that the NI-B will work flawlessly.

 

Has anyone had any issues with the NI-B BCG at the range?

 

Do I need to keep testing headspace?

 

Your thoughts and comments are appreciated.

 

 

 

 

[unforgiven]

Welcome from Indiana brother 512.Others here have more trigger time with LR308 they will be able to help you.

[survivalshop]

Most modern head space gages have a slot for the extractor ( for easy removal ), but the ejector should be removed because it can give a false reading because of the pressure it exserts on the head space gage.

I seldom even use the "Field" gage , only if I think the" NO GO" gage feels sloppy . You should not have to use any thing but very light pressure on seating the BCG whan testing, one finger should work to seat it & not much pressure .

Your NIB BCG set has a little thicker coating & will be a little tighter ,as with the whole action of a newly built rifle , so more resistance than the Phosphated BCG.

Lube her up wet & I use Gun Slick grease if you want ( or some kind of gun grease )on the back part of the bolt lugs for newly build actions until they break in .

Load one round in the mag & don't sissy , or follow the BCG closed , pull the charging handle back all the way & let it fly or drop the bolt release if its holding the BCG .

If the round chambers to full battery , fire it & then load two, then if all goes well , then load three . If the FCG works like it should ,load the mag to full capacity & have at it.

Note ; if you are hard up for cash , sell the Bolt , but if not , keep it for a spare .

Edited April 13, 2013 by survivalshop

[EasyEJL]

the bolt isn't supposed to close on a field gauge.

 If the bolt closes on a No-Go gauge, the Field gauge is used for an additional check. If the bolt then closes on the Field gauge, the rifle is considered unsafe to shoot, you’ll have to have the barrel set back and rechambered.

[survivalshop]

Yes , I should have put the "NO" In front of it .

Quote from Forster Products,

A rifle with correct head space should close easily and with out feel on the "GO " gage but should not close on the "NO GO" gage. If it does close on the "NO GO " gage , but not the "FIELD " gage the rifle is still considered serviceable , although its not advisable for best accuracy, any rifle that will close on the "FIELD " gage has dangerously excessive head space and should not be fired under any circumstances .

About the as said above.

Edited April 13, 2013 by survivalshop

[jrtMA]

It sounds like all of us with this BCG are seeing similar "issues". I would imagine that the facts being that it is new going into a new rifle and having the coating are making it exceptionally tight. I am not firing 7.62 out of mine until I have a few hundred rounds of .308 fired out of it. Things might break in a bit. As of right now it will not turn on no go .308 gauge and will not turn on go gauge with .002 added to it. It is very tight turning on a 7.62x51 M80 round...very tight in deed. Only time will tell.

[Micksixnine]

Same issues with my GB-purchased NB BCG. I have a brand new build with an SI Defense GEN4 matched upper/lower set with an 18.5" Lightweight chrome lined FA Criterion barrel. I have Forster Go and No Go guages and I cannot even close on the Go guage. I can close on an empty case but it is extremely tight. I was barely able to get the bolt back out. Does anyone know what the mil-spec dimensions of the bolt lugs are supposed to be? I'm guessing these bolts are at the high end or out of spec??

[vtecpaoche]

Did you remove the extractor and the ejector before testing?

 

That's concerning that it does not close on the go gauge.  As for tightness, my barrel is very tight.  I have a hard time extracting the snap caps.

[jrtMA]

Did you remove the extractor and the ejector before testing?

 

That's concerning that it does not close on the go gauge.  As for tightness, my barrel is very tight.  I have a hard time extracting the snap caps.

I stripped my bolt down completely. I added the .002 but did not have a caliper to confirm that number. That's when I had issues with the go gauge. My rifle has now safely fired .308 WIN and has done so incredibly well. I will not currently fire 7.62 for the previously stated reason. I will fire another 150 + rds out of it before I will recheck headspacing for 7.62. I think everything will be fine in the long run and a few hundred rds may have absolutely no impact. I will likely take it to my local GS to confirm before I start the 7.62 testing. I think the worse case scenario is that it will fire but have extraction issues...another more experienced member might be able to add to this guess.

[Micksixnine]

I did remove the extractor and the ejector before testing. Would anyone with calipers be willing to check their lug height and bolt face depth (where the case or go guage seats)? My bolt has a lug height of .315" and seat depth of .128".

[jrtMA]

I've now been to the range with my Mega build about 6 times and the last 2 have seen some 7.62 M80 ball (kinda sh!itty) down range. I have not had a single issue firing it, even with the very tight headspacing results on the 7.62 vs. the .308 with the GB BCG.

As Edgecrusher can attest to, that sh!tty ammo was actually surprisingly accurate out of my Mega. It fired just as accurately out to 100 yards yesterday for me. A small problem is finding more at a reasonable price as it now just went up to a mind-numbing 47 dollars a box now (50 count).

The only problem that I have with the BCG is seemingly inferior coating. It has chipped off a bit where the bolt meets the barrier. This isn't a big deal. The machining seems solid and I don't want to pony up the big bucks for a JP so it is what it is. The BCG was still $350 so I'll be damn if I'm not going to get my $$$ worth out of it.

Edited May 29, 2013 by jrtmasp

[vtecpaoche]

Nice, I fired my Maten build a few weeks back for the first time with the same BCG.  I have an adjustable gas block on the build.  I dialed the gas way down for the first shot.  After firing the round, the BCG was pretty much lodged.  I tugged at the charging handle and no luck.  My brother in law had to use a piece of wood and hammer to tap the BCG out.  This happened a few times until I dialed the gas to lock the bolt back.

 

I was able to chamber the 7.62 round in but did not fire it.  I'm pretty sure it would not have been an issue.  Like mentioned above, I plan on getting my money's worth on this one.