6mm BR question

[Crossfire64]

According to 6mmbr.com maximum OAL is 2.4409

Previously I determined that my OAL was 2.345

I replaced my barrel nut & recoil lug from Northland shooting supply.

the recoil lug is twice as thick as the factory lug

I have reset my head space with a go gauge. I inserted the gauge, closed the bolt & screwed the action onto the barrel until the chamber bottomed out with the gauge.

I put scotch tape on the base of my go gauge adding 0.002 a created a no go gauge.

My bolt would not close on the no go

Repeated testing resulted in the go gauge continually chambering & the no go NOT chambering. Exactly as I'd want.

The action & the chamber are now farther apart because of the thicker recoil lug.

Using the Hornady OAL guage & modified 6mm br case I an continually getting an OAL measurement of 2.244.

The previously loaded rounds with the OAL of 2.345 consistently chamber.

This is a major change in OAL. I do not understand why this is so. It seems as if I've missed something

Any ideas?

 

[DocDoc]

How are you measuring OAL? When you set the headspace with the go-gague, that does not depend on the recoil lug or the barrel nut, but is sets the space from the face of the bolt to the shoulder of the case. The position of the recoil lug and barrel nut may shift, but the distance between face of bolt and shoulder of the case against the barrel does not. Certainly not by as much as 0.1.

I think something has changed in how you are measuring OAL.

 

[Crossfire64]

I am measuring OAL using Hornady's OAL gauge, threaded modified 6mm br case & Berger 105gr VLD.

A buddy of mine who helped me with this build used the same tools & we got the 2.345 measurment.

I agree 0.1 is a huge delta & pretty sure I'm doing something wrong or missing something

 

[Rogue Hunter]

Its irrelevant how thick the lug is. The headspace should be the same when set to the headspace gages, and the seating depth will be the same. -You are threading the barrel into the receiver to the same place. The throat would have to cut deeper in order to seat the bullets out farther.lightbulb

-Mike

 

[RichinVA]

Ejector removed?
(I'm assuming so, just trying to eliminate stuff)

 

[Crossfire64]

Let me assume that the 1st time I measured head-space was wrong at 2.345

Is anyone getting 2.244 OAL from a 6mm br using Berger 105gr. VLD's?

I've never loaded a bullet that far from the maximum OAL.

I don't know what I've done but if feels like I screwed something up.

But my go gauge IS chambering & my no go IS NOT.

I guess I'm asking, Can 2.244 be right?

And if so, Why are my previous loads with 2.345 OAL able to chamber OK. That seems like one heck of a long jam.

 

[Crossfire64]

i did not remove the ejector

 

[DocDoc]

Which is correct? The original post said 2.449. Oops, on second look I see also, 2.249 as well. If you are not using the same bullet as the one used to measure 2.345 you can get a different OAL. 0.1 difference would be too large, unless they were different styles or manufacturer. There should not be more than a few thousandth difference for the same brand and model.

AI uses a 0.004 crush fit, so again 0.1 is way too much and there must be something going on in the measuring. The gauge sets the distance between bolt face and shoulder on the barrel.

 

[RichinVA]

It needs to be removed to get an accurate feel for the go gauge. With it in, you are trying to deal with the gauge AND pressure from the ejector.

 

[FearNoWind]

"I put scotch tape on the base of my go gauge adding 0.002 a created a no go gauge" Really?
That, coupled with the information that the firing pin/extractor weren't removed from the bolt, makes me wonder if any of the "testing" is being done correctly.
Are we using go no-go gauges, field gauges, or something else.
Are we using the same bullet in the Hornady test in both setups.
Take this rifle to a competent gunsmith, have him check it for safe operation, and go shooting.

 

[RichinVA]

Gordy uses tape, that's good enough for me.

Leave the extractor, remove the ejector and the FP.

 

[Crossfire64]

I just want to re state that I am a beginner

A buddy helped me build this in 2014

he set the barrel, head-space & OAL of 2.345 using the Hornady OAL guage

I was shooting at the range last month & notice my groups expanding
upon inspection I found the barrel nut was loose & the barrel could be unscrewed by hand.

The buddy who originally helped me is no longer available to diagnose.

Gunsmith #1 said "Wow! I didn't know they made these anymore & I wouldn't be able to get any parts for it" He clearly is quite confused. He then went on to say "just crank the barrel down tight & don't worry about headspace"

I picked up my gun and immediately left

Gunsmith #2 said he could do it in 6 months & $185.00

I figured that if I am going to do this seriously, I need to figure it out on my own.

i contacted Northland Shooting supply & spoke with Jim who was amazingly helpful. I bought an action wrench, barrel nut wrench, barrel nut, recoil lug & trigger spring.

I then went to Brownells & bought my go gauge, OAL gauge (same as my buddies) and comparitor gauges.

My installation of my new parts went very well. My gun is reassembled. And when I check my OAL I noticed the huge difference. Same Berger 105 vlds same kind of OAL gauge.

The gun is chambering as it should with the go gauge & I can not close the bolt with tape on the bottom of my go gauge.

If the bergers are normally shot close to 2.244 maybe I'm correct now and was wrong earlier but my buddy was seating his 6mm br around 2.350 with the same bullets

 

[DocDoc]

Jim is helpful. Your procedure of tightening with barrel nut and wrench on the go-gauge is correct, so you should be good to go. You can get a difference in OAL with different throating than your friends. If he has a deeper throat to his barrel, the OAL will be longer than yours. You should however, get the same OAL with your barrel as you had before.

 

[Buttermilk]

Two different barrels, correct?

That means the chamber throat of the second barrel is different than the chamber throat of the first barrel. Simple as that.

One is throated longer than the other.

Headspace has nothing to do with OAL, since it is based on the case body (shoulder).

OAL is independent of headspace.