Short-stroke question.

[Tedward]

I spoke to Dan today. Here are his measurements from the AA Bolt he has and the LBC bolt on hand. I guess with everyone's different measurements must mean different batches that were made at different times, or something. Again a guess, but that is why when they make match barrel and bolt sets, they need the bolt to be matched to the barrel.

Here are his measurements today. Not .006 difference, it was the back of the lug to the front of the bolt measurement that didn't match up.

[FONT=&quot]From:[/FONT][FONT=&quot] Daniel Lilja [mailto:lilja@riflebarrels.com]
Sent: Wednesday, December 04, 2013 3:05 PM
To: Edward Sperry
Subject: RE: 6.5 Grendel Head Space[/FONT]

Hi Ted,

I’m measuring the LBC at a counterbore depth of .133” and a lug length of .277”

The AA bolt is .133” counterbore and .280” lug length.

Best regards,

Dan

[FONT=&quot]Daniel Lilja [/FONT]
Precision Rifle Barrels Inc.

[LRRPF52]

Is the rounding thing also a good idea on other AR bolts, or is it ONLY a PPC case thing?

People do it to .223 guns, and the Dutch Armalite AR10's had a beautifully radiused ejector. They were one of the best production Stoner designs ever made, in my opinion.

You see it as a common tweak on the .223 hi-power AR15's, in addition to a laundry list of other reliability and accuracy enhancing techniques.

[NugginFutz]

The LBC bolt lugs measure 0.276" and the bolt face 0.133"-0.134".
The AA bolt lugs measure 0.278" and the bolt face 0.134".

I measured these with my Mitutoyo digital calipers.

I am a little fuzzy on lapping the bolt. I have built a tool in the past for lapping a bolt gun. So are you using the front half of a case cut in half with a spring to hold pressure on the lugs to lap against the barrel extension?

[attachment=2747]

Like this...

[KentuckyBuddha]

What kind/grit lapping compound do you recommend for this gambit of fitting?

[maverick5582]

LappingCase.jpg

Like this...

Thanks for the illustration. Now if I can just find an extra piece of AA brass.

[SHORT-N-SASSY]

People do it to .223 guns, and the Dutch Armalite AR10's had a beautifully radiused ejector. They were one of the best production Stoner designs ever made, in my opinion.

You see it as a common tweak on the .223 hi-power AR15's, in addition to a laundry list of other reliability and accuracy enhancing techniques.

http://www.ar15.com/archive/topic.html?b...3&t=525843 (Scroll down to the tenth photo on the Page: the Portuguese variant of the original AR-10 bank-vault Bolt geometry)

[LRRPF52]

The exact picture I was thinking of. Now that's a beefy BCG right there. Those rifles seem to have superbly accurate barrels for a military rifle too.

I shot under 1.5" at 150m with one in Finland a few summers ago, with iron sights and South African surplus 7.62 NATO.

[NugginFutz]

Thanks for the illustration. Now if I can just find an extra piece of AA brass.

All you need is a piece of 7.63x39. Run it through your 6.5G sizer, and then cut it. That way, you don't waste any good brass.

[NugginFutz]

Thanks for the illustration. Now if I can just find an extra piece of AA brass.

All you need is a piece of 7.63x39. Run it through your 6.5G sizer, and then cut it. That way, you don't waste any good brass.

Just be sure to remove the ejector, before lapping the lugs.

What kind/grit lapping compound do you recommend for this gambit of fitting?

My understanding is that 600 grit compound works well.

[KentuckyBuddha]

thanks!

[maverick5582]

[IMG][/IMG]

Finished the ejector tool and the spring loaded cartridge for lapping the bolt. The bolt lapped in well the black oxide finish was completely removed from the back of the bolt lugs.

Appreciate all the input. All the information that is discussed here makes the learning curve less painful. I will try the bolt next week and see how it goes.

Maverick

[rasp65]

Budda Here is Robert Whitley's article from AccurateShooter,com http://bulletin.accurateshooter.com/2013...artridges/

[KentuckyBuddha]

thanks rasp65

[maverick5582]

[IMG][/IMG]

Finished the ejector tool and the spring loaded cartridge for lapping the bolt. The bolt lapped in well the black oxide finish was completely removed from the back of the bolt lugs.

Appreciate all the input. All the information that is discussed here makes the learning curve less painful. I will try the bolt next week and see how it goes.

Maverick

The bolt worked and cycled fine. Lapping it in appears to be the solution.