Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
A lot depends what you intend to use them for, For long range competition a tight one inch, maybe a half thou under one inch, to the other extent if they are to be used on top of class 3 lowers (M16's) a little loose would be more reliable, maybe 1.002. I kinda like them when it takes just a little heat for the barrel to fit in, although some barrel extensions are made a whisker oversize for this reason. The tighter the better for accuracy but a little looser for a blaster, just my opinion I'm sure others have different ideas, Jon P.
I think you should use a boring head and boring bar. That will give you the best control over location. Drilling/reaming location will be worse.
Although I see you plan to use a CNC mill. In that case, I would rough drill the hole and then mill the hole to desired dimension. That should give you good control over location. If milling doesn't give you the desired diametral precision, you could mill undersize and ream.
From what I understand the best uppers are drilled, bored undersize, reamed, then honed to final size.
FWIW, make the bore true 1" not over, not under. reason is that barrel extension to bore fit is critical for accuracy and function. If you are worried about to tight a fit of the bolt carrier in the bore, its pretty easy to polish the humps on the bcg that they ride on in the bore, but Ive never ever seen a bcg that's too tight cause problems.
What I have seen is a barrel extension that was too sloppy a fit in the oversized upper to give good accuracy without putting a shim in it or using an oversize extension.
Kennametal makes a drill for that has replaceable tip I use a carbide tipped reamer. Do you have thru spindle coolant ? It takes a tall z to drill that. I mount right to table and I use up all of a 20 inch z no 4th axis. I’m not sure you can do it with 20” and a trunion
Thanx Don
Sent from my iPhone using Tapatalk Pro
I made fixtures for each op. If you don’t have thru coolant I think you will have to peck the shit out of it. But the ream does leave a nice finish. The worst part of the deal is the hole for the bolt cover. That is a long way down to it
Sent from my iPhone using Tapatalk Pro
The small hole that holds the bolt cover on
Sent from my iPhone using Tapatalk Pro
wtf, why would you need a forward assist with a PCC?here is one I built
Sent from my iPhone using Tapatalk Pro
Notice
This website or its third-party tools process personal data (e.g. browsing data or IP addresses) and use cookies or other identifiers, which are necessary for its functioning and required to achieve the purposes illustrated in the cookie policy. To learn more, please refer to the cookie policy. In case of sale of your personal information, you may opt out by sending us an email via our Contact Us page. To find out more about the categories of personal information collected and the purposes for which such information will be used, please refer to our privacy policy. You accept the use of cookies or other identifiers by closing or dismissing this notice, by scrolling this page, by clicking a link or button or by continuing to browse otherwise.