Jump to content
308AR.com Community
  • Visit Aero Precision
  • Visit Brownells
  • Visit EuroOptic
  • Visit Site
  • Visit Beachin Tactical
  • Visit Rainier Arms
  • Visit Ballistic Advantage
  • Visit Palmetto State Armory
  • Visit Cabelas
  • Visit Sportsmans Guide

PTG "AR-10" Upper Receiver Lapping Tool


COBrien

Recommended Posts

Working on building up my CSASS-type rifle, and realized I might need/want to lap the front of the upper receiver. This is a DPMS-pattern build.

PTG makes an "AR-10" upper receiver lapping tool...

http://pacifictoolandgauge.com/ar-tools/10318-ar-15-upper-receiver-lapping-tool.html

If this is, truly, an AR-10 tool, is there any reason (I.D. of the receiver, specifically) it shouldn't work for an LR-308 pattern receiver?

Link to comment
Share on other sites

I have used that tool for a Matrix and Fulton Armory uppers, both LR-308's, with excellent results. The Fulton might not count as it was very even to start, more confirmed it was square than squared it.

8 minutes ago, COBrien said:

If this is, truly, an AR-10 tool, is there any reason (I.D. of the receiver, specifically) it shouldn't work for an LR-308 pattern receiver?

 

Link to comment
Share on other sites

Just now, jtallen83 said:

I have used that tool for a Matrix and Fulton Armory uppers, both LR-308's, with excellent results. The Fulton might not count as it was very even to start, more confirmed it was square than squared it.

 

My upper will be Fulton, as well, so that's great to know!

As an aside, I recently lapped 2 Fulton AR-15 uppers. One was perfect from the start -- perfectly round shiny spot after "touching" it with the lapping tool, just as a guide.

The second one, on the other hand, was a beast...

Link to comment
Share on other sites

Just now, COBrien said:

The second one, on the other hand, was a beast...

Two DPMS AR-15 uppers pretty much ruined my AR-15 lapping tool they needed so much off. These tools are an expendable thing unless you get a machinist to reface them after wearing a groove and they would most likely charge as much or more than a new tool.

Link to comment
Share on other sites

13 minutes ago, jtallen83 said:

These tools are an expendable thing unless you get a machinist to reface them after wearing a groove and they would most likely charge as much or more than a new tool.

I know a machinist who would do it for you free if you paid the shipping cost.

Link to comment
Share on other sites

16 minutes ago, jtallen83 said:

Can you do both large and small frame versions? I may just take you up on that come late summer/early fall when I will be around home a bit.

Sure can, as far as I know there's no difference in the specs, but that's a trivial problem if any.

Link to comment
Share on other sites

39 minutes ago, jtallen83 said:

If I hear of some of those carrier weights becoming available I might drop it in the mail so the shipping can be cost averaged a bit, suckers are heavy! :thumbup:

 

22 minutes ago, jtallen83 said:

Can you do both large and small frame versions?

They're identical - same part, dimensions don't change.  I have one in a 16" 5.56 precision gun, and one in a LR-308.  :thumbup:

Link to comment
Share on other sites

26 minutes ago, Matt.Cross said:

Sure can, as far as I know there's no difference in the specs, but that's a trivial problem if any.

 

20 minutes ago, 98Z5V said:

 

They're identical - same part, dimensions don't change.  I have one in a 16" 5.56 precision gun, and one in a LR-308.  :thumbup:

Can they be made in different weights? 

Link to comment
Share on other sites

1 hour ago, 98Z5V said:

1.  Housing alone. 

2.  Housing with steel insert.

3.  Housing with Tungsten insert.

3 total possibilities.  :thumbup:

Tungsten, Carbide, Steel, Aluminum, Plastic....

The insert possibilities are endless, the housing necessarily needs to be machinable, but there's also many possibilities there.

Link to comment
Share on other sites

Now, then, we know this will work in DPMS-pattern uppers.

Will it work in Armalite uppers?

I have a buddy who's just bought a complete AR-10 who wants to install a JP handguard on it. While we've got it apart, I'd like to lap the upper for him.

Does anyone have a blueprint and/or measurements for the I.D. of an LR-308 upper vs. an AR-10 upper?

Link to comment
Share on other sites

2 hours ago, COBrien said:

Now, then, we know this will work in DPMS-pattern uppers.

Will it work in Armalite uppers?

I have a buddy who's just bought a complete AR-10 who wants to install a JP handguard on it. While we've got it apart, I'd like to lap the upper for him.

Does anyone have a blueprint and/or measurements for the I.D. of an LR-308 upper vs. an AR-10 upper?

Blueprint not necessary.  It will work.  I have an AR-10 barrel mounted in a DPMS-based rifle - fits.  It'll work.  :thumbup:

Link to comment
Share on other sites

  • 5 months later...

The problem with lapping an anodized surface is how hard the surface is. Some say it is as hard as sapphire. IMHO looking at the tool you could lay a emery cloth on something truly flat, say plate glass, and carefully dress it flat again. A lap works be embedding the abrasive into it...but there is a contest between the lap and the work, if the abrasive becomes embedded into the work (because it is softer than the lap) then the work starts cutting the lap. With a hard anodized aluminum part the anodized surface is very hard, the aluminum underneath is very soft (in comparison). So once you get through the anodize odds are that the abrasive loads into the aluminum then starts lapping the tool. One thing that will help is to make sure there is NO loose abrasive present. A lap should be loaded with abrasive then any loose abrasive should be rinsed off. There is a lot more to lapping than meets the eye :-). Many folks at first think that a huge amount of loose paste between the two parts is what is wanted/needed, the reverse is true. Loose abrasive is an uncontrolled process basically.

Bill

Edited by willbird
Link to comment
Share on other sites

Before surface grinders and magnetic chucks became so good and widespread most fine finishing was done by lapping, ultra fine finishing still is. But old school was to have 3 lapping plates, and with 3 of them you can work with them and make them all flat. They still use a lapping process to come in and make granite surface plates flat again. For the receiver lapping tool cast iron might actually be a very good material choice for the portion that does the cutting once loaded with abrasive. No reason you could not have a series of laps to use on that tool, keeping one for the final finish..and others to do the rough work if needed.

Bill

Link to comment
Share on other sites

  • 2 years later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...