In the following posts:
- AR-MPR: Accurizing the Upper Receiver – Part II: Milling and Receiver Face Truing
- AR-MPR: Accurizing the Upper Receiver – Part I: Prep and Welding
- AR-MPR: Accurizing the Upper Receiver – Overview
I’ve documented an experiment in accurizing the upper receiver of the AR-MPR rifle. It was a bit painful to file away hard anodizing, followed by drilling, welding, milling, and finally epoxy bedding. The whole point was to remove slop between the upper and lower receivers on the AR-MPR rifle.
I finally had a chance to test out the rifle with the modifications in place. I did a quick sight-in on the paper at 25 yards, then dialed it in at 100 yards. From a bipod and rigged up rear rest, the first 5-shot group measured just .604″ (.577 MOA) – well within the .5-.75 MOA goal for the project.
Next, I’m looking forward to shooting off a proper rest, and experimenting with different loads to see how good this rifle can get.
I’m confident that this rifle will continue to turn in more great groups. Stay tuned, because there’s another related project coming up!
-Gavin
Gavin,
Noticed that you are using 52Gr. bullet. What is the twist rate of the Sabre Defense barrel. Tried to look up but could not find. I know my JP shoots 1 in. with factory 52Gr Hornady and I get .5 in. to .75 in at 200 yds. with my handloaded 69 gr. Sierra and 24.3 Gr. Varget. The twist rate is 1:8.
My 1:9 Shoots 60gr A-Max over H335 – .250″-.350″ at 100yrds
haha…. V-Max – Can you fix that and delete this post?
Gavin,
I’m a little confused by the results here. When the gun was taken out on the initial range trip group sizes of 0.285 and 0.435 were reported.
http://ultimatereloader.com/2011/02/13/ar-mpr-1st-range-report-unexpected-results/
Now after the accurizing process the rifle is printing 0.604 groups.
Where did the accurizing process go wrong?
That’s a totally fair question 🙂
The big difference is 3-shot groups (former results) versus 5 shot groups (latter).
-Gavin
I suppose that’s a fair reply.
I actually didn’t pay attention to the shot counts and made the incorrect assumption they were consistent between the tests.
I know there are forums I visit where 3 shot groups are scoffed at as evidence of accuracy, even though they seem to be the industry norm’, and 5 shot groups are held in much higher regard.
And a 0.6″ group is nothing to sneeze at whether 3 shots or 5.
Thanks for entertaining the question, I’m looking forward to the progress on the AR-308 project.