Posted by: reformedmusings | October 12, 2009

Range report – my 6.8 mm SPC AR-15 Carbine

I finally was able to get to the range today to fire the new AR-15 I built. I discussed it construction in this post, and the optic in this one.

I had trouble finding appropriate ballistic tables. Most assume that one will sight in at 100 yards. Great idea, but one has to drive a long way here in NoVA to find that long of a shooting range. The longest one locally is the NRA HQ Range. I love that range. It’s computerized so you can easily send your target to the same distance repeatedly after changing targets with just one button push. The facility is well-ventilated and one can shoot pistol or centerfire rifle up to .460 Weatherby Magnum there. The staff is very friendly and helpful. The only problem is that they are usually carrying a waiting list. Today the range opened at 1000, I got there at about 1002, and there was already a short waiting list.

I should also mention that I lubed the AR-15 with Gunzilla again the night before shooting. I decided to stick with Gunzilla because parts lubed with it virtually repel carbon. That seemed like a good idea on a direct-gas impingement carbines like AR-15s. For ammo, I went with Silver State 115 gr. OTM (Open Tip Match). I didn’t build this as a match carbine (no match trigger, short barrel, etc.), but the medium-weight barrel should have match-grade accuracy and I like to hit where I aim.

Bottom line on the carbine: SWEET! It shot like a dream. It took about 20 rounds to sight in because the Aimpoint T-1 Micro seemed to be defaulted way low and to the right. Part of that could be because of the higher LaRue mount, which placed the Micro at the perfect height for a comfortable cheek weld. During and after the sight-in, I shot some sub-MOA groups with it using only my range bag as a rest. Not bad for a 4-mil red dot. The DPMS parts-kit single-stage trigger is one of the cleaner that I’ve shot on an M4/M16/AR-15, but it’s definitely not match grade. Overall, the carbine performed perfectly. Not bad for a first-time build!

The Aimpoint also performed perfectly. I used its adjustment cover caps to zero it just as one would in the field. The caps even have the setting directional arrows etched inside of them. I had no difficulty dialing the Micro in. The 4-mil dot almost covered the center of a 100-yard sight-in target at 50 yards. Aiming at the corner diamonds involved a bit of guess work, as they were completely obscured by the dot. The dot is designed for rapid target acquisition, not target shooting. It excels at rapid target acquisition, but is accurate enough for tight groups.

Recoil of the 6.8 mm AR-15 is slightly more than a 5.56 mm version, but significantly less than 7.62 mm out of a two-pound heavier rifle. 6.8 mm seems like a nice compromise between effectiveness and shootability. 5.56 mm is good for varmints, but nothing bigger. The 5th Special Forces Group did a great job in creating the 6.8 mm SPC. The overall cartridge length is identical to the 5.56. The beauty of this approach is that any M4/M16 can be converted to 6.8 mm SPC simply by changing the barrel, bolt, and magazines, or just swapping upper receivers which can be done in the field simply by pulling the takedown and pivot pins as one does when cleaning the carbine. Plug and play.

After initial sight-in, I shot some offhand. The quad-rail upper and medium-weight barrel add some heft to the front end. That enables more rapid follow-up shots, but gets tiresome to hold up after a while. I burned about 60-70 rounds offhand, and all landed center-of-mass (COM) – mostly center of COM. As a plus, the holes weren’t the tiny 5.56 mm/.223 ice-pick variety, but easily visible 6.8 mm ones!

Cleaning wasn’t bad. Unlike the government M4, the enhanced bolt assembly from LMT have additional heat treatment and coating. That makes them more heat resistant and easier to clean. I cleaned and lubricated with the non-hazardous Gunzilla again. I routinely use Otis’ outstanding Deluxe Military Cleaning Kit, which covers all common calibers for breach-to-muzzle cleaning. Works like a charm and preserves your firearm investment. Their optional Brass Scraper Tool Set makes a great addition for the AR-15, as much carbon must be scraped with a direct-gas system.

This AR-15 turned out better than I expected. Although I’d shot similar carbines before, I wasn’t a believer in 6.8 mm SPC until today. Kudos to Lewis Machine Tools for an outstanding, accurate monolithic upper receiver/barrel combination, and Silver State for making tack-driving ammo. They made for a great day!



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