Hi guys,
Rifle (
Sierra 316H) is relatively new. Purchased in August of 2013. Since then, I have shot maybe 500 rounds through it total. This has been brass-cased ammo, with VERY LITTLE Tul/Wolf/MFS etc fired through it, maybe 50-75 rounds total.
Recently I purchased a railed front gas block and a quad rail, and had the local gunsmith install them. Everything else is stock as from the factory. Only other addition has been an EoTech 512 and MBUS rear sight. The rifle originally shot fine for awhile, but now, randomly, it has been choking badly. Now it will ONLY fire 55gr M193. Anything else -- be it Speer Gold Dot 64gr, V-max 55gr, Hornady 75gr TAP, Black HIlls 69gr OTM, Federal Fusion 62gr, or MK318 Mod 0 --- simply will not feed. The rifle will fire fine for 2-3 rounds, then the next round will slam into the feedramp and jam the bolt, stopping it from going forward; instead of the round angling up and into the chamber it just plows right into the ramps and stops. This happens with enough force to cause setback in the non-cannelured rounds and greatly scars/gouges the case neck and ogive of bullet in the cannelured rounds. Racking the charging handle to the rear smartly and then releasing will re-feed the round, and the rifle will fire fine for an additional 4-5 rounds before the EXACT same thing happens.
If you look at the feed ramps, you can see a spot where the finish looks lighter grey than the surrounding areas on both the left and right feed ramps.
So I googled it, and came up with a list of possible issues, which I have addressed as below:
- Dirty chamber/feed ramps/barrel extension/bolt carrier/bolt/firing pin channel. I addressed this by stripping the rifle into bolt, firing pin, cam, retaining pin, BCG and upper, then hosing down with Gunslick Foaming Bore Cleanser. I let this sit for 20 minutes then went to town scrubbing everything with a Wheler AR15 upper cleaning kit (upper brush, BCG brush, and chamber 'star' brush). Then I hosed everything down with BC Gun Scrubber. Repeated the above a second time, then lubed and reassembled. Same problem. So probably not related to grit or grime.
- BCG and upper too dry. Squirted down everything with CLP until a visible sheen was present on all moving parts of the upper, and reassembled. Still no dice, same exact issue.
- Magazine sitting too low in mag well. To address this, I disassembled into upper and lower, depressed the mag release button fully with the tip of an M855 round, and tried various positions on the mag catch screw; threads flush, threads protruding, threads recessed. Still the same issue
- Burrs on the feed ramp. I haven't actually tried sanding yet, but isn't 500 rounds a pretty strange time for burrs to pop up?
That's it, I'm out of ideas. Del-Ton has offered to inspect and repair it for me, but I'd like to not be without my rifle if it's possible there's a home-fix. Any thoughts, guys? Anyone with similar issues?
Thanks
DTG