SPR Suddenly Blowing Primers

[WestDesertPRS]

I have a custom-built AR15/SPR-ish rifle that I've been running for about 10 years. It's built on an 18" SPR profile WOA match barrel with a headspace-matched bolt and It's always been a tack-driver.

It doesn't get a ton of rounds through it....maybe 200-300 year. It's always run with factory match loadings FGMM 77gr or Norma Match

On my last range trip it started blowing primers halfway through a magazine. It jammed and when I cleared it the case had no primer. I checked the ground and found multiple cases with no primers in the pocket.

I gave the BCG a look and didn't see anything visually wrong with it. I swapped with a BCG from another rifle I had with me and no problems so I assume it's the bolt even though it looks normal?

Has anyone seen this before?

 

[TonyTheTiger]

Weird. Try just swapping bolts back and forth and check gas ring seal between the two in the carrier you've been using.

 

[Snuby642]

Wag.
Carbon buildup on backside of bolt / face of carrier where they mate?

I use an Otis bone tool.

 

[loveha]

Could it be a bad lot of ammo?

 

[Snuby642]

The problem went away with a different bcg, I think he has it narrowed down to that.

Imho

 

[WestDesertPRS]

Agreed. Appears to have gone away in a quick test with a different BCG. It just concerned me a bit to see overpressure signs pop up like that without obvious signs.

I my just replace the bolt and move on but it still just digs at me to not have a definite anawer...

 

[The King]

Headspace check. That’s key.

 

[Snuby642]

Have you stripped the bcg and checked out the mating surfaces, inside face of bcg and back of bolt that contacts it?

It's a spot I used to negligent myself.

 

[WestDesertPRS]

Have you stripped the bcg and checked out the mating surfaces, inside face of bcg and back of bolt that contacts it?

It's a spot I used to negligent myself.

Good call. Bolt face looks pretty clean...I'd say no more than normal fouling. I'll check that tonight.

 

[Snuby642]

I started getting buildup there shooting suppressed.
So I got one of the Otis bone tools to give that a quick clean.

Maybe the bolt is not shot.
Goog luck

 

[WestDesertPRS]

I started getting buildup there shooting suppressed.
So I got one of the Otis bone tools to give that a quick clean.

Maybe the bolt is not shot.
Goog luck

Otis BONE tool ordered. Should be here tomorrow (gotta love Amazon for that kind of stuff). I'll give that a shot (no pun intended) and hopefully range-test next weekend.

 

[WestDesertPRS]

Also...I see this thing has an NSN on it. Wish we would have had that tool when I was in the Corps....

We used to scrape out the inside the carrier with tip of the firing pin to get clean enough to keep the armorers off our ass....this would have saved about an hour...

 

[Snuby642]

One of my sons after being deployed turned me on to them.

 

[bfoosh006]

IMHO, given 200-300 rds a year , Be sure to give the chamber and bore a good cleaning.

 

[Dev L]

Excessive headspace, most likely.

 

[Greg Langelius *]

Check the bore just ahead of the throat for a carbon ring, even if the BCG replacement/cleaning fixed it.

Sometimes a problem has more than one cause...

Greg

 

[WestDesertPRS]

I'll do that. I was out of town for a couple days so didn't have access to it. Got it apart last night to check things out. I hit the carrier, bolt and firing pin with my new Otis BONE tool. That thing is pretty handy. I'd say the BCG was due for cleaning but it wasn't terrible...just what I would consider normal amount of carbon buildup.

I'll hit the bore and chamber really well this weekend and give it a test-fire whenever I get the chance. I'd love to be one of those guys with a 1000m range off my back porch but unfortunately I'm stuck with either the public range (yuck) or some good spots I know out in the desert.

 

[Greg Langelius *]

West Desert, eh?

Like where, more precisely...?

Greg

 

[WestDesertPRS]

I have a spot out in the Tonopah area (West of Phoenix) where I can get 600m pretty easily and a bit farther if you can elevate your shooting position (bed of a truck for instance). The ground in that spot is a bit lumpy so it can be hard to get a clean sight-line from ground level (off a bipod).

I have another spot east of Phoenix (out towards Superior) where I can get 800m or a little more. That's my preferred spot but it tends to fill up with "blasters" on the weekends who just like to mag-dump their AR15s for no purpose.

I have some 9x13 silhouettes, a 12x20 silhouette and 6" and 8" gongs I put out for targets.

 

[Greg Langelius *]

Sounds excellent.

I'm down in SE Cochise, about 50mi N of the Border.

Greg

 

[WestDesertPRS]

Sounds excellent.

I'm down in SE Cochise, about 50mi N of the Border.

Greg

I've never shot down in that area. If I had guessed I would have thought you had some nice open territory. There are some decent places around Phoenix if you know where to go but its all an hour drive or more from my house. And as you know you have to shot *early* in the summertime so you don't get cooked.

 

[Greg Langelius *]

I shoot to 100yd local, and to 300m down 50mi South in Douglas, on the Border.

Heat and health have kept me housebound from Dec until now. Expecting to be out and around in another two or three weeks.

I've got a whole mess of projects that have been on hold and accumulating.

Much of this area is cattle/agriculture, and much is also off limits due to wildfire danger. The BLM land has a lot of Jeep, bridle, hiking trails, so I'm disinclined to shoot there.

While is have shot 600yd at Ben Avery, the trip is far enough to need a room overnight.

Greg