Red_SC

Different stroles for different folks- my favorite is the SD-E. I've owned the Super 3 Gun, and HATED it.

I've had one JP barrel, although it was in 5.56 in a CTR02. In short, it was all it was rumored to be. The first owner ran it hard with mostly Wolf ammo, and wouldn't even guess at the round count when he sold it. I know him well, and he shoots a lot. I put a 1-4x on it for 3 gun use, but ended up shooting it to 600+ a number of times. It did great at that range, even with the low powered optics. I ran thousands of rounds through it, and when I sold it it would still hold 2" groups at 100 with good ammo. I'd love to know the round count on that barrel. I've shot several JP.308's that belong to friends. None have regretted their choice.

At the expense of battering the poor horse again, I'll give my experience. Once upon a time I was a sponsored 3 gun shooter from a small AR builder. He liked side chargers back before they were common, and his method was pretty crude but effective. He cut a slot down both sides of a machined ('billet') receiver that he made himself, drilled a hole in the carrier, and ran a high strength threaded rod through it with a handle screwed onto each side. The handles were 1/2" thick, and had a small boss that fit down into the receiver slot to hold the handle away from the receiver to keep it from binding. The handle wouldn't hit the receiver when pulled completely to the rear, but after I ran 1000 rounds through it I could see peening from impact with the upper. So, each shot was bottoming the buffer in the tube hard enough to compress it a little and make contact. This was a great, flat shooting rifle, not overgassed at all. Eventually it preened that boss off the handle during a big out-of-state match and started causing malfunctions, fortunately on the last stage. Side note, after shooting his a while, I sketched a non-reciprocating handle for him that I thought would be perfect, but he never tried to make it. Not long after, JP came out with their side charger of a very similar design.

Hah! With the cost and wait time on that thing, I'm not touching it! It uses 51t mounts, it looks like it's compatible with the 5/8 version.

They come from here. :)) Cutting 5/8 threads on my .223's gives me the option to run .308 cans as well without an adapter. I shoot a .308 can on .223's fairly frequently. The only .223 can I have is an M4-2000, so if I can run a 5/8 thread on that one too, it gives me a lot more flexibility.

Hoping the trend continues, the ATF cashed the check for an AAC SR7 about 5 weeks ago. I've had some go nearly a year in the past, 4 months is still a long time but it's much better than it was!

To answer my own question, research indicates the 51t adapters are all the same length, so a M4-2000 will happily mount onto a 5/8-24 brake.

Has anyone confirmed this is always the case? I'd like to mount my m4-2000 on a 5/8-24 thread .223 but thought that can was designed to not thread on the bigger mounts.

AI mags allow a long OAL, I don't know offhand how long but I can measure when I get home. They're $39 in stock at Midway right now. My SPS Tactical looks very similar to yours, I've set the barrel back and rechambered to .223AI and threaded the barrel. It's going to be getting a new barrel in a couple months.

The small firing pin

Changing primers helps, but doesn't always solve the problem. My theory on why it's more common on other calibers than it is in .308 is the powder used. The case capacity is very close, but a .260, 6.5 Creedmore, or 6.5x47 shooting 123-142gr bullets or a .243, 6 Creed, or 6x47 shooting 105-115's typically uses a slower powder like 4350 or RL22. I'm guessing the high pressure part of the pressure curve is fractionally longer with the slower powder, putting pressure on the unsupported primer over the firing pin hole for a little longer. Whatever the case, the phenomenon is fairly common in these calibers, and JP has sold a ton of their high pressure BCG's at close to $500 a pop to fix it.

Sure. The primer isn't being pierced by the firing pin, but by the case pressure. The hammer falls on the pin, which flies forward and impacts the primer, dents it, and stops. The primer ignites the powder and pressure builds. The majority of the case head is supported, but the firing pin hole is a spot under the thinnest part, the primer cup, that is supported only by the resting firing pin. Having a smaller firing pin hole makes the unsupported area smaller. I don't know why, but many 6mm or 6.5 loads that are safe and show no primer pocket loosening or case head expansion will have a primers flow back into the firing pin hole or pierce in AR's, but it doesn't seem to happen often to .308's. Accuracy International rifles also have this issue, 308's run perfectly and many people have no issue with smaller calibers, but a significant number of people have had factory ammo or handloaded starting loads that pierced primers. The answer there is to have the firing pin turned down and the bolt face bushed, but few smiths will do it to the hardened AI bolts. I know I'd be hesitant to do it.

It reduces pierced primers or primer blanking, but it doesn't do anything to keep primers from coming out of the pockets.

The firing pin is smaller, around .062, to reduce pierced primers. This is a lot bigger problem on 6mm and 6.5mm calibers than .308. I know JP and Rubber City make a small firing pin BCG they call a High Pressure bolt, and LMT bolts and the newer DPMS G2 are supposed to have small pins by default. Here's a pic I found comparing JP's standard and HP bolts. http://williamjmeyer.com/SH/LW_AR308_Build_0008.jpg

Have you considered a BCG with a small firing pin? This platform is taking off in various 6mm and 6.5mm calibers, and a lot of us are buying small firing pin bolts to reduce primer piercing that's more common in those calibers. The few available like the JP are twice the price of a standard BCG.

Excellent.

I don't live in a state with those laws so I'm ignorant, but would pinning and welding a QD mount satisfy it? The biggest problem I'd see with that type mount would be barrels with bores not concentric to the outside. I've seen some quality barrels with significant runout, but I'd think most AR barrels would be turned between centers after being cut to length. That would minimize runout.

Hah, you're right. I didn't realize the threads here were so old.

I'd be interested to find out what size gas port you need. I'm starting a 6mm SuperLR build, which is a slightly modified .243.

Homemade barrel vise. Bore a hole in a square aluminum bushing the size of the barrel and split it, put it in the vise, and crank down on the press to secure it. I'm torquing an action on in this picture, but it works for muzzle work too.

A PSA complete lower with UBR stock and MOE grip. I needed the furniture for building my first large frame AR, but for the price I basically got a free AR15 lower with parts kit. My dealer got my check for a Mega MKM set today, but I don't know if he's ordered it yet or not.