Home Forums Hunting & Shooting AR and Tactical Rifles 10.5" AR-15 5.56 Pistol

I was looking at the heavier bullet ballistics in a 10.5". Looks like 2400 fps is realistic with the 75/77gr bullets.

This is a JBM calc on the Sierra 77gr TMK at 2400 fps, in local atmo,

I am curious if you have a round house figure for rounds down range and have there been any functioning issues.

Not many rounds at all. Maybe 100 or so.

The only ammo I've used so far is PMC X-TAC 62gr green tip LAP. Roughly an M855 equivalent.

So far no malfunctions or stoppages at all.

When I put it together I did throw in an H3 buffer from the start. Tested it for positive bolt lock-back on the last round and it worked fine, so I ran with it.

A standard carbine buffer probably would be fine too, but I didn't try that.

I have a kit on order from PSA with the standard carbine buffer. I’ll report out on any stoppages, if I get stoppages.

I think the trouble most commonly associated with the 10.5" with the carbine gas system is the short dwell time, causing an under-gassed condition.

If that is the case, the lighter buffer would probably be better than a heavy buffer.

Anyhoo, I'm going to run with the H3. If I run into any cycling issues down the road I'll share the info. With the H3 and the ammo I'm using, I don't feel any thump from the buffer hitting the back of the extension tube. It's real smooth.

MM,

I going to get the 7.62x39 carbine upper from PSA when they are back in stock.

What buffer do you run in yours?

I've got an H3 in the 16" 7.62x39.

It ran OK with a standard buffer, but I could definitely feel it hitting the back of the extension tube. The H3 smoothed it out real nice.



Another reason I went to the H3 in the 7.62 was because I figured delaying the unlocking a bit, should help reduce or eliminate the chance of losing a bolt lug. Apparently that has happened with the 7.62x39 in the AR.

Thanks

some of the pistol uppers are over gassed, the H3 makes some sense. I think the heavier bullets do better at longer ranges.

The heavies with the higher BC always win at distance.

Muzzle velocity numbers impress sometimes, But high BC is the gift that keeps on giving.

I see they have a chromed version as well, probably not as accurate.

The nitride barrels do seem to shoot a little better, on average.

You're assuming the underlying barrels are equal. They are not.

Most of PSA's chrome lined barrels are made by FN, their nitrites are made by some second tier producer.

I trust FN to make a good barrel.

so your saying that an FN chrome lined barrel would be more accurate than a second tier nitrided barrel? I don't dispute that they would be more durable.

You can nitride a turd and it's still gonna be a turd.

You need to start out with a good barrel and they seldom come as the cheapest option.

Yep.

This:

Yep I owned an FN double chromed barrel, in one of the early Noveske guns, it was a 2.5 MOA barrel with xm193 did not shoot much better than that with Hornady 55 grain Vmax factory ammo. They replaced the barrel with a new one when I complained that the barrel seemed a bit rough and the new one shot about the same. They are milspec barrels. I have spoken to a Knight armament dealer and he said the Knight barrels are about the same until you get 1000 rounds down the tube and they smooth up a bit. Again I am no expert here as many others are, but have owned a few chromed barrels. Colt has made a decent barrel.

Did you try any 75/77gr match ammo? M193 is 3.5 MOA at best, and usually between 4 and 5 MOA.


Every FN Double chrome lined barrel I’ve seen (100-125) has been a sub 2 MOA for ten rounds with 77gr Blackhills.

It was about 2.5 maybe 3 MOA for 5 shots with an NXS 1-4 in a LaRue Mount.. I never shot any 77’s. It was a reliable gun, sold it for too little. These days a PSA upper with an FN barrel which I assume is the same as what Noveske offers and a PSA premium bolt would be my choice over any intruded barrel

I'm don't understand your logic.

I feel the reason as to why 7.62x39 breaks lugs on bolts is that the lugs on the bolt have to be much smaller than the lugs on a .223 sized bolt. Also, The pressure on the 7.62x39 bolt is much higher than the pressure on a .223/5.56 bolt. (7.62 Case has a larger bolt surface area than a .223 bolt area hence more load is applied to the bolt). I understand 7.62x39 does not have an issue with breaking lugs in an AR10 or similar platform. I am not comfortable running 7.62x39 loads in an AR15 sized platform due to the smaller bolt lugs and increased load on the bolt.