6.5Creedmoor Overpressure AR15?

[Buckshot]

A friend of mine just bought a 6.5 Creedmoor AR15 in a heavy barrel varmit configuration. He also purchased a suppression device for it. He brought them out to my house and was shooting Hornady factory ammo in it without the suppressor and it looked like the loads were borderline too hot. Then he put on the suppressor and was getting heavy ejector marks and occasional blown primers. My advice was to stop shooting it with that ammo but since he had 1500 rounds purchased, I think he is going to continue shooting it. My question is...Can anyone explain whats happening and what could happen with continued firing of this rifle ammo combo. I have very little experience with semi autos and I dont want to be telling him its dangerous if it isnt or NOT telling him to stop before he has a bunch of AR parts embedded in his face.

Thanks

 

[Forum Boss]

He should stop shooting that ammo. Pronto. Blown primers is a serious problem.

Was this the 120gr or 140gr load?

Hornady has changed the load on the 120 grain Amax 6.5 Creedmoor because of reports of pressure problems.

I don't know why the suppressor will make a difference, but possibly it increase back-pressure. You'd have to consult someone more knowledgeable about suppressor performance.

FYI he should also do a serious barrel clean. If he is getting bad copper or carbon fouling, this can increase pressures.

From Sept. 7 Daily Bulletin:

We recently spoke to Dennis DeMille, General Manager of Creedmoor® Sports and two-time NRA National High Power Rifle Champion. Dennis has been one of the driving forces in the creation of the new 6.5 Creedmoor round,see video below). He alerted us to a recent change in the 120gr version of the factory-loaded 6.5 Creedmoor ammunition.

120gr Load Changed to Reduce Pressure
Hornady sells two types of 6.5 Creedmoor ammunition, one loaded with 140gr Amax bullets and a second loaded with 120gr Amax bullets. Hornady has changed the 120gr load because there were some reports of pressure issues — stiff bolt lift and primer cratering — with the “first generation” load. The new load for the 120-grainers uses 40.3 grains of Hodgdon Varget. Previously Hornady was pushing the 120s with 44.5 grains of Hodgdon H4350. The old load was rated at 3020 fps from a 28″ barrel. According to Hornady, the new 120gr Varget load “sacrifices about 75 fps”, which means the Varget load should offer about 2945 fps velocity.

 

[Buckshot]

He was shooting the 120s. Ill make sure he is made aware of the pressure issue


Thanks!

 

[Rob01]

Mod we had heard that to but last we were told from Hornady they talked about that change but haven't done it yet. The Varget being a faster burning powder might work better in the shorter barrels but I have never had a problem with any of the 120s loaded with H4350 I have used in my 28" bolt gun.

 

[Buckshot]

Thanks for your input folks. This issue has been resolved. It turns out that the barrel groove diameter wasnt up to spec

http://www.websitetoolbox.com/tool/post/6mmbr/vpost?id=3145890