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Discussion Starter #1
I have exclusively used 2000MR firing over 3000 rounds with no cycling issues. I am tired of the filthy 2000mr despite the good performance. I would also prefer a more temp insensitive powder. I pressure tested H4895 & 8208xbr today and it failed to strip the next round or lock the bolt back on the last round. I fired 24.0, 24.5, & 25.0 grains of both powders. No pressure signs using CCI450 primers in Starline brass. Velocities are
where I want but I have the cycling issue. H4895 was a little faster. I did a thorough cleaning and disassembled the gas block from the barrel. I ensured there is no blockage and verified the AGB is wide open and wiped down the BCG with CLP. Cycles by hand like butter. I believe the Gas port is .098 from ARP I have never touched it. I ordered a reduced power buffer spring today. Hopefully the reduced power buffer spring will do the trick. I run a carbine buffer tube with a standard spring and carbine weight buffer. BCG is full mass. What am I missing?
 

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Danno, I have the same barrel and have been using 2000MR, Varget, R17, and W760 under mostly 75 A-Max, 77 SMK, 85.5 Hybrids, 88 ELD-Ms, and 95 SMKs. I have 90 VLDs and A-Tips waiting for the next range session. I have plenty of comments for you but first need to know what specific bullet you are shooting and your velocities so my feedback is relevant.
 

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Discussion Starter #3
Xman, Here are velocities with 85 RDF's fired at 90°F.

8208
24.0 - 2712
24.5 - 2720
25.0 - 2767

4895
24.0 - 2685
24.5 - 2758
25.0 - 2821
 

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Wouldn't you know it. The one VLD bullet I haven't shot. I have found that the typical pressure signs I get with the 6.8mm are not showing up with the Valkyrie. I've seen high pressure cause loss of primer pockets with no swipes or primer craters. I've only shot 800 rounds down my barrel and just had to do a deep clean. It had carboned up more than I have ever experienced with my .223s. Did you get the carbon out of the BCG? You may also want to mic the nipple on the gas tube to see if it is worn.

Where are you getting your load data? Sierra data is below. Extrapolating, their publish max would be about 1.0 grains less than for an 80gr bullet. Your charge weights are significantly higher. It is possible your pressure is too high and causing the case wall to still be held against the chamber when the bolt begins to open.

61578
 

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Discussion Starter #5
Wouldn't you know it. The one VLD bullet I haven't shot. I have found that the typical pressure signs I get with the 6.8mm are not showing up with the Valkyrie. I've seen high pressure cause loss of primer pockets with no swipes or primer craters. I've only shot 800 rounds down my barrel and just had to do a deep clean. It had carboned up more than I have ever experienced with my .223s. Did you get the carbon out of the BCG? You may also want to mic the nipple on the gas tube to see if it is worn.

Where are you getting your load data? Sierra data is below. Extrapolating, their publish max would be about 1.0 grains less than for an 80gr bullet. Your charge weights are significantly higher. It is possible your pressure is too high and causing the case wall to still be held against the chamber when the bolt begins to open.

View attachment 61578
I loaded based on loads other people are shooting on the Facebook forums. I realize that It is high pressure end of things. My 2000mr load shoots at 2700 fps consistently with low SD and es. I was hoping to match that. There seems to be a speed node around 2700. I'm not chasing speed. I am after consistent sd and es for long range.

What should the gas tube nipple diameter be?
 

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I was getting some impressive muzzle velocities with 2000MR also. But notice that 8208 and 4895 do not have the same potential and will be 100 to 150 fps slower than 2000MR at the same chamber pressure. Will your prior 2000MR loads cycle the action?

My new gas tube measures 0.183". I've had a couple wear enough that they needed to be replaced along with the rings on the bolt. I had enough wear on BCG that the gas key needed to be replaced also.
 

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Discussion Starter #7
I was getting some impressive muzzle velocities with 2000MR also. But notice that 8208 and 4895 do not have the same potential and will be 100 to 150 fps slower than 2000MR at the same chamber pressure. Will your prior 2000MR loads cycle the action?

My new gas tube measures 0.183". I've had a couple wear enough that they needed to be replaced along with the rings on the bolt. I had enough wear on BCG that the gas key needed to be replaced also.
I have zero issues using 2000mr other than it cakes up the bolt and carrier. I have to scrape off everything after 200 rounds. It makes sense that the tube could be worn. I get a lot of carbon on the bolt and blown into the lower receiver. My gas rings are good. I will check the tube tonight after work. Thanks for the sharing your knowledge. I always look forward to reading anything you post on the forum.

PS: Factory Hornady 88 ELD's won't cycle in my rifle either.
 

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Danno, what was your 2000MR powder charge weight for the 85 Nosler?
 

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Discussion Starter #9
Xman, 26.9 grains using Federal brass. It shoots well out of both ARP barrels. 6.5t and 7.7t. BTO=1.750. It touches the rifling at 1.803". So jumping about .053".
 

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Xman, gas tube measures .177". There is basically no resistance inserting it into the carrier key. BCG is a DLC toolcraft with around a 1000 rounds on it. I will order a gas tube for sure. Where is the best place to buy a rifle +2 tube?
 

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Danno, White Oak Armament sells the +2 gas tubes. I bought 2 initially to make sure I had a spare. Can you see the wear on the gas tube compared to a new one?

I don't believe the gas tube or low pressure is your problem. If you basically are running 27 grains of 2000MR you are below published max. However, your 8208 and 4895 charge weights are well over published maximums (interpulating between the 80 and 90 grain bullet weights). These high pressure charges can cause short cycling. If the chamber pressure is still high when the action begins to open, the brass is still being held against the chamber wall and can over power/delay extraction to a point there is insufficient pressure remaining to fully cycle the action. Are any of the primer pockets loose on the brass you just shot with these loads?
 

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What is the relationship of the gas block to the boss shoulder on the barrel... and what type of hand guard?
 

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Discussion Starter #13
Danno, White Oak Armament sells the +2 gas tubes. I bought 2 initially to make sure I had a spare. Can you see the wear on the gas tube compared to a new one?

I don't believe the gas tube or low pressure is your problem. If you basically are running 27 grains of 2000MR you are below published max. However, your 8208 and 4895 charge weights are well over published maximums (interpulating between the 80 and 90 grain bullet weights). These high pressure charges can cause short cycling. If the chamber pressure is still high when the action begins to open, the brass is still being held against the chamber wall and can over power/delay extraction to a point there is insufficient pressure remaining to fully cycle the action. Are any of the primer pockets loose on the brass you just shot with these loads?
Xman, I don't have a new tube laying around. But, compared to the others I have it looks to have more wear. Primer pockets were good on the brass I used. I will test 23.5 gr of 4895 and 8208 and see what happens. I ordered a melonite rifle +2 gas tube from larue. All the tubes I've used before have been stainless.
 

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What is the relationship of the gas block to the boss shoulder on the barrel... and what type of hand guard?
Ratdog68, ARP Barrel has the dimple drilled that indexes the gas block. It appears to be positioned perfectly based on the carbon ring around the barrel gas port when I removed the block. Upper is an Aero enhanced receiver and handguard. Inside diameter is larger than most ar15 handguards. Definitely not touching gas block or anything else attached to the barrel if that's what you are getting at.
 

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Ok... some just butt the GB to the boss and tighten it... then the hole isn't aligned. That gap (present when a full float HG is used) needs to be there. The G.I. type HG uses that gap. Sounds like you've got that base covered.
 

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Discussion Starter #16
Update.... I installed the new gas tube and reduced power buffer spring and fired the two rounds I had loaded of 23.5 grains of H4895 and 8208xbr. It fully cycled on the first round and loaded the next round then locked back on the empty mag. Now to load 24.0 grains of each and make sure it fully cycles. Previous velocities at 24.0 was right around 2700 fps. That's right where my 85 RDF load with 2000MR performs well. Last weekend my son and I had impacts out to 1320 yards. Farthest I have ever attempted to shoot. Both our rifles like this load. We rang steel out to 1000 yds consistently.
 

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Those +2 gas barrels should have a .098" port but a .100 or .102 will not hurt. 224 Grendel or 224 Valkyrie.
 

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Discussion Starter #18
Thanks Mr. H. If I still have issues I will consider drilling the port as a last resort. The other powder I want to test is Varget. I have never tried it with the 85 RDF's. I tested 80 Eld's with Varget but the velocities were considerably slower than 2000 MR.
 
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