At the end of part 3, the rifle was assembled and the glass was on and bore sighted. I first shot the rifle after one of the regular carbine training get togethers I participate in. The rifle had a few teething problems.
I had an issue where it was having a sort of malfunction where an empty case and the next cartridge were jammed together. The cause was that the case wasn’t getting ejected properly. Since I was not in a position to begin tearing it down to find an issue, some searching online found the answer almost immediately. Others had had the same issue due to a weak spring.
The extractor claw was easily moved with just finger pressure and obviously the dual ejectors were overpowering the weak extractor spring. A temporary double o-ring around the spring to increase tension totally fixed the issue on a later trial run. So I contacted Sprinco and ordered their AR10 dual extractor spring set. This uses an extra power extractor spring with a second smaller spring inside to really increase the tension.
This ended up being a great upgrade that should last a long time and at under $10 delivered it is a bargain. The rifle runs flawlessly with the gas block set to just past where it always will lock back on an empty magazine and ejects at about 4-4:30 in a nice pile.
I have replaced the KVP Linear brake with a (louder) much more effective 3 chamber flat styled brake. The linear, while less noisy, did little to help mitigate rifle movement. Much better now. I also modified the Magpul bipod to go to a 45* position like an Atlas bipod which allows me to get lower when prone.
Initial shooting is very positive with Hornady American Gunner 140g HPBT ammo (not match ammo, as close to plinking ammo as is available in 6.5C). Next steps will be shooting more now that colder weather is here and possibly adjusting the gas to be sure it functions 100% in cold temperatures. Also getting some Hornady 140 or 147g ELDM match ammo to see what sort of consistency the rifle can produce with good pills.
Chances are, this rifle will remain a “hobby” and never need be employed for anything more serious than a match. I sure hope so. Capability is not something one usually regrets even if it isn’t needed. Part 5 should have some shooting results.
While confessing up front I have zero experience with adjustable gas blocks, I have zero experience with adjustable gas blocks for a very good reason: I want all the gas. And if I did ever use one I would never tune it too finely. My advice is to tune the spring-mass system with springs (recoil spring weight) and mass (buffer weight), not with gas. Then test both clean and dirty with all likely ammo for function. My AR (20″ rifle gas, magpul UBR, standard carbine spring and carbine-size buffer) will reliably shoot / cycle / lock open 55, 62, 75 and 77 grain factory ammo, as well as my 73 gr and 80 gr (competition) reloads. The installed carbine buffer has all three tungsten weights. Brass is all at 4 o’clock except for the 62 gr stuff, which goes to 1 o’clock.
One exception: if you plan to use a suppressor, adding the suppressor will GREATLY increase the speed of the bolt / buffer, as the suppressor slows the gas venting-to-atmosphere process, raising port pressure. So being able to adjust port pressure would be very helpful.
The apparent ejection issue you experienced can also be caused by bolt carrier / buffer speed being too high (buffer too light, spring too weak (less likely), too much gas).
Keep tinkering! Your 6.5C semi will be a very useful addition to your toolkit. The cartridge is capable of good accuracy with readily available factory ammo. Have considered one myself.
I appreciate the reply. I agree with you on 5.56 ARs that most of the time the gas is fine and a heavier buffer can fix an otherwise abrupt cycle (especially suppressed or pistol length gas systems).
On big ARs it is a whole different world. Gas volume is significantly more than in 5.56 and most every big AR is well over gassed. Trying to tune them with different buffer weights and even springs without getting the gas correct is all but impossible and will lead to functioning problems in different weather and in using different ammo.
The gas is what unlocks the bolt and too much will unlock it too early regardless of buffer weight. A heavier buffer may affect bolt unlock some as will a heavy spring but what they really do is mask the issue of too much gas. Both will slow the action and help in smoothing the cycling but if the rifle is over gassed neither will fix it. I chose an H3 buffer and Tubbs spring because many others have gone down this road before me and they are proven the best combo in 6.5C.
The extractor being so weak you can easily move it with your fingers is going to cause issues on even 5.56 … and will most definitely cause issues with a bolt made with high pressure dual ejectors like this one. The ejectors simply put so much pressure on the case head that the extractor cannot keep its grip. It then left the case in the action with the next cartridge coming up under it. Rubber D rings and O rings are a thing in 5.56 Guns because of this very reason.
Thanks for replying. I suspect nearly all AR-pattern rifles are overgassed, I think it is the default design config in an attempt to keep the rifle running when dirty.
Among the reasons I have not pursued an AR10 platform rifle (and this platform positively begs for being built in 6.5C) are:
1) I dont think it is yet well understood enough, in comparison to the 5.56 AR15, which the NRA across the course highpower rifle community (among others) understands completely, inside and out. I was able to take advantage of that. Do this do this do this do this, boom it works. Also, stock buffers are too light. Period.
2) waiting for the jury to come in on the 140 vs 150+ gr bullets, ballistics and downrange performance, powder choices for mag length ammo, non-standard chambers, etc. IOW, I have thought about it but I’m waiting for Gen 2.1.
If the range of gas requirements is that broad, I have a question: are we talking about a quarter turn of the adjustment screw, half a turn, full turns? Can the adjustment be marked or indexed? Can it drift? I truly do not know. My experience loading for the Garand taught me to be sensitive to port pressure and bullet weight, though for a different reason (op rod damage). Is there a click-index gas cylinder available with marked increments? Should there be?
All of that said, I’ll bet with a good brake the thing performs beautifully and is a joy to shoot!
You are spot on, there are no standards for big ARs, even parts won’t always interchange. It is best to stick with a manufacturer that meets your financial requirements and produces a solid product that has a track record of being around.
If you want to see folks very upset, read about people who spend $2500 to 4K on a turn key big AR that has teething problems. They all need to be “figured out” and tweaked to run well. The good thing is that if you use good springs and are methodical in setup the gun will be super reliable.
On ammo, keeping the discussion pointed toward long range, the 147ELD is where it’s at right now (see my post last week though on the new A-tip!) with it’s superb BC. Since it easily fits in a SR25 mag and offers such incredible down range performance, it is the pinnacle of store bought ammo.
On adjustable blocks, nicer ones have detents for “clicks” but once you have the gun running properly you most likely won’t need to move it. I adjusted this one in 1/4 turns from wide open (from approximately 3 turns out) til it wouldn’t lock back on an empty magazine. Then I went back to the last setting that would and added 1/4 turn for cold weather insurance. Another “tell” it is right is when the brass ejects about 4:30 and lands consistently in the same area.
Not coincidentally, the setting ended up being right where most folks with this same setup also decided to stay. Message boards with people who have figured this out almost to a science are worth gold here.
If I leave the rifle out on a freezing night and shoot it the next morning I will know for sure it is spot on but if it were to malfunction due to a short stroke I’d know I need 1/8 turn more (rinse, repeat another night) until I am 100% satisfied.
One more comment, big ARs have a huge mass of the BCG/buffer and by tuning the gas so that this mass isn’t slamming the buffer into the back of the receiver extension (buffer tube) and bouncing hard back into battery….
You have less of the “chug chug” recoil common in the platform. This means it becomes easier to stay in the scope and on target/targets with less time between follow ups.
Frank explains it well in this video. Follow through is much more critical in this platform than boltguns and mitigating/slowing cycling to reliable but manageable level is key. Adding an even heavier buffer in an attempt to slow the bolt will have a negative effect on this recoil impulse by adding mass slamming home when chambering.
https://www.youtube.com/watch?v=1f_f-WNSxEM
If semi-auto is truly to be a force multiplier (and it is) then it’s main attribute must be preserved… fast followups.
Try the witt directional 3 piece comp. it does everything you want, and more.
Great post.
This platform does not come with an easy button. I waffled between the 224V, 6.5G and the Creedmoor for a good while. All of them need some tuning and all face their own issues.
The Grendel is really close to .308 performance in a small package but magazines seem to still be a sticking point along with bolt head issues. The bolt has very little meat left once machined for the large head of the Grendel.
The 224 Valkyrie has had an up and down life. Some rifles shoot lights out and some are disasters. The twist has been blamed and the new standard is 1:6.5 (the original 1:7 was not stabilizing 80g^ pills) but it still is having some inconsistency. When right though…woo boy!
In the end, the C won due to ammo literally being everywhere, match ammo being as cheap or cheaper than .308 and the stunning performance.