Great advice, thank you. I am working on slowly adjusting the gas block but seems to be very finicky etc. So if i get that tuned correctly you think that will take care of it or what else should i do?
6.5 Grendel
- Thread starter krhuntin
- Start date
Gas system controls the amount of gas that comes back which depending on the severity of the imbalance can usually cure any timing issues. Buffer weight then spring strength can alter when the brass starts to move out of the chamber. So if the gas system alone can't cure the timing then change buffer weight. If those combined don't fix it add a change in spring strength and those 3 combined can do anything you want lol. That procedure cured the timing problems on a 28" standard rifle length gas system lobbing 130s at 2500 fps. If it can fix that abomination (that rifle now wears the moniker "The Platypus") it can fix your issues.
The solid coppers are not known for speed or accuracy, just so you know. So don't expect those to match the accuracy or velocity of lead core match bullets of similar weight. Also they don't expand well at lower velocity. You may want to consider a different bullet. The combination of slow speed, lower bc, and higher velocity needed to mushroom can severely limit your effective range with those pills. Food for thought.
Lastly take the rifle apart and reassemble it. Make a note of any wiggle room any part that doesn't need to move has and try to eliminate it. Lapp your receiver face, bed the barrel extension, add shims to tighten gaps between upper and lower, ect... and get a good trigger. Stuff like that can make most ar15s shoot like a stud.
Curious, did you do load work-ups or pick a load and shoot it? There's a lot of maybes here and I'd hate to share a load openly that someone tries to plug n play... I've found grendel to be very forgive mg in accuracy dept. 1.5" groups at 100y being the worst of my load development on 3 rifles... Maybe something else is the issue? Can you give more information or detail on how you arrived at the loads you've tried?
Gas system has very little to do with accuracy, but functionality absolutely. My suggestion is to open it up, find a load that feeds well and shoots well, then adjust the gas system.
-Mac
No. I started at bottom charge weight for each and stopped at the top weight for each as they were getting hard on brass. I see a lot of people mention the 8208 xbr with 28.5. I didn’t go any higher after seeing my brass. But now I think I will try to tune my rifle first then worry about the accuracy.
A copper 120 is going to be much different than a jacketed lead 120. Load data won’t be comparable.
Ok, understood. It's a bit of balance between the two. The 6.5 grendel forum guys really are a mixed bag on 8208, as it reaches pressure quickly and can be very "peaky" so easy does it and that may explain some of your trouble with gas system adjustment.
Personally, I'll recommend that you find an accuracy load first and tune the cycling 2nd; simply because different powders have different pressure profiles / burn rates and ARs with a fixed length gas system would have different settings for different loads; i do think some others are on to something with polishing the lugs on the extension. Something no-one mentioned often is that an upper/lower/mag combo for ARs can have a tolerance stackup issue in presenting the bullet to the chamber. Combined with barrel extension machining sharp corners, and several issues can occur. Make up a few dummy rounds and cycle them from the mag to the chamber. You may find some deep scratches on the bullet / case neck from feeding which would certainly shorten your brass life and ruin accuracy.
I'm an old schooler on the grendel forum, I'd recommend H335 or BLC2 to get your rifle cycling. What primers are you using? CCI450 being my recommendation, certainly use what you got...
H335 would be a ~25gr-28gr load; BLC2 you'll be right about there too.
I enjoy 600y match shoots with 123 Sierra and Lapua brass, though for plinking I've become extra cheap on my grendel, I form 7.62x39 brass, load WC846, and shoot sub 130gr whatever's on sale... I'm shocked with how accurate and forgiving this cartridge is.
-Mac
Thank you for all the suggestions. Unfortunately I have never reloaded for an AR platform before. Been reloading for bolts for about 20 years. Starting to figure this AR out. H335 has always been my go to for the smaller calibers. The Grendel in my platform just hates it. Going to give the load a different tweak or two and go from there. Thanks.
Cool, and welcome to ARs. Lots of AR loading info here; so I'll make this suggestion. Hypothetically, if you turn your gas system all the way off, it's a straight pull bolt action rifle (with poor mechanical leverage). Accuracy obtained this way removes any of the feeding / cycling battering that can affect the system in secondary ways.
Method for tuning the gas system is empty magazine lock-back. From a reduced gas setting, open 1/4 at a time until a single round fired from a mag will lock back on the now empty mag reliably.
If you've too much gas, you'll see "case head swipe" which is the ejector plunger scribing an arc on the case head.
Change powders or charges significantly and you'll likely need to adjust the gas system. Typically not super finicky, there is typically a generate range of allowable and functional.
-Mac
DHD
Silver $$ Contributor
Lots of good information in this thread. Reloading for AR's can be challenging if you are only used to reloading for bolt guns as usual pressure signs can be from another issue not necessarily high pressure.
A good point made above is about "swipe" on case heads and AR's. My Grendel would show a swipe even when I knew I wasn't at a high pressure level. I probably saw it on the Grendel forum some years back about polishing and putting a radius on the ejector and this helped in my case. I will admit I have used bad language while removing and reinstalling ejectors at times. They do like to shoot out somewhere in the shop when you're not careful.
As I mentioned earlier, another trick I now use for all AR builds is to gently file/polish the locking lug recesses in the barrel extension and if necessary clip a coil or so off of the ejector spring while the ejector is out getting it's due diligence. As I kinda enjoy putting these things together, I also shim every barrel and use heat for a thermal fit, true/flatten the front of the upper, fuss over gas rod/gas key alignment, make sure my gas port and gas block align, use Young Manufacturing NM bolt carriers, and use a shim kit for upper/lower fit. It takes some time but it has at least made a difference for my toys. I have no idea which of the steps I do provide the most bang for the buck (bang for the effort actually) but it makes a difference for me. You could say I like to make it harder than necessary and you wouldn't be wrong...
If I had to I'd only use 2 powders. LeverRevolution for 120's and above and 8208 for everything below 120's. Primers are a study unto themselves most times but I have good luck with 450, 7 1/2, and my favorite for the Grendel at least, Wolf SRM (I have enough for a barrel or 2 but are no longer available).
AR's are a tinkerer's wet dream it seems.
In effect that's what we shoot in the UK. We have a whole genus of AR-15s (and a handful of 'big ARs') that have been built without gas systems and often with modified bolts minus gas rings with a sturdy side-handle bolted onto the carrier and a slot in the upper receiver side for its rearward travel. This is thanks to all semi-auto and pump-action rifles being banned here except those chambered for .22 rimfire cartridges since 1989.
A well-specced and built 223 'straight-pull' will shoot remarkably well, many capable of superb precision, and they can be fired accurately and very fast in Tactical, Civilian Service Rifle etc match disciplines by practised users.
The one downside is that you refer to - the absence of primary extraction camming in the design. Full CIP / 5.56mm Nato spec pressures (up to 62,000 psi) sees a hard tug needed to start the bolt moving. US SAAMI pressure rounds at under 55,000 psi PMax are easy/sweet operating in a good chamber. This has pretty well limited the genre to 223 and 6.8mm SPC. The Grendel and similar take so much effort that shooters struggle with them unless their pressures are so restricted that they lose their ballistic advantages over 223. I'm told that the 224 Valkyrie works better in them mechanically and improves ballistics, but few people have adopted it.
I'll be the odd ball; once I got past my fear of temperature sensitive powders, BLC2 is great in the Grendel, and I'm a cheapo, WC846 is great too. I do my load work-ups in the hot summer for safety, and check velocity for the winter. I have a huge temperature difference, and the shooter is still the biggest variance in my system.
I use a lot of 8208 in a straight 6 Grendel with 80's. It's been my go to powder for that cartridge for a few years. The current shortages have me looking and testing available alternatives. There are several but 8208 is still my favorite.
I have used Win 748, H335 and Power Pro Varmint with 120 SMKs, 120 Match Burners, 123 SSTs and 123 Scenars. All out of an AR platform. I could not get the SSTs to shoot. The best load for the match burners and SMKs was with Varmint loaded hot. About 1/2 to 5/8 MOA. I only used H335s with the Scenars and had about the same results; however, I shot it recently and could not duplicate the results.
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