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Old 10-11-2021, 10:06 PM
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6.5 Creedmoor AR-10 Accurate Only With Hot Loads



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Finally got me some 140gr SMKs and loaded up some Federal match primers and StaBall underneath them. Starting load, which ended up matching factory Hornady Eld-M for velocity, gave me a 1 5/8" group at 100 yds. No pressure signs. Next load in the ladder showed 40% just-starting-to-flatten primers, no swipes, and group went to 3/4". Next step, similar (60%?, no swipes) primers, 2709 average velocity, 1/2" group with a called flier.

Similar results with Eld-Ms and 4350, but pressure signs sooner at lower velocity.

A: StaBall is supposed to be consistent but slow (rings true with Eld M, but the SMKs are moving fast)

B: Keep shooting them and quit worrying about it, or start looking for another solution? Rifle is made of good parts, 9310 bolt in a Proof barrel.

All loads are within Winchester published limits. I stopped about a grain shy of their max.
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Old 10-12-2021, 10:29 PM
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What twist rate is your barrel? Thinking it might be 1:10... if so, pushing the 140's faster is necessary to stabilize them and dropping to 129grn pills may cure your problem, without running full house loads. I've used 123grn Sierra MK's in slow barrels with great results...

Last edited by Chickenhater; 10-12-2021 at 10:33 PM.
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Old 10-13-2021, 10:16 AM
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It's 1:8
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Old 10-13-2021, 11:55 AM
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Try some different powders and see if that helps. If you're flattening primers you are already on the ragged edge, regardless of what the book says about "max loads".... Also, a lot of ARs require you to seat the bullets deeper than bolt rifles to fit the magazine. This alone can push up pressures a bit, along with a host of other issues.

Bob
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Old 10-13-2021, 02:22 PM
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I've tried a couple of RLs (16 and 17 maybe?) and 4350, they work fine but my ES numbers are high, like in the 70s sometimes. StaBall is the first that's given me ES numbers in the teens and SDs in single digits. My COAL is 2.810, longest I can get to fit in Pmags with a hair to spare. I feel like I have a lot more bullet out of the case than with the ELD M, but I haven't measured them against each other.
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Old 10-13-2021, 03:03 PM
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ES numbers don't always equal better accuracy. Working up loads to me is finding the most accurate loads and that usually means finding a powder charge and that is close to optimum for the cartridge and rifle, adjusting my seating depth to the throat- usually about .005" off the lands if the mag length allows, then adjusting as I need to with minor adjustments to both. I have always completely ignored ES numbers over the years and yet still have some very accurate rifles.

Sometimes a change in bullets is called for. I have rifles that shoot Nosler partitions fairly well, but change to a Nosler Ballistic Tip hunting bullet in same weight and the groups shrink to cloverleafs. Others are just the opposite. I have had up and down results from SMK's and ELDM's in my experiments with them. Same with Barnes- but my buddies shoot bugholes with them.. go figure..

Each rifle will like a different bullet/load/etc... so you have to find what it likes IMO... If you're at max loads and not finding the accuracy you need, time to change some component in the process... Also, don't ignore your brass prep, sorting, and seating technique...

Sometimes it all just comes together by accident like it did in my 22-250 and Varget powder... from a good 3/4" shooter with everything I tried to an honest .2"-.3" shooter with Varget and 40 grain ballistic tips....

Bob
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Old 10-13-2021, 07:27 PM
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I too have an AR-10 (actually DPMS style), in .308 Win.

It shoots very well, but I occasionally get slightly flattened primers, even though I'm not near max loads. From what I remember reading somewhere, the AR-10 has a different pressure curve, than a bolt gun, and loads that are fine in a bolt gun, will flatten primers occasionally. In fact, a number of people recommend a smaller diameter firing pin bolt hole, that uses a different type of bolt assembly.

It might be made by JP enterprises, but I don't remember.... I do know that some shooters of 6.5 Creedmoor, using an AR-10 platform, recommend using the smaller diameter hole bolt.

https://www.rainierarms.com/jp-enter...t/#description

This below gives a better idea, of what i was trying to articulate:

https://jprifles.com/1.4.7_Bolt.php

Click on high pressure bolts.

Last edited by Flintlock28; 10-13-2021 at 07:33 PM.
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Old 10-13-2021, 08:19 PM
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Bob, one issue I've got during these times is availability. It took me a year to find those SMKs and I had to buy 500 of them to try out 20. I'm down to about 50 ELDs, powder is running low and I think I've got 75 of the Federal primers left. Plenty of BR-2s if needs be though. I'm also of the understanding that a big ES and SD will lead to serious vertical strings at 1000 yds, which is my goal with this rifle. I've had an ES over 100 shoot incredibly at 100yds, but there's not much bullet drop happening at that range. Maybe I can try backing down from that 2709 load .1 at a time and see if I can shake the flat primers and still hold the accuracy.

Flint, that's the bolt I'm using. I read the same thing about the two firing pins, so I figured since I was spending a mortgage payment on a Proof barrel, might as well match it to the JP bolt. Matter of fact, Proof pretty much demanded that I use that bolt, they said they headspace off of them specifically.
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Old 10-13-2021, 09:16 PM
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Well 1:8 is certainly fast enough for the heavier bullets, up to 147grn anyway. I've loaded 140's and found them difficult to tune in my Remington, Sako and DPMS actions. I could get decent groups out of them with a lot of extra work, but even then they wouldn't match the 142 MK's. Why? I cant say, but I'm not alone in this, several other of my silhouette shooting friends have expressed the same difficulties, with 120 and 140 MK's. 123's and 142's MK's have been an easy go to with 44 grns of 4831sc with fed 210gm or cci200's, nice tight groups, no problem. 123's with 38.5 grns of RL15 is another solid performer. Let us know how you progress with this issue. These are 260 rem loads.... but friends with 6.5 creedmore chamberings have had similar results.

Last edited by Chickenhater; 10-13-2021 at 10:07 PM.
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Old 10-13-2021, 10:18 PM
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I was going to suggest a slightly slower powder like H4831SC or similar to see if that will help. Changing components can be a tedious process, but can yield huge results at times. Start with one component at a time like powder, bullets, primers, etc... and work up as though you are starting over each time. You certainly have enough bullets to get there....

I know how hard components are to find right now. I'm in the same boat as I reload for myself and my son and brother. Hopefully I have enough ammo reloaded now after workup to last me until this dry spell is over... just about out of H4831 though.... which is my go to powder for almost everything except for varmint loads and my overbore 26 Nosler....

Eventually you will find the load you are looking for, but it may take some time- or it may be your next load... You certainly have the right AR components for it...

Bob
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