SD Expectations between BA and AR-10

rustyinbend

rustyinbend

GySgt USMC 1976-1992
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Minuteman
    • Dec 9, 2018
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    Bend, Oregon
    #1
    I have my Tikka 6.5-CM tuned to SD's of about 5.5 and nice tight groups. Declared victory on that reference load. I also shoot a LWRCI REPR MK2 Elite ... a VERY nice AR-10 in 6.5-CM ... and I've tuned it to SD's in the 14-to-15-ish range (and really tight groups) without a great deal of effort. Here's my question ... for those of you that shoot 6.5-CM AR-10 form-factors and handload for those ... Are SD's of 15-ish "good enough", or should I keep working this expecting load refinement to drive it down? Asked differently ... should I "expect" higher SD's in an AR-10 from those I get in a bolt action of the same caliber, just because of the variability of a BCG vs. a stand-alone levered bolt? Thoughts please ...
     
    #2
    What are your requirements?

    Generally, 10-15 for an SD over at least 30 round sample of your load is fine for practical shooting applications (you already mentioned it groups to your satisfaction). Dont get wrapped around the axle, burning components chasing single digit SDs.

    If your numbers are from 5-10 shots id take it to distance, gathering your drop data over 30-40 rounds.

    Sounds like a solid set up.
     
    #3
    nn8734 said:
    What are your requirements?

    Generally, 10-15 for an SD over at least 30 round sample of your load is fine for practical shooting applications (you already mentioned it groups to your satisfaction). Dont get wrapped around the axle, burning components chasing single digit SDs.

    If your numbers are from 5-10 shots id take it to distance, gathering your drop data over 30-40 rounds.

    Sounds like a solid set up.
    Click to expand...
    That's kind of what I was thinking. I shoot this rifle primarily in the monthly gas-gun competitions at my local range, and even with factory ammo ... it's usually the most accurate gas-gun on the firing line. Taking this load to 1,000 yards and tuning BC at this point, is probably the way to go. Still ... I'm so used to chasing single-digit SD's as one of the challenge/fun aspects of this hobby, is always on my to-do-list. Need to relax, declare victory, and just go shoot the damn thing.

    Reminds me of another story ... I spent a decade totally tricking out my 2001 Heritage Softail Classic, and went to my Harley guy and asked "What do we do next?". His response was "Wash it and ride it." Haven't changed a thing since 2010 and it's still the prettiest bike at the coffee shop.

    Need to get better at learning when to "stop". LOL

    1643651273111.png
     
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    #8
    And... there better be more pictures of the bike at the end of the range report....

    SDs in the range of 15 are typical of a good AR-10 or AR-15 platform for target work. It means you are doing very good loading work as well as using a good rig.

    A good AR platform with good loads can shoot a clean score on the Service Rifle targets and I'm guessing yours would probably do it with a high X count. Remember, the F-Class targets are half the size in the 10 and X ring, so we just don't see many folks trying to run the gas guns in those games (or many folks trying to run their bolt guns in the XTC games). At a typical Mid Range club match, folks running their AR must single feed, so they run a long round, typically something like an SMK 80.

    Since the vast number of Service Rifle rigs in the last 20 years are typically AR-15 in 223, the 600 yard line is a pretty good statistical background for what an AR platform can do when in the hands of the MA and HM folks. These days, the majority of those shooting XTC will load longer than mag length for the 600 yard line, but there are still a few folks shooting the same mag length ammo at 600 that they use at 200, 300, who can shoot in the top of the pack.

    There was a time when The Wooden Guns were used, so the historical 30-06 in Garands and the 308 in the M-14, were also vary carefully prepped guns and rounds. Again, an SD in the range of 15 was considered good back then, and you occasionally saw values lower for their 600 yard loads. I had an Oehler 35P back in those days, so I chronographed loads for club mates all the time.

    Only a few guys would shut off the gas system that I can recall, but I also recall there was enough difference in the results they would have to tune the load to that condition. There were many HM and DR folks who didn't shut off their gas that I never bothered to track the differences. I would guess you will see differences with the gas shut off, but can't guess if that will be better or worse unless the load is tuned for this condition.

    It will be interesting to hear how your rig compares with the gas shut off, and even better if you post more bike photos.... Good Luck.
     
    #9
    RegionRat said:
    And... there better be more pictures of the bike at the end of the range report....

    SDs in the range of 15 are typical of a good AR-10 or AR-15 platform for target work. It means you are doing very good loading work as well as using a good rig.

    A good AR platform with good loads can shoot a clean score on the Service Rifle targets and I'm guessing yours would probably do it with a high X count. Remember, the F-Class targets are half the size in the 10 and X ring, so we just don't see many folks trying to run the gas guns in those games (or many folks trying to run their bolt guns in the XTC games). At a typical Mid Range club match, folks running their AR must single feed, so they run a long round, typically something like an SMK 80.

    Since the vast number of Service Rifle rigs in the last 20 years are typically AR-15 in 223, the 600 yard line is a pretty good statistical background for what an AR platform can do when in the hands of the MA and HM folks. These days, the majority of those shooting XTC will load longer than mag length for the 600 yard line, but there are still a few folks shooting the same mag length ammo at 600 that they use at 200, 300, who can shoot in the top of the pack.

    There was a time when The Wooden Guns were used, so the historical 30-06 in Garands and the 308 in the M-14, were also vary carefully prepped guns and rounds. Again, an SD in the range of 15 was considered good back then, and you occasionally saw values lower for their 600 yard loads. I had an Oehler 35P back in those days, so I chronographed loads for club mates all the time.

    Only a few guys would shut off the gas system that I can recall, but I also recall there was enough difference in the results they would have to tune the load to that condition. There were many HM and DR folks who didn't shut off their gas that I never bothered to track the differences. I would guess you will see differences with the gas shut off, but can't guess if that will be better or worse unless the load is tuned for this condition.

    It will be interesting to hear how your rig compares with the gas shut off, and even better if you post more bike photos.... Good Luck.
    Click to expand...
    Wow ... great data and historical context. Our gas-gun matches aren't anywhere near that formal. They're distances from 200-to-900 yards, and it's all steel tactical targets (IPSEC, Peepers, Movers, etc.) and a hit is a hit, a miss is a miss. The "movers" they have on rails at 400, 600, and 800 are challenging. It's a lot of fun, mostly just competing against yourself, but they totalize and keep score of hits and misses. I've learned that coming to this match with my LWRCI REPR MKII Elite (6.5-CM) ... is almost not fair when most of the guys are shooting 223's, Grendal's, Valkyrie's and the like. That said, I can live with "unfair" since I'm old, I have crappy eyesight (complete with floaters), and my mild Parkinson's isn't helpful once the meds wear off.

    One thing hampering small SD's is that I load to the max mag length, which is a big jump to the lands. I'm just not a "single-shot" kind of guy.

    Will report back with no-gas SD ... just doing it for fun, but really interested in the result.

    And in the meantime, since you asked, here's another "Hog-Shot" taken from the exhaust side ... sporting a matching Corbin flaming saddle. And "yes" ... the pipes are Vance & Hines Long-Shots. Virtually no baffles - super loud. I love driving through supermarket parking lots and setting off the car alarms. (Yup, I'm that kind of guy.)

    1643747830780.png
     
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    #12
    I dont recall ever having much difficulty getting a single digit SD load. I've been running gas guns in PRS since 2014. Only sporadically lately, but since no one even picked up the Gas Gun trophy at the NW Regional Finale last year, I've cracked out my 6.5 Creed to make sure that doesn't happen again in 2022. Just having fun at the Regional level this year. Seems like a nice gasser is the perfect way to do that..

    My current load with 140gr Matchburners and 41.8grs H4350 is a 6 to 7 SD spread out over about 22 to 25 rounds if I recall.

    It's certainly doable.
     
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    #13
    RegionRat said:
    @Jefe's Dope
    Yes, that FGMM M2 is magic in some guns.

    What chamber/bbl are you running?

    With that bullet at 2530, the rig should do well for at least 800 yards and sometimes more. What kind of elevation waterline does your rig hold?
    Click to expand...
    Whatever chamber PSA uses. I haven't really had a chance to really shoot it. I took it out to 700 yards at Pawnee last year but it was super windy, like 25 mph constant and some huge gusts. Once dialed, it had no issues. But I wasn't able to really see how good. The pic above is from Sunday when I was getting sighted in for a 200 yard match. So, no real distance. I was having issues with it over gassing too. I'm still dialing it all in. Looking for an adjustable gas block as we speak. And some more of that ammo. I just sold my .308 dies too.
     
    #15
    OK Gang ... I have DATA !!!

    A great suggestion was to shoot some identical cartridges (a) with a couple of different bullets, and (b) with, and without "gas" ... to see if my 6.5-CM AR-10 reacted differently with (1) a different projectile, and (2) running single-shot vs semi-automatic ... basically take gas-driven bolt action out of the equation. The results are VERY Interesting (10-shot measurements of each configuration) ...

    First ... Berger 140's with "NO GAS" (single shot)
    • Average: 2610
    • SD: 20.45
    • ES: 54
    Second ... Hornady 147's with "NO GAS" (single shot)
    • Average: 2649
    • SD: 10.29
    • ES: 29
    Third ... Berger 140's with "GAS" (semi-auto)
    • Average: 2650
    • SD: 22.94
    • ES: 68
    Fourth ... Hornady 147's with "GAS" (semi-auto)
    • Average: 2632
    • SD: 15.52
    • ES: 42
    So here are my findings from this exercise ...
    1. The Hornady configurations tended to group slightly tighter than the Bergers (sorry ... didn't keep the targets), but they were both acceptable.
    2. The "NO GAS" configurations delivered smaller SD's than the Semi-Auto configurations.
    3. The "NO GAS" Hornady configuration approached single-digit SD's (10.29) ... none of the others came close
    So to the burning question ... Will an AR-10, all other things being equal, with the gas shut off (single shot) deliver better Standard Deviations than the same configuration running in semi-automatic mode?

    The answer is ... "YES" ... you will get lower SD's with the gas "off", extrapolated further ... meaning you can expect that your bolt-action rifle will naturally be more accurate and consistent than the semi-automatic version of the same caliber.

    Did anyone else find this interesting? I hope so.

    In God We Trust ... all others - BRING DATA.
     
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    #16
    rustyinbend said:
    OK Gang ... I have DATA !!!

    A great suggestion was to shoot some identical cartridges (a) with a couple of different bullets, and (b) with, and without "gas" ... to see if my 6.5-CM AR-10 reacted differently with (1) a different projectile, and (2) running single-shot vs semi-automatic ... basically take gas-driven bolt action out of the equation. The results are VERY Interesting (10-shot measurements of each configuration) ...

    First ... Berger 140's with "NO GAS" (single shot)
    • Average: 2610
    • SD: 20.45
    • ES: 54
    Second ... Hornady 147's with "NO GAS" (single shot)
    • Average: 2649
    • SD: 10.29
    • ES: 29
    Third ... Berger 140's with "GAS" (semi-auto)
    • Average: 2650
    • SD: 22.94
    • ES: 68
    Fourth ... Hornady 147's with "GAS" (semi-auto)
    • Average: 2632
    • SD: 15.52
    • ES: 42
    So here are my findings from this exercise ...
    1. The Hornady configurations tended to group slightly tighter than the Bergers (sorry ... didn't keep the targets), but they were both acceptable.
    2. The "NO GAS" configurations delivered smaller SD's than the Semi-Auto configurations.
    3. The "NO GAS" Hornady configuration approached single-digit SD's (10.29) ... none of the others came close
    So to the burning question ... Will an AR-10, all other things being equal, with the gas shut off (single shot) deliver better Standard Deviations than the same configuration running in semi-automatic mode?

    The answer is ... "YES" ... you will get lower SD's with the gas "off", extrapolated further ... meaning you can expect that your bolt-action rifle will naturally be more accurate and consistent than the semi-automatic version of the same caliber.

    Did anyone else find this interesting? I hope so.

    In God We Trust ... all others - BRING DATA.
    Click to expand...
    10 rounds per test group is insufficient to draw the kinds of conclusions you are drawing. Your OP mentions getting 14-15 SD presumably with the gas on. That’s immaterially different than those above test groups w/gas off. Besides, you don’t plan on running that thing gasless do you?
     
    #18
    nn8734 said:
    10 rounds per test group is insufficient to draw the kinds of conclusions you are drawing. Your OP mentions getting 14-15 SD presumably with the gas on. That’s immaterially different than those above test groups w/gas off. Besides, you don’t plan on running that thing gasless do you?
    Click to expand...

    No it isn't. AR10s (all gas operated rifles do for that matter) begin to unlock under pressure. If they're beginning to unlock under pressure then they are changing the combustion characteristics between gas and no gas. Rusty measured a velocity difference because the gas system bleeds pressure during the dwell time. Whether or not the difference matters is debatable, the difference does exist though.
     
    #19
    The original question was "mine" (I'm the OP) ... just looking for advice on if that 15-ish SD was expected and good enough on an AR-10 caliber when I have a bolt gun delivering much better SD's. Got some interesting questions and suggestions, and thought a test would be fun.

    The participants were interested in me sharing the data ... so I did.

    Guys ... lighten up. It was just a fun sunny day "I'm retired so I can" range exercise.
     
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    #20
    rustyinbend said:
    The original question was "mine" (I'm the OP) ... just looking for advice on if that 15-ish SD was expected and good enough on an AR-10 caliber when I have a bolt gun delivering much better SD's. Got some interesting questions and suggestions, and thought a test would be fun.

    The participants were interested in me sharing the data ... so I did.

    Guys ... lighten up. It was just a fun sunny day "I'm retired so I can" range exercise.
    Click to expand...
    What I would take away from your test Rusty, is that you need to continue load development with an operating gas system. A 20 and 22 SD while operating the bolt is a horrible load.

    I've been running precision 308 and 6.5 gas guns since 2010. I cant recall ever having trouble getting single digit SDs. Even 8 and 10 years ago before all of this new technology hit the market and made it so much easier.

    Just keep plunking away, you'll find it.
     
    #21
    Cascade Hemi said:
    No it isn't. AR10s (all gas operated rifles do for that matter) begin to unlock under pressure. If they're beginning to unlock under pressure then they are changing the combustion characteristics between gas and no gas. Rusty measured a velocity difference because the gas system bleeds pressure during the dwell time. Whether or not the difference matters is debatable, the difference does exist though.
    Click to expand...
    It’s irrelevant unless he plans on running it gasless.

    That said, real world difference (hit probability variation between gas vs no gas at all ranges to transonic, all other things equal) is likely to be non existent once you factor in or out shooter, wind compensation, production consistency (headspace, “neck tension/interference fit, seating depth, yada yada).

    He needs at least minimum of 30 per each test sample (gas vs gasless) to make any inferences about the consistency of his rounds. For all we know, those samples may have significantly better consistency than his limited data shows or they are markedly worse. All the test samples ive tested over the years, SD seems to peak between 10-15 rounds and starts coming back down once at least 20 rounds are fired.
     
    #22
    rustyinbend said:
    The original question was "mine" (I'm the OP) ... just looking for advice on if that 15-ish SD was expected and good enough on an AR-10 caliber when I have a bolt gun delivering much better SD's. Got some interesting questions and suggestions, and thought a test would be fun.

    The participants were interested in me sharing the data ... so I did.

    Guys ... lighten up. It was just a fun sunny day "I'm retired so I can" range exercise.
    Click to expand...

    0 SD > Your Loads
     
    #23
    Birddog6424 said:
    What I would take away from your test Rusty, is that you need to continue load development with an operating gas system. A 20 and 22 SD while operating the bolt is a horrible load.

    I've been running precision 308 and 6.5 gas guns since 2010. I cant recall ever having trouble getting single digit SDs. Even 8 and 10 years ago before all of this new technology hit the market and made it so much easier.

    Just keep plunking away, you'll find it.
    Click to expand...
    Interesting ... well ... I get consistent single-digit SD's with my variety of bolt guns in 6.5-CM, 300-WM, 300-PRC, and 338-LM ... so I know I'm capable of quality load development in bolt action rifles. It's this 6.5-CM AR-10 that's kicking my ass ... the closest I can get is 15-ish. I'm not giving up (yet) ... just trying to decide if sub-MOA groups and clean hits at 1,200 yards with 15-ish SD's is a place I should stop and declare victory. Still pondering that one. I did find it interesting that with all other things being equal, the SD's were consistently lower with the gas shut off.
     
    #24
    rustyinbend said:
    Interesting ... well ... I get consistent single-digit SD's with my variety of bolt guns in 6.5-CM, 300-WM, 300-PRC, and 338-LM ... so I know I'm capable of quality load development in bolt action rifles. It's this 6.5-CM AR-10 that's kicking my ass ... the closest I can get is 15-ish. I'm not giving up (yet) ... just trying to decide if sub-MOA groups and clean hits at 1,200 yards with 15-ish SD's is a place I should stop and declare victory. Still pondering that one. I did find it interesting that with all other things being equal, the SD's were consistently lower with the gas shut off.
    Click to expand...

    Not all bullet and powder combinations produce the same results in all rifles. Let me know if there is another combination you want to try that you don't have. I probably have every common powder on the market in my cabinet and I'd be happy to give you whatever you want to try.
     
    #25
    rustyinbend said:
    The original question was "mine" (I'm the OP) ... just looking for advice on if that 15-ish SD was expected and good enough on an AR-10 caliber when I have a bolt gun delivering much better SD's. Got some interesting questions and suggestions, and thought a test would be fun.

    The participants were interested in me sharing the data ... so I did.

    Guys ... lighten up. It was just a fun sunny day "I'm retired so I can" range exercise.
    Click to expand...
    Thought that would be about what you would see. Fun experiment and thanks for sharing.
     
    #26
    rustyinbend said:
    Interesting ... well ... I get consistent single-digit SD's with my variety of bolt guns in 6.5-CM, 300-WM, 300-PRC, and 338-LM ... so I know I'm capable of quality load development in bolt action rifles. It's this 6.5-CM AR-10 that's kicking my ass ... the closest I can get is 15-ish. I'm not giving up (yet) ... just trying to decide if sub-MOA groups and clean hits at 1,200 yards with 15-ish SD's is a place I should stop and declare victory. Still pondering that one. I did find it interesting that with all other things being equal, the SD's were consistently lower with the gas shut off.
    Click to expand...
    Try using a #34 primer in it. I think you will see an improvement. I've gone totally to them in my AR-10s.
     
    #27
    Cascade Hemi said:
    Not all bullet and powder combinations produce the same results in all rifles. Let me know if there is another combination you want to try that you don't have. I probably have every common powder on the market in my cabinet and I'd be happy to give you whatever you want to try.
    Click to expand...
    Only one I haven't tried is my 4350 ... that's probably next. What's your 4350 recipe for 6.5-CM AR-10 loads using Hornady 147 ELDM's and/or Berger 140's?
     
    #29
    Birddog6424 said:
    I dont recall ever having much difficulty getting a single digit SD load. I've been running gas guns in PRS since 2014. Only sporadically lately, but since no one even picked up the Gas Gun trophy at the NW Regional Finale last year, I've cracked out my 6.5 Creed to make sure that doesn't happen again in 2022. Just having fun at the Regional level this year. Seems like a nice gasser is the perfect way to do that..

    My current load with 140gr Matchburners and 41.8grs H4350 is a 6 to 7 SD spread out over about 22 to 25 rounds if I recall.

    It's certainly doable.
    Click to expand...
    Nooooooo. I want to be the only one.

    Funny. I had the same thought. Typically only a few gassers if any at local matches. I can be competitive in a field of 1.
     
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    #34
    2aBaCa said:
    Yeah, just moved to Meridian. Looking at shooting my 1st with a gasser at Parma on the19th. Kept an eye on matches last year and noticed a lack of gas gun shooters.
    Click to expand...
    Haha, what a small world moment 🤣

    I'll be the Match Director at the Parma match! My name is Ja, I live in west Boise, look me up and say hello.

    Honestly, if I see a guy or two competing in Gas Gun with plans on going to the Regional Finale at the Lead Farm in August in hopes of taking home the trophy, I'll bow out. I'm the PRS Northwest Regional Director this year, so I'm focusing on making sure everyone else has a good time. I'm only running gasser because I refuse to see the trophy go to waste. I won't stand in anyone's way of winning a division.
     
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    #35
    Birddog6424 said:
    Honestly, if I see a guy or two competing in Gas Gun with plans on going to the Regional Finale at the Lead Farm in August in hopes of taking home the trophy, I'll bow out. I'm the PRS Northwest Regional Director this year, so I'm focusing on making sure everyone else has a good time. I'm only running gasser because I refuse to see the trophy go to waste. I won't stand in anyone's way of winning a division.
    Click to expand...
    No Mercy GIFs - Get the best GIF on GIPHY
     
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    #37
    UPDATE ... I tried a few of the suggestions here. Tweaking a few things has gotten me to an Average of 2639, and a SD of 11.2 ... and nice tight groups. For my AR-10 in 6.5 Creedmoor, I feel like that's "good enough" considering my SD's started in the 20's. I'm declaring victory. Thanks Guys. For anyone that cares ... my "Reference Load" record is below:

    1645281088967.png
     
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    #40
    rustyinbend said:
    It's a combination of case, bullet, powder, and measurements ... that is my "personal best" that I'll use for competition. If I want to load my very best, I go to my "Reference Load" (which I track on a spreadsheet), and build cartridges to that specification.
    Click to expand...
    What barrel? How did you arrive at the the 43.2gr mark?
     
    #41
    2aBaCa said:
    What barrel? How did you arrive at the the 43.2gr mark?
    Click to expand...
    22" Proof Research carbon fiber barrel on my LWRCI REPR MKII Elite. Arrived at the 43.2gr through starting low, testing up until pressure signs (mostly cratered primers), backing down, and then ladder testing to find a velocity node. 43.2gr gave me the most consistent velocity with speeds above 2600, no pressure signs, and acceptable groups.
     
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    #42
    rustyinbend said:
    22" Proof Research carbon fiber barrel on my LWRCI REPR MKII Elite. Arrived at the 43.2gr through starting low, testing up until pressure signs (mostly cratered primers), backing down, and then ladder testing to find a velocity node. 43.2gr gave me the most consistent velocity with speeds above 2600, no pressure signs, and acceptable groups.
    Click to expand...

    Is that with the 147s?
     
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