Fine Tuning the AR-10T

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14 years 6 months ago #4338 by Laughing Elk
Fine Tuning the AR-10T was created by Laughing Elk
I have been a member of this forum for a couple of years now and have learned a lot about the AR-10 platform. Most everyone here realizes what a great resource this website is. To those Subject Matter Experts (SME's) who consistently come here and share their knowledge and expertise, I want to say THANK YOU!

I've had some work done by MMSSHH and have been really happy with the results. The work included squaring the action, re-crowning the factory muzzle, installing a gas screw to regulate pressure, and a couple other minor adjustments.

I thought I share a load and group from yesterday's trip to the range. Three shots at 100 yards, 0.260". The load information is as follows:
43 grains Varget
Lapua Brass (once fired)
Bullet seated out to practical limits of mag (2.855"). Freebore measured at around 0.030"
Hornady Match 168 grain BTHP
CCI BR2 Match primers

Ambient temp was approaching 100 degrees F. Standard Deviation for the three shots was 5. Average Velocity was 2559 fps and about a minute between shots. Cartridges were single loaded.

I've been talking with MMSSHH regarding case prep and the variance between single loading cartridges and cartridge loading through the magazine. I am seeing groups go up about 1" to 1.5" when going from one to the other (respectively). I'm approaching it as a friction problem - not enough neck friction to keep the bullet from seating deeper into the case cavity, etc. I use Redding Type S dies with interchangeable neck bushings. Today I ordered a couple more bushings with one- and two-fewer thousands than the bushing I am presently using. This will hopefully choke down the brass a bit more and increase the friction of the neck on the bullet. Hopefully this will correct the issue and maintain accuracy. Has anyone else overcome this problem and what did you do to correct it? Anything else you can suggest would be appreciated.


Laughing Elk

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14 years 6 months ago #4341 by BUILDING MY SASS
Replied by BUILDING MY SASS on topic Re:Fine Tuning the AR-10T
Thanks for the posting LE...I too have learned alot about the rifle...and from MSH...and from a few others....
I too need to get back out and do some testing...even if mine is just stock...
I always seem to be busy... :dry:

Thanks again for the report.... B)
BMS

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14 years 6 months ago #4347 by Laughing Elk
Replied by Laughing Elk on topic Re:Fine Tuning the AR-10T
I guess there are darn few of us out there who couldn't use some more time or practice. Considering the demands on our time in our current economy it's tough to keep the bench stocked with reloading components, put in time at the range and keep memberships in all the various deserving and necessary organizations that need our support.

MSH has also suggested I check my set-up on the bench and make sure I'm not rushing my shots. He sent along an article on the subject of sandbags, fliers and vertical stringing in general. It's a good reminder on technique and I'll be checking myself on my next trip out to the range.

Anyway, take care and thanks.
Elk

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14 years 6 months ago #4366 by BUILDING MY SASS
Replied by BUILDING MY SASS on topic Re:Fine Tuning the AR-10T
Keep up the reports.....look forward to more info... ;)
BMS

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14 years 5 months ago #4506 by Laughing Elk
Replied by Laughing Elk on topic Re:Fine Tuning the AR-10T
It was an interesting day at the range today. I took the best 3-shot load from my last outing and used it as a baseline for this series of loads. I wanted to see what the group differentials would be on (Load 1) single loading without crimping, (Load 2) magazine feeding without crimping, (Load 3) magazine feeding with light crimping,(Load 4) magazine loading with heavy crimping.

A couple of qualifiers: 1. my electronic scale was dropped accidently about 2' between my last loading and this one. I use a My Weigh Gempro 250 which measures down to .01 grains +-.02, it seeems to have survived the drop alright, but took a while to settle down when I first set-up for reloading these rounds. All loadsd are measured individually on an anti-static mat properly grounded. Regardless, I may yet send it in to be checked as I am not 100% comfortable with its accuracy as you will see from the Standard deviations from the loads. 2. We had quite a bit of wind today. Seemed to be about 10 mph gusting up to 20 mph. Wind direction was variable coming from my 6 o'clock or quartering from my 8 o'clock. Temperature hovered around 90 degrees F. Rifle was cold and clean to start. Two fouling rounds were used to start. Groups were fired with 1 minute between rounds and 10 minutes between groups.

The loads are as follows:
- Lapua Brass .308 Win, New and unfired, Not sorted by weight but same lot, Full length resized
- CCI BR2 Large Rifle Match Primers
- 43 grains of Varget Powder
- 168 grain Hornady BTHP Match bullets (No Cannelure)
- cartridges measured on ogive to give matching OOL (On Ogive Length) using a stoney point gauge, but Overall Cartridge Length (OACL) was limited by box magazine length.
- Redding Reloading Type S dies were used. A .334 bushing was used along with a Redding free floating carbine sizing button to increase neck tension. This bushing was used to help increase neck tension; but may tweek some more to see if it can be crimped using a larger bushing so I am not 'overworking' the brass.
- A Lee Factory Crimp Die in .308 Win was used to crimp cartridges. Lee recommends a half turn after seating bullets; however for the light crimp a 3/8 turn was used and a 1/2 turn was used for the heavy crimp. Length was measured between case head and shoulder prior to and after application of crimp. No significant change was recorded (shoulder bulge was <.001" in all cases)

The load was chosen due to the low standard deviation of the three shot group from the previous test as well as the (smallest) group size. Today's loads were shot holding bullseye. Shots were measured at longest edge to edge and then subtracting .308 from the measurement. Subgroups are reported where there are a minimum of four shots grouped together with one 'flier' for the fifth round. Todays test results were as follows:

Load 1 (Single Loaded, No Crimp) - Average Velocity 2512 with Standard deviation 38, groups size = 1.014 with a subgroup size of 0.584
Load 2 (Magazine Loaded, No Crimp) - Average Velocity 2497 with standard deviation of 14
Load 3 (Magazine Loaded Light Crimp) = Average Velocity of 2505 with a standard deviation of 23, group size = 0.865
Load 4 (Magazine Loaded, Heavy Crimp) = Average Velocity of 2509 with standard deviation of 23, group size = 1.355 with a subgroup size of 0.584"

RESULTS
I am not happy with the standard deviations I achieved and am concerned that my scale my not be at 100 %. The groups were okay and Load three had the smallest group and no fliers, but substantially larger in size from what I achieved the last time at the range. I should definitely be happy because my rifle is shooing MOA or Sub MOA groups. I will likely reload and return to the range with at least two of the loads above. Between the third and fourth group, I adjusted the scope about 3/4". The first round of the 4th group was a flier about 3/4" out and the remainders all landed inside a half an inch. My suspicion is that the scope settled in with the first shot after adjustment. Regardless, crimping did appear to help the grouping. I will have to repeat this to confirm.
Thanks
Elk

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14 years 5 months ago #4508 by a Guest
Replied by a Guest on topic Re:Fine Tuning the AR-10T
Elk the barrels dont settle down until they get a 100 rounds through them and a Lilja takes up to 300 rounds. Keep that thought on any barrel they are like race engines. I don't even try to collect any data until then.MSH

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14 years 5 months ago #4511 by Laughing Elk
Replied by Laughing Elk on topic Re:Fine Tuning the AR-10T
You're right, MSH. I had forgotten and should have remembered. Guess I got ahead of myself and a bit excited to boot. I did learn quite a bit in the process and am really enjoying the platform.

Thanks
Elk.

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