AR Testing / Changes in Accuracy Using a MagnetoSpeed Chronograph

I did a little horse trading this past week and have another rifle on the way (which will be named later.)  To put my Sightron S-Tac on it, I will need an AR height mount.  I ordered a AR-Stoner Extended 1 Piece 30mm Cantilever Scope Mount from MidWayUSA for $49.  I decided to go ahead and mount my scope in it so it will be ready when the new rifle comes in next week.  With everything leveled up, I thought why not mount it on my AR-15.  The 20x Sightron is a HUGE upgrade from the 3-9 Bushnell.  So that catches you up to today’s outing.

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So most of my 223 rounds I shoot both through my AR and my 223 Savage Axis.  When I size my brass, I am not quite full length sizing it.  I am bumping the shoulder, but more than a few thousandths.  It is just enough that I have no cycling issues in the AR.  Most of the rounds were developed for the Axis, but shoot okay through the AR.  Today I wanted to test out my ammo with the good scope on it and with the MagnetoSpeed.  Conditions weren’t the greatest today.  We had about 2 inches of rain yesterday and it was very breezy today with the temperature in the low 80’s.

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The AR is one that I put together a few years back.  I started with an Anderson Lower, filled with a Palmetto State Armory Lower Build Kit.  I have a Magpul Stock and grip on it as well.  The upper was purchased as a complete unit from Hardened Arms.  It is a 16 inch 5.56, 1-9 Twist barrel.  It originally came with a 15 inch quad rail that I replaced with an eBay 12 inch slim M-lok rail.  I like it much better than the quad rail.  I have a mil-spec trigger with a Taylor Tactical reduced spring kit.  It’s not a bad trigger, much lighter than the original one.  I also have a cheap eBay TPI Compact Muzzle brake threaded on the barrel.

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With the MagnetoSpeed Sporter Chronograph strapped to the rifle, I started with some Hornady 68g BTHP on a Charge of Accurate 2230.  I just fired 3 rounds because they were all over the place.  The 1-9 twist and 2607 fps Average velocity (SD of 18) weren’t enough for them to fly true.  I figured this would happen but wanted to try a few to be sure.

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The rest of the groups today prove why I don’t shoot every group through the MagnetoSpeed when I do load development.  I have seen some major point of impact changes as well as group sizes from using it and not.  I didn’t photograph everything I shot today, just the paper.  I shot several groups at 100 and 200 yards on steel that proved my point as well.

The next group was the Hornady 40g V-Max loaded up with a charge of IMR4198.  This is a load my 223 Axis loves and has been decent in the AR.  The first group is with the Chrono, and the second with out.  I had a velocity of 3119 fps with a SD of 18.

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I did make a scope adjustment before the second group.  I also shot them at 200 yards on steel having the same results.  The 40g V-Max shoots better with the Chronograph.

Next up was the 55g V-Max loaded with Varget.  The 5 shots through the Chronograph yielded a velocity of 2846 fps and a SD of 12.  The groups had the opposite effect from the last groups.  The one without the Chronograph did much better.

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I shot several groups today with this charge and it shot awesome.  I was keeping it right under 1 MOA at 100 and 200 yards.  The 55g V-Max shoots better without the Chronograph.  

Obliviously I didn’t shoot all these groups in this order.  I shot everything through the Chronograph then without.  Every 10 rounds I gave the gun some cool down time.  As some of you may know, I picked up a Chamber Chiller this week and put it to the test today.

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This is the Beta 60 model that is designed for use in the 308 type of case family.  It is a little big to fit in the ejection port of an AR-15.  However I found out it I remove the BCG and insert it from the bottom it will work.  It did a very good job of maintaining the barrel temperature.

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I opted for the model with the USB Power cord.  I really didn’t want to mess with AA batteries, and I already had this battery pack that I use to charge phones and camera’s.  About 5 minutes would drop the temp of the barrel from burning you, to a warm but touchable temperature.  So far I am very pleased with this purchase.  Back to the groups.

Next up was some Hornady 55g Soft Points that I loaded up a couple years ago.  These were just loaded as plinking bullets, so I wasn’t expecting much.  The first 5 shot Average was 2919 fps with a SD of 25, Then I shot another 5 getting 2936 fps and a SD of 11.  The first group on paper with the Chrono surprised the heck out of me.  I also shot them at 200 with the chrono getting 2948 fps and a SD of 32.  I shot all 15 without a cool down explaining the increase in velocity as the barrel heat increased.  The 200 yard group was around 3 inches.  Not bad for a cheap soft point.

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My mouth dropped after the first group, so I shot another one.  If I remove the flyer from the 2nd group it would also be under an inch.  I was amazed.  So with the Chrono removed the 3rd group opened up to just over 2 inches.  The Hornady 55g Soft Points shoot better with the Chrono.

The last thing I shot was some factory Wolf Gold 223.  For some reason this rifle has always shot it great.  I have shot a couple thousand rounds of it and it’s always right at that 1 MOA mark.  I didn’t chrono it today, but it runs in the 2900 fps range and it pretty accurate out to 400 yards.  Today’s 5 shot group on paper was 1.143″ and the steel groups were right at 2″ at 200 yards.

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To to wrap up today’s post, I confirmed my suspicions on accuracy with and without the MagnetoSpeed Chronograph.  I think it’s a great tool, and it’s very accurate, but groups are not repeatable once you remove it on this gun.  Other guns such as my Ruger American in 6.5 Creedmoor don’t seem to matter if it’s on or off.  It’s definitely a gun to gun issue. Things such as barrel profile and the use of a muzzle brake will make a huge difference in results.  It’s something to consider when doing load development with one.  Now that this scope is mounted to this one piece mount it will be easier to move from gun to gun, however it’s going to be a little high on a bolt gun.  Hopefully I can catch another one on sale in the near future.  Look for some load testing in the future featuring this rifle.  Thanks for stopping by and have a great day.

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