AR-15 Carbine Action Spring Performance Differences

In the past, I have used high speed video to analyze various aspects of AR-15 operation. Today, I did some testing at the range with several action springs. This is intended to be an ongoing test, so all three action springs were brand new. They are:

– Tactical Springs/Sprinco “Blue” recoil spring
– Brownells M4 Recoil Spring – Chrome Silicon
– Brownells AR-15/M4 Recoil Spring

The test weapon was a 16″ carbine gas AR-15 with a .063″ gas port, H buffer, 5.56mm NATO chamber, M16/Auto bolt carrier, and AR-15 fire control group. The bolt carrier group was cleaned and wiped down with a dry cloth before the test. Two types of ammunition were used, Prvi Partizan M855 and Federal XM193. One magazine, a Lancer L5 20rd, was used for the test, and it was always loaded to 20 rounds at the beginning of each string of fire, which consisted of five rounds.

Rate of fire calculation is based on the time it takes for the bolt carrier group to fire, unlock, extract, eject, cock, feed, chamber, and lock, plus the time it would take for a standard M16A1 fire control group to allow the hammer to fall once more. These calculations are therefore theoretical, but this method has always been verifiable when compared to actual M16A1 high speed video testing.

Rate of Fire

The rate of fire was highest with the Springco Blue action spring (726rpm M855/680rpm XM193), median rates of fire were achieved with the Brownells Chrome Silicon spring (685rpm M855/667rpm XM193), and the lowest rates of fire occurred with the Brownells AR-15/M4 recoil spring (656rpm M855/626rpm XM193). The differences in cycle time and bolt carrier velocity between the three springs were always noted during the feeding, chambering, and locking portions of the cycle of operations; put simply, the lower rates of fire came as a result of reduced forward bolt carrier velocity. As forward velocity fell, so did consistency.

Standard Deviation

Relative to the other action springs, the Sprinco Blue action spring was very consistent overall, with a total cycle time standard deviation of .55 for M855 and 3.03 with XM193. The Brownells Chrome Silicon spring was not far behind, with M855 and XM193 standard deviations of 1.87 and 3.81, respectively. The Brownells AR-15/M4 recoil spring could not be considered as consistent, with standard deviations of 5.59 and 12.87.

Further testing will be conducted.

More Vuurwapen Concepts Produced Videos on the GunsForSaleDotCom YouTube Channel

As regular readers of this blog know, I went to Europe a few months back and was able to tour a number of firearm manufacturers as well as attend the IWA trade show. The videos taken on this trip have been posted on the GunsForSaleDotCom channel. I think that a number of the folks who are only aware of VuurwapenBlog on YouTube might not know about these videos, so I put together a little montage of teaser footage.

I’m spending a good bit of time working on the GunsForSale videos, but don’t worry, I’m still doing reviews for VuurwapenBlog. Beyond that, the experience gained making the best videos I can for them has, I think, “trickled down” and improved the quality of my regular videos.

New M4 Comparison Chart

Rob_S, creator of the oft-discussed spreadsheet comparing M4 rifles from various manufacturers known simply – and ominously – as “The Chart,” has released a long-awaited new version which includes more testing, features, and is based on a survey of manufacturers.

This “new chart” includes Accurate Armory, Bravo Company, CMMG, Colt, Daniel Defense, LMT, Noveske, SIONICS, Spike’s Tactical, and Stag. Olympic is also listed, but apparently didn’t provide any information other than their telephone number.

SOCOM kicks MK16 to the curb…along with telling MK11/MK12 that they are too old and fat!

As posted over on The Firearm Blog, FN SCARs in 5.56 currently “owned” by USSOCOM will be soon “divested.” Why? Well, it really doesn’t do anything that the M4A1 doesn’t do, but more importantly, it doesn’t do anything that the MK17, its 7.62x51mm bigger brother, doesn’t do – and the MK17 can be converted to 5.56, as well as other calibers that may not exist in the pipeline yet. We already knew that the MK16 was on its way out, but this serves as official confirmation.

Conversion kits to 5.56 for the MK17 may seem puzzling to some in light of the MK16 rejection, but they make a lot of sense, really. One serialized item that can do the work of two simplifies logistics.

We knew that there was an improved carbine competition, and it shouldn’t come as any real surprise that, if adopted, it would replace the M4A1 in SOF use. What many manufacturers participating in the competition might wish to take note of is the part that says “caliber-tbd.” Speculation on my part, but could something like 300 Blackout have a chance as a primary caliber here? Or will we be back to the 6.5 vs 6.8 wars of the last decade?

Also of note in the pdf shown on The Firearm Blog is that SOCOM is getting rid of the MK11 and MK12. The MK11 is a Knight’s Armament SR-25 variant, and the MK12 is a heavily modified AR-15 variant. They are, however, keeping the M110, which is a different SR-25 variant. There’s also a mention of an M110 A1 Compact, which could be interesting. The SR-25 EM Carbine comes to mind.

The MK17 and MK20 variants of the SCAR Heavy will be replacing the MK11 and MK12 in the semi-auto precision rifle role, but there’s also mention of the current M24 SWS – and the highly modified M2010, and the MK13 bolt action .300 Win Mag – being replaced by an unnamed Precision Sniper Rifle (PSR). Everything I had heard about the MK17 SSR/MK20 until now had been that it was exceptional, so its replacement of the MK11 comes as no real surprise.

Blog updates

As you can probably see, I’ve changed the configuration of the blog. If anyone has issues, especially configuration issues, please let me know. Oh, and if you hate the new look, feel free to let me know that as well.

I would especially like input from mobile users.

Swiss Arms High Res Photos

Just in case anyone wants some new desktop wallpaper, here are some great high-res shots of Swiss Arms rifles, courtesy of Swiss Arms. If you can’t see the images, try clicking on the linked text.

SAN 511, .50 BMG precision rifle

A slightly different SAN 511.

Perhaps this is the “entry carbine” SAN 511? I am joking, of course… For more technical data about the 511, check out the Guns, Holsters, and Gear posts by Richard.

751 SAPR Long Barrel.

751 SAPR Short Barrel. I would like to see this fired at night…

553-CH. I like this one. A lot. The lower receiver is milled aluminum and it has a 4-position adjustable gas regulator. Also, the mainspring, or action spring, is in the standard 550/551 location as opposed to the rear 552 position, which complicated disassembly.

553-US. There’s a video about this one over on The Firearm Blog that I did while at IWA. In addition to the 553-CH changes, it takes STANAG/M16 magazines. I like the idea of magazine commonality, but I like the idea of using the magazine that the weapon was designed for even more. So although they’re both “forbidden fruit” here in the USA, I’d rather have the 553-CH. Oh, and I’ll take a 751 also…I won’t be picky about which model.