December 30th, 2014

.260 Remington in the AR-10 Platform — A Smart Solution

The AR-10 was designed to handle the 7.62×51/.308 Winchester and other .308 “family” cartridges such as the .243 Win and .260 Remington. Our friend Dennis Santiago recently put together an AR-10 to shoot the accurate .260 Rem cartridge. Here is his initial report:

AR-10 Platform Chambered for .260 Remington by Dennis Santiago
I was very curious to see how the .260 works in the AR-10 compared to a .308. I’ve always thought about chambering a bolt gun in .260 but before doing so I thought it’d be good to try it using a less expensive entry point. With an AR platform’s easy interchanging of barrels, it seem like the best way to test out the .260 Rem chambering. So far, it’s most impressive.

DPMS LR-308 in .260 Remington getting function cycle tuned and zeroed
.260 Rem AR10 AR-10 Scenar H4350

I took the AR-10-type .260 Rem a step closer to being ready for matches yesterday. The first order of business was to confirm which buffer spring to use with both the 123 grain and 140 grain bullet loads. My .260 Rem loads, on average, are using 4-5 grains less powder than the .308 loads. In a semi-automatic action that means less gas/energy to work the mechanics. The solution in an AR-10 platform is to either cut coils in the .308 spring or use a weaker AR-15 buffer spring; yup they are not the same. In this case, a CS flat spring for the AR-15 did the trick.

I also put a very nice NightForce Benchrest 12-42x56mm scope that came via friend Mark Gravitt on it and got zeros. This scope’s 1/8th MOA clicks are nice. The AR-10 had previously mounted a NightForce F1, a more “field tactical” 3-15X system. This 12-42X scope now sets this gun up as more of a target cannon. Field of view is limited when your minimum magnification is twelve. Maybe I’ll put an auxiliary red dot on it just to find the target.

.260 Rem AR10 AR-10 Scenar H4350

Pet Loads: H4350 and Lapua 123gr Scenars
Comment by Daily Bulletin Editor
Over a two-year period, this Editor put a lot of rounds through a .260 Remington. I did a ton of load testing with that Savage-actioned rifle (before it was rebarreled as a 6mmBR Norma). I tried two dozen load recipes with five different powders and bullets ranging from 100 grains to 142 grains. Hodgdon H4350 was my “go-to” powder. As many 260 Rem shooters have discovered, H4350 is a winner in the .260 Rem. This propellant delivered the lowest ES in my rifle and nothing beat H4350 for consistent accuracy with bullets in the 120-140 grain range. My most accurate load was with Lapua 123gr Scenars, pushed by H4350 and CCI 250 primers. The 123gr Scenars worked well jumped as well as seated into the lands. Best accuracy, in my 24″-barreled .260 Rem, was right about 2950 fps. Other powders work well, but H4350 is a very good choice for the .260 Remington (as well as the smaller 6.5×47 Lapua cartridge).

Permalink Reloading, Tactical 7 Comments »
December 30th, 2014

Life and Death of a Barrel — Can Barrel Useful Life Be Predicted?

We can predict, with some certainty, how long a light bulb will last (in use), or a shingle roof, or even a nuclear reactor. But how about barrels? Is there a way to reliably estimate barrel life based on known characteristics? This article explains one effort to quantify barrel life…

Rifle Barrel Life CalculatorHow long will a barrel last before the accuracy “goes south”? There are so many variables involved (powder type, bore diameter, bullet coatings etc.) that it’s hard to predict. You might say “Well, my buddy has a .243 and he got 1500 rounds before the throat was shot out” — those kind of comparisons can be useful, but they’re not very scientific, and they won’t help much if you’ve got a gun in a new chambering (such as the 6.5×47) for which long-term test results are lacking.

Is there a more reliable way to predict barrel life — one that will work for a broad range of calibers? Well, Forum member MikeCr has developed an Excel spreadsheet that accounts for a number of variables, and gives a pretty good estimate of useful barrel life, whether you’re shooting a .223 Rem or a 338 Lapua Magnum. Mike’s program predicts barrel life using five variables: 1) Bullet Diameter; 2) Powder Charge weight; 3) Powder Heat Potential (KJ/kg); 4) Pressure (in psi); and 5) Bullet Coating (yes/no). Mike provides a table with Heat Potential ratings for most popular powder types. The user needs to know the pressure of his load. This can be estimated with QuickLOAD.

You can download the lastest version of Mike’s spreadsheet below. You’ll need Excel or an Excel viewer to open the file.

Click to Download Spreadsheet: Barrel Life Spreadsheet (Latest Version)

Shown below is Mike’s Spreadsheet, with variables for a 6BR shooting 105gr “naked” bullets with 30.3 grains of Hodgdon Varget powder. The formula predicts 2401 rounds of barrel life. That corresponds pretty well to what we’d expect for a 6BR — about 2500 rounds.

Barrel Life ProgramBarrel Life Program

Mike observes: “There has been a lot of discussion lately related to cartridge design and resulting barrel life. This is a really important factor to consider amongst a myriad of choices. Barrel life is controversial, and subjective. There are no clear-cut standards for comparison. But a few years ago, I put together a spreadsheet based on Bart Bobbit’s rule of thumb. It worked pretty good, only occasionally failing some tests when validated against posted barrel lives.

According to Ken Howell, I had to account for pressure. And Henry Child’s powder temperature testing provided another piece needed. So, I’ve tweaked it here and there to pass more tests. From 223 Rem to 300 UltraMagnum. Another element added, but turned off, is shot interval. I would need way more tests to lock in on this. But everyone knows, the faster you shoot, the worse the barrel life.

Anyway, another factor hard to define is ‘accurate’ barrel life. This cannot be quantified without standards. Barrels are replaced when expectations are no longer met. I feel that a [barrel] passes peak potential in a finite period due to throat erosion. But that don’t mean it’s toast, if it still shoots well enough. It’s just as likely that many of us never see that peak potential anyway. It’s a slippery thing. Point-blank BR competitors will toss a barrel when it leaves the 1s. I could get another 4000 rounds from it, and be content with its performance, I’m sure.”

NOTE: Mike says: “This spreadsheet may show a lower barrel life than you prefer. But it pretty well spotlights cartridges to stay away from if you plan much time at the range or in dog town.”

Editor’s Comment: Mike’s spreadsheet is a helpful tool, but it is NOT a definitive “take-it-to-the-bank” indicator of barrel life. Mike cautions that predicting barrel life involves so many different factors (including how hot the barrel is run), that the task is a bit like predicting tread life on car tires. Still, the spreadsheet is very helpful. It can certainly warn us that some chamberings (such as the 6-284) are likely to be barrel burners. That can help you make a smart decision when choosing a chambering for your next rifle.

Permalink - Articles, Gunsmithing 2 Comments »
December 30th, 2014

Amazing Deals: Get 40% Off At Midsouth on Clearance Items

Midsouth Shooters Supply Clearance Sale 2014Midsouth Shooters Supply is having a huge End-of-Year Sale. Hundreds of clearance items are marked down 40% (or more) through the end of 2014. For the next couple of days there are amazing deals to be had on ammo, optics, scope rings, gun cases, reloading dies, muzzle-loader rifles, cleaning supplies and much more. Below are some of the top deals we found this morning. (NOTE: This is just a tiny fraction of the hundreds of 40% OFF clearance items.) Remember, these deeply-discounted deals expire soon — you snooze, you lose.

Go to Midsouth End-of-Year Clearance Sale.

Sample Sale Items (hundreds more products are 40% off):

Midsouth Shooters Supply Clearance Sale 2014

Midsouth Shooters Supply Clearance Sale 2014

Midsouth Shooters Supply Clearance Sale 2014

Midsouth Shooters Supply Clearance Sale 2014

Midsouth Shooters Supply Clearance Sale 2014

Midsouth Shooters Supply Clearance Sale 2014

Permalink Hot Deals, Optics, Reloading No Comments »