Jim Kauber
Alpha Munitions CSO
alphamunitions.com

President / Director of Training
The Site Firearms Training Center
thesitetraining.com

If you hear it and repeat it enough it has to be true! Just ask me and my internet-based opinion will verify it! Such is the ongoing discussion that theorizes the significant benefits in accuracy, ignition consistency, single digit standard deviations (SD) low extreme spreads (ES) and extended case life of the small rifle primer (SRP) brass over large (LRP). When I see this on our social media sites I wonder if the individuals are parroting the aforementioned or have actually done their own head to head SRP/LRP comparisons, collected the data and summarized the observed differences in an unbiased, comprehensive format.  If they have, I think all the rest of us would be interested in seeing the results.

One of the great benefits of being a member of this fantastic Alpha Munitions Team is having the time, resources and support to implement our own evaluation processes to any number of given subject matter, which brings us back to the SRP/LRP data comparison or lack thereof. Since this seems to be a predominant subject to many in the precision rifle disciplines especially those of us that reload, we thought it beneficial to conduct our own testing with our own ultra-premium brass offered in both large and small primers. That being said though, let me state that these tests were not conducted in a controlled laboratory setting but rather in the cold, damp environment of the Pacific Northwest winter where Density Altitude spanned – 1061’ to +360’ and temperatures ranged from 29° to 51° F. Also, rest assured velocities were not cherry picked in order to show better data. On a couple occasions with both LRP and SRP I’d see a single spike or drop in a velocity outside the norm. These stayed, as this is reality; unexplained, but reality nonetheless.

Here’s the testing equipment used:

Rifles:

260 Remington – built by Benchmark Barrels http://www.benchmark-barrels.com

  • Remington 700 short action
  • 26” Sendero contour 1:8 twist 5 groove barrel w/Benchmark Miller Brake™ – Medium
  • Bedded in a HS Precision PST 25 stock
  • Nightforce 5-25 ATACR, MOAR reticle in Vortex Precision Matched Rings
  • Jewell trigger

6.5 Creedmoor – built by Benchmark Barrels

  • GA Precision Tempest action
  • 24” Sendero contour 1:8 twist 5 groove barrel w/Benchmark Tactical Brake™ – Std W/Pinch Bolt
  • Bedded in an Accuracy International AX stock
  • Nightforce NXS 5.5-22X56, MOAR reticle in NF Ultralite rings
  • Jewell trigger

6 Creedmoor – built by Benchmark Barrels

  • GA Precision Tempest action
  • 24” MTU contour 1:7.75 twist 5 groove barrel w/Benchmark Tactical Brake™ – Std W/Pinch Bolt
  • Bedded in an Accuracy International AX stock
  • Nightforce 5-25 ATACR, MOAR reticle in a Spuhr SP4603B, 20 MOA ring mount
  • Jewell trigger
Reloading Equipment:
  • Forster Co-Ax press
  • Forster FL sizer die w/Ultra Micrometer Seater die
  • RCBS Chargemaster 1500 w/McDonald’s straw modification to minimize overthrows.
  • Forster Co-Ax Primer Seater
  • Lee Decapping die
  • Lyman Case Prep Xpress
  • Wilson Case Trimmer
  • Hornady Lock-N-Load Overall Length Gauge
  • Sinclair Concentricity Gauge w/Clockwise Tools Electronic Dial Indicator
  • Forster Co-Ax Case and Cartridge Inspector
  • Forster Datum Dial
  • Forster High Pressure Case Sizing Lube
  • Sinclair small primer pocket uniformer
  • K&M large primer pocket uniformer
  • Thumler’s Tumbler Ultra-Vibe 10 w/untreated corncob media
  • HFS Minus Pin Gauge set

Chronograph: MagnetoSpeed V3

  • In addition to the 10 test rounds of each caliber and primer size, I loaded an additional 10 to shoot without the MagnetoSpeed attached. What I found was the MagnetoSpeed shifted the point of impact generally high left .5 – 1.25 MOA but did not affect group size.
Reloading Data:

260 Remington

  • Alpha Munitions LRP / SRP trimmed to 2.025 at each firing
  • Primers: CCI BR 2 Large Rifle, CCI 450 Small Rifle Magnum & CCI *BR 4 Small Rifle Match
  • Powder: Hodgdon H4350 @ 43.0 gr
  • Bullet: 142 Sierra Matchking seated .025 off rifling, Case Base to Ogive, CBTO 2.234

*In addition to CCI 450 small rifle magnum primers, the 260 test included CCI BR-4 small rifle match primers but misfires were occurring at a rate of ≈8% primarily during the 1st firing. Though you’ll see the results of using the BR-4 primers in the Table 4 graph, I dropped these in the 6.5 and 6 Creedmoor tests.  I wouldn’t recommend using standard or match small rifle primers with these calibers.

6.5 Creedmoor

  • Alpha Munitions LRP / SRP trimmed to 1.912 at each firing
  • Primers: Federal 210M Large Rifle Match, CCI 450 Small Rifle Magnum
  • Powder: Hodgdon H4350 @ 41.5 gr
  • Bullet: 139 Lapua Scenar seated .020 off rifling, Case Base to Ogive, CBTO 2.210

6 Creedmoor

  • Alpha Munitions LRP / SRP trimmed to 1.912 at each firing
  • Primers: Federal 210M Large Rifle Match, CCI 450 Small Rifle Magnum
  • *Powder: Alliant RL-16 @ 40.5 gr., first 2 strings, 40.2 gr., third string, 39.8 gr., fourth string.
  • Bullet: 110 Sierra Matchking seated .010 off rifling, Case Base to Ogive, CBTO 2.155

* While shooting the LRP/SRP version of our 6 Creedmoor I was experiencing VERY high spikes in pressure evident by blown primers and hard bolt lifts even when the velocities remained close to the same. With each string these pressures increased to the point I was dropping .3 – .4 grains of RL 16 to compensate but the pressures just kept building. After calling Ron Sinnema, owner, CEO of Benchmark Barrels, and an endless resource of technical information, his single question was; “Have you been staying ahead of the carbon ring build-up in the barrel?” Well, no but I have been cleaning on a regular basis was my response. Just let me say that after I removed the hardened carbon ring according to Ron’s procedure, that SRP RL-16 load of 39.8 grains dropped from an average velocity of 3058 fps, SD 7, ES 23 to an average of 2960 fps, SD 4 and ES 15.

I’m going to drop the carbon build-up issue for now because this gives me another noteworthy subject to address in the very near future. 

Loading and Firing Procedures

10 cases of 260, 6.5 CM, 6 CM, LRP and SRP were randomly selected from batches of 100 each caliber, primer size sent from our Ogden, UT factory. All 10 cases for each caliber weighed within 1 grain. Each was prepped and loaded exactly the same with the same lot number of components to ensure loaded ammunition consistency. The loaded ammunition was then shot and chronographed in five, 10 shot strings per caliber, primer type for a total of 300 firings; 150 LRP, 150 SRP.

Fired cases were prepped the same way:

  • Cases cleaned
  • De-primed
  • Full length re-sized
  • Shoulder bumped back .002 from fired dimensions
  • .002 neck tension
  • Trimmed to length
  • Case mouth chamfered and de-burred
  • Powder thrown to .1 grain
  • Bullets seated to consistent, specified depth
  • Rifles were cleaned between each 10 round string, let sit for 15 minutes to cool barrels between each string then 2 fouling shots were fired prior to chronographing.

 

260 Remington Data

Figure 1: Velocity Comparison of 260 Remington LRP and SRP looking at the average velocity of each shot string and the corresponding statistical data.

 

6.5 Creedmoor Data

Figure 2: Velocity Comparison of 6.5 Creedmoor LRP and SRP looking at the average velocity of each shot string and the corresponding statistical data.

 

6 Creedmoor Data

Figure 3: Velocity Comparison of 6 Creedmoor LRP and SRP looking at the average velocity of each shot string and the corresponding statistical data.

 

Observations, personal opinion and what you didn’t see:

Looking at the performance data for these calibers, the 260 SRP clearly had the lowest SDs and ESs. The 6.5 Creedmoor LRP had lower SDs and ESs in 3 of 5 firings and the 6 Creedmoor SDs were essentially the same though the LRP exhibited slightly lower ESs. So, at least in our 300 shot LRP/SRP comparison test, there wasn’t the monumental SRP performance advantage over the LRP like anticipated, actually just the opposite occurred. The differences for the most part were insignificant when it comes to range performance. A few consistent observations during these tests though:

The large primer, given all else is exactly the same, produces higher velocities.

In every fired string, the small primer groups were slightly smaller than the large.

If the SRP is fired in a firearm using the large, .078 firing pin and large firing pin hole, you will experience cratered or pierced primer cups at higher pressures/velocities.

What you didn’t see, though I suspect some would like solid information, was a case longevity test. I’ve done this before, as have several of our top ranked competition friends including those at Team Area 419 with everyone coming to the same conclusion; when pushed to maximum velocities and pressures, the SRP will out live the LRP before the large primer pockets expand to a point where they will no longer hold the primer.  At no point during any of the testing I’ve done to date did the small primer pockets expand greater than .173, a dimension that will still adequately hold the primer in place.  The same can’t be said of the large primer brass. What are these case life numbers? The loading component lot differences, barrel, chamber differences combined with the public’s reloading expertise are unknowns that are just too varied to come up with solid numbers. The only aspects we can control are our brass dimensions and quality. The rest is up to you.

In conclusion, should you wait on or switch from LRP to SRP? Only you can determine that answer. Each of us has our reasons to stay or switch. If you’re like me, and I suspect a lot of you are, and were able to score on a case of Federal 210Ms for example, I’m staying. If you’re on the fence and want to make a change to SRP, then there’s absolutely no down side to doing so. When you look at 30, ten shot strings, 29 were all single digit SDs regardless of large or small primers used and all groups were sub ¾ MOA. 

Stay safe.