6.8SPC Load Data


This document and the data contained herein is © Copyright 2004 Zak Smith, All Rights Reserved. It may not be reproduced without explicit written consent from the author.

Send questions or comments to zak@computer.org.

Please read the introduction. It provides important safety information.

There is more 6.8SPC information in the 6.8SPC FAQ (frequently asked questions).

Thanks to Marty ter Weeme for initial help with the internal ballistics modeling.

Background & Limitations

There is no published reload data form 6.8SPC as of even August 2004, so reloaders are in uncharted territory.

I bought an 18" AR15 upper from MSTN in March 2004, and dies from Hornady early in April. I've been doing reloading experiments since then.

The following loads were developed basically from scratch. The results are repeatable in my 6.8SPC upper. I have no direct way to measure pressure, so I am limited to examining brass and primer condition, observing the operation of the AR15 action, and simulating the internal ballistics using numerical methods.

WARNINGS

  1. Always use safe reloading practices
  2. Always start 10-15% under the max load and work up slowly, carefully observing for pressure signs
  3. If you do not understand what pressures signs are, do not proceed until you do
  4. If you do not understand what something means, stop immediately and get help
  5. If you do not understand what is going on, stop immediately and get help
  6. This data was run in only one 6.8 barrel. Your barrel might be significantly different and produce much different results
  7. This data is meant as a ROUGH GUIDE ONLY. DO NOT EXPECT THE SAME RESULTS IN YOUR RIFLE. WORK UP LOADS SLOWLY AND CAREFULLY.
  8. It is possible that errors or "typos" exist in this data. Double-check the data for sanity before using.

DISCLAIMER

Reloading may be extremely hazardous if not done properly and carefully. Death or grave injury may result from unsafe reloading practices. The following loads worked in the author's firearm, but may be unsafe in a different firearm, under different environmental conditions, or following different reloading practices. By using this data in any capacity, you assume all risks associated with reloading.

There is no official "known safe" load data out there for 6.8SPC as of August 2004. The following represents a best guess at load starting and ending points. No direct pressure measurements were done on any of these loads. USE AT YOUR OWN RISK.

Notes on components

Cases

As of August 2004, new brass is not yet available. The brass used in my experiments is from a batch of pre-production Remington ammunition which I obtained in March 2004.

I used a bullet puller to obtain primed cases from this loaded ammo. After pulling, I neck-sized the cases to restore neck tension. The downside to this is that we don't know exactly which primer was used. After the initial firing, all the brass was recycled into reloads.

The factory rounds have a case over-all-length of 1.675" (head to case mouth). There is no published spec for maximum case length or trim-to length. When my cases exceed 1.680", I am trimming them back down to 1.675".

Bullets

The bore size of 6.8SPC is 0.277" -- the same as .270 Winchester. Because the overall length of the cartridge is limited to fit magazine length, bullets 115gr or lighter will leave more usable case volume. The bulk of my experiments have used the 110gr Hornady VMAX (BC 0.370). Both Hornady and Sierra have a 115gr OTM bullet, but these are not yet available commercially (8/5/2004). There are several soft-point 100-110gr bullets, and several varmint 90gr hollow points. Barnes used to make a 100gr "X" bullet, but it was discontinued in 2002.

Primers

6.8SPC uses Large Rifle primers. I have used the Remington primers from the preproduction ammo, Federal Match 210M, Remington 9.5, and CCI Bench Rest, without much change in velocity. The primers in the Remington preproduction ammo are much harder than Federal primers. Cupping is readily apparently in the Federal primers, but I've never seen it in any of the primers from the preprod ammo (ie, when pulled down and loaded with experiments).

I have not tested magnum primers in any of my 6.8SPC loads. In other calibers, it is often recommended to use magnum primers when using ball powder. I don't know if this is appropriate for 6.8SPC or not. If you choose to try magnum primers, further reduce the powder charge again by 1.0gr and work up slowly.

The Remington #9.5 primers are harder than the others and seem to fare better under the pressure.

Dies

I am using a custom set of Hornady "Competition" dies, which consists of an inline seater, and a bushing-style FL resize die. I am using a 0.296" diameter bushing.

Notes on case preparation

Do proper case prep like you would with any match rounds.

Notes on cartridge over-all length (OAL)

The loaded cartridge over-all length:
  1. Determines the distance from the bullet's ogive to the barrel's lands. The ogive should be no less than 0.010 - 0.020" from the lands; more clearance is fine. If the bullet contacts the lands upon chambering, there will be a dangerous initial pressure spike. This distance changes from bullet to bullet, and the minimum distance must be re-established when changing bullets.
  2. Determines the initial volume at powder ignition. A shorter OAL takes up more internal volume of the case and will raise pressures. Generally extending OAL will lower pressure but reduce muzzle velocity, and shortening OAL will raise pressure but increase muzzle velocity. Do not shorten your loads without lowering the powder charge if you are near max.
  3. Determines if the cartridge will fit in and run through the magazine properly. The maximum cartridge length that will fit in a 5.56mm AR15 magazine is between 2.275" - 2.285", depending on the magazine. The maximum cartridge length that will fit in a proper 6.8SPC magazine from PRI (Precision Reflex, INC) is 2.315".
The cartridge OALs listed in this data were safe in my rifle. You should use a Stoney Point OAL gauge to determine sufficient lands clearance in your rifle. The Remington preproduction 115gr Hornady OTM loads have a cartridge OAL of 2.225".

The Data

I have only listed loads I have personally chrono'd in my rifle and the internal ballistics modeling reports less than MAX pressure. This doesn't guarantee it is under MAX pressure, but that along with the lack of physical indicators of overpressure is a pretty good set of clues. The maximum pressure for 6.8SPC is 55,000psi.

Using Federal Match primers (210M), loads at the simulation maximum have round primer edges and rounded firing pin dents. Loads even a couple tenths of a grain above the maximum have primer cupping. If you see primer cupping, STOP!

As reference, the pro-production 115gr OTM shoots about 2700fps from my 18" barrel.

Environmental conditions: Unless otherwise noted, the loads were shot from an 18" barrel, at 5000' elevation and 80-95F ambient temperature.


Bbl Barrel length used
COAL Cartridge overall-length
V Chrono Velocity
V_m Predicted velocity from modeling
P_m Predicted max pressure from modeling

Send questions or comments to zak@computer.org. More loads will be added as time and money allows.
Bbl COAL Bullet Powder Grains V (fps) V_m P_m (psi) Notes
H322
18" 2.290" 110gr VMAX H322 28.0 2546 2546 47378 starting load
18" 2.290" 110gr VMAX H322 29.0 2625 2638 53043 Close to MAX. Low SD
 H322 is just about as accurate as 10X, but attains higher velocities.
RL10X
18" 2.285" 110gr VMAX RL10X 26.0 2520 2531 48356 starting load
18" 2.285" 110gr VMAX RL10X 27.0 2629 2623 54405 Close to MAX. Low SD
 RL10X is my favorite powder for 6.8SPC right now. It's an extruded powder so it avoids the common problems of ball powder. It also shoots accurately in my barrel.
With some other bullets:
18" 2.285" 90gr Sierra HP RL10X 28.0 2732 2730 43822 Just one point.
18" 2.285" 115gr Hornady OTM RL10X 27.0 2539 unknown? unknown? Unknown pressure - no bullet data.
18" 2.300" 100gr "X" RL10X 28.0 2580 2709 50578 Had to use a different 100gr bullet in model
 The 120gr X Bullets are not accurate in my barrel. The 100gr X bullets are reasonably accurate.
AA-2230
18" 2.285" 110gr VMAX AA-2230 28.5 2513 2429 44391 starting load
18" 2.285" 110gr VMAX AA-2230 29.0 2530 2477 47185  
18" 2.285" 110gr VMAX AA-2230 29.5 2565 2525 50184  
18" 2.285" 110gr VMAX AA-2230 30.0 2633 2573 53408  
VV-N133
18" 2.285" 110gr VMAX VV-N133 26.0 2355 2359 41216 starting load
18" 2.285" 110gr VMAX VV-N133 27.0 2591 2448 46231 case full
 It's probably not possible to hit MAX pressure with any amount of N133 or N135 you can fit in the case and still seat the bullet.
VV-N135
18" 2.285" 110gr VMAX VV-N135 27.0 2335 2299 35074 starting load
18" 2.285" 110gr VMAX VV-N135 28.5 2460 2439 41808 case full
H335
18" 2.285" 110gr VMAX H335 28.0 2466 2378 39866 starting load
18" 2.285" 110gr VMAX H335 29.0 2554 2470 44606  
18" 2.285" 110gr VMAX H335 30.0 2607 2563 49993  
18" 2.285" 110gr VMAX H335 30.2 2609 2582 51159  
18" 2.285" 110gr VMAX H335 30.4 2634 2600 52357  
 H335 is not accurate in my barrel.
Benchmark
18" 2.285" 110gr VMAX Benchmark 26.0 2418 2318 40560 starting load
18" 2.285" 110gr VMAX Benchmark 27.0 2482 2407 45290  
18" 2.285" 110gr VMAX Benchmark 28.0 2573 2497 50610  
With the 90gr Sierra HP
18" 2.285" 90gr Sierra HP Benchmark 29.0 2647 2582 41297 Just one point.
AA-2460
18" 2.285" 110gr VMAX AA-2460 28.0 2386 2334 38634 starting load
18" 2.285" 110gr VMAX AA-2460 29.0 2484 2428 43501  
18" 2.285" 110gr VMAX AA-2460 30.0 2587 2523 49085  
18" 2.285" 110gr VMAX AA-2460 31.0 2635 2620 55522 Just over MAX.
 The 31.0gr point is "just" over the MAX pressure. Do not use it, but a couple tenths under should be under max.
RL15
18" 2.285" 110gr VMAX RL15 28.0 2343 2293 35958 Just one point reported.
 RL15 is too slow.
RL7 is too fast. Do not use it.
AA-1680 is too fast. Do not use it.

This document and the data contained herein is © Copyright 2004 Zak Smith, All Rights Reserved. It may not be reproduced without explicit written consent from the author.

[Zak Smith] [zak@computer.org] [/~zak/firearms/6.8SPC/loads.php]
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