6.8SPC Load Data

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

Primers

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

Notes on case preparation

Notes on cartridge over-all length (OAL)

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 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.