6.8SPC Load DataThis 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 & LimitationsThere 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
DISCLAIMERReloading 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 componentsCasesAs 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". BulletsThe 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.Primers6.8SPC 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. DiesI 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 preparationDo proper case prep like you would with any match rounds.Notes on cartridge over-all length (OAL)The loaded cartridge over-all length:
The DataI 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.
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. |