Safe-Pressure work-up data for upcoming BBTI(ballistics by the inch) focusing on heavier than standard 308win bullets.

These loads are non-standard loads and SHOULD NOT be considered safe in any rifle other than the rifle they were developed for!!!

In the upcoming weeks, we will be performing a pretty exhaustive bbti study looking at not only standard 308win bullets(there are several out there already with standard weight bullets), but also heavier than standard weight bullets. Even though we have loads developed for a 20” 308, we figured it best to start from scratch on developing the heavy bullet loads for this rifle (26” rem700sps-v, with a 10k+ rds factory 12twist barrel). This rifle has a loooong factory chamber and will accept loads beyond the 2.960” that an aics mag will accept. With my comparator, the throat of this rifle requires 2.470” base to ogive to touch the lands with a Berger 185 juggernaut, which because of ogive shape is .010” longer than Hornady 168bthps require (for reference, this means that a 185jug has to be loaded to a .070” longer coal than the referenced 168, to achieve the same base to ogive measurement). With the mag length and BTO measurements taken into consideration, I decided that No load would exceed either 2.950” coal or 2.470” BTO for the purposes of function and safety in this rifle.

I will also note, these loads are not accuracy loads, and with the 12 twist barrel they are not stable with 225gn Hornady bthps or the 230gn Berger hybrid OTMs, but this study is going to be about velocity changes with barrel length changes. These loads are merely to establish SAFE loads in this rifle.

The data listed below is bullet, brass, primer, coal, BTO measurement, powder charge(of CFE223), and shot velocity. 208s and 210s were 2rds per charge over 5 different charge wts, the 225s and 230s were single shot per charge for 10 different charge wts, primarily because we started very low on the bullets that data didn’t exist for, and we had limited matching lot brass for pressure loads and for loading the BBTI loads. I will note here that NONE of the loads tested showed any signs of pressure in this rifle with these loadings. Also, all brass was fireformed in this rifle and then sized with a Redding body die with a +.006” competition shellholder, and necksized with a Lee collet necksizing die. Velocity data was recorded with a magnetspeed sporter.

The DATA:
208amax, LC-11, WLR, 2.950”coal, 2.213”bto
1. 42.5, 2419
2. 42.5, 2409
3. 43.0, 2441
4. 43.0, 2417
5. 43.5, 2468
6. 43.5, 2459
7. 44.0, 2507
8. 44.0, 2492
9. 44.5, 2523
10. 44.5, 2515

210vld match, LC-11, cci34, 2.950”coal, 2.277”bto
1. 42.5, 2312
2. 42.5, 2318
3. 43.0, 2342
4. 43.0, 2356
5. 43.5, 2375
6. 43.5, 2365
7. 44.0, 2422
8. 44.0, 2424
9. 44.5, 2453
10. 44.5, 2455

225bthp Hornady, Win, cci34, 2.950”coal, 2.290”bto
1. 36.5, 1967
2. 37.0, 1960
3. 37.5, 1984
4. 38.0, 2054
5. 38.5, 1982
6. 39.0, 2100
7. 39.5, 2126
8. 40.0, 2086
9. 40.5, 2140
10. 41.0, 2280

230hybrid OTM, LC-11, cci34, 2.950”coal, 2.255”bto
1. 36.5, 1949
2. 37.0, 2051
3. 37.5, 2060
4. 38.0, 2085
5. 38.5, 2063
6. 39.0, 2089
7. 39.5, 2177
8. 40.0, 2176
9. 40.5, 2231
10. 41.0, 2259

Some take-aways; I should’ve prepped more brass so that I could’ve worked up a little hotter. When I say there were no pressure signs, I mean NONE, bolt lift was on par with my sub-sonic 155amax trailboss loads, as in lighter than factory ammo. Most of the velocities attained are pretty close to the Berger Reloading manual Max velocities, but without the associated pressures due to longer than saami loading, but it does show that with the proper chamber dimensions and a longer mag, the potential is there for decent velocities with heavyweight 308 bullets. I will also say that even with the 208s/210s, the report was very modest, which means that bore pressures had dropped significantly by the time the bullet exited which means that the bullet was probably not accelerating and possibly “coasting” before exiting, but that is what we’re going to find out with the BBTI, because when case volume is limited by bullet length, and burn rate is limited by bullet weight, It’s not a stretch to think, that when you limit volume against a known max pressure, you may have too much barrel for your bullet.

 update 09-14-16, had a few extra pieces of brass for the 208 loads and the 230 loads, loaded up a few more steps because I feel like the previous were a little on the light side. will run them tomorrow and then start loading the heavies for the BBTI.