I did this test this spring. I kept good records, used the same box of primers, bullets and pound of powder. The same cases were compaired before and after forming from the same barrel.
This is the rifle in question
![[Linked Image]](http://www.imagestation.com/picture/sraid192/pe0d6fd899fbc5735161929bfc91ad43a/f1afd6b1.jpg)
The specs are Mod 70 Win push feed. Boyds laminate stock, 26" Gaillard match grade barrel 1in 14 twist.
The rifle was built as a 223 and fired 600 rounds before the rechamber, done by the same smith.
The pre rechamber load was 26.25gr H4895 Win brass (sorted by wt to 92.5gr+- .5 gr) Rem br primer, Hornady 50gr Vmax No moly. col. 2.275(10thou off the lands). This load averaged 3554 fps for 4 five shot groups at 24C. 15 ft from the muzzle. Groups size was .568" for the four test groups. The brass had been loaded three times. This part of the test was done July 23 2004. I had bee using this load for years in this gun.
The rifle was then sent to the same smith for a rechamber. I was having another 223AI built on a Rem 700 action. I saved about twenty rounds of loaded 223 ammo for testing and kept all the same components to work up a load after the rechamber.
Once I got the rifle back. I started the experiment. On June 28 2005 I fire formed the remaining 223 ammo. Four five shot groups averaged 3411 fps at 15ft from the muzzle, 14C. A drop of 143fps. This was very low pressure and would not form the shoulder and blackened the cases halfway down the body. Accuracy was .728" for the four groups. I then began load work up. 27gr of H4895 completely formed the brass with a velocity of 3530fps.
I had saved the original cases from the 223 loads to compare for pressure signs. I realize that primer flattening/pitting and case head expansion may not be all that accurate so I though I would decap the primers and mic them for comparison as well. I think a strain gage added to this experiment would add alot.
Anyway load work up with the 223AI and formed brass gave these results
H4895 27.5gr 3554fps col 3.005(10 thou off lands)
28 3610
28.25 3664
28.5 3699
29.0 3781 max load primer pitting noted but no ejector marks or loose pockets. Primers were on average 10 thou wider when measured and compared to the original 223 load.
As best as I can tell pressures were similar to the 223 load of 26.25 grains when the AI was at 28.5 grains. Note the throat after the rechamber was about 30 thou longer
The difference in case volume that I measured before and after forming the same case was an average of 1.9 gr H2O, 1.5gr of H335 powder,1.3gr Benchmark and 1.2gr H4895. these are average numbers for 5 cases.
Althought the pressure comparisons are subjective I feel quite comfortable running this rifle around 3700 fps with 50 Vmaxs. I have reloaded the same 20 cases 7 times at this speed with no evidence of loose primer pockets. This rifle showed an increase of 135 fps after the rechamber. Funny that the original drop was 143 fps.
I have three other 223AIs and can run the same load in two of them. One has a factory barrel rechambered and does show signs of pressure.
The accuracy After the rechamber is unchanged althought as an AI it seems to prefer Benchmark powder and still shoots around half inch groups.
As stated earlier a strain gage would be ideal for this kind of testing as I think that these small cases are more difficult to read for pressure and the Ackely improved case may alter bolt thrust and therefore discount my attempt at objective comparison.
So what do you all think? Will a 1.9 gr increase in volume (about 6.5%) alow for a 150 fps increase? More?
Looking at that Quick load data showing 65000psi in the 3500fps range all I can say is that the three match grade barreled 223AIs I have run those speeds at much lower charges.
I have always felt that if you can reload the same brass multiple times with out stretching your primer pockets your load should be ok.
Any comments or concerns?
Growler
