Data differences

[Ganderite]

From time to time I have to remind posters here that the loading manual refers only to the rifle they used to develop the data, and each rifle will be different.

I was given 6 relatively new Savage 223 rifles to test. I shot about a dozen different loads (including 3 factory loads) through each of them.

Results were all over the place.

So I decided to use some match bullets (75 gr Hornady from Mystic) to develop a load that would work reasonably well in all of them. According to my log book, RL15 would be the powder to use, but I don't have enough on hand to load 4,000 rounds. My choices, based on suitability and stock on hand is some slow 4895 and some Olin 844 (BLC2).

I did some preliminary loads and Chrony testing here at the farm, and decided to load a series of loads from 23 gr to 25 gr to accuracy test. I double check velocity from the bag of 25 gr ammo and was shocked to find the velocity somewhat lower than I expected, so I loaded a bag of 25.5 of 4895 to test as well.

Today I took the rifles to the range and shot groups. The first rifle shot 23.0, 23.5 and 24 just fine, but showed pressure at 24.5 and blew the primer from the first round of 25. WTF!!

When I was done, I discovered that Savage used a 223 SAAMI chamber on some rifles and a 5.56 type throat in some others. The big difference in throats changes pressures quite a bit.

I just reminded my self that each rifle is different, and even rifles from the same maker can be quite different in dimensions.

 

[bigedp51]

Ganderite

What was the twist rate on the short throated .223 rifle you shot. I see Savage has 1in12 twist and 1in9 twist .223 rifles.

My Savage 223 with a 1in9 twist had a throat longer than my AR15 rifles. I think Remington does the same thing with the .223 and different twist rates.

And thank you for the testing and information.

 

[Ganderite]

Savage used to make 223 in 1:12. I was ragging on them to go faster (this was back in the 80s).

One day they called to say they were making some changes and were considering a faster twist. I asked for 1:8 but they said that was too radical, but were considering 1:9.

They shipped me 20 prototypes to get into circulation. I put 19 of them out there to be used and kept one. I reported back that it would shoot the Sierra 80 gr, so long as velocity was kept up. (This test was in the winter, so it basically confirmed that 1:9 was fast enough.)

I reported that I had to touch each chamber with a throating reamer, so the 80 gr bullet could be set out a bit and suggested they use the Wylde chamber. They declined, but decided to use a chamber of SAAMI spec but use the NATO chamber throat. This seemed reasonable, and for the longest time, that is what they produced.

The 6 rifles I played with are three blue 1:9 barrels with SAAMI 223 chambers (short throats), two stainless 1:9 barrels with the longer throat and a stainless 1:7 with a longer throat.

I discovered the short throats when I tried to shoot some of the original Savage test ammo loaded with the 80 gr Sierra (24 gr RL15). It shot great in the stainless barrels but would not chamber in the blue ones.

All 6 rifles are relatively new.