6.5-284 Norma Winchester vs. Lapua case capacity. Anyone know?

[skiutah02]

After several threads about my (laughable) journey to try this caliber. I transformed straight 284 Winchester brass to 6.5-284 brass (sad thread). After neck turning, I started fireforming/preliminary load testing. I am using IMR4350 (another thread explains why). It was suggested that I should try 142 SMKs jammed 10-15 thou and proceed carefully to 49.0 gr. They are barely in my case (trimmed to 2.160) at 0.015 jam with 0.002 neck tension (0.292 loaded, 0.180ish bearing surface in neck) because of a looooong savage chamber. I'm getting around 2800 fps with 48.0-48.5 gr. Only one round was above 2900 (2903) at 44.8. I gain about 30 fps on the second firing (only tried 10 so far) and about 10 fps if I jump them (0.040), so I will be a bit higher with same loads in the FF brass, but will need to go higher to get the 2950-3000 mark that is referenced in multiple sites. There is no signs of pressure at all yet, and alot of space for more powder since the base of the bullet is so far forward, so I will carefully go higher, but I thought though I'd ask if someone already knows if 284 Win brass necked down to 6.5-284 has a higher case capacity than Lapua 6.5-284.

In my 308, Winchester brass needs more powder to achieve same velocity vs Lapua brass, so it got me wondering about if that was the case with 284 brass that I am converting to 6.5-284.

Drew

Oh, and so far the accuracy is > 1 MOA at 100 yds

 

[Laurie]

After fireforming in my 'straight 284', Winchester brass has a marginally lower water capacity, 66.0gn v 66.7gn for Lapua 6.5-284 necked up. Winchester cases are on average 10gn (~5%) heavier and produced a very much larger weight spread from a sample of 40 or 50 than Lapua did. The other thing to note is that Winchester starts off with a smaller diameter in the lower body, case-web area, some 10 thou' smaller diameter. Norma increased this dimension slightly when it adopted and developed the 6.5/284 Win wildcat. So, a standard 6.5-284 chamber, or a 'straight 284' equivalent specified for Norma / Lapua brass is a bit loose in this area and sees Winchester cases bulge marginally on fireforming.

 

[Patch700]

What Laurie has stated is correct and explains your gained case capacity.

If you were to measure your straight 284 brass at the base you would most likely come up with a measurement in the .497 -.498 range , and if you measure your fire formed loads even though they maybe safe pressure wise they will probably measure .499-.500"

For reference you can checkout load data (specifically case dimensions) for a straight 284 win and compare it to 6.5x284 Norma data (again pertaining to case dimensions) and you will see what Laurie is referring to.

To answer your question , I myself have never had good luck using ww brass in this cartridge , the best case life and quality of brass allowing max velocity came from Lapua.

 

[effendude]

Drew,
Don't worry about jamming. You have a very generous throat on the Savage barrel. Attempting to reach the lands is only going to cause other issues. Sierra bullets are very jump tolerant. Pick a reasonable seating depth and work up a load. You most likely will be pleased.
Scott

 

[ebb]

The problem is not the case its the powder choice. H4831, VV165 and there is another VV powder that is in the triple based powders, 5XX something. 4350 works well with lighter bullets. Ditch the SMKs and try some Bergers. All will be well with your 6.5-284.

 

[ebb]

Sorry I didn't ask before, whats the barrel length? If its not 28-30 that might be the problem.

 

[skiutah02]

Thanks for all of the responses. I'll still play around with this barrel, but don't want to switch powders until I use up/sell the 10lbs of imr4350 i bought thinking it was h4350 and/or get an actual match barrel. Just a ftr guy testing the waters...oh well.