6mm-284 lets hear it!

[mcr-85]

I have a Winchester 70 in 270 that really wants to become a 6mm-284 or 6-06ai. Haven't decided which but it's happening soon.

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[DaveBarrows]

i have two 6.5/.284 s both shoot very well but this caliber is very hard on barrel throats when loaded to max i get great velocity as per my oehler chrono but i am loading very hot

 

[mcr-85]

My first load ladder works up to 57.4gr of Retumbo at a COAL of 3.1". This is way over any book data you will find, but keep in mind that book data is almost always for a 2.8ish inch COAL, which has the bullet eating up a lot more volume inside the case.

GRT says at this COAL I should be able to work up to 60.4gr, for a 2900fps muzzle velocity (from an 18" barrel). For comparison, the 24" barrel that most reloading data muzzle velocities are based off of puts it at 3160fps:
View attachment 853841

I think I'm going to skip over some of my lower ladder rungs (I originally started at 50gr), which were based on load data with the much shorter short mag COALs. I'll probably fire a few at 53gr (book max for the short COAL) and then start heading up from there based on what I see. Lapua cases and a BAT action should tolerate any accidental higher pressure I might run into doing this, but I don't want to start too low, because that can actually cause even worse pressure issues to show up.

Retumbo in this case should like to run pretty close to slightly compressed based on everything I can find.

Where did you get on load development on your 6-284. I finally got my Model 70 rebarreled.

 

[cal30_sniper]

Where did you get on load development on your 6-284. I finally got my Model 70 rebarreled.

I’ve settled on a load of Retumbo right at about 2900fps from the 18” barrel. I shot some loads as hot as 3000fps but pressure signs were there for sure.

The max no-pressure velocity ended up right at where GRT said it would (2900fps) but took less powder than predicted.

Thread 'UM-built 6mm-284: Initial Range Report'

Oct 5, 2025

I finally got a chance to start load development in my new 6mm-284 UM build, and figured my info/results may be of interest so some of the others that have been experimenting with various small-caliber recipes. This is an old cartridge, but one I feel deserves a second look with the rise of slow burning powders and heavy for caliber bullets that didn't exist when it was essentially written off as a barrel-burner in its previous life.

I agonized over interior ballistics and mag length dimensions for quite a while before arriving on this as a "goldilocks" solution. Initially I had hoped to...

• cal30_sniper
• Replies: 30
• Forum: Firearms

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