284 Win build COAL ?

I am currently building a 284 win for target and long range hunting. I just started building my own rifles three or so years ago. I have built 4 or 5 AR’s 5.56 , 6.5 Grendel and 308 win most of them sub moa. I built a 270 win with a McGowen 26” barrel 1 x8 twist for the purpose of firing the Berger 170gr EOL. turned out great get them up to a hair over 2,900 fps sub moa. I built this off a rem 700 270 win doner. So I then decided I wanted to get a little more thump so I built from parts a 338 win mag 26” 1-10 twist with a Mac gun works NWP brake. Another awesome rifle sends a 285 gr ELD M down range at 2,650 FPS. Sub MOA. I hand load my rounds. So naturally when things are going well build more. So now I am at a 284 win build. Purpose to send heavy hunting and target bullets down range with real precision. So I ordered a McGowen Precision 28” Remage Barrel 1-8 twist. Threaded for a brake. it is chambered in 284 Win Match GAP. I want it throated so I can push the COAL for these heavies as far out if the case as possible. So I got some match dies and I am going to load some dummy rounds so they can use this round to custom free-bore the chamber. So I figured get the longest bullet and go from there. I ordered some Sierra 195 SMK’s and I started looking at what makes sense in terms of COAL. Loading the bullet to a COAL of 3.395 the boattail is all that extends into the case, so the bearing starts at the base of the neck. I would like to be able to fire down to 180 Berger VLD’s as well. Is this to big a spread form the 197 SMK 1.692 OAL, to the Berger 180 VLD 1.549 OAL. Or am I really limiting my rounds to the 183 SMK 1.620 and the 195 Berger EOL 1.659. Does not matter to me really just as precision loading and custom chambering is new to me. Or should I go a little longer or shorter with the 197. New country for me but dam I love building them. Next a bigger safe.


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I'd suggest considering a few things before making the throat that long:

1) The 190 looks good on paper, but with the .284, can you really drive it fast enough to outperform a 175? There is a breakpoint at which one adds bullet weight and improves the BC, but gives up enough muzzle velocity that the higher BC never recovers the velocity advantage over a slightly lighter bullet downrange. Remember, it is ALL about time of flight...

2) If you cut the throat long enough to accept a bullet seated out that far, you are locked in to that combination. Lighter bullets will have to jump so far to engage the rifling that performance will never be satisfactory.

One of my students went through this with another cartridge and ended up going back to a more customary throat length due to the above factors.

Actually I have done a lot of research on hand-loading data on all thee rounds. For a 28” 1-8 twist barrel based up hard data here is the data on the Sierra MK 175, Berger 195 EOL and Sierra MK 197.

Assumes a 10 mph cross wind at sea level 300 yd zero. Mil adjustments required to adjust poi.

At Muzzle

Bullet. Speed. Energy. Vert Corr. Hor Corr

175 SMK. 2,864. 3,187
195 EOL. 2,711. 3,184
197 SMK. 2.675. 3,129

At 500 yds
Bullet. Speed. Energy. Vert Corr. Hor Corr

175 SMK. 2,157. 1,806. 1.4. .69
195 EOL. 2,174. 2,046. 1.5. .62
197 SMK. 2,148. 2,018. 1.8. .43

At 1,000 yds

Bullet. Speed. Energy. Vert Corr. Hor Corr

175 SMK. 1,656. 1,066. 7.0. 1.59
195 EOL. 1,702. 1,254. 6.7. 1.32
197 SMK. 1,689. 1,248. 6.6. 1.07

So at 500 the bullet vertical correction are closest 175 has least amount of drop due to velocity advantage. But at 500 the velocity of the 175 falls behind the both the 195 EOL and 197 SMK and both heavy rounds are delivering 200 more foot pounds of energy on target.

At 1,000 yds the heavies are winning in terms off vertical correction with the 197 being the flattest. The big advantage is in wind deflection? This is the one variable we can not project. Bullet drop versus time is a constant wee can project. Therefore bullets with lower horizontal offset will retain the highest probability of hitting the target.

So heavies win even those get hey have a huge deficit to make up in initial velocity’s I also compared a 183 SMK at 1,000 correction are vertical 6.5. Mills Horizontal correction 1.4 which just over a 197. So high BC wins. This is the case with the 270 win and the 338 Win Mag. At 500 yds the heavies drop is slightly more but they deliver more energy on target and less deflection in wind. Past 500 yds it is not even a contest.

So following this principal if your looking for 500 yds or less generally speed wins, but while the lighter bullets get you to the target quicker, they have less energy but less energy. As with the above series of bullets roughly 10%. Heavies will deliver more energy on target the entire bullet path and the higher the NC the less the drifts.

However there are two other factors to consider. Bullet selection in High BC bullets are limited and many bullets like the Nosler Partitions have lower BC’s but bullet design allows for better more consistent expansion. Ultimately it would be good to have two barrels on for work say 400 yds and one inside four hundred out.

Velocity is the other consideration. Higher velocities cause more hydrostatic shock but for me, I would value the range and accuracy most. In that way I can target shoot or hunt. While inside 400 yds heavies are giving up some in bullet selection and very little real advantage in energy within those limits both bullets are moving so fast a well place bullet makes little difference.

The only real downside is what if my barrel does not like the heavies and no matter what I do I can not get them to shoot sub moa. I am kind off screwed because most likely because of my supper long throating 150’s and 162’s will be a mile off the lands. This has no raided its head to me in my last two bolt action builds. But there is always a first time. But I am increasing my chances by going with a heavy Sendero profile non fluted barrel. My guess is the rig will run 14 pounds . Does not matter to me though I am 6’-5” and 285 lbs and athletic. But I would imagine for the average guy there is no way they would lug that type of equipment around with them. So in the end it might be hard to sell. Does not bother me though because if you are selling my guns I am no longer above the dirt. It is then my kids problem.





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