.308/.260 high BC bullet question

[yellowfin]

What's the limit on bullet size/length when working with the .308 AR platform in both .308 and .260? I gather .223 is limited to 77 grain, otherwise it's too long for the magazine. I know that 175 grain in .308 is pretty typical for length––will it handle 190 grain bullets feeding from the magazine, and similarly with .260 can it feed the 142 SMK's? Just thinking ahead in terms of what can be done with it.

[ICANHITHIMMAN]

Bottom line is mag length and you can load any bullet you want. You will be giving up case capicty to larger(longer) bullets but you can still shoot them at slower speeds. When loading for gas operated weapons we have to be careful we dont over stress the system they arnt bolt guns.

What I'm saying is powders that will get you more speed out of a heavy bullet in a bolt gun are sometimes a no go for gas guns.

Hope this helps

[Belmont31R]

It depends on the specific bullet not a specific weight. Thats why you don't see a-max bullets in heavy grains in 223/556 loads. The polymer tip would make the round too long but a 75/77 grain all metal bullet works fine.


For 308 I think the heaviest you want to go is 178. Hornady makes a bullet in that weight that is all metal. Sierra makes a 175 SMK. No idea on 260.

[yellowfin]

How much case room and velocity loss?

[Belmont31R]

A 175 should be able to be loaded normally. Hornady also has a factory load with the 178.




Have you checked out snipers hide forums? Lots of guys over there reloading 308 with the 175's and 178's.

[Matt-man]

In the .260 I've loaded 123gr Lapua Scenars to magazine length (2.750") with good results. I've seen guys load 142gr SMKs to mag length but I've never done it. Note that both of these scenarios were for bolt guns, so YMMV in an AR platform.

The 175gr Sierra MatchKing can easily be loaded to mag length in a .308; I believe M118LR is just that in 7.62 NATO.

Here's a quick photo I threw together of loaded rounds and loose bullets that I have on hand. You can get an idea of how much these bullets intrude into the case body when loaded to mag length from this. In case you're curious the small grid lines are 1/8" apart.


Left to right:
.308 Win, 168gr SMK loaded to 2.800"
.260 Rem, 123gr Scenar loaded to 2.750"
.308" 155gr Sierra MatchKing Palma
.308" 168gr Nosler Custom Competition (very similar to a 168gr SMK)
.308" 175gr Sierra MatchKing
.264" 120gr Sierra MatchKing
.264" 123gr Lapua Scenar
.264" 139gr Lapua Scenar
.308" 180gr Nosler AccuBond (just cause I had one laying around)

The .264" 142gr Sierra MatchKing is similar in length to the 139gr Scenar. I just don't have any handy at the moment. I wish I had some 178gr A-max and some of the .308" Scenars to include here, but I've never used them.

[yellowfin]

Excellent, so by that pic it appears the 139/142 shouldn't be a problem at all b/c of the negligible difference in length as compared to the difference between the 175 and 180/190. Great info, thanks so much!

[m1ajunkie]

FWIW, I am loading the 178 amax in my .308 at 2.81" with good results.

[CC556]

I've loaded Berger 140 VLDs to mag length in a 6.5 Creedmoor AR10. They or the other 140/142 grain bullets like the Match King will work just fine out of a normal magazine.