Need a little help-Building a custom .308 (ammo?)

[BigtimeAub]

Not sure if this is the right forum, so please go easy on me.

I have a question about ammunition as it concerns a stage in the construction of my rifle.

I'm having a Rem700 .270la rechambered to .308. It's going to be loaded into a McMillan A4 and barreled by Kreiger with a 30" 5R, medium Palma countour, 1:10 twist. The gunsmith asked me to provide 1 round of whichever ammo I am going to use to shoot so that he can get the tolerances balls on for my ammo of choice. My purpose for the rifle is to be able to shoot out to 1000 yards, maybe just a little further if I ever develop my skills enough to actually hit the target.

My question is, will the Southwest Ammunition 175gr SMK and SMK Premium get me to within 1/2 to 1 MOA at 1000 with the configuration mentioned above? If not, does anyone have any suggestions? I've been reading on here for months trying to learn everything I can without asking questions but there is just so many differing opinions, it's hard to tell which direction to go. Just figured I would go with the majority that replies here.

Thanks for any replies, helpful or not! Lol

 

[turbo54]

Re: Need a little help-Building a custom .308 (ammo?)

You have a few considerations:

1. Will you/do you desire to feed from a magazine?
2. Will you/do you reload your own ammo?

If you do not reload, and will not be reloading, your best bet is to pick your favorite factory ammo and give one to your gunsmith. FGMM 168/175 or SW 175 would be just fine.

If you require feeding from the magazine, you'll have to either make sure your favorite factory ammo feeds from the mag - and give one to your smith.... or.... You'll need to ask yourself what bullets you care to use, and expect to use when you load ammo, then load a dummy cartridge that is capable of fitting in your magazine, then consider if that is a "reasonable" COAL for that cartridge/bullet...

Example:

I'm building a 284win on a short action FN SPR. 284 really works best at ~3.2" COAL (cartridge overall length), but my magazine limits me to 2.985. The bullet I want to use, the Hornady 162 Amax, likes to be close to the lands in most guns. So, I loaded a dummy round to 2.975" COAL, so that it will fit in my magazine with a little clearance... And supplied that dummy round to the company making my chamber reamer, so they could make a reamer that will allow me to have the cartridge as long as my mag will allow, and at the same time, allow the bullet to be on the lands.

 

[former naval person]

Re: Need a little help-Building a custom .308 (ammo?)

Using a long action frees you up to load to whatever length you wish in .308 Win. I'd load a dummy with a 175 SMK, since that seems to be bullet one you want, with the leading edge of the base taper even with the base of the neck. That should give you plenty of neck alignment as well as not encroaching on the limited powder space. If you don't reload, and plan on using the ammo you mention, then just hand a round of that to your gunsmith. The ammo you mention should get you 1 K without problems. The .260 Winchester seems to be a better selection for 1000 + yards. There is a thread on the site that takes you to 6mmBR for a discussion of the various 6.5 cartridges out there. GO War damn Eagle! (My wife is a GA grad) FNP

 

[Jethro3898]

Re: Need a little help-Building a custom .308 (ammo?)

This is no help to your question, but

WAR EAGLE.

 

[BigtimeAub]

Re: Need a little help-Building a custom .308 (ammo?)

Thanks Turbo. I'm going with a single load configuration. At the moment, I don't hand load but I would like to in the future. The only reason I'm asking specifically about the SW ammo is because I already have some. Also, in my sig pic, I'm shooting a friend's .308 and we were using the SW ammo with great success. It's all he uses. I'm the type that gets stuck on something just because other swear by it. I know that my rifle will be different from anyone else's and my have a unique appetite for ammo that no one else uses. I'm not necessarily asking for the best ammo for my rifle right now, especially never having shot it. I'm just look for a good round to use as a foundation that will give me a good baseline to work with.

Thanks 'former naval person'! I'm going with the .308 because I'm going to shoot this rifle in F T/R matches as well in addition to my recreational shooting. What other length casings could I use for .308 besides a standard length .308 casing or a 7.62X51mm? By the way, I'm a 'former Marine person' myself. Semper Fidelis, and War Damn Eagle!

Jethro, War Eagle! to you as well, kind sir!

 

[Truck10]

Re: Need a little help-Building a custom .308 (ammo?)

Any reason your going with such a long barrel length?? A 20-24" barrel with that twist is plenty to get 155-200gr bullets to 1K plus save you a bit of weight.

I would also consider getting into reloading sooner than later. It will give you the versatility to experiment with different grain bullets and loads. Good luck.

 

[Longshot38]

Re: Need a little help-Building a custom .308 (ammo?)

I agree with 10Truck. Why such a barrel. a 20-22 inch barrel is all you need. As for the ammo. Simple just start reloading. SW does good work and you can reproduce their load when you start handloading. But why wait just go ahead and start rolling your own, you will eventually anyway.

 

[XTR]

Re: Need a little help-Building a custom .308 (ammo?)

If you get serious into F-TR you will probably end up with something other than the 175SMK, at least for matches, in my rifle shooting Berger 185BTs probably buys me a couple of points a match due to it's better BC and less windage. (though they do cost a lot more)

You will want to reload.

The idea is to cut the throat so the bullet is just out of the lands w/o pushing it into your case volume or having it seated too long. If you start with a factory Southwest Ammunition 175gr SMK you should be fine. They should have an OAL of about 2.80. I seat my 175s and my 185 Bergers BTs .020 off of the lands. Last time I checked I was seating my SMKs at 2.825, they still fit in an internal mag, my Bergers are well over 2.9 and don't. My rifle shoots well below .5 MOA if I do my part. (I shot a .342 MOA group from a cold bore yesterday, the picture is posted over in the gallery)


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 10Truck</div><div class="ubbcode-body">Any reason your going with such a long barrel length?? A 20-24" barrel with that twist is plenty to get 155-200gr bullets to 1K plus save you a bit of weight.</div></div>

If you are planning to shoot in F-TR go as long a tube as you can get and still make the 18lb weight limit. The guys here love their little stubby 20" tubes, they are very "tactical" but at 1000 yds the wind laughs at 308s anyway. A 30" tube will buy you a several inches of windage per full value MPH. If all you are doing is trying to ring a 24" gong at 1000 then fine, lop it short, but if you are shooting for a 5" X-ring and a 10" 10-ring then get all you can get. I've got a 31" Kreiger Heavy Palma blank standing by my desk now, and after I mount that if there is room the next one will finish at 32.


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 10Truck</div><div class="ubbcode-body">I would also consider getting into reloading sooner than later. It will give you the versatility to experiment with different grain bullets and loads. Good luck.</div></div>

^^ This

 

[BigtimeAub]

Re: Need a little help-Building a custom .308 (ammo?)

XTR - Thanks for the response, that was exactly the answer I was looking for. And thanks for answering Trucks question for me. I knew the answer to the question myself, but definitely couldn't have answered it as thoroughly and elegantly as you just did. The only reason I'm not getting into reloading right away is because I'm a full time college student with only a part time job. I'm still working on paying for my rifle, and still have to get some glass for it. Speaking of that, I was thinking (and since I'm going to shoot some F T/R matches), would the NF NXS 8x42x56 be too much? I already understand about mirage and all that jazz. I've just never used glass that strong before but I've seen where the US F T/R team captain has recommended it on numerous occasions on here. It's just kind of hard for me to argue his opinion when he is the one on a world stage doing exactly what it is that at this point I can only dream of doing. What are your thoughts on this?

Thanks again for the reply/explanation.

 

[XTR]

Re: Need a little help-Building a custom .308 (ammo?)

I shoot with a 32BR. If you go with a 42 it has less vertical adjustment. You may not be able to get a 100 yd zero. Not impossible but you need to be in the bottom 1 or 2 moa. It has 40 I think and it will take you right at 36 to get to 1000. Magnification is good. You can always dial back.

 

[BigtimeAub]

Re: Need a little help-Building a custom .308 (ammo?)

If I went with the 42power glass, would a 20moa rail and high rings over come the lack in elevation? Or would you still recommend going with the 32power?

 

[XTR]

Re: Need a little help-Building a custom .308 (ammo?)

It will depend on the rifle and the scope you get. Not all scopes come from the factory with the erector centered in the adjustment range at 100 yds, and not all barrels are true to the action.

When I mounted my 32BR on my rifle with a 20MOA rail I was still 18MOA from the bottom. A 32BR has 50MOA of adjustment, and it takes about 36 to 36.5 MOA to get a 175SMK out to 1000 yds from a 100yd zero.

36+18=54, as my little boy would say, Uhoh!? So mine sits on a 30MOA rail now and I'm fine.

The 42 has 40MOA in the 42BR and 45MOA in the 42NSX so to get a 100 yd zero. So to have a 100yd zero and enough elevation for 1000 you will want to get the scope on at 100 in the bottom 3MOA, that leaves you 37+ to adjust to 1000. It is probably doable, but you'll have to shoot it with some rail mounted then figure out whether you need a 20/25/30 or more. There are a lot of rail options out there.

Or if you are really just shooting at 1000 don't worry about 100, zero it where you can and then take it up. I almost never take the 1000yd dope off of my scope. Most of my shooting, 90% or more is at 1000, with the occasional trip to the 800 or 900 yd lines.