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View Full Version : Barrel length/twist and bullet type trade-offs


Harbinger
03-02-2007, 8:47 AM
Hey guys, I'm just looking for a sanity check.

When I picked my upper, I really had no concept of what makes a good twist/length/bullet combination. I don't reload, so my only requirement was that it would tag squirrels out to AT LEAST 150yds.

I truly lucked out, and found that my new 1/12 twist 24" barrel shot about 1/2 moa at 100yds with very little drop at 150-200, which must be due to the velocity of the 40gr Nosler-tipped reloads I'm buying from Ultramax.

So, here's my question, which my Google-Fu has failed me on: What compromises have I made by getting a 1/12 and using extremely light bullets? Don't get me wrong, I'm happy with the performance... but I want to know, are the assumptions I'm making, correct??

- POSITIVE -

Higher than average velocity due to bullet weight, barrel twist and length
Tremendous fragmentation due to the above
Minimal bullet drop at 150 - 200yds

- NEGATIVE -

40gr bullets have minimal penetration (only for VERY small game/varmints)
40gr bullets are affected by crosswind much more than heavier bullets (62, 77gr)
1/12 twist barrels aren't useful for anything more than 55gr loads
Higher velocities will wear the barrel faster (still talking 20,000rds+, though)

Thanks...

Mike

bu-bye
03-02-2007, 10:13 AM
All your pros and cons looks right to me. If you are just tagging little four leg critters I would not worry about what you bought. Most of the critter shooter I hang with buy 1:12 bolt actions and push 40-50gr bullets with great accuracy. replacing an AR barrel really isnt that hard. You can buy a really nice barrel for a couple bills and install it in your garage with a $20 tool.

Oh, and you can take coyotes easy even with 40gr loads. It is small but when you push it close to 4000fps it works great

6172crew
03-02-2007, 10:28 AM
Seems to me the black hills light grain bullets are cheaper.

70+ grain is a arm and a leg but you can shoot the really light stuff with that twist.

Sydwaiz
03-02-2007, 11:13 AM
What .223 load pushes 40grainers at 4000fps? A 22-250 yes, but .223 no.

mltrading
03-02-2007, 11:36 AM
Check Ammo Oracle (http://www.ammo-oracle.com/). This topic has been brought up for too many times.:)

Harbinger
03-02-2007, 1:27 PM
The topic of "what's the best twist rate" HAS been brought up a million times, yeah.

This was really just a sanity check for me. The Ammo Oracle is a great resource, but many of the 'key facts' are spread out. I wanted to make sure my summary was correct.

In regards to the Black Hills 40gr.... they are SLIGHTLY cheaper, but for some reason, my upper groups tighter with the Ultramax. After break-in, I tried:

WWB 45gr Varmint
Hornady 40gr Varmint
BH 40gr Varmint
BH 55gr FMJBT
Ultramax 40gr Varmint

Ultramax was the most consistent... and achieved the tightest groups.

ETA: I forgot to mention that Ultramax estimates their 40gr's muzzle velocity to be around 3200fps from a 16" barrel. Ammo oracle doesn't have a very good velocity chart and doesn't directly address 40gr varmint bullets, but I think we can assume that a 24" barrel will add at least 200fps to that base velocity.

Thanks again guys!

Mike