Range Report Shooting .308 bullets through 1:8 twist barrels

[Tx_Flyboy]

All,

I accidentally picked up a 30-cal barrel blank with a 1:8 twist rate.

This barrel will be used for service rifle competitions, shot at 200yards, 300yards, and 600yards. Occasionally, it will be used in 1,000yard service rifle NRA prone competitions.

All of the above competitions are shot with slings and iron sights, therefore, extreme accuracy required of benchrest rifles will not be essential.

Here are my concerns:
1. Does anyone have any first hand experience shooting AMAX or other thin-jacketed bullets out of this fast a twist? I am worried about jacket separation with such a high twist. I will primarily be shooting 178AMAX at the short lines (200yards & 300yards), and 208 AMAX at the long lines (600yards and 1,000yards).
2. How is accuracy compared to slower twists such as 1:10 or 1:12?
3. Does a barrel such as this experience any untoward physical issues such as increased fouling, increased throat erosion etc?

The DTA covert thread has some info on shooting a 16" 1:8t 308, however, none of those bullets are thin-jacket types such as the AMAX.

If i experience bullet failure with this twist, i will simply shoot SMKs and Hornady BTHPs instead, however, i have 2,000+ 178AMAX & 208AMAX bullets on hand and would like to shoot what i have.

Thanks to everyone for their constructive input.

 

[MitchAlsup]

Re: Shooting .308 bullets through 1:8 twist barrels

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tx_Flyboy</div><div class="ubbcode-body">Here are my concerns:
1. Does anyone have any first hand experience shooting AMAX or other thin-jacketed bullets out of this fast a twist? I am worried about jacket separation with such a high twist. I will primarily be shooting 178AMAX at the short lines (200yards & 300yards), and 208 AMAX at the long lines (600yards and 1,000yards).
2. How is accuracy compared to slower twists such as 1:10 or 1:12?
3. Does a barrel such as this experience any untoward physical issues such as increased fouling, increased throat erosion etc?</div></div>

1: Don't know
2: At short ranges, the loss in accuracy is pretty tiny--might be very difficult to actually measure (assuming excellent quality barrel and gunsmithing). At long ranges, the added twist will prevent the bullet from nosing down and decrease the BC of the bullet by a measurable triffling. In addition, at long ranges, you will see more spin-drift--probably just barely measurable.
3: assuming that this is a hand lapped barrel, you should expect no more fouling than any other hand lapped barrel. If you keep the pressures the same, the rate of throat errosion should not be usefuly diferent.

 

[Tx_Flyboy]

Re: Shooting .308 bullets through 1:8 twist barrels

Thanks for the input Mitch.

I was begining to think no one would respond to this thread.

I did some clacs and noticed that my barrel will spin any bullets i put in there less than a 1/8 or 1/7 twist 556, .243, .260, .25cal etc. Guys that run those calibers are not complaining about loosing bullets.

Additionally, when you consider that the same 30-cal bullets are desinged to be shot out of 300WM, 300RUMs etc, the bullet is designed to be shot about 400-800ft/s faster than i will be shooting it. Of course, my bullet rpms are about 5%-10% higher than the 30-cal magnums (with 1:10 twist barrels), but with less stress on the bullet in the bore.

I think it won't be a big deal...i'll post pictures and range reports since there's a dreath of information on this topic online.

 

[sinister]

Re: Shooting .308 bullets through 1:8 twist barrels

I would recommend a lighter bullet (110-168) for the short lines and reserve the 178s for 600.

Heavier bullets will do two things: exaggerate throat erosion and give you heavier recoil (and delay recovery) during the rapids. You'll get around 3,000-5,000 rounds of life from a competitive .30-cal barrel, maybe not so long using heavier bullets.

A lighter bullet will also buck and kick less during the off-hand stage.

Your best course of action will be to shoot the most accurate bullets you can for each stage. I know several folks who shot 80-grain 5.56 bullets standing because they were the most accurate out of their rifle.

A-Maxs fly true but you may have better luck with heavier-jacketed Match Kings as your throat wear increases and roughs up bullets during initial contact with the rifling. Nothing more frustrating than launching your first slow-fire shot for score and watching it spin apart about 75-125 yards downrange.

The 178s will be good for 1,000-yard Service Palma. I don't know if you can get 208s out fast enough from a Service Rifle.

 

[Tx_Flyboy]

Re: Shooting .308 bullets through 1:8 twist barrels

Thanks Sinister.

I have only run the 178s/175s at reduced course matches, and had no problem with recoil, recovery during rapids, or anything else...the only incident was a reminder that nose-to-charging handle does not work with 308s...i got a bloody nose to prove it.

My goal is to keep things simple. One bullet, one powder charge, as often as practicable. For me that means 175SMK or 178AMAX on top of 47.5gr 2000MR in Winchester cases using WLR primers. This combination is good for about 2,680ft/s in the winter when i got my dope...it'll prolly be a little faster now with the warmer weather.

I am looking for an advantage in the wind at the long lines, which is why i have invested in the 208AMAX. G1 BC = .649 vs .495 for the 175/178.

I don't know if you've checked out the ballistics of the 208AMAX. At 2,500ft/s, they equal 155s at 3000 & 175s at 2800ft/s in terms of wind drift. Since i cant shoot those 155s/178s/175s at those velocities from my 20" tube, my best bet is to get that advantage with a better bullet.

I know i can get the 208s up to 2500ft/s easily out of my 20" rig based on what others have reported. Montanamarine got them up to 2650ft/s out of a 20.5" barrel, but his bullets were molyd and shot from altitude.

Please keep the advice coming.

Btw, thse matches & loads were developed with my hunting 308 AR (20", 1:10 DPMS factory barrel)...i dont know how the same combos wil perform when my barrel comes in (20" 1:8 Bartlein)...holding my breath.

 

[sinister]

Re: Shooting .308 bullets through 1:8 twist barrels

The AP4 and AR-10 are technically NRA Service Rifles for NRA Long Range Prone. You can, of course, shoot them as NRA Match Rifles Across-the-Course but not in CMP Matches (The President's Match and the National Trohpy Individual at Camp Perry, or regional or state Excellence-in-Competition Matches).

Does your rifle feed magazine-length A-Maxs OK (for across-the-course)? The AMU is shooting 180 or 185 Bergers at 1,000 from 20-inch AR-10s.

I personally think you're giving up points across-the-course shooting a 7.62 (as opposed to an M16), and will be spending more as far as your handload component costs.

 

[Tx_Flyboy]

Re: Shooting .308 bullets through 1:8 twist barrels

Sinister,

I understand that 308ARs, conforming to the M110 configuration are service rifles for NRA matches, but not for CMP matches. I have a rock river AR-15 for those events (just bought it in parts, its not even put together yet).

I am only a marksman classification, and don't have the experience you do. However, i'm not new to shooting ARs. The load i mentioned in my previous post has netted me a 1/8" group at 100yards (scoped) and still under MOA at 300yards (also scoped). Therefore, i dont understand this bit about "giving up points to an M16".

My 308AR is as accurate as any 556AR. My shooting skill with irons sucks, but i dont understand why I'd be giving up points because i'm shooting a larger caliber. The recoil from my rifle doesn't bother me, and if my new barrel is as accurate as my factory barrel, thennothing will change

Are you drawing this conclusion based on people's experience with an M1A/M14? I dont like shooting an M14/M1A. I find the recoil bothersome, and the propensity of the barrel to climb is much more apparent than in a 308AR...i can see your points being valid if I was shooting this platform. But i dont see it in a 308AR...its a different animal altogether.

I do agree vehemently with you on cost. I looked up 556 reloading components a couple of weeks back and almost fell off my chair. $17/100 rounds of 75gr AMAX? double the number of loads from a given powder purchase? Ya, shooting the 556AR will be fun, and who knows, i may shoot it more often than the 308 to keep costs down.

However, i have shot thousansds of rounds through my 308 AR, i know its accurate, I'm comfortable with it, it will give me a ballistic advantage compared to the 556, so i dont see how i'll be dropping points...caould you elaborate please?