Results: Shooting 180 grain bullets in a 1:12" 308 Win barrel

[Bart B.]

Shredder, that's right on large vs. small groups. The proof is firing 20, 30 or even 40 shot test groups. Note also that if a given load doesn't produce the same size groups all the time (within 10% extreme spread), you're not shooting enough shots per group to make them at least 90% represent the real accuracy of your stuff as you shoot it.

Your bullet's seated out too far when:

* the round won't fit in and load reliably from the magazine.

* bolt won't close easily on the round as it jambs into the rifling.

* it's not held good enough by the case neck to withstand normal handling and works loose from being seated to shallow.

 

[old roper]

shredder4286, If you don't get my PM I'll see tomorrow

 

[shredder4286]

shredder4286, If you don't get my PM I'll see tomorrow

I got your PM- see you then

The proof is firing 20, 30 or even 40 shot test groups.

Consecutively, as in- same day, same session?

Your bullet's seated out too far when:

* the round won't fit in and load reliably from the magazine.

* bolt won't close easily on the round as it jambs into the rifling.

* it's not held good enough by the case neck to withstand normal handling and works loose from being seated to shallow.

That makes sense. That allows you to seat the bullet .10 or so over COAL listed in the manual so that you can have your bullet touching the lands.

 

[Jimro]

Just to caveat what Bart B said about the 190 SMK through 308 service rifles, the Air Force team had to drill a gas relief port in their M14s to handle the added pressure, which is why that particular modification is still CMP legal for EIC matches. I don't want anyone to take the recipe Bart listed and fire it in a stock M1A thinking that it is fine, odds are they'd get a damaged oprod very quickly.

Brass life with the 190 load was very short (but brass life is generally very short from an M14/M1A platform), but the load did win matches.

With the introduction of the 175 SMK, pretty much everyone has given up on the 190's for High Power/EIC competitions as now they can use a 175 SMK "across the course" load.

Jimro

 

[WWWJD]

I had mentioned earlier that I had played with the 190; attached is one of the test runs. Group 3 was getting there. If I were to go back and try again, I'd probably start here and work up and down in .2 gr increments. Then play a bit with seating depth in large increments; see if that goes anywhere.

 

[shredder4286]

Looks good man. Even if my model 70 doesn't shoot anything over 180 grains well, I'll be satisfied. An accurate load flinging a 180 grainer will make a mighty fine elk slayer

 

[Bart B.]

Jimro, when the USN's Small Arms Match Conditioning Unit in San Diego got their first Springfield Armory Garand 1:12 twist barrels chambered for the 7.62 NATO round, first tests showed gas port pressure was too low for reliable cycling with both M80 and M118 match ammo. They drilled them out a few thousandths. The Air Force followed suit.

It was the Air Force (I personally know the Airman who did it) that later developed the 190-gr. load with 44 grains of IMR4320 and shared it with the USN SAMCU for reloading M118 primed cases. It produced much higher port pressure and the port's original size worked well. THE USN SAMCU made some Garands for long range use only without drilling out that gas port. Some shot good enough at 800 through 1000 yards that two or three USN team members made the US Palma Team with them.

 

[Jimro]

Bart B.

Thanks for the info on the Garands. I knew about the M14 mods needed to safely fire the 190gr load, but didn't know a stock gas port in a Garand would work. Hell in the back of my mind I'm still scratching my head, as that load recipe doesn't follow the conventional wisdom of "Nothing faster than 4894 or slower than 4064" when talking about the M1 gas system. But then again that gas port is way out there at the muzzle so in a 308 M1 I guess having only 44gr of powder evens things out.

Did you ever get good results from the 308 chamber insert to convert a 30-06 chamber? Just curious.

Jimro

 

[Bart B.]

Jimro, the USN Small Arms Match Conditioning Unit made the first of those chamber inserts for 30 caliber M1's so the NATO round could be used. That was before they got NATO chambered barrels from Springfield Armory in MA. Those that needed to be driven in with a mallet smacking a tool to seat them (tight chamber where the insert fit) stayed in; sometimes the accuracy was pretty good. Other inserts that went in more easily oft times came out with the fired case in the first few rounds fired. The idea was quickly scrapped as it was too dangerous and accuracy wan't all that great over all; worse than 30 caliber ammo.

Although a NATO round chambered in a 30 caliber Garand chamber typically fired and ejected with the case shoulder an most of its neck blown out to chamber specs (1/16th inch of shoulder and no neck at all), it was just beyond the cliff edge of safety. Many civilians buying those inserts from folks making them who didn't totally understand the safety issues oft times had them come out. So, I'd melt down all those inserts and make nails out of them; they would better serve humanity that way.

Note that 190 load the USAF and USN used was somewhat higher in pressure than the 50,000 cup spec for NATO ammo. Op rod's ringed quite nicely and the felt recoil with them drove the M1 back noticeably harder. Op rods had to be perfectly bent and fitted to much tighter specs than military standards; there were only 2 or 3 'smiths in the country back then who fit them correctly and they would last for the life of the barrel or even one or two more barrels. There's only one still alive as far as I know and he's in his 80's now. "Op rodding" a Garand has become a lost are as far as I know.

I give credit to those 7.62 NATO Garands (most used by ex-USN team members) shooting higher scores in the long range service rifle matches at the Nationals than what the M16/AR15 versions did shooting 22 caliber bullets. The US Army got the NRA rules changed so they could use AR10's in 7.62 versions 'cause nobody could get 5.56 NATO ammo shooting as accurate past 600 yards as the 7.62 NATO stuff did in Garands and a few M1A's.

 

[Jimro]

Bart B.

The NRA rules changed after the Army adopted the M110 (aka Knights SR25) as a service rifle. In theory it is supposed to be both a Sniper rifle and a "Squad Designated Marksman" rifle, but I've never seen enough of them in a unit to get them down to the SDM level. Same reason that an M4 clone is allowed as a "service rifle" even though no one uses them because of the short sight radius.

I honestly don't see the AR10's breaking any records too soon, at least not in the traditional High Power course of fire.

It's a pity they never changed the rules to use the M24 with the Redfield Olympic irons issued with the system, although reloading that thing for rapid fire would be problematic without the DBM upgrade. Shooting a 190gr SMK through that let you bump the pressure a tad without worrying about a gas system.

Jimro

 

[Bart B.]

Jimro, regarding the Army's use of AR10's breaking records, check the "New 1K Service Rifle Record" part in:

http://bulletin.accurateshooter.com...set-1k-records-at-interservice-championships/

They got the rules changed in 2009 so they could shoot better scores than what some 7.62 NATO Garands and M1A's were shooting at the long range matches at the Nationals outscoring what the 5.56 ammo produced. No M14NM's were in inventory that could do that. The load for the AR10's was approximately 45 gr. of Varget with the Berger 185 LR bullet. That's normally the max load of Varget under a 155 so I can imagine what the peak pressure is. That bullet needs at least 2550 fps to do well at 1000 and the AR10's barrel is only 20" long.

Also note those Redfield Olympic (like their International) rear sights were notorious for slop as elevation increased. Redfield's Palma rear sight was better. But none of them had enough windage to correct for winds more than 20 mph when shooting the .308's at 1000 yards. 20 MOA don't cut the mustard which is why the Clerke, Wilkes (from England), DeFina and later Warner rear sights with at least 30 MOA of windage either side of zero were preferred as well as having near zero slop and backlash in their adjustments.

 

[Jimro]

Bart B.

Good to know the 1K service rifle record was broken using AR-10s. I think SPC Dunfey had a really good day, and I hope he can shoot that well consistently. A 200-10X is an amazing accomplishment at 1K (at any distance for that matter). He accounted for almost a full third of the teams X count.

Jimro