Freebore / jump issues -- .300 Win Mag in A-Bolt?

[Richard.Howe]

Anyone out there have a favorite pet load in 300 Winnie for the A-Bolt?

I ask because...I'm still having trouble with my handloads. I've tried to use the Barnes Triple-Shock, but if I load the bullet out to 0.050-0.070" off the lands, then my round won't fit in the magazine. I've had the chamber cast to make sure it's within SAAMI spec, and it is. If I set the bullet just deep enough to fit the mag, it sprays patterns like my 870, even with a variety of powders and charge volumes.

So, it looks like this bullet design's ogive is a bit long for this chamber / magazine combination.

Do you have a good pet load for accuracy? Also, do you have a favorite reduced load?

Thanks!
Rich

 

[theCZ]

Is there any chance that if you use a lower weight bullet it will be shorter and you'll still be able to have the right amount of freebore and they will load in the magazine? Also, .050 to .070 seems pretty far out there, I've never had to load more than .030 or so for my hunting rifles, and .020 optimum for my varmint rifle. If you've found .050 to .070 to be the optimum distance, I would suggest a lighter bullet I guess.

 

[Richard.Howe]

Yes, I thought about that, but realized that bullet weight only affects the amount of the bullet *inside* the case.

If I'm aiming for 0.050" off the lands, that's 0.050" whether I'm using a 130 gr. or 180 gr. bullet.

I'm just going to try another bullet with a more abrupt ogive.

 

[Jaywalker]

I'm having a little trouble understanding the issue. The ".050 to .070" inches off the lands isn't a bullet seating longer, comparitively, it's seated shorter than a standard bullet, for a longer jump to the lands.

How are you measuring the distance to lands?

FWIW, most of my handloads are about .020 to .030 off the lands, so that's where I started Barnes XXX, at .030 (6.5X55). The groups weren't bad, but I expect them to improve when I seat a little deeper, as Barnes recommends.

Jaywalker

 

[Richard.Howe]

I'm having a little trouble understanding the issue. The ".050 to .070" inches off the lands isn't a bullet seating longer, comparitively, it's seated shorter than a standard bullet, for a longer jump to the lands.

My A-Bolt magazine won't permit a round loaded to an OAL that corresponds to 0.050" off the lands. The round just won't fit in the box mag...

I'm measuring distance to lands off a Stoney Point OAL guage.

 

[Jaywalker]

Okay, got it. Does that mean you're something like .090" of the lands with the bullet seated as far out as it will go?

After you get the ogive length to the lands with the Stoney Point OAL Gauge, how do you translate that back to seating depth on your cases to be fired? There are basically two ways - (1) with a comparator and (2) by measuring case head to bullet tip. The latter has some drawbacks on standard bullets, of course, but less so with the all-copper Barnes.

I presume you've checked the usual suspects, like measuring .308 diameters to ensure no one packed a .284 in by mistake, concentricity of the loaded round, and so forth?

The situation does seem odd, like the throat is eroded.

Jaywalker

 

[Richard.Howe]

Does that mean you're something like .090" of the lands with the bullet seated as far out as it will go?

Sorry, I'm just not being very clear...

Sequence: I use the Stoney Point to find the lands with the mock-up round, consisting of the threaded case and a bullet I intend to use. In this case, the Barnes Triple-Shock. Then I measure the OAL using my dial calipers.

Next, I back the OAL measurement off by 0.020" or 0.030" and load a round. This round , when chambered, now theoretically has a distance of about 0.020"-0.030" between the start of the lands and the first interference point on the ogive of the bullet.

Problem is, when the OAL is determined this way, the round will not fit in my magazine!

My choices appear to be: 1) shorten the OAL of my loaded rounds so that they fit the mag, 2) load the round relative to the lands and don't use my magazine, or 3) pick a different bullet with a more "stunted" point.

Frustrating situation. That's why I'm looking for those with pet loads I can try.

Take care,
Rich

 

[Jaywalker]

Well, I no longer load .308s, so I can't help directly. I measured some current .264 bullets to their ogives (Stoney Point Comparator), though, and if they keep the same design approach, maybe it'll be similar to the ogives on the .308.

Barnes Triple-Shock 130g - - 0.829"
Hornady A-Max140g - - 0.767"
Hornady 140g Interlock - - 0.752"
Speer 140g HotCor - - 0.739"

Of this bunch, the Speer is stubbiest, but it gives poor results above 2800 fps or so, I understand. (Not sure I'd trust the Interlock up there, either, but I don't know.) Their Grand Slam probably works, and it appears even stubbier in the picture.

I have in the past got some wildly divergent readings from the Stoney Point OAL gauge, even when using the accurate comparator. I finally realized I was "etching" the bullet's soft copper jacket with the steel lands, causing the bullet to slide past its first resistence point. Now, when I've used a bullet in the OAL Gauge once, I set it aside in a baggy as unfit for future OAL gauging, though it's fine for shooting. This allowed my results to normalize.

Not much help, I know, but maybe there's a thread you can use.

Jaywalker

 

[Rockstar]

I think you see your options accurately. What you seem to be inclined to do is look for a bullet design that gives you minimum jump to the lands, but where your loaded round will fit in your mag.

About the only other option would be to do what I do...get a benchrest follower and just load one-at-a-time. You're not usually going to get a second shot anyhow, are you?

Of course, the practical solution would be to just sacrifice a little accuracy for convenience and just load as long as you can to fit your mag.